Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Abstract

Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α 2 + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α 2 , rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings.

Metals Challenged by Neutron and Synchrotron Radiation

“…More often, titanium aluminides are processed under extreme conditions, including high pressure, which gave myself and others, Liss et al [11], the motivation to investigate a γ-based titanium-aluminide under high pressure and temperature. We used a 15 MN press to impose on a volume containing a 1.5 mm 3 sample inside a heating element while synchrotron X-ray diffractograms were recorded.…”

Simulation Analysis of Friction and Wear of New TiAl based Alloy Joint Bearings

“…TiAl-based alloys have high specific strength, low density, good corrosion resistance and good mechanical properties such as high temperature creep resistance under high temperature conditions [2,5]. TiAl alloys are considered to be the most promising new generation of alloy materials [6]. This makes it possible for TiAl-based alloys to be ideal joint bearing materials under high heavy load conditions.…”

A Study on the Zener-Holloman Parameter and Fracture Toughness of an Nb-Particles-Toughened TiAl-Nb Alloy

“…TiAl-based alloys are currently of considerable interest as advanced high-temperature structural materials owing to their low density, good elevated-temperature strength, and high oxidation resistance [1][2][3]. Recently, many kinds of Nb in the order of 5~10% have been used to develop new kinds of TiAl alloys, such as Ti-45Al-(5-10)Nb alloys.…”