Formation of Microstructure and Mechanical Properties of Co-Cr-Mo Alloy by Hot Forging and Subsequent Radial Shear Rolling

The improving of metallic biomaterials, such as Co-Cr-Mo alloys, is an important task for increasing the durability of orthopedic implants. In this study, the deformation method of the Co-28Cr-6Mo alloy including hot forging and subsequent radial shear rolling was tested for the first time. For the obtained bars, the analysis of the microstructure formation and mechanical properties was carried out. The proposed method of thermomechanical processing made possible to form a duplex structure (γ-FCC + ε-HCP) in the alloy, in contrast to the hot forging at which a single-phase structure (ε-HCP) was observed. The resulting structure provided higher strength characteristics at the bar surface such as YS ∼ 715 MPa, UTS ∼ 1164 MPa due to the higher content of the ε-phase, while in the central zone these indicators were YS ∼ 492 MPa and UTS ∼ 948 MPa. The main effect of hardening after forging was grain refinement and formation of a single-phase composition (ε-HCP). While in the context of radial shear rolling, there was a reduction in grain size and an increase in the volume fraction of the deformed structure. Moreover, the plasticity almost did not change over the cross-section of the bar due to combination of structural and phase composition obtained after radial shear rolling. The results can provide the basis for development of industrial technology to produce long deformed semi-finished products for medical application.