Effect of Diffusion Annealing and Aging Post-Treatments on Scratch Properties of Boride Layers on CoCrMo Alloy

Abstract

In this study, the influence of post-treatments on the adhesive properties of a cobalt boride layer was studied. At first, a powder-pack boriding process was performed on CoCrMo alloy (C1). A CoB-Co₂B layer with total thickness ~ 36 µm and diffusion zone ~ 32 µm was obtained for C1. Additionally, C1 was subjected to two post-treatments: (1) an aging treatment (C2), and (2) a diffusion annealing process followed by an aging treatment (C3). For C2, a Co₂B layer ~ 39 µm in thickness and diffusion zone of ~ 45 µm was achieved, whereas for C3, a Co₂B layer with thickness ~ 29 µm and diffusion zone of ~ 55 µm were obtained. The depth-sensing Vickers micro-indentation technique was used to evaluate the boride layer-substrate systems. The hardness, elastic modulus, and residual stresses were estimated along all circumstances, applying a constant load of 500 mN. Subsequently, the practical adhesion of C1, C2, and C3 was evaluated by the scratch test with a Rockwell C diamond indenter, incrementally increasing the normal force from 5 to 150 N. Notably, the critical load required for complete detachment of the boride layer exhibited an increase of about 19% for C2 and approximately 41% for C3 compared to C1.