Influence of Oxygen on Microstructures of Ti-Mo-Cr Alloy

Abstract

In this study, the effect of oxygen addition on the microstructures of Ti-18%Mo-10%Cr alloy was investigated. The alloy was fabricated by a powder metallurgy method. The samples were subjected to sintering at 1300°C for 4 hours and furnace cooling. A Bo-Md method was initially applied for predicting stable phase. Calculation using the Bo-Md method showed that Ti-18%Mo-10%Cr alloy have bcc (β) phase at ambient temperature. All samples with various oxygen contents exhibited needle-like structures within equiaxed grains. The increase of oxygen content promoted formation of porosity in the α phase. Calculation of phase stability using JMatProTM showed that the decrease of β phase’s stability was not due to formation of the α phase on sintering, but due to promotion of nucleation and grain growth of diffusional α phase upon furnace cooling. It was also shown that vol.% of porosity of the alloy slightly increased with increasing oxygen content. Therefore, the increase of oxygen concentration could accelerate the formation of α phase and reduce the alloy’s density. The hardness increased as the oxygen concentration increased. The increase of the hardness might be due to combination of the solid solution hardening of oxygen and the precipitation hardening of α phase.

Microstructure and Mechanical Properties of Ti-Mo-Zr-Cr Biomedical Alloys by Powder Metallurgy

“…Ho et al [26] stated that the dependence of the modulus had a more sensitive effect on the phase/crystal structure than on other factors. It is widely known that the β phase Ti alloys generally have a lower modulus level than the α or α+β phase-type alloys [22][23][24][25][26]. Additionally, the Ti15Mo6Zr2Cr alloy had the lowest elastic, compression and bending moduli, which were lower than that of the Ti15Mo6Zr base alloy.…”

“…As mentioned in Introduction to this study, the use of implant materials with lower moduli (closer to that of a human bone) can reduce the stress-shielding effect. Additionally, implants bearing heavy loads must be strong and durable enough to withstand their physiological responsibilities over the years [22][23][24][25][26]. As such, achieving high strength under the conditions of a low elastic modulus that is close to the modulus of the implant's surrounding bone is central to alloy development.…”

“…In fact, Cr has already been used for many years as a major constituent in dental casting alloys [22]. Syarif et al explored the stabilization of the  phase with the addition of different Cr contents on Ti18Mo alloys [23] as well as the influence of oxygen in the microstructure of the Ti18Mo10Cr alloy obtained by powder metallurgy [24]. In the current study, the effects of Cr on the microstructure and mechanical properties of a Ti-15Mo-6Zr based alloy were investigated in an effort to develop new alloys for biomedical applications.…”