In-Situ Synchrotron X-Ray Diffraction of Ti-6Al-4V During Thermomechanical Treatment in the Beta Field

Abstract

This work aims to identify the mechanisms of restoration occurring in Ti-6Al-4V during hot plastic deformation and subsequent heat treatment. The allotropic phase transformation that occurs during cooling distorts the interpretation of the restoration mechanisms taking place at high temperatures. Therefore, analysis of deformed samples by conventional microscopy have led to controversies in the interpretation of the main dynamic restoration mechanism. Additionally, static restoration of the microstructure can occur during slow cooling, modifying the microstructure. These facts were mainly the reasons why discontinuous dynamic recrystallization and/or dynamic recovery has been reported as the main dynamic restoration mechanism for Ti-6Al-4V. In this work, we use in-situ synchrotron X-ray diffraction combined with conventional microscopy to determine the dynamic and static mechanisms of restoration during and after deformation at different strain rates. The results show dynamic recovery as main mechanism of restoration during deformation in the β field, denoted by sub-grain formation and a misorientation dependency of the strain rate. After deformation, static recrystallization, grain growth, and coarsening of the β grains can be observed, especially at strain rates higher than 0.1s−1. It is also demonstrated that the nucleation of new grains can occur within the very first seconds of the isothermal heat treatment.

The Behaviours of Alloys under Thermo-Mechanical Treatment

“…The second and third contributions deal with the characterization of nickel-based superalloy [2] and titanium alloys [3] under hot deformation, respectively. In the work of B. Zhang et al [4], a nickel-based superalloy was produced by welding a powder metallurgy superalloy (the rim) with the wrought superalloy (the bore).…”

“…The hot deformation mechanisms and the flow behaviour of the couples are similar to those of the single alloys, with larger activation energies. The work of F. Warchomicka et al [3] deals with the characterization of the evolution of the microstructure of Ti64 alloy using in situ synchrotron diffraction during compression and annealing. The authors demonstrated that dynamic recovery happens during hot deformation and that the recrystallization occurs statically during the heat treatments.…”

High speed synchrotron X-ray diffraction experiments resolve microstructure and phase transformation in laser processed Ti-6Al-4V

“…Fast detectors (up to 20 kHz) have been employed to examine phase evolution under rapid processing [10,[15][16][17][18][19][20][21][22], such as welding and AM processing, and combination with ultrafast imaging provided new insights into the AM process [9,18,22]. Studies with high angular resolution and a relatively large area detector have revealed details of lattice changes for external mechanical and temperature factors [11,[23][24][25][26][27][28]. Our recent report presented an in-situ study of Ni-alloy 718 with a multi-panel area detector with an unprecedented combination of high 2θ-angular resolution and a 250 Hz frame rate [29].…”

In Situ Analysis of the Phase Transformation Kinetics in the β-Water-Quenched Ti-5Al-5Mo-5V-3Cr-1Zr Alloy during Ageing after Fast Heating

“…Analyses using these techniques are not always complete or easily carried out and interpreted. However, the development of high-energy X-ray diffraction (HEXRD) using synchrotron radiation allows real-time (in situ) observation of microstructural evolution and phase transformations [3,6,10,11,13,14]. HEXRD presents the advantage of short acquisition times and high resolution, and for this reason has gained momentum in the metallurgy area for providing the possibility of precisely elucidating phase transformation phenomena [11,12,15].…”