Precipitation Behavior of Ti15Mo Alloy and Effects on Microstructure and Mechanical Performance
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JMEPEG https://doi.org/10.1007/s11665-019-04456-7
Precipitation Behavior of Ti15Mo Alloy and Effects on Microstructure and Mechanical Performance Tiewei Xu, Shanshan Zhang, Ning Cui, Lei Cao, and Yong Wan (Submitted April 7, 2019; in revised form October 31, 2019) Precipitation behaviors of Ti15Mo alloy subjected to 3, 5, 10 and 20 °C/min cooling from the b phase field were investigated, and the variation trend of the activation energy during the cooling process was analyzed with DSC measurements and the Flynn–Wall–Ozawa method. The texture and microstructure of the phase transformation in different isothermal aging conditions were analyzed with XRD and TEM. The patterns of x and x/a in specimens aged at 450 and 500 °C show that b fi x and b fi x/a phase transformations occur, respectively. XRD spectra and SAD patterns illustrate that the precipitates transformed during aging over 525 °C are a phase. The morphology of the precipitation indicates that the size of the a phase formed in the isothermal treatment increases with increasing aging temperature. In contrast, the intensity of the (10-11)a texture decreases with increasing aging temperature. The tensile properties and fractures were investigated to determine the correlation between phase transformation and mechanical performance. The alloy has the highest ultimate tensile strength (UTS) at 1440 MPa because the x phases transform during aging at 450 °C. A good combination of tensile properties, with a UTS of 970 MPa and an elongation of 14.5%, was obtained in the specimen aged at 550 °C for 8 h. Keywords
mechanical properties, microstructure, precipitation behavior, TEM, titanium alloy
1. Introduction Titanium alloys have been widely applied in the medical field in past decades because their excellent properties are beneficial in satisfying the requirements of biomedical applications (Ref 1, 2). However, conventional medical titanium alloys (Ti6Al4VELI, Ti6Al7Nb, etc.) contain Al and V toxic elements and are not an optimal choice for implantation into the human body (Ref 3). In the past few years, neotype Ti-Mo alloys have been designed to address the nontoxic and lowmodulus requirements of medical metals. Ti-Mo alloys have combination properties (high strength and low elastic modulus) and exhibit a potential advantage in biomedical applications (Ref 4, 5). Microstructural evolution and its effects on the mechanical performance of Ti-Mo alloys have been studied by many scholars (Ref 5-12). Langmayr et al. (Ref 13) reported that the size of x precipitates are restricted to less than 16 nm, and x fi a occurs with the dissolution of x particles in a Ti-12 at.% Mo alloy. Devaraj et al. (Ref 14, 15) found that x embryos are transformed by the collapse of the {111} planes of the parent bcc structure and are accompanied by the composition variation of phase-separated regions in a Ti-9at.% Mo alloy. Chia et al. (Ref 16) reported that the deformation behavior in a solution-treated Ti-Mo alloy was influenced by the grain size Tiewei Xu, Shanshan Zhang, Ning Cui, Lei Cao, and
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