Increasing knowledge and suggesting new heat treatment parameters for improved very high cycle fatigue (VHCF) strength of austempered ductile iron (ADI) are the main purposes of this thesis. The work was performed within Epiroc a mining and infrastructure company. They have performed internal research on VHCF properties of ADI had previously for one set of heat treatment parameters. The scientific community in contrast have extensively studied fatigue properties of ADI in the low to high cycle regime (≤10⁸ cycles) but only scarcely in the VHCF regime (>10⁸ cycles). Therefor the thesis is built upon the hypothesis: ‘Improvements in HCF strength should also mean improvements in VHCF strength’. Enabling utilization of published research on heat treatment effects on fatigue strength in the HCF regime (≥10⁷ cycles).

Finding an efficient way of exploring heat treatment parameters and their effects on the given Cu-Ni-Mo ADI alloy were a main objective. Thus, finding mechanical- and material properties characteristic for high cycle fatigue strength in the HCF regime became crucial. The potential in using these properties to develop and execute an experimental plan to evaluate heat treatments, yet minimizing the amount of fatigue testing required.

The first step was identifying the heat treatment parameters (and parameter ranges) that showed high HCF strength, which are: Austempering temperature (T_aus), austempering time (t_aus) and austenitization temperature (T_γ). Then finding the characteristic mechanical- and material properties for said high HCF strength material, found to be: high- ductility, unnotched impact energy and volume fraction of carbon stabilized austenite (VRA). With both heat treatment parameters, mechanical- and material properties distinctive of high HCF strength material an experimental plan was developed based on a full factorial design (2³). The factorial design was chosen for its simplicity and inherent strengths, especially as both individual and interaction effects can be estimated for all factors (heat treatment parameters). Two levels (2³), one high and one low, for each of the three factors (2³) were determined necessary, giving a total of 8 heat treatment trials. The primary response variables of interest (evaluated properties) for each heat treatment trial were: ductility, unnotched impact energy and volume fraction of carbon stabilized austenite. Meaning usage of the following tests: Tensile testing, impact energy testing, and X-ray diffraction. Specimens for testing were extracted from austempered Y-block type III, initially cast by a commercial foundry with an Epiroc specified chemical composition. The main and interaction effects from the heat treatment parameters on the response variables were both calculated and visually determined. The experimental data was validated against literature found data for similar heat treatments. The evaluated experimental results showed good correlation with literature for the given chemical composition. Ultimately resulting in recommendations for a new heat treatment parameters for improved high cycle fatigue strength.

NiP (P > 10 wt.%) coatings are amorphous coatings whose structure can be transformed by heat treatment into a crystalline structure and hardened by precipitation of Ni3P. In this study, NiP coatings and composite ones with SiC nanoparticles were produced by electrodeposition, and their structural transformation by heat treatment was studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The microhardness and the scratch and corrosion resistance of the coatings were evaluated and compared before and after different heat treatments. The results showed that in as-plated condition, the addition of SiC particles in the coatings did not modify the microstructure, microhardness, or electrochemical behavior. However, the SiC particles’ role was disclosed in combination with heat treatment. Composite coatings that were heat treated at 300◦C had higher microhardness and scratch resistance than the pure NiP one. In addition, composite coatings maintained their scratch resistance up to 400◦C, while in the case of the NiP ones, there was a reduction in scratch resistance by heating at 400◦C. It was also concluded that heating temperature has the main role in hardness and corrosion resistance of NiP and composite coatings, rather than heating time. The optimum heat-treatment protocol was found to be heating at 360◦C for 2 h, which resulted in a maximum microhardness of about 1500 HV0.02 for NiP and its composite coating without sacrificing the corrosion resistance.

Electrodeposition of NiP composite coatings with nano and sub-micron sized SiC has been carried out to investigate the possibility of replacing hard chromium coatings. The composition and structure of the coatings were evaluated by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis, respectively. Microhardness was measured by Vickers indentation and polarization measurements were carried out to study the corrosion behavior of the coatings. The results showed that submicron particles can be codeposited with a higher content as compared to nano sized ones. However, even if a smaller amount of the nano-sized SiC particles are incorporated in the coating, the contribution to an increasing microhardness was comparable with the submicron sized particles, which can be related to the higher density of codeposited particles. SiC particles did not change the anodic polarization behavior of NiP coatings in a 3.5% NaCl solution. Finally, the effect of heat-treatment on the coatings properties at 400 °C for 1 h was studied to investigate the contribution of particles and heat-treatment on hardness and corrosion properties. It was found that the heat-treatment doubled the microhardness and changed the anodic polarization behavior of the coatings from passive to active with respect to the as-plated conditions.

High-pressure torsion (HPT) processing was applied to cast pure Mg pieces and its effects on microstructure, hardness and tensile properties as well as corrosion resistance were evaluated. The microstructure of the processed samples was examined by electron backscatter diffraction (EBSD) and the mechanical properties were determined by microhardness and tensile tests. Corrosion resistance of the samples was studied via electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The results showed that HPT refined the grain size of Mg very effectively from millimeters in the cast structure to a few micrometers homogeneously through the thickness and created a basal texture on the surface. One or five turns of HPT produced no significant difference in the grain size of the processed Mg but the hardness was a maximum after one turn. The yield strength of the cast Mg was increased by seven times whereas the corrosion resistance was not affected by the HPT processing.

High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing. 

This study aimed to deposit high entropy alloy (HEA) coatings with five different elements, Ni, Co, Cu, Mo, and W, from a single aqueous bath. The influence of pH, current density, and complex agent on the composition of deposited coating was examined. It was shown that Mo and W were codeposited mainly with Ni and Co. pH had the most impact on the codeposition of reluctant elements like Mo and W, while current density had the minimum effect. The deposited coating had a metallic, dense, and nodular morphology with configurational entropy of around 1.6 R.

