Microstructure and mechanical properties of a forged β-solidifying γ TiAl alloy in different heat treatment conditions

Abstract

In the cast condition γ titanium aluminide alloys that solidify completely through the β phase are characterized by fine and homogeneous microstructures, weak textures and low segregation. For these reasons such alloys have a relatively good workability and can be closed-die forged without preceding ingot breakdown even if the alloys contain no large fractions of the β phase at the working temperature. The present work was devoted to a combined study of the constitution and microstructural morphologies that develop in various two-step heat treatments of a single-step forged β solidifying alloy. The study included highenergy X-ray diffraction for in situ investigations of the constitution at the heat treatment temperature. It was observed that the phase transformations are quite sluggish in the material which results in fine microstructures and some conditions that significantly deviate from thermodynamic equilibrium. Further, tensile and creep testing was carried out on the different material conditions in order to identify the range in which the properties can be varied. It is found that this easily forgeable material exhibits comparable strength, ductility and creep strength as more conventional peritectically solidifying alloys.

Microstructure of γ-titanium aluminide processed by selective laser melting at elevated temperatures

“…In a recent publication [5] the transition temperatures for this specific alloy were determined by differential scanning calorimetry and high energy X-ray diffraction.…”

In Situ Characterization Techniques Based on Synchrotron Radiation and Neutrons Applied for the Development of an Engineering Intermetallic Titanium Aluminide Alloy

“…Adapted post-forging heat treatments have been reported in [20,28,29,115,116,[128][129][130]. These heat treatments typically comprise three steps [131].…”

“…The applied methods included short-and long-term heat treatments combined with metallography, dilatometry, differential scanning calorimetry, micro-hardness testing and TEM. Diffraction methods, such as HEXRD, have been used for the investigation of phase fraction evolutions as a function of temperature and time [50,51,65,77,82,128,130].…”

Cyclic oxidation behaviour of intermetallic Ti-46Al-8Ta alloy in air

“…Titanium aluminides as attractive materials for high-temperature structural applications in automotive, aerospace and power industry have been extensively studied for more than twenty years [1,2]. In recent years, different thermo-mechanical treatments and many different alloying additions have been explored to increase room temperature ductility, strength, high-temperature mechanical properties and also to improve high-temperature oxidation resistance of TiAl-based alloys [3][4][5][6][7][8][9][10].…”