Fatigue property and cytocompatibility of a biomedical CoCrMo alloy subjected to a high pressure torsion and a subsequent short time annealing

Abstract

In the present study, we evaluated the effects of high pressure torsion (HPT) and subsequent short time annealing processing on fatigue properties and cytocompatibility of the biomedical CoCrMo alloy (CCM). Before processing, CCM was solution treated (CCMST) to achieve a microstructure composed of coarse single £-phase equiaxed grains with no internal strain. Through HPT processing, an inhomogeneous microstructure containing both micro- and nano-scaled grains is obtained in CCM specimens, which were named as CCMHPT, accompanied by high internal strain and extensive ¾ martensite. Following a subsequent short time annealing, a uniform single £-phase ultrafine-grained microstructure with small local strain fields dispersed forms in CCM specimens, which were named as CCMHPTA. This microstructure change improves fatigue strength in CCMHPT, and further in CCMHPTA, because of the enhanced crack initiation and/or propagation resistance. For cytocompatibility evaluation, the cells cultured on CCMST show an immobilization tendency, while those cultured on CCMHPT exhibit a locomotion tendency. The cells cultured on CCMHPTA have an intermediate pattern. Compared with CCMST, much larger numbers of cells are proliferated in both CCMHPT and CCMHPTA. All these results demonstrate that the CCMHPTA offers an improved fatigue property and a good cytocompatibility. Therefore, it is promising for use in biomedical applications.