The purpose of the study is to assess the influence of SiC particles and heat treatment on the wear behaviour of Ni–P coatings when in contact with a 100Cr6 steel. Addition of reinforcing particles and heat treatment are two common methods to increase Ni–P hardness. Ball-on-disc wear tests coupled with SEM investigations were used to compare as-plated and heat-treated coatings, both pure and composite ones, and to evaluate the wear mechanisms. In the as-plated coatings, the presence of SiC particles determined higher friction coefficient and wear rate than the pure Ni–P coatings, despite the limited increase in hardness, of about 15%. The effect of SiC particles was shown in combination with heat treatment. The maximum hardness in pure Ni–P coating was achieved by heating at 400◦C for 1 h while for composite coatings heating for 2 h at 360◦C was sufficient to obtain the maximum hardness. The difference between the friction coefficient of composite and pure coatings was disclosed by heating at 300◦C for 2 h. In other cases, the coefficient of friction (COF) stabilised at similar values. The wear mechanisms involved were mainly abrasion and tribo-oxidation, with the formation of lubricant Fe oxides produced at the counterpart.

Selective laser melting is one of the additive manufacturing technologies that have been known for building various and complicated shapes. Despite numerous advantages of additive manufacturing technologies, they strongly influence the microstructure and typically show a relatively high surface roughness. In this study, maraging steel was produced by selective laser melting (SLM), and its microstructure, hardness and corrosion behavior before and after heat treatment were studied and compared to traditionally manufactured ones (wrought, forged samples). In addition, the effect of electropolishing on the surface roughness was evaluated. The microstructural study was carried out by scanning electron microscopy equipped with electron backscattered diffraction in three different sections: parallel to the top surface (xy), transverse cross section (xz) and longitudinal cross section (yz). The same characterization was applied to heat-treated samples, austenitized and quenched as well as the aged ones. The results showed that selective laser melting produced a fine grain martensitic structure (in the as-printed condition) with a surface roughness (R-a) of about 10 mu m. There was no sign of preferred texture or anisotropy in the microstructure of as-print SLM materials. The SLM microstructure was similar in all 3 sections (xy, xz and yz). Despite finer microstructure, nano-hardness and corrosion behavior of SLM and conventional wrought maraging steel in heat-treated conditions were similar. Aging resulted in the maximum nano-hardness and the minimum corrosion potential values. Precipitation has the main role in both hardness and corrosion behavior. Electropolishing was optimized and reduced the surface roughness (R-a) by 65%.

In this study, electrodeposition of Ni-P composite coatings has been carried out to investigate the possibility of replacing hard chromium coatings. Therefore, electrodeposition of Ni-P based composite coating with different SiC particle size (50 nm, 100 nm and 500 nm) or B4C (500 nm) was performed. The coating’s composition was evaluated by energy dispersive spectroscopy (EDS), microhardness of the coatings was measured by Vickers indentor and polarization measurements were carried out to study the corrosion behavior of the coatings. The results showed that B4C particles can codeposit in higher percent respect to SiC ones. Ceramic particles increased microhardness of Ni-P coatings to 700HV0.01. The polarization behavior of all the coatings in 3.5% NaCl was similar in as plated state proving that particles did not hindered the passive behaviour. Finally, the effect of heat-treatment (at 400 ºC for 1 hour) on the coating’s properties was studied to compare the contribution of particles and heat-treatment on mechanical and corrosion properties of the coatings. Heat-treatment increased the coating’s microhardness and changed the anodic polarization behavior of the coatings respect to the as plated conditions.

This study is focused on finding optimised conditions for electrodeposition of NiP and NiP/SiC coatings, which enhance the coatings' microhardness. Both the effect of particles and the effect of heat treatment at 400°C for 1 h on the microhardness of the coating were studied. The effects of pulse electrodeposition parameters including duty cycle, frequency, and peak current density on the composition of NiP and NiP/SiC composite coatings were examined, and the results were compared with those from direct current plating. Pulse plating increased the current efficiency of NiP deposition while decreasing the phosphorus content of these coatings in comparison to direct plating, resulting in higher microhardness values. It was also shown that wt.%P in NiP coating depends not only on peak current density but also on bath charge of pulse plating. Pulse plating parameters (duty cycle and frequency) and the low incorporation of SiC particles did not affect microstructure or the microhardness of the coatings, while heat treatment was the main factor that increased microhardness.

In this study, electrodeposition of NiP composite coatings with the addition of SiC 100 nm was carried out on low carbon steel studying the effect of additives (sodium dodecyl sulfate, saccharin), particles load (10 or 20 g/L) and current density (1, 2 and 4 A/dm2). As a benchmark, coatings from an additive-free bath were also deposited, despite additives being essential for a good quality of the coatings. The coating's morphology and composition were evaluated by scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). It was shown that by addition of sodium dodecyl sulfate (SDS), pure NiP coating with a higher P content was achieved, and their morphology changed to nodular. SDS also reduced the codeposited fraction of SiC particles, while saccharin increased it. SiC loading and current density had less impact respect to the additives on codeposition of SiC particles. Finally, the microhardness of NiP coatings did not increase linearly by codeposition of SiC particles. 

