Bio-tribo-corrosion behavior of additively manufactured Co-Cr dental implant alloy

Abstract

A CoCr-based dental alloy was deposited upon layer built-ups through a laser-assisted directed energy deposition (L-DED) technique. Microstructural studies, including grain morphologies, crystallographic texture formation and nano planar defects were conducted utilizing advanced characterization techniques based on the scanning and transmission electron microscopies. Also, the biocompatibility and cell viability were evaluated with MG-63 cells via MTT assay and cell adhesion test. Additionally, mechanical properties of the deposited alloy, specifically hardness and wear resistance, were assessed through indentation micro-hardness measurements and tribological behavior examinations in simulated oral environments under different loading conditions. Finally, the resistance to corrosion was investigated in Ringer's solution by electrochemical techniques. Microstructural characterization revealed the formation of gradient structure along the building direction due to the combination of columnar/equiaxed dendritic morphologies upon rapid cooling, resulting in the generation of preferred 〈001〉 growth direction with a maximum misalignment of ~25° along scanning direction. In addition, the presence of dense stacking faults interacting with each other and carbides was identified as one of the key factors for strengthening, leading to a high average microhardness of 542 HV_0.2 and excellent wear resistance of around 4.2 × 10⁻⁵ mm³/N.m when subjected to a 50 N load. The remarkable viability of ~94.6 % for MG-63 cells cultured on the surface for a week, together with excellent cell spreading and adhesion, indicated the absence of any cytotoxic response. The high polarization resistance of ~650 kΩ.cm⁻² in simulated oral medium owing to the development of a mixed oxide layer suggested that the fabricated CoCr-based alloy was suitable for dental applications.