Nanoscale Mechanical Evaluation of Electrochemically Generated Tribolayer on CoCrMo Alloy for Hip Joint Application

Abstract

Cobalt chromium molybdenum alloy (CoCrMo) is widely employed in the orthopedic device industry due to a combination of properties that include low wear, high mechanical strength, and high corrosion resistance. However, when used as the bearing component of total hip implants, this material can be susceptible to wear and corrosion, which can be triggered or exacerbated by factors such as changing pH, biological fluids and cell interactions, particle release, and friction. The physiological fluid, which is composed of electrolytes, proteins, and other organic species, plays a critical role in the tribological behavior of CoCrMo alloy. The aim of this work is to generate a proteinaceous layer electrochemically and carry out nanoscale mechanical and surface evaluation of CoCrMo to understand the feasibility of a pre-treatment on this material. The treatments consisted of electrolytes, with different protein concentrations, and pre-selected transpassive potentials at +0.6, +0.7 and +0.8 V and a passive potential of −0.4 V. These observations will help in determining the electrolyte concentration and potential combination that would yield the most protective film layer. The results demonstrated that all the positive transpassive potentials and electrolyte combinations led to surface degradation processes causing more material removal as seen by the formation of localized corrosion at carbide and grain boundaries. Only the negative potential of −0.4 V, used by itself as a pre-treatment and in combination with an electrolyte with 30 g/L of bovine calf serum (BCS), demonstrated more homogeneous oxide layer and proteinaceous layer distribution respectively.