Effect of Supra-Transus Deformation Conditions on Recrystallization of Beta Ti Alloy

Chao Voon Samuel Lim,Chen Ding,Yang Liu,Aijun Huang

doi:10.3390/met11081278

Chao Voon Samuel Lim, Chen Ding + Show 2 more

Open Access

https://doi.org/10.3390/met11081278

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Journal: Metals	Publication Date: Aug 12, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: Monash University, Materials Science & Engineering

Abstract

There is increasing usage of high strength Beta Ti alloy in aerospace components. However, one of the major challenges is to obtain homogeneous refined microstructures via the thermo-mechanical processing. To overcome this issue, an understanding of the hot deformation conditions effect on the microstructure, prior to and after annealing, is needed. In this work, the effect of strain levels, which is more precise than percentage of reduction, and strain rate under supra-transus deformation temperature on beta annealing are studied using a double cone sample. The Electron Backscattered Diffraction (EBSD) is used to determine the deformed microstructure and texture evolution, as well as the static recrystallized grains evolution using the ex situ annealing approach. This work provides evidence that the mechanisms of dynamic recovery and recrystallization, along with texture evolution, are affected by the deformation conditions, which in turn affected the subsequent static recrystallization during annealing. It will also be shown that high levels of strain do not necessarily lead to an increase in the rate of recrystallization. Finally, the results obtained provided several examples of guidance in designing the TMP processes for obtaining not only a refine microstructure, but a more homogeneous beta microstructure during the beta processing of Beta Ti alloy.

Highlights

There is a morphological correlation with the strain range wherein the initial generally equiaxed beta grains became more elongated with strain. These were observed from the Electron Backscattered Diffraction (EBSD) data obtained as shown in Figure 3, irrespective of nominal strain rates
When the grains were deformed to higher strain ranges/levels greater than 1.25, the beta grains have developed mainly similar orientations of {001} as shown in the inverse pole-figure (IPF) microstructure map for sample deformed with nominal strain rate of 0.1 and 0.01/s (Figure 3b,c)
The strain level from our study indicates that recrystallization is not dependent on high strain levels

Summary

Introduction

Thermo-mechanical processing (TMP) and heat treatment are used together in Ti alloy billet production to bring the initial cast ingot down to size, but to improve their mechanical properties by modifying the microstructure [1,2]. All Ti alloy billets will be hot processed initially in the supra-transus region (above beta transus) to break down the cast microstructure, and to refine the beta grain size [3]. This will be followed by sub-transus hot processing or a combination of sub-transus–supratransus–sub-transus processing. It is to be noted that how the TMP is conducted/designed has a considerable influence and effect on the microstructure and the mechanical properties of the Ti alloy

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