In this study, the fracture toughness of the multi-layered commercial pure aluminum samples (AA1050) prepared by warm accumulative roll bonding (WARB) was investigated for the first time. Based on the ASTM E561 standard, the R-curve method was utilized to measure the plane stress fracture toughness. Compact tension (CT) samples were prepared from the sheets that were processed by different ARB cycles. Mechanical properties, microstructure, and fracture surfaces of the CT samples were studied by uniaxial tensile test, electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM), respectively. By increasing the number of WARB cycles, fracture toughness increased; after five cycles, 78% enhancement was observed compared to the pre-processed state. A correlation was seen between the fracture toughness variations and ultimate tensile strength (UTS). WARB enhanced UTS up to 95%, while the grain size showed a reduction from 35 to 1.8 μm. Measured fracture toughness values were compared with the room temperature ARB outcomes, and the effective parameters were analyzed. Fractography results indicated that the presence of tiny cliffs and furrows and hollow under fatigue loading zones and shear ductile rupture in the Quasi-static tensile loading zone.

Several studies had been performed on accumulative roll bonding (ARB) for AA1050; however, most of them were conducted at room temperature. Here, the ARB process was performed on AA1050 plates through nine cycles at elevated temperature. An innovation introduced a new parameter (UTS×El.ε) to compare the strength-elongation balance between the present study and previous works. Also, as another parameter, the toughness was compared. Comparing these parameters with previous works showed that the considered samples in the present study performed 14 to 63% better than the other samples, so they were more industrially favorable in terms of mechanical behavior and performance. ARB process at elevated temperature may slightly lead to grain growth compared to room/cryogenic temperature, but creates a better elongation, which ultimately leads to a better balance of the strength-elongation parameter. The results showed that the effect of inter-cycle heating was found significant on microstructural evolution and mechanical behavior. Upon five cycles of the process, the grain size was decreased from 35 to 1.8 μm. The yield strength and ultimate strength increased up to 305% and 94%, respectively. Microhardness test showed that warm ARB reduces inhomogeneity factor in the thickness after 3 cycles. Fractography by SEM showed that the sample failed through shear ductile rupture and that the dimples became smaller, more elongated, and shallower onto the failure surface as the number of ARB cycles increased. In short, the warm process is preferred to the cold process to achieve better mechanical performance and toughness.

Thermal resistance and temperature distribution for high-power AlGaInN LED chip-on-board arrays were measured by different methods and tools. The p-n junction temperature was determined through measuring a temperature-dependent forward voltage drop on the p-n junction, at a low measuring current after applying a high heating current. Furthermore, the infrared thermal imaging technique was employed to obtain the temperature map for the test object. A steady-state 3D computational model of the experimental setup was created including temperature-dependent power dissipation in the LED chips. Simulations of the heat transfer in the LED array were performed to further investigate temperature gradients observed in the measurements. Simulations revealed possible thermal deformation of the assembly as the reason for the hot spot formation. The bending of the assembly was confirmed by surface curvature measurements.

This paper reports the hardness, elastic modulus and refractive index values of the oxynitride glasses prepared from woody biofuel ashes. The glasses were prepared in nitrogen atmosphere at 1350-1500°C with addition of Ca metal as a precursor to the extra addition of this modifier. The glasses were homogenous, but appeared translucent grey to black. They contained up to 23 eq% of Ca and 5 eq% of N. The glass densities vary slightly between 2·76 to 2·92 g/cm3. The molar volume and compactness values vary between 8·01 cm3/mol to 8·31 cm3/mol and 0·446 to 0·462 respectively. Mechanical properties like hardness and reduced elastic modulus show values, up to 10 and 105 GPa, respectively. These properties are strongly correlated with the amount of N in the glass. The refractive index (1·54-1·75) increases with increasing N and Ca contents.

All devices working in hazardous environments have specific requirements to reduce the intervention of human power as much as possible. The robot that this thesis is focused on is no exception to this rule. This dissertation summarized theprocess followed to achieve a theoretical design of a traction system for the CERNBot, the robot that operates at CERN facilities.

This traction system had to be capable of achieving a speed of 10 km/h, going upstairs and make tight turns without draining completely the battery of the device. For that purpose, it was decided to include three types of traction systems such apneumatic wheel, a track system and a mecanum-wheel (an omnidirectional wheel capable of moving in any direction). This design had to include as many commercially available pieces as possible to maintain the costs contained.

In order to comply and extend the battery lifetime as much as possible, topological optimization was applied to the non-commercial pieces, reducing the weight of thepiece by 25%.

After achieving the weight reduction, a discussion about the best manufacturing methodology is done, comparing the manufacture using a CNC machine or casting the device, including the possible defects and costs that both models can have.

The results show that manufacturing this piece with casting can lead to a cheaper and more complex piece.

Cast iron is one of the most used materials in the industry due to its wide properties. Specifically, graphitic cast iron is used in applications where the material is submitted to high temperatures due to its high conductivity and thermal shock resistance. Depending on the graphite morphology, thermal conductivity or mechanical properties can be controlled in graphite cast iron. Spheroidal morphology (SGI) promotes good mechanical properties, while lamellar morphology (LGI) improves thermal conductivity. Graphite can also appear in an intermediate shape, called vermicular (CGI) that presents medium mechanical and thermos-physical properties. Nevertheless, how these properties change when the graphite change from SGI to LGI is still not completely known. 

The present work pretends to clarify the relation between thermo-physical properties and the graphite morphology in cast iron, from SGI to LGI. This work uses solidification experiments to control the chemical composition of the alloy, more specifically, the Mg content. At higher content of Mg, the graphite nucleates and grows in nodular shape, at lower Mg content, the graphite appears in lamellar morphology [1, 2]. Once different graphite morphologies are obtained, the thermo-physical properties will be measured. 

It was found that nodularity decreases linearly with the time that the alloy stays over the liquidus temperature. Nevertheless, to times longer than 80 min, the nodularity decreases slower, showing, and exponential variation. Thermal conductivity decreases abruptly when the graphite changes from lamellar to 5% of nodularity, then continues decreasing slower when the nodularity increases. 

