The objective of this project is attempting to use nickel high phosphorus alloy coating to substitute hard chromium coating and studying how to improve the hardness of the electroplated samples.

Chromium coating is widely used as a protection to industrial products due to its high hardness and good wear resistance. But hard chromium plating is not environmentally friendly. Now, finding a substitution for hard chromium plating is urgent.

Nickel phosphorus coating has been researched by many researchers for a long period of time as it has the possibility to achieve high hardness and wear resistance.

This project is investigating in the electroplating of NiP alloy by the pulse current. The experiments will be divided into several groups by different parameters. These parameters include current variables such as current density and duty cycle and bath variable such as particle load. After the experiments finished, this project will focus on the characterization of the as-plated samples to collect data. The data types include coating quality, current efficiency, coating composition, surface morphology and hardness.

In this work, there are two methods to improve the coating hardness. The first is adding reinforcing particles. By adding the SiC hard particles to the metal matrix, the coating hardness can be different. And there’re four different variables can affect the SiC content in the coating. It includes three different current variables and a bath variable: current density, duty cycle, pulse plating frequency and a load of SiC particles in the bath. In this part, the experiments can be divided into four groups according to these four variables. The second method is heat treatment. The coating hardness after the heat treatment can be different. After measuring as-plated coating hardness, the coatings are heat-treated and compare their hardness to as-plated ones.

The characterization methods include five processes. The first is checking coatings’ appearance. The evaluation variables here can be the burning area and brightness. The second one is current efficiency. It is used to evaluate the electroplating process. Normally, a successful plating’s current efficiency is not low. The next is coating composition. It is carried by using the EDS machine to check different elements’ content in the coating. These elements are nickel, phosphorus and SiC particles. The next step is to check coating surface morphology by using SEM machine. The morphology is nodular. The last characterization is hardness for both as-plated coatings and heat-treated ones which was measured by Vickers indenter. After making indentations on the coating, the hardness can be calculated by the diagonal length of the indentations. By comparing these data, the effect on coating properties from each variable can be seen.

From the data collected, the duty cycle of 50% and the current density of 2A/dm² have good coating appearance. After the heat treatment, the hardness of the coating increases a lot. And the heat-treated NiHP-SiC coating has a much higher hardness than just NiHP coating (the NiHP in this project is an indicator of nickel high phosphorous alloy). And a higher SiC content in the coating is observed with the frequency of 0.1&100 Hz comparing to 1&10 Hz.