Alessandra Cremasco

Ti-Mo alloys employed as biomaterials: Effects of composition and aging heat treatment on microstructure and mechanical behavior

The correlation between the composition, aging heat treatments, microstructural features and mechanical properties of β Ti alloys is of primary significance because it is the foundation for developing and improving new Ti alloys for orthopedic biomaterials. However, in the case of Ti-Mo alloys, this correlation is not fully described in the literature. Therefore, the purpose of this study was to experimentally investigate the effect of composition and aging heat treatments on the microstructure, Vickers hardness and elastic modulus of Ti-Mo alloys. These alloys were solution heat-treated and water-quenched, after which their response to aging heat treatments was investigated. Their microstructure, Vickers hardness and elastic modulus were evaluated, and the results allow us to conclude that stabilization of the β phase is achieved with nearly 10% Mo when a very high cooling rate is applied. Youngs modulus was found to be more sensitive to phase variations than hardness. In all of the compositions, the highest hardness values were achieved by aging at 723K, which was attributed to the precipitation of α and ω phases. All of the compositions aged at 573K, 623K and 723K showed overaging within 80h.

Effects of Cooling Rate and Sn Addition on the Microstructure of Ti-Nb-Sn Alloys

Ti-based alloys present unique properties and hence, are employed in several industrial segments. Among Ti alloys, β type alloys form one of the most versatile classes of materials in relation to processing, microstructure and mechanical properties. It is well known that heat treatment of Ti alloys plays an important role in determining their microstructure and mechanical behavior. The aim of this work is to analyze microstructure and phases formed during cooling of β Ti-Nb-Sn alloy through different cooling rates. Initially, samples of Ti-Nb-Sn system were prepared through arc melting furnace. After, they were subjected to continuous cooling experiments to evaluate conditions for obtaining metastable phases. Microstructure analysis, differential scanning calorimetry and X-ray diffraction were performed in order to evaluate phase transformations. Depending on the cooling rate and composition, α” martensite, ω phase and β phase were obtained. Elastic modulus has been found to decrease as the amount of Sn was increased.

Effects of Aging Heat Treatment on the Microstructure of Ti-Nb and Ti-Nb-Sn Alloys Employed as Biomaterials

The mechanical behavior of β titanium alloys applied as orthopedic biomaterials depends directly on their microstructural features, and can be improved by tailoring the microstructure through the control of their phase transformations. The aim of this investigation is to discuss phase transformations during the aging heat treatment of β Ti-30Nb and β Ti-30Nb-2Sn alloys and to correlate microstructure and mechanical behavior. The results of high temperature XRD experiments showed decomposition of orthorhombic α” phase, followed by the precipitation of ω and α phases. The mechanical behavior of Ti-Nb and Ti-Nb-Sn alloys was found to be highly sensitive to the microstructural changes caused by the addition of Sn and by heat treatments.

Effect of Heat Treatments on Mechanical Properties and Fatigue Resistance of Ti-35Nb Alloy Used as Biomaterial

Titanium alloys form the most versatile class of metallic materials used as biomaterials. Among them it is foreseen that the  type titanium alloy will be a prominent one for orthopedic applications. Aim of the present work was to prepare and characterize a  type titanium alloy containing 35 wt.% Nb. Samples were cooled from the  phase temperatures at different rates. This work includes the effects of heat treatment on the microstructure and hardness, tensile and fatigue properties in air at room temperature. The results showed that microstructure of slow cooled samples are formed by precipitates of  and  phases in a  matrix. After rapid cooling, the microstructure consists of  phase and ” martensite. Mechanical testing showed that the elastic modulus and Vickers hardness of slow cooled samples were significantly higher than that obtained by rapid cooling. On the other hand, it was observed that slow cooled samples showed higher tensile strength and lower ductility. The rapid cooled sample showed fatigue resistance higher than that of slow cooled samples.