Strain rate sensitivity, temperature sensitivity, and strain hardening during the isothermal compression of BT25y alloy

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ichong Yuan China National Erzhong Group Co., Deyang 618013, People’s Republic of China (Received 19 May 2016; accepted 25 July 2016)

The high-temperature flow behavior and flow stress sensitivity of BT25y alloy were investigated. Results show that hot deformation is accompanied by the dynamic competition between work hardening and flow softening. The strain rate sensitivity exponent m tends to decrease with the strain rate after a first rise, and reaches the maximum at strain rate of 0.1 s1. There is a large temperature range exhibiting m values above 0.2 at strain rates of 0.01–0.1 s1. The temperature sensitivity exponent s shows an overall dropping trend with elevated temperature. The strain hardening exponent n first decreases and then increases with the strain at strain rate of 0.01 s1. Large positive n values lie in areas with high strain rate, and small negative n values are located in areas with lower temperature and small strain rate. Secondary lamellar a appears near the phase transition temperature. The microstructure presents elongated characteristics at high strain rate.

I. INTRODUCTION

Titanium alloys are getting extensive applications in aerospace industry with excellent mechanical properties like low density, high specific strength, good corrosion resistance, and elevated service temperature.1,2 However, with the rapid development of aero-engines, higher requests for elevated-temperature strength and thermalmechanical stability have been raised for working under extreme environment.3 Thus an increasing number of studies on high temperature titanium alloys have been performed, and BT25y alloy is one of the satisfying alloys. The BT25y (Ti–6.5Al–2Sn–4Zr–4Mo–1W–0.2Si) was improved from BT25 alloy, which was developed by BHAM in the former Soviet Union.4 Due to the addition of b eutectoid element tungsten and neutral element stannum, the alloy possesses qualified comprehensive mechanical properties at the working temperature of 550 °C. BT25y is an ideal heat-strength titanium alloy for manufacturing components in aero-engines and will get widely used in the aerospace field. However, the Russian BT25y alloy is seldom known in the west countries, public information concerning its hightemperature deformation behavior can almost not be found. Primarily, the BT25y alloy is a martensite a 1 b titanium alloy, which can be adopted to produce Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.294

compressor disks with outstanding tensile strength and creep resistance at a high temperature of 550 °C.5 In recent years, increasing attention has been paid to BT25y in China due to its potential for manufacturing dualproperty blisk.6 The dual-property blisk consisting of basket-weave structure in disc section and equiaxed structure in the blades is dramatically influenced by the deformation parameters like strain rate, deformation temperature, and strain.7 Thus, it is crucial to study the high-temperature deformation behavior and sensi

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