Tensile properties and fracture toughness of a Ti-45Al-1.6Mn alloy at loading velocities of up to 12 m/s
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INTRODUCTION
THE g TiAl intermetallic compound is receiving considerable attention from research laboratories and industries because of its high specific strength, high specific stiffness, and good oxidation resistance at high temperatures, compared to the conventional high-temperature alloys.[1] In order to achieve a better combination of fracture toughness and ductility, TiAl alloys with a duplex microstructure composed of lamellar colonies and equiaxed g grains have been developed and studied extensively.[2,3] Recently, gbase TiAl alloys have been considered as attractive candidate materials for the exhaust valves of automobile engines and gas turbines.[1,4–6] Mechanical properties such as the