The conductivity of LGI decreases when the temperature increases while to CGI and SGI, the conductivity increases with temperature until it reaches a maximum, then the conductivity starts to decrease. The differences between LGI, CGI, and SGI conductivity shorten as temperature increases. 

In this work hypoeutectic lamellar graphite iron alloyed with seven different levels of molybdenum was studied in order to characterize its thermal and mechanical properties. Several tests were conducted and experimental data was collected from, laser flash (LFA), differential scanning calorimeter (DSC), dilatometer and tensile test.

Micrographs taken from the polished specimens were captured and studied through quantitative measurements of several parameters, e.g. graphite fraction, shape, form. Afterward, the same samples were colour etched with picric acid in order to perform a qualitative analysis of the matrix.

It was concluded from the data collected, that molybdenum has a significant influence in the UTS. Such influence, increases the UTS strongly with the amount of molybdenum. It was also found that the pearlitic matrix changes into ausferrite matrix, for the 0.96% of molybdenum, but ausferrite it is detected from 0.65% of molybdenum onwards. Regarding thermal properties, molybdenum does not have noticeable effect but it is possible to see a clear worsen in the conductivity in the specimen, which has ausferrite as matrix.

Graphite does not seem to have a clear behavior with the different concentration of molybdenum but in the other hand, the matrix shows clear differences as it was mention before.

During solid state reaction, it was detected a clear influence of molybdenum additions, where the latent heat and the volumetric change were measured during the eutectoid reaction and show a decreasing behavior for molybdenum contents above 0.65%.

The use of recommended S-N curves, presented in current literature, to analyse and determine the fatigue life of a part is common practice in, inter alia, the construction industry.However, the recommended S-N curves are generally created for larger components used in mainly the construction industry. Hence, the use of S-N curves for the evaluation of smaller parts, may result in over-dimensioning of such parts. For this reason, evaluation and designing of smaller parts could benefit from the development of an in house S-N curve specific for the part.

The purpose of this thesis is to generate and validate an in-house method for creating a S-N curve, for a specific part to be compared with recommended S-N curves in the literature. The specific part used for the generating of the method is a welded steel joint with the geometry of two steel pipes, welded together in a t-formation and which has been provided by Thule AB for the purpose of the thesis.

The method presented uses the results from 1) physical fatigue tests using a fatigue testing machine and 2) static FEA to derive a S-N curve for the specific part using the least squares method. A fatigue testing rig enables the gathering of data of the number of cycles to failure when the part is subject to a given cyclic load. The rig uses pneumatics to control the forces applied onto the part with the use of a cylinder. Furthermore, the fatigue testing rig was designed to be controlled by the applied force, meaning, that the rig ensured a homogeneous load cycle by measuring the force from a load cell and alternating the direction of the cylinder with an electrically controlled pressure valve. The performance of static FEA evaluations aim at locating stresses in the part. For this thesis the stresses were evaluated using the hot spot method due to the part's welded geometry.

The data gathered from the physical fatigue tests and the static FEA evaluations are subsequently combined deriving S-N curves applicable to the part.

From the fatigue tests and FEA evaluations for the t-shaped welded steel part, four S-N curves were derived of which two curves showed the results of a linear fitted curve whereas the other curves used the recommended slope of $-1/3$. The results showed that the S-N curves derived, using a set slope, resulted in similar curves to the recommended S-N curve provided by the literature. However, the linear fitted S-N curve showed that the part, according to the S-N curve, had a higher fatigue resistance than recommended.

 Due to limitations in the thesis work, the S-N curves derived within the framework of this thesis should be regarded as theoretical and have been strictly used to identify whether the method generated is applicable for deriving of S-N curves.

Large caliber gun barrels are exposed to deferent kinds of high strain, from pressure to wear, with influence of chemical, and thermal effects. With the ever increasing demand on better guns, the demand on the barrel increases as well. This study will go through the thermal part of the strain that affect the gun barrel steel. The will be experiment on how thermal cyclic load affect low alloy steel, documentation the cracks, hardness and create computer simulations on the physical experiments.

The heating experiment is carried though by the help of an induction coil that is the supplement for the burring propellant to not get any unwanted chemical residue. The heat and timeframe of one cycle, does not one hundred percent representative the reality but it will still give a got comparison of the materials tested. The experiment was completed on five different material 1.2709-A1, -A2, -B, CrMoV, and H13, which are all used in the tooling industry and therefore interesting material in a gun barrel.

The material show vastly different cracks intensity and crack length, with is connected to grain size, thermal conductivity, coefficient of the thermal expansion, strength, toughness, and hardness. The hardness measurement showed a phenomena that does not happen in a fired gun barrel, which is thermal softening. Thermal softening happens in this test for the simple reason that the temperate was never high enough to make the steel phase change to austenite. This makes the secondary carbide crystals to recrystallize into larger ones to lower their energy, in turn reducing hardness and strength. The simulations show that there is tensile stress at the outside, closest to the induction coil, and compressive stress on the inside of the test sample. It also gave a good insight on how the properties affect the steel. 

The material 1.2709B got the best results from the experiment conducted in the study, few and short cracks, almost nonexistent hardness softening. It has the ductility and toughness to reduce the softening and the strength and thermal conductivity to stand against the major crack formations.

