Strain-induced phase transformation during thermo-mechanical processing of titanium alloys

Abstract

Strain-induced phase transformation studies have been conducted in a Ti-6Al-2Sn-4Zr-6Mo alloy. This alloy was subjected to b sub-transus deformation upon slow cooling from the b-phase field and the effect of strain on the extent and morphology of the phase transformation during hot-deformation was determined. In addition, the transformation kinetics and the morphology of the newly formed a-phase were studied following deformation under different cooling conditions. By applying strain, the rate of the b-to-a phase transformation increased significantly during deformation as well as during slow cooling following deformation. This increase in the kinetics of the b-to-a transformation can be ascribed to straininduced phase transformation. Also, the extent of deformation of the b-phase had a marked effect on the resulting morphology and size of the newly formed a-phase. Transformation of un-deformed b-phase rendered a-phase of acicular morphology only. However, following deformation of the b-phase, acicular as well as globular a-phase morphologies have been observed upon cooling. alloy. This alloy was subjected to β sub-transus deformation upon slow cooling from the β-phase field and the effect of strain on the extent and morphology of the phase transformation during hot-deformation was determined. In addition, the transformation kinetics and the morphology of the newly formed D-phase were studied following deformation under different cooling conditions. By applying strain, the rate of the β-to-α phase transformation increased significantly during deformation as well as during slow cooling following deformation. This increase in the kinetics of the E-to-D transformation can be ascribed to strain-induced phase transformation. Also, the extent of deformation of the β-phase had a marked effect on the resulting morphology and size of the newly-formed D-phase. Transformation of un-deformed β-phase rendered D-phase of acicular morphology only. However, following deformation of the β-phase, acicular as well as globular D-phase morphologies have been observed upon cooling.

Microstructure and Crystallography of α Phase Nucleated Dynamically during Thermo‐Mechanical Treatments in Metastable β Titanium Alloy

“…The phase transformation is obviously retarded (Figure 4), which is contrary to the understanding of deformation induced phase transformation. [10] From the Section 3.2, we did not find that the b ! a phase transformation happened immediately with the starting of the deformation (Figure 2a 3 ).…”

“…[4][5][6][7] The b ! [10] Some other researches also implied a competitive relationship between precipitation and recrystallization. Generally, heterogeneous nucleation mechanisms include grain boundary nucleation, dislocation nucleation, and vacancy nucleation.…”

“…[20] The transition of the semi-coherent interfaces into incoherent ones can also accelerate, significantly, the spheroidization of the lamellar microstructure. [10] The aforementioned investigations are useful for understanding microstructural evolution of metastable b titanium alloys during hot deformation. a phase transformation.…”

“…Hence, dynamic stress induced phase transformations (DSIPT) might happen during the thermo-mechanical processing due to the more nucleation sites and accelerating growth of a precipitates. [10] Some other researches also implied a competitive relationship between precipitation and recrystallization. [11,12] Unfortunately, except earlier studies of martensite-based strain induced transformation following cold deformation, [13] the DSIPT about b $ a phase transformation in titanium alloys does not seem to have been fully assessed and exploited.…”

“…Furthermore, hot deformation could give a significant effect on the morphology of the subsequently precipitated a phase. [10] The aforementioned investigations are useful for understanding microstructural evolution of metastable b titanium alloys during hot deformation. However, a clear understanding about the characteristics of the dynamic a precipitation during deformation is still not entirely available, and even be ignored.…”