High Temperature Mechanical Properties of Additive Manufacturing CoCr F75 Alloy

Abstract

Additive Manufacturing (AM) has emerged as a promising technology for producing customized and complex design parts across various industries, including medical, automotive, aerospace, defense, tooling, jewelry, and fashion. By alloying cobalt with refractory elements, satisfactory oxidation resistance, and good hot corrosion resistance can be achieved. In this study, the mechanical properties of a Co-Cr-Mo alloy were investigated using stress-strain tests conducted at room temperature and elevated temperatures of 600˚C, 700˚C, 800˚C, 900˚C, and 1000˚C. The results revealed a systematic decrease in ultimate tensile strength (UTS) and a non-monotonic trend in yield stress, characterized by a notable increase at 800˚C. This increase in yield stress, accompanied by a decrease in elongation, represents anomalous behavior requiring further physical metallurgical explanation. It is hypothesized that the deformation mechanism changes at 800˚C due to alterations in the alloy’s metallurgical structure. The failure mechanisms and deformation modes of AM-printed samples of this specific Co-Cr-Mo alloy were also analyzed at high temperatures. Post-mechanical testing, sections of each sample were cut near the neck region to examine their cross-sections. These sections were prepared for optical metallography and SEM-EDS inspection along the tensile axis to observe flow deformation patterns and near-neck characteristics. The ductility, dimples, and partial twins observed at lower temperatures (between room temperature and 700˚C) are attributed to the γ -FCC phase formed during heat treatment. The recovery of the ɛ -HCP phase, stable during tensile testing at 800˚C, is assumed to contribute to the decrease in ductility. At higher temperatures, between 900˚C and 1000˚C, the increase in total deformation is attributed to the reformation of the γ -FCC phase at these elevated temperatures.