Investigation of the wear transition in CoCrMo alloys after heat treatment to produce an HCP structure

This study reports that the wear rate of the heat-treated CoCrMo alloy shows a sudden transition of more than 5-fold when the load/contact pressure increases from 45 N (3.6 GPa) to 50 N (3.7 GPa). Heat treatment was used to change the structure of the commercially available CoCrMo from the initial face-centred cubic (γ-fcc) with a small amount of hexagonal close-packed (ε-hcp) to predominantly hcp ε-phase with dispersed nanoscale precipitates of σ-phase. PeakForce QNM was used to quantitatively map the local mechanical properties of the surface at the nanoscale. High-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscope (STEM), energy-dispersive X-ray spectroscopy (EDX), and precession electron diffraction (PED) integrated with the TEM is used to characterize the structure and chemical composition of the worn surface and tribofilm. The possible reason for wear transition was discussed.