Improving the tribological behaviour by Hertzian strain hardening pre-treatment of CoCrMo alloy

• Determine the optimal conditions for strain hardening of the Co28Cr6Mo • Improving Mechanical Properties by strain hardening • Improving Tribological behaviour • Wear is closely linked to the formation of oxides The objective of the present research work was to investigate whether strain hardening induced by Hertzian contact with friction is effective in increasing wear resistance. A Co28Cr6Mo alloy was selected considering the known strain hardening effect of these alloys. Cross cylinder configuration geometry rotating against a WC-composite specimen was chosen to behave as a rigid body. The results show that the wear occurring at the surface is closely linked to the formation and attachment of oxides at the wear marks. The development of those oxides occurs under specific conditions of normal force (simulated through tribological tests), promoting the creation of a protective layer against wear. The surface hardening of this alloy carried out under specific conditions (normal pressure) leads to a large formation of oxides at marks. Besides, the wear resistance was improved, namely reducing the volume of material removed when subjected to wear. Thus, the results of this research work allowed: (i) quantify the influence of oxides in the protection of this alloy against wear; (ii) define the optimum conditions of mechanical treatment (strain hardening) that would be associated with this improved tribological behaviour. The surface hardening treatment increased the near-surface hardness of Co28Cr6Mo by approximately 15–18% (from 500 HV to 580 HV). Under optimal conditions (medium pressure, 10.57 N), the wear coefficient decreased by one order of magnitude (from 4.4 × 10⁻⁵ to 4.4 × 10⁻⁶ mm³/N·m), correlated with an oxide coverage of approximately 40%. These results confirm that wear resistance is directly enhanced by controlled oxide formation induced by pre-strain.