Abstract
The effect of initial structure on phase evolution in continuous heating of a near-α TA15 titanium alloy (Ti-6Al-2Zr-1Mo-1V) was experimentally investigated. To this end; three microstructures were obtained by multiple heat treatment: I-bimodal structure with 50% equaixed α, II-bimodal structure with 15% equiaxed α, III-trimodal structure with 18% equiaxed α and 25% lamellar α. Differential scanning calorimetry (DSC), dilatometry and quantitative metallography were carried out on specimens with the three initial structures at heating rates from 5 to 40 °C/min. The transformation kinetics was modeled with the Johnson–Mehl–Avrami (JMA) approach under non-isothermal condition. It was found that there exists a four-stage transformation for microstructures I and III. The secondary and third stages overlap for microstructure II. The four stages of phase transformation overlap with increasing heating rate. In the presence of α laths, the phase transformation kinetics is affected by the composition difference between lamellar α and primary equiaxed α. Phase transformation is controlled by the growth of existing large β phase.
Highlights
Titanium alloys have been gaining more applications in many industry fields due to the high specific strength, good thermal stability and excellent corrosion resistance [1]
The secondary and third stages overlap for microstructure II
In the presence of α laths, the phase transformation kinetics is affected by the composition difference between lamellar α and primary equiaxed α
Summary
Titanium alloys have been gaining more applications in many industry fields due to the high specific strength, good thermal stability and excellent corrosion resistance [1]. Found that the α lamellae can nucleate in a sympathetic way or by interface instability during slow cooling He et al [7] examine the orientation relationship between α and β phase after β working. Barriobero-Vila et al [14] examined the element partitioning and related phase transformation kinetics in heating of a bimodal Ti-6Al-6V-2Sn alloy by in-situ high energy synchrotron X-ray diffraction They found that partitioning of solutes leads to nonlinear variation of the lattice parameters of the β phase. The effect of initial structure on the phase evolution in continuous heating of TA15 titanium alloy was investigated. To this end, multiple heat treatments were employed to obtain three different microstructures from a wrought billet. The results can be used for quantative control of phase constitution in hot working
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