Influence of zirconium and oxygen on the structure, microstructure and mechanical properties of alloys of the Ti-Mo-Zr system

Author(s)

Raul Oliveira de Araújo

• Document type: Doctoral Thesis
• Press: Bauru. 2017-10-11.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Ciências. Bauru
• Defense date: 2017-08-28
• Advisor: Carlos Roberto Grandini

Abstract

Due to several factors such as the number of accidents in sports, traffic, diseases like arthritis, osteoporosis, and the loss of biological functions related to aging, among others, lead to a search for materials with the ability to fulfill the function of replacing parts or organic functions of the human body. Among the materials with the function of replacing human tissues that load-bearing, are the class of metals, and among this class are the Co-Cr alloys, the ASTM F138 stainless steel, the pure titanium and the Ti-6Al-4V alloy. However, there is a need for alloys that promote better mechanical and biological compatibility. In this sense, this work aims at the preparation and characterization of the Ti-10Mo-xZr alloys (x = 5, 10, 15 and 20 wt%) for biomaterial applications. These alloys were subjected to several kinds of thermomechanical treatments, such as hot rolling, annealing, solubilization and heat treatment in an oxygen controlled atmosphere, in order to incorporate this element into the alloy. The alloys were chemically characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), energy dispersive spectroscopy (EDS), in addition to gas and density analyzes. Structural and microstructural characterization were made by X-ray diffraction measurements, with refinement by Rietveld’s method, optical and scanning electron microscopy. Mechanical characterization was made by Vickers microhardness and elastic modulus measurements, and biological characterization was made by in vitro cytotoxicity assays. The alloys presented desirable stoichiometry with good chemical homogeneity. Regarding to structure and microstructure, there is a predominance of  phase, which becomes more stable with the increase in zirconium concentration in detriment of other phases as ’, ’’ and . In this way, the microhardness decreases with the addition of the substitutional element (from 451 HV to 372 HV), due to a higher  phase stability, in detriment of those secondary phases. The same behavior was verified in relation to the elastic modulus (from 98 GPa to 77 GPa). With respect to the influence of oxygen, there is an increase in the values of microhardness and elastic modulus with the addition of this element. Biological tests did not indicate cytotoxic effects. For biological applications, the Ti-10Mo-20Zr alloy becomes the most promising because it has a low astic modulus compared to ASTM F138 stainless steel, Co-Cr, cp-Ti, Ti-6Al-4V and Ti-15Mo alloy. (AU)

• FAPESP's process: 13/09063-5 - Effect of substitutional element and interstitial oxygen in the structure, microstructure, in some selected mechanical properties and biocompatibility of the Ti-Mo-Zr system alloys
• Grantee: Raul Oliveira de Araújo
• Support Opportunities: Scholarships in Brazil - Doctorate