Effects of Ni and Mo on the microstructure and some other properties of Co–Cr dental alloys

Abstract

Influences of adding Ni and Mo on the microstructure and properties of as-cast Co–Cr base alloys have been investigated in order to determine the region of their optimal characteristics for biomedical application. The alloys were produced by arc-melting technique under argon atmosphere. Using optical metallography and scanning electron micro analyser it has been established that among 10 samples of Co–Cr–Ni alloys only samples 5 and 9 with the composition Co 55Cr 40Ni 5 and Co 60Cr 30Ni 10 have appropriate dendritic solidification microstructure. This microstructure, typical for commercial dental alloys, appears and beside greater number of as-cast Co–Cr–Mo alloys. The results of hardness and corrosion resistance measurements revealed the strong influence of different alloy chemistry and of as-cast microstructure. Hardness of alloys decreases with nickel content, but increases with chromium content. Therefore all Co–Cr–Ni alloys have significantly lower hardness than Co–Cr–Mo alloys. Corrosion resistance of alloys in artificial saliva was evaluated on the base of pitting potential. Superior corrosion characteristics have the samples with typical dendritic microstructure and higher chromium content, until nickel content have not significant effect. According to this, in ternary Co–Cr–Ni phase diagram was located the small concentration region (about samples 5 and 9) in them alloy properties can satisfied the high requirements for biomedical applications. This region is considerably larger in Co–Cr–Mo phase diagram.