Characterization of Microstructural Evolution for a Near-α Titanium Alloy with Different Initial Lamellar Microstructures

Hui Li,Zhanglong Zhao,Yongquan Ning,Hongzhen Guo,Zekun Yao

doi:10.3390/met8121045

Abstract

The effects of initial lamellar thickness on microstructural evolution and deformation behaviors of a near-α Ti-5.4Al-3.7Sn-3.3Zr-0.5Mo-0.4Si alloy were investigated during isothermal compression in α + β phase field. Special attention was paid to microstructural conversion mechanisms for α lamellae with different initial thicknesses. The deformation behaviors, including flow stress, temperature sensitivity, and strain rate sensitivity, and processing maps and their dependence on initial lamellar thickness were discussed. The detailed microstructural characterizations in different domains of the developed processing maps were analyzed. The results showed that the peak efficiency of power dissipation decreased with increasing initial lamellar thickness. The interaction effects with different extents of globularization, elongating, kinking, and phase transformation of lamellar α accounted for the variation in power dissipation. The flow instability region appeared to expand more widely for thicker initial lamellar microstructures during high strain rate deformation due to flow localization and local lamellae kinking. The electron backscatter diffraction (EBSD) analyses revealed that the collaborative mechanism of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) promoted the rapid globularization behavior for the thinnest acicular initial microstructure, whereas in case of the initial thick lamellar microstructure, CDRX leading to the fragmentation of lamellae was the dominant mechanism throughout the deformation process.

Highlights

Near-α titanium alloy with an attractive combination of properties has been extensively applied as advanced structural material for aeroengine components [1,2]
Discontinuous dynamic recrystallization (DDRX) promoted the rapid globularization behavior for the thinnest acicular initial microstructure, whereas in case of the initial thick lamellar microstructure, CDRX leading to the fragmentation of lamellae was the dominant mechanism throughout the deformation process
To investigate the deformation behavior of the alloy in α + β phase field, cylindrical specimens of 8 mm diameter and 12 mm height were machined for isothermal compression tests which were performed on a Gleebe-3500 thermo-mechanical simulator

Summary

Introduction

Near-α titanium alloy with an attractive combination of properties has been extensively applied as advanced structural material for aeroengine components [1,2]. The Ti-5.4Al-3.7Sn-3.3Zr-0.5Mo-0.4Si alloy discussed in the present work is a type of near-α high-temperature titanium alloy for advanced gas turbine compressor disk application, which exhibits excellent thermal capability properties under the servicing temperature of 600 ◦ C [3,4]. The mechanical properties linked with the final microstructures of titanium alloys are dependent on a set of typical hot-working steps involving primary cogging in β phase field, thermo-mechanical processes below the β-transus, and subsequent heat treatment [5]. It is necessary to have an in-depth knowledge about the deformation behavior, hot workability, and microstructure development of the material in the process in order to obtain optimum process schedules and achieve the desired microstructure and mechanical properties. Jackson et al [6]

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