High-Temperature Environmental Embrittlement of Thermomechanically Processed TiAl-Based Intermetallic Alloys with Variou
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High-Temperature Environmental Embrittlement of Thermomechanically Processed TiAl-Based Intermetallic Alloys with Various Kinds of Microstructures T. Takasugi, Y. Hotta, S. Shibuya, Y. Kaneno, H. Inoue and T. Tetsui1 Department of Metallurgy and Materials Science, Graduate School of Engineering, Osaka Prefecture University, 1-1 Sakai, Osaka 599-8531, Japan 1 Mitsubishi Heavy Ind Co Ltd, Nagasaki Research & Development Center, 5-717-1 Fukahori-Machi, Nagasaki, 851-0392, Japan ABSTRACT Thermomechanically processed TiAl-based intermetallic alloys with various alloy compositions and microstructures were tensile tested in various environmental media including air, water vapor and a mixture gas of 5vol.%H2+Ar as a function of temperature. All the TiAl-based intermetallic alloys showed reduced tensile fracture stress (or elongation) in air, water vapor and a mixture gas of 5vol.%H2+Ar not only at ambient temperature (RT~600K) but also at high temperature mostly from 600K to 1000K (sometimes higher temperature than 1000K). The high-temperature environmental embrittlement of TiAl-based intermetallic alloy depended upon the microstructure. The possible species causing the high-temperature environmental embrittlement are hydrogen atoms decomposed from water vapor (H2O) or hydrogen gas (H2), similar to those causing the low-temperature environmental embrittlement. INTRODUCTION Gamma (γ) TiAl alloys have been considered as a potentially important aerospace and vehicle structural material because of their lightweight, good high-temperature mechanical properties, and oxidation resistance [1]. Various kinds of microstructures could be obtained by compositional modification and microstructural control on intermetallic alloys based on gamma (γ) TiAl. Depending on desired properties and applications, the most appropriate microstructure could be chosen from these microstructures. However, they generally exhibit low ductility and poor fracture toughness until intermediate temperature. The influence of hydrogen on the ambient mechanical properties of intermetallic alloys based on gamma (γ) TiAl has been focused by some researchers [2-6]. Also, it has been reported that the so-called environmental embrittlement occurs at ambient temperature in intermetallic alloys based on gamma (γ) TiAl [7-11]. In these cases, hydrogen is introduced from test atmospheres such as hydrogen gas or air, the moisture in which reacts with the alloy and to generate atomic hydrogen, resulting in reduced tensile elongation. Using Ti-49at.%Al alloy with a dual-phase microstructure and Ti-48Al-2Cr-2Nb alloy with a γ phase structure, it has been recently reported that the presence of hydrogen resulted in a reduction in the tensile elongation in the temperature range until 973K [12-14]. In this study, thermomechanically processed TiAl-based intermetallic alloys with various kinds of microstructures are tensile tested in various environmental media including air, water vapor and a mixture gas of 5vol.%H2+Ar from room temperature to 1100K. It will be shown tha
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