Recent X-ray diffraction (XRD) measurements have revealed that plastic deformation and a residual elastic strain field can be present around the graphite particles in ductile cast iron after manufacturing, probably due to some local mismatch in thermal contraction. However, as only one component of the elastic strain tensor could be obtained from the XRD data, the shape and magnitude of the associated residual stress field have remained unknown. To compensate for this and to provide theoretical insight into this unexplored topic, a combined experimental-numerical approach is presented in this paper. First, a material equivalent to the ductile cast iron matrix is manufactured and subjected to dilatometric and high-temperature tensile tests. Subsequently, a two-scale hierarchical top-down model is devised, calibrated on the basis of the collected data and used to simulate the interaction between the graphite particles and the matrix during manufacturing of the industrial part considered in the XRD study. The model indicates that, besides the viscoplastic deformation of the matrix, the effect of the inelastic deformation of the graphite has to be considered to explain the magnitude of the XRD strain. Moreover, the model shows that the large elastic strain perturbations recorded with XRD close to the graphite–matrix interface are not artifacts due to e.g. sharp gradients in chemical composition, but correspond to residual stress concentrations induced by the conical sectors forming the internal structure of the graphite particles. In contrast to common belief, these results thus suggest that ductile cast iron parts cannot be considered, in general, as stress-free at the microstructural scale. 

In the initial stage, the sample preparation was done by using the techniques of Anodic etching and anodic forming processes where a repeated trial and error method of sample preparation headed towards making out a suitable sample set for characterization. After this step, the set of 2 different industrial samples were introduced and anodic oxide forming process was carried out in different electrolytes.

 In the sample preparations, 4 different electrolytes were used 15% wt. Ammonium Adiphate, 1.5% wt. Ammonium Phosphate, 7% wt. Boric acid and 15% Penta Borate at different stages for performing the anodic oxide forming process. Minimum forming voltages of 20V to a maximum of 100V was employed in the sample preparation and to overcome the waiting time in forming the etched samples a higher current of 0.5A was used.

After the samples preparation, Electrochemical Impedance spectroscopy was used as a tool for characterising the various groups of samples and for observing the micro structures of various samples, they were fractured and the observed on the cross section by SEM.

After the analysis of the etched samples was made, an attempt to compare the results of the data of these samples to that of the 2 set of industrial samples was made and found that the resultant data wasn’t stable enough to characterize since huge scattering were occurring and whereby the simulation of the CPE circuit for the chosen circuit in the analysis was not possible.

Under the analysis, a randomly chosen industrial sample was also used and the resultant data was utilised in understanding the response of the system to different electrolytes.

In this study, damage initiation micromechanisms in friction stir-welded DP600 steel sheets during tensile deformation were studied by scanning electron microscopy (SEM) and electron backscatter diffraction. For this purpose, DP600 steel was welded using friction stir welding with two combinations of rotational and transverse speed, to prepare joints with low and high heats. Microhardness measurements on the cross section of the weldments revealed the formation of a softened zone in the HAZ as a result of the tempering of the martensite, which led to the localization of strain and failure during the tensile testing. SEM observations on the cross section of tensile tested specimens showed that ferrite–martensite interface decohesion and martensite fracture are the main void nucleation mechanisms in the DP600 steel. For the sample welded with low heat input, ferrite–martensite interface decohesion started at higher strains compared to the DP600 steel. A new void initiation mechanism including plastic deformation of tempered martensite, necking, separation of martensite fragments and formation of a void between the separated segments was also suggested for this sample. For the sample welded with high heat input, formation of void at the ferrite–cementite interface was the main void nucleation mechanism and ferrite–martensite interface decohesion was an inactive mechanism.

The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.

Commercially pure copper rod was successfully subjected to severe plastic deformation by applying the continuous equal channel angular pressing (ECAP-Conform) method at room temperature. Microstructural characterizations of copper rod samples at various stages of plastic deformation were carried out by optical microscopy and electron backscatter diffraction methods. X-ray diffractometry and Kernal average misorientation were used for dislocation density estimations. Microstructural evaluations revealed grain size change of 30 mm for the initial annealed copper rod to less than 5 mm and even 100 nm for severely deformed samples. Mechanical behaviors of samples after different deformation stages were characterized using tensile and hardness tests. The ultimate tensile strength of the severely deformed copper rod was increased threefold by ECAP-Conform while elongation halved in comparison to the initial annealed copper. Low-temperature annealing of severely plastic deformed samples led to bi-modal grain size distribution and lowering of strength accompanied by the increase of elongation. Tensile properties of severely deformed and then annealed copper samples showed around a 40% increase in both ultimate tensile strength and elongation in comparison to the initial annealed copper rod.

In a quest to develop new light metal alloys that can perform excellently at elevated-temperatures (from 300°C to 400°C), a ternary eutectic Al-Cu-Si alloy was exploited to gain a deeper understanding of the alloy system and its suitability for high temperature applications. The alloys studied, with chemical composition of Al-27%Cu-5%Si (by weight percent) with Ni addition in the range of 0 to 1.5%wt, were cast in a rapid solidification casting technique. The solidification characteristics of the alloy was studied using the Thermo-Calc software. Microstructures were characterized in a scanning electron microscope coupled with energy dispersive spectrometry (SEM-EDS). Finally, the elevated-temperatures tensile properties of the alloys were investigated. Comparing the microstructures and mechanical properties of these Al-Cu-Si(-Ni) alloys with conventional Al-Si alloy A319, the refined microstructure with dispersed Ni intermetallic particles formed in the as-cast Al-Cu-Si(-Ni) alloys deliver improved elevated temperature properties. In particular, the yield strength and ultimate tensile strength of the new alloy with 1.5% Ni at 400?C were observed to be 220% and 309% higher, respectively, than for conventional A319 alloy.

