Dynamic fracture toughness of a Ti-45Al-1.6Mn alloy at high temperature
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I. INTRODUCTION
GAMMA-BASE TiAl intermetallic compound has received considerable attention as a possible future lightweight structural material at high temperature because of its high specific strength, high specific stiffnes, and good oxidation resistance at high temperature.[1] However, its low ductility and toughness restrict applications of TiAl intermetallics. The mechanical properties and toughening mechanisms of g-base TiAl have been examined in a number of studies.[2–8] A strong strain-rate dependence of yield stress for duplex TiAl was reported by Jin et al.[7] above 873 K. They found strong positive temperature dependence in the yield stress for strain rates higher than 1 s21 and negative temperature dependence in the yield stress for strain rates lower than 1 s21. This indicates that there may be a great difference in fracture and toughening mechanisms between static and dynamic loading conditions. Enoki and Kishi[5] investigated the loading rate dependence of fracture toughness in TiAl alloy and discussed the toughening mechanisms of TiAl alloy and estimated the amounts of toughening due to microcracking and shear ligament. They concluded that the microcrack toughening mechanism could not arise under dynamic loading because of the lack of nucleation time for microcracks. In another study, high-temperature fracture toughness of TiAl alloy under static loading conditions was investigated by Gnanamoorthy et al.[4] The results of this study indicated that fracture toughness of duplex TiAl increases up to 1073 K and then decreases after attaining the maximum value. All structural materials are considerated to receive H. FUKUMASU, formerly Graduate Student, Department of Production Systems Engineering, Toyohashi University of Technology, is with Mitsubishi Aluminum Co., Ltd., Susono 410-1217, Japan. T. KOBAYASHI, Professor, and H. TODA, Associate Professor, are with the Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan. K. SHIBUE, Head, is with the Research and Development Center, Sumitomo Light Metals Industries Ltd., Nagoya 4550011, Japan. Manuscript submitted April 5, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
dynamic loads upon use. It is important to the investigate fracture toughness and toughening mechanisms of TiAl intermetallic compound under dynamic loading conditions at high temperature, because this compound is expected to have application as high-temperature structural materials.[9,10] However, reports on fracture toughness under dynamic loading conditions on at high temperature are quite limited. The objective of the present study was to investigate the high-temperature dynamic fracture toughness and toughening mechanisms of reactive sintered[11] g-base TiAl alloy. For this purpose, a dynamic fracture toughness test and the stop block method[12] were employed. The dynamic fracture toughness of the alloy was measured at loading velocities of 0.1 and 1 m/s. Fracture surface observation was carried out using a scanning electron micro
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