Physical properties and corrosion behaviour of Co-Cr-Ni alloy developed by powder metallurgy

Abstract

Cobalt-based alloys have been widely used in biomedical application. In this research, 11 different compositions of cobalt-chromium-nickel (Co-Cr-Ni) alloys were developed by powder metallurgy route. Scanning electron microscope (SEM) in conjunction with energy dispersive x-ray spectroscopy (EDS) was used for morphology and elemental observation of the raw materials. The particle size distribution of the Co, Cr and Ni particles were characterized using Malvern particle analyzer. X-ray diffraction (XRD) was carried out to analyze the phase transformation of raw materials. The raw Co-Cr-Ni powders were first milled using planetary mill and compacted using uniaxial hand press to a pellet shape before being sintered using tube furnace under argon atmosphere. The samples were sintered at 1000°C for 2 hours. Percentage of porosity, density, shrinkage and hardness test were carried out to correlate physical and mechanical properties with composition of Co-Cr-Ni alloys. The dimensions of the samples before and after sintering were measured and the percentage of shrinkage of the samples was calculated. Density measurement was carried out by Archimedes technique while percentage of porosity was calculated based on the density data. Hardness testing was performed using Vickers hardness machine. The microstructure and the phase transformation of sintered samples were also being characterized using SEM and XRD respectively. In order to understand a relationship of corrosion resistance with composition of Co-Cr-Ni alloy, an immersion test was executed in a water bath using 0.9% sodium chloride solution while maintaining the temperature of 37°C. Weight loss measurement and corrosion rate were carried out to analyze the corrosion resistance of the immersed samples. The results showed that the percentage of porosity of the samples increased with increasing Cr content and decreased with increasing Co content. The density and the percentage of shrinkage of the alloys increased with increasing Co content and decreased with increasing Cr content. Hardness increased with increasing Co content while decreased with increasing Ni content. Sample with composition of Co4Cr5Ni was found to have the highest corrosion resistance after 30 days immersed in 0.9% sodium chloride solution. In contrary, sample with composition of Co37Cr5Ni evidenced the lowest corrosion resistance.