Owing to its many qualities, cast iron is one of the most commonly utilized materials in the industry. Cast iron having graphite spheroids scattered throughout the matrix is referred to as Ductile cast iron or Spheroidal graphite iron (SGI). The mechanical and thermo-physical properties of ductile iron are influenced by the microstructure phases that constitute the metallic matrix as well as the number, the size, and the nodularity of the graphite particles. Casting industries face challenges to optimize the shape and size of their casting components to reduce environmental impact and increase their performance. They also employ numerical simulation software for casting process simulation and material property prediction, as part of product development. Reliable material property models constitute an important prerequisite for cast component simulation. The microstructure of SGI can be adjusted by varying cooling conditions and the chemical composition. The purpose of this thesis is to investigate how the cooling rate and the carbon content influences the microstructure morphology and the mechanical and thermal properties of SGI. Five different cooling rates and two different carbon contents (hypereutectic and hypoeutectic) were utilized in this thesis. The results show that the mechanical and thermal properties do not depend on the cooling rates, as long as the matrix microstructure (ferrite/pearlite ratio) remain similar. Furthermore, the different carbon contents have no sizeable impact on the different microstructure features and consequently on the mechanical and thermal properties. The microstructure investigation shows that the increase in the cooling rate results in a significant increase of small graphite nodules at the thermal center of the castings. This observation indicates a secondary nucleation event at the last to solidify areas and requires further investigation. 

Experimental evaluation of several active anti-condensation methods for application in non-hermetic electronics enclosures was performed in harsh climatic conditions, including RH = 70% and T = 43 °C. The studied methods included blowing the air along the exposed surface, combination of blowing and air heating as well as local heating of the exposed surface in natural convection conditions. The purpose was to prevent/remove the dew on/from the exposed surface of a micro-condensation sensor. The difference between the methods was quantified in terms of time for dew removal. The power consumption aspects were discussed. A CFD based optimization methodology was developed to determine the heating profiles for the local anti-condensation PCB heater in a non-hermetic cabinet exposed to the quickly changing climatic conditions. The potential for 60% energy savings was revealed by simulation.

Thermal conductivity is an important property for many iron cast components, and the lack of widely accepted thermal conductivity model for cast iron, especially grey cast iron, motivates the efforts in this research area. The present study contributes to understanding the effects alloy microstructure has on thermal conductivity. A thermal conductivity model for a pearlitic cast iron has been proposed, based on the as-cast alloy composition and microstructural parameters obtained at different solidification rates. According to the model, available parallel heat transfer paths formed by connected graphite flakes across eutectic cells are determined by the space between dendrite arms. The uncertainties both for model inputs and for validation measurements have been estimated. Sensitivity analysis has been conducted to result in better understanding of the model behaviour. The agreement between modelled and measured thermal conductivities has been achieved within 5% on the average for the investigated samples.

The finite element three-dimensional transient model of the annealing process, including conductive and convective heat transfer in an aluminum (Al) coil was developed, implemented, and validated. It combines winding force dependent effective radial thermal conductivity model and the novel convective heat transfer modeling methodology. Experimental validation of the finite element model was performed for two industrial coils having different dimensions, strip thickness and crowning depth. The general agreement between the predicted and measured temperatures for most of the probes was better than 10% at the target material temperature. A series of measurements were configured and performed to supply both the input and validation data for the simulations. The effect of the additional wetted area on the convective heat transfer at the coil base was quantified. The guidelines on the virtual prototyping of the Al coil annealing process were provided, which can be of interest for the process designers.

A methodology for evaluation of transient performance of, and comparison between plate heat exchanger and plate-fin-and-tube heat exchanger was developed and realized, including experiment and 3-D simulation. Heat transfer from water to a gas medium was addressed. The heated gas volume was the same for both heat exchanger designs. This was achieved by placing the plate-fin-and-tube heat exchanger into enclosure. The volume average temperature of the gas as function of time was computed. Estimated material cost for the studied designs was at least seven times lower than for the stainless steel plate heat exchanger. The performance of the selected plate-fin-and-tube heat exchanger design was found comparable to the plate heat exchanger, when both fin and tube materials were set to Al, and the enclosure was a light-weight thermal insulator. Transient behavior of the studied heat exchangers should be of interest for micro-grid applications, but also for thermal management in electronic cabinets and data centers.

A mathematical model of a multi-phase power conversion system composed of modified bridge-elements (B-system) capable for parallel computation has been developed. Experimental validation on the example of a power system including a synchronous generator and an AC-DC rectifier has been performed. A mathematical algorithm for B-system assembly and steps to obtain mathematical model of the B-system have been developed. Integration of mathematical models of conversion system into the complete model of a multi-phase power system has been explained and evaluation of computational efficiency of parallel computation techniques for the developed model of an AC-DC-AC converter has been performed. The presented modelling method can be employed in the design phase of smart grids, for power quality and conducted emission analysis. 

The work presented aims to reduce the amount and viscosity of the slag produced in the furnace during the production of Compacted Graphite Iron in SCANIA foundry and simulate the actual process using thermodynamic calculations to estimate the amount and the composition of the slag.

The estimation of slag amount and slag compositions was done using CALPHAD (Calculation of Phase Diagram) method which can be done using the thermodynamic software Thermo-Calc using the composition of the raw materials and the phase diagrams calculation. In the present work, an appropriate calculation method to estimate the amount and composition of slag was established and based on the calculations, strategies to decrease the viscosity were suggested.

There are great energy savings to be made by recycling aluminium; as little as 5% of the energy needed for primary aluminium production may be required. Striving to produce high quality aluminium castings requires knowledge of microstructural imperfections, which is extra important when casting recycled aluminium that generally contains higher levels of imperfections compared to primary aluminium. Imperfections include amongst others Si, Fe, and Mn as well as oxides. Si is needed for castability, but it may also initiate fracture. There are different types of Fe-rich intermetallics influencing properties of castings, generally in a negative direction. Oxides constitute cracks and they are elusive because they are difficult to quantify.

