Effect of molybdenum on structure, microstructure and mechanical properties of biomedical Ti-20Zr-Mo alloys

Titanium has an allotropic transformation around 883 degrees C. Below this temperature, the crystalline structure is hexagonal close-packed (a phase), changing to body-centered cubic (( phase). Zirconium has the same allotropic transformation around 862 degrees C. Molybdenum has body-centered cubic structure, being a strong 3-stabilizer for the formation of titanium alloys. In this paper, the effect of substitutional molybdenum was analyzed on the structure, microstructure and selected mechanical properties of Ti-20Zr-Mo (wt%) alloys to be used in biomedical applications. The samples were prepared by arc-melting and characterized by x-ray diffraction with subsequent refinement by the Rietveld method, optical and scanning electron microscopy. The mechanical properties were analyzed by Vickers microhardness and dynamic elasticity modulus. X-ray measurements and Rietveld analysis revealed the presence of alpha' phase without molybdenum, alpha' + alpha phases with 2.5 wt% of molybdenum, alpha + beta phases with 5 and 7.5 wt% of molybdenum, and only beta phase with 10 wt%, of molybdenum. These results were corroborated by microscopy results, with a microstructure composed of grains of beta phase and lamellae and needles of a' and a phase in intra-grain the region. The hardness of the alloy was higher than the commercially pure titanium, due to the action of zirconium and molybdenum as hardening agents. The samples have a smaller elasticity modulus than the commercially pure titanium. (C) 2016 Elsevier B.V. All rights reserved.