Role of ω phase in the formation of extremely refined intragranular α precipitates in metastable β-titanium alloys

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• 作者：Yufeng Zheng^a ; Robert E.A. Williams^a ; Dong Wang^b ; ^c ; Rongpei Shi^a ; Soumya Nag^b ; Pavani Kami^b ; John M. Sosa^a ; Rajarshi Banerjee^b ; Yunzhi Wang^a ; Hamish L. Fraser^a ; ^{fraser.3@osu.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Titanium alloys ; Phase transformations ; Heterogeneous nucleation ; High resolution electron microscopy ; Phase field method
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 January 2016
• 年：2016
• 卷：103
• 期：Complete
• 页码：850-858
• 全文大小：4697 K

文摘

Coupling high-resolution characterization and phase-field microelasticity modeling, the non-conventional transformation pathway, mediated by ω precipitates, that leads to super-refined intragranular α precipitates in a metastable β Ti-alloy (Ti–5Al–5Mo–5V–3Cr, all in wt%) has been rationalized for the first time. Samples are initially solution treated above the β transus, rapidly cooled to room temperature, and then slowly heated (in the range 20°C–1 °C/min) to 600 °C. Interrupted tests, coupled with characterization involving scanning electron microscopy (SEM), transmission electron microscopy (TEM), high angle annular dark field-high resolution scanning transmission electron microscopy (HAADF-HRSTEM) and atom probe tomography (APT), have revealed the role of the ω phase on the copious nucleation of α leading to super-refined precipitation. Thus, both stress and compositional variations associated with the development of isothermal ω during heating contribute to an extra driving force for nucleation. It is also found that the interfaces between the super-refined α and the β matrix are relatively coherent, unlike the case of such interfaces in α/β Ti alloys. The experimental results have been combined with CALPHAD and phase field microelasticity modeling to assist in developing a robust notion of the factors influencing copious nucleation in these samples.