This thesis aims to increase knowledge about imperfections in recycled aluminium castings originating from alloying elements and the melt. Experiments were performed in advanced laboratory equipment, including X-radiographic imaging during solidification and in-situ tensile testing in a scanning electron microscope. Experiments were also performed at industrial foundry facilities.

The experiments showed that the nucleation temperature of primary α-Fe intermetallics increased with higher Fe, Mn, and Cr contents. Primary α-Fe are strongly suggested to nucleate on oxides and to grow in four basic morphologies. Lower nucleation frequency of α-Fe promoted faster growth and hopper crystals while higher nucleation frequency promoted slower growth rates and massive crystals. Results also showed that a decrease in the size of the eutectic Si and plate-like β-Fe intermetallics improved tensile properties, foremost the elongation to fracture. In β-Fe containing alloys the transversely oriented intermetallics initiated macrocracks that are potential fracture initiation sites. In alloys with primary α-Fe foremost clusters of intermetallics promoted macrocracks. In fatigue testing, a transition from β-Fe to α-Fe shifted the initiation sites from oxides and pores to the α-Fe, resulting in a decrease of fatigue strength. Oxides in Al-Si alloys continue to be elusive; no correlations between efforts to quantify the oxides and tensile properties could be observed.

Morphology and growth of primary α-Al(FeMnCr)Si intermetallics have been studied in-situ during solidification of a commercial secondary aluminum alloy employing X-radiographic imaging combined with deep-etching. The α-Al(FeMnCr)Si intermetallics were found to nucleate primarily on surface oxides, and the continued growth yielded both rhombic dodecahedrons and elongated rod-like morphologies. Both morphologies were observed as hopper and massive types, where the hopper intermetallics had the higher growth rates. The growth rate, which determines the type, appears to be linked to nucleation frequency; higher nucleation frequency promoted massive types and lower nucleation frequency promoted hopper intermetallics. 

To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were investigated by in-situ tensile testing in the scanning electron microscope. In the first alloy, large plate-like β-Fe intermetallics oriented parallel to the test direction were the first to crack at an elongation of about 1.8%. More transversely oriented intermetallics caused crack initiation in the matrix which linked up with the final fracture. In the second alloy, the cracking of α-Fe intermetallics initiated at an elongation of about 0.9%. It is concluded that large α-Fe intermetallics crack first and that clusters of α-Fe are the most potent crack initiation sites.

Aluminium-silicon alloys have gained increasing market share in the automotive and aerospace industry because of increased environmental demands. These alloys have a high strength-to-weight ratio, good corrosion resistance, castability and recycling potential. However, variations in properties and limited performance at elevated temperature are restricting these alloys from use at elevated temperatures. During the last decades, researchers have investigated ways to improve the properties at elevated temperatures. However, the effect of some transition elements is not well understood. The aim of this work is to investigate the aluminium-silicon alloys with addition of cobalt and nickel for high temperature applications. Tensile testing and hardness testing were conducted on samples produced by directional solidification in a Bridgman furnace with condition generating a microstructure corresponding to that obtained in high pressure die casting, i.e. SDAS ~ 10 µm. The results show that cobalt and nickel improve the tensile properties up to 230 °C.

Global warming is driving industry to manufacture lighter components to reduce carbon dioxide (CO₂) emissions. Promising candidates for achieving this are aluminium-silicon (Al-Si) cast alloys, which offer a high weight-to-strength ratio, excellent corrosion resistance, and good castability. However, understanding variations in the mechanical properties of these alloys is crucial to producing high-performance parts for critical applications. Defects and oxides are the primary reasons cast components in fatigue applications are rejected, as they negatively impact mechanical properties.

A comprehensive understanding of the correlation between fatigue performance and parameters such as the α-aluminium matrix, Al-Si eutectic, surface roughness, porosities, hydrogen content, oxides, and intermetallic phases in Al-Si castings has not been reached.

The research presented in this thesis used state-of-the-art experimental techniques to investigate the mechanical properties and crack-initiation and propagation behaviour of Al-Si-Mg cast alloy under cyclic loading. In-situ cyclic testing was conducted using scanning electron microscopy (SEM) combined with electron back-scattered diffraction (EBSD), digital image correlation (DIC), and focused ion beam (FIB) milling. These techniques enabled a comprehensive study of parameters affecting fatigue performance, including hydrogen content, surface roughness, oxides, and intermetallic phases. More specifically, we investigated the effect of melt quality, copper (Cu) content, oxide bifilms, surface quality, and porosity.

The increased Cu concentration in heat-treated Al-Si alloys increased the amount of intermetallic phases, which affected the cracking behaviour. Furthermore, oxide bifilms were detected at crack-initiation sites, even in regions far away from the highly strained areas. Si- and Iron (Fe)-rich intermetallics were observed to have precipitated on these bifilms. Due to their very small size, these oxides are generally not detected by non-destructive inspections, but affect mechanical properties because they appear to open at relatively low tensile stresses. Finally, Al-Si alloy casting skins showed an interesting effect in terms of improving fatigue performance, highlighting the negative effect of surface polishing for such alloys.

For reducing the CO2 footprint in many industrial fields, the goal is to produce lighter components. The aluminium-silicon (Al-Si) cast alloys are promising candidates to fulfill these goals with a high weight-to-strength ratio, good corrosion properties, excellent castability, and recyclable material. However, the variations within these components need to be understood to produce high-performance components for critical applications. The main reason for the rejection in these applications is defects and microstructural features that reduce the mechanical properties. The addition of copper (Cu) is one way of increasing the mechanical properties in Al-Si alloys and is commonly used in the automotive industry. Casting defects harm the mechanical properties, and these defects can be reduced by improving the melt quality, the correct design of the component, and the gating system.

The study aims to investigate the static mechanical properties and the crack initiation and propagation under cyclic loading in an Al-7Si-Mg cast alloy with state-of-the-art experiments. The main focuses were on the effect of the HIP process and the role of Cu addition. In-situ cyclic testing using a scanning electron microscope coupled with electron back-scattered diffraction, digital image correlation, focused ion beam (FIB) slicing, and computed tomography scanning was used to evaluate the complex interaction between the crack path and the microstructural features.

The amount of Cu retained in the α-Al matrix in as-cast and heat-treated conditions significantly influenced the static mechanical properties by increasing yield strength and ultimate tensile strength with a decrease in elongation. The three-nearest-neighbor distance of eutectic Si and Cu-rich particles and crack tortuosity were new tools to describe the crack propagation in the alloys, showing that a reduced distance between the Cu-rich phases is detrimental for the mechanical properties. Three dimensional tomography using a FIB revealed that the alloy with 3.2 wt.% Cu had a significantly increased quantity of cracked Si particles and intermetallic phases ahead of the crack tip than the Cu-free alloy. The effect of Cu and HIP process in this work shows the complex interaction between the microstructural features and the mechanical properties, and this needs to be considered to produce high-performance components.

During in situ cyclic testing of hot isostatically pressed and heat-treated Al-5Si-0.5 Mg-1Cu alloy castings, cracks were observed to open up in places far away from the area of stress concentration. Cyclic testing was interrupted to assess these cracks. Analysis showed that these cracks originated from oxide bifilms that were entrained in the liquid state. Moreover, Si and Fe-rich intermetallics were observed to have precipitated on these bifilms. These finding makes it necessary to re-evaluate how damage is interpreted in mechanical studies. Entrainment damage, which takes place in the liquid state, may remain invisible in non-destructive inspection and can significantly affect fatigue properties when bifilms open up under low tensile stresses and present the propagating crack a path of low resistance during propagation.

Increasing environmental demands are forcing the automotive industry to reduce vehicle emissions by producing more light-weight and fuel efficient vehicles. Al–Si alloys are commonly used in automotive applications because of excellent castability, high thermal conductivity, good wear properties and high strength-to-weight ratio. However, most of the aluminium alloys on the market exhibit significantly reduced strength at temperatures above 200 °C. This paper presents results of a study of the effects of Co and Ni in a hypoeutectic Al–Si alloy on microstructure and mechanical properties at room and elevated temperature. Tensile test specimens with microstructures comparable to those obtained in high-pressure die casting, i.e. SDAS ~ 10 µm, were produced by directional solidification in a Bridgman furnace. The results show an improvement in tensile properties up to 230 °C.

Prototyping prior high pressure die casting (HPDC) is used for product/mold design optimization. Plaster mold casting is a cost-efficient prototyping technique providing good surface quality and dimension accuracy, similar to HPDC components. However, the corresponding mechanical properties of a component produced with these two methods are diverging significantly, mainly due to differences in the cooling rate. This work presents a procedure to optimize the plaster mold casting for prototyping to replicate mechanical properties of a commonly used Al-Si alloy (A380). Two commercial alloys with compositions close to the A380 alloy (A356.0 and A360.2) were used. Yield strength was considered as the main design criteria, thus the target mechanical property. Tensile testing results showed that with an optimized T6 heat treatment, not only the yield strength, but also ultimate tensile strength and elongation correspond well to the properties in the HPDC component.

The study aimed to investigate crack initiation and propagation at the micro-scale in heat-treated Al–7Si–Mg cast alloys with different copper (Cu) contents. In-situ cyclic testing in a scanning electron microscope coupled with electron back-scattered diffraction and digital image correlation was used to evaluate the complex interaction between the crack path and the microstructural features. The three-nearest-neighbour distance of secondary particles was a new tool to describe the crack propagation in the alloys. The amount of Cu retained in the α-Al matrix after heat treatment increased with the Cu content in the alloy and enhanced the strength with a slight decrease in elongation. During cyclic testing, the two-dimensional (2D) crack path appeared with a mixed propagation, both trans- and inter-granular, regardless of the Cu content of the alloy. On fracture surfaces, multiple crack initiation points were detected along the thickness of the samples. The debonding of silicon (Si) particles took place during crack propagation in the Cu-free alloy, while cracking of Si particles and intermetallic phases occurred in the alloy with 3.2 wt% Cu. Three-dimensional tomography using focused ion beam revealed that the improved strength of the α-Al matrix changes the number of cracked particles ahead of the propagating crack with Cu concentration above 1.5 wt%.

The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt% to Al-Si-Mg alloys changes the fatigue behaviour that a rapid failure occurs. 

Al-Si alloys are the most popular casting alloys due to their excellent castability combined with high strengthto-weight ratio. This paper investigates the role of Si content in the range of 6.5 wt. % to 14.4 wt. % on the microstructure and mechanical properties of Al-Si-Mg casting alloys. All alloys were modified with 90-150 ppm Sr. No grain refiner was added. The samples were produced by directional solidification providing a microstructure that corresponds to microstructures found in die castings. From the phase diagram and coupled zone, increasing the Si level up to 14.4 wt. % is expected to start a competition between formation of α- dendrites and a fully eutectic microstructure. However, it is known that Sr-modification shifts the eutectic to higher Si contents. For the lower Si contents, the microstructure of the samples consisted of α-dendrites and a modified Al-Si eutectic. At 12.4 wt. % Si and above, a cellular eutectic microstructure was observed. No primary Si was observed even at 14.4 wt. % Si. The mechanical properties in terms of yield and tensile strength did not vary remarkably as a function of the Si level unlike the elongation to failure that dropped from 12 % at 6.5 wt. % Si to nearly 6 % at 14.4 wt. % Si; but still the material is exhibiting an elongation to failure that is far higher than normally expected.