The Effect of Particle Type and Size on CoCr Surface Properties by Fine-Particle Shot Peening

Abstract

Cobalt–chromium (CoCr) alloy is widely used for medical implants such as for dental or joint replacements because of its strength and high corrosion resistance. By throwing a spherical media against a material surface, fine-particle shot peening can modify surface properties and, as a result, has been widely used as a low-cost and simple method to increase a metal’s wear resistance. However, no recent literature has reported the effect of particle type and size on the surface properties of CoCr alloys. This study examined two different particle types (ceramic (alumina–zirconia composites) and silica (SiO2)) and three different particle sizes to determine their effects on CoCr’s surface properties after fine-particle shot peening. The surface properties, including morphology, roughness, hardness, residual stress, and cytotoxicity, were tested to evaluate the effect of the process. The larger size and higher hardness of the particle (ceramic) changed the surface microstructure more than particles with smaller sizes and lower hardness (silica). The results of the cytotoxicity test showed that the fine-particle shot peening on the CoCr material did not affect cell viability, an important fact when considering its potential use as a surface material for medical implants. The results showed that fine-particle shot peening on CoCr material can improve several surface properties and that the larger ceramic particle offers the best results.