Surface Treatments for Protecting from Fracture and Fatigue Damage II

By generalizing the theory of contact of solids for the case of triple contact of working bodies, the powder particle, the treated surface and the problem of establishing an optimal value for the amplitude of ultrasonic exposure, at which the coating process proceeds most efficiently, were solved. The relevance of such a solution is directly determined by the need to obtain high-quality coating. Analytical expressions of the desired values for the physical parameters of the materials of the objects participating in the working process were obtained. Possible limitations regarding the most important characteristics of the installation were analyzed. Approximate evaluation of the optimal number of working bodies for the resonant chamber was derived. The basic time of the process duration was estimated for the total treatment of the chosen surface by working bodies. Full article

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. Full article