Effect of duplex aging on microstructural and mechanical behavior of a new β-Ti alloy for biomedical applications

Abstract

The influence of duplex aging on the microstructural and mechanical behavior of Ti–25Nb–10Ta–1Zr-0.2Fe alloy was investigated. The first step of duplex aging (DA) treatments was carried out at 300 °C or 400 °C for 20min and 1 h, followed by the second step aged at 550 °C for 20min-24 h.A small amount of athermal ω (ωath) formed in the β matrix after solution treatment and water quenching. During single aging (SA) at 550 °C, upon slowly heating process, the ωath→isothermal ω (ωiso)→isothermal α" (α"iso) might occur. Subsequently, the α"iso dissolved rapidly and transformed into α phase at the early stage of aging, resulting in a fine distribution of α precipitates in the β matrix. During DA treatments, the fine ωiso and α"iso were observed in the first stage aging at 300 °C/400 °C, then the metastable ωiso and α"iso decomposed into α phase at higher temperature of 550 °C. Besides fine α laths, ladder-shaped α clusters with large size were observed after DA. There was a single-peak in the hardness curve of SA, and the peak hardness was associated with the uniform distribution of fine plate-like α phase. After DA treatments, the alloy showed stronger age-hardening and displayed obvious double-peak precipitation hardening. The first hardness peak was the result of the dense ωiso nano-particles formed in the first aging stage, while the second one could be mainly attributed to these large ladder-shaped α clusters in the second aging stage. Compared with SA, the balance between high strength and low modulus could be improved by an appropriate DA treatment.