Influence of Precipitation Hardening on the Mechanical Properties of Co-Cr-Mo and Co-Cr-W-Mo Dental Alloys

Abstract

Co-Cr alloys have good mechanical properties such as high hardness, excellent magnetic properties and good corrosion resistance. For this reason, they are most commonly used as dental and orthopaedic implants. Generally, cast Co-Cr-Mo alloys and forged Co-Ni-Cr-Mo alloys are used for the production of implants. In this study, we investigated two dental alloys, namely, Co-Cr-Mo and Co-Cr-W-Mo alloys. The aim of this study was to determine the effect of heat treatment on the development of the microstructure and to evaluate its influence on the alloys’ mechanical and tribological properties. The samples were first solution-annealed at 1200 °C in an argon atmosphere for 2 h, then quenched in water and subsequently aged at 900 °C in an argon atmosphere for 1, 3 and 12 h. A microstructural analysis was performed using SEM, with EDS for microchemical analysis and EBSD for phase identification. In addition, the Vickers hardness and wear resistance of the two alloys were analysed before and after heat treatment. The Co-Cr-Mo alloy showed better wear resistance and also a generally higher hardness than the Co-Cr-W-Mo alloy. Both alloys showed signs of abrasive and adhesive wear, with carbide particles detaching from the Co-Cr-W-Mo alloy due to the lower hardness of the matrix. The Co-Cr-Mo alloy showed the best abrasion resistance after the longest aging time (12 h), while the Co-Cr-W-Mo alloy showed the best as-cast abrasion resistance. With ageing, the wear resistance of both alloys increased.

Analysis of Microstructure Evolution of Co-Cr-Mo Alloy during Isothermal Forging

“…The grain boundary precipitates of excess σ-phase were completely dissolved in the solid solution matrix. Numerous intersecting bands were observed in the grain structure, which, according to the data [3], corresponded to the mixed structure of the austenite (γ-Co) and martensite (ε-Co) phases. The spectrum regions 1-4 for EMPA and the phase composition of these spectrums are presented in Figure 6b,c-f, respectively.…”

“…Co-Cr-Mo alloys are among the advanced materials used in medicine to produce different implants and their components. While in service in the human body, these implants are subjected to cyclic loads, corrosion environments, and significant wear [1][2][3]. Co-Cr-Mo alloys are characterized by high values of mechanical properties combined with good resistance to corrosion and wear [4][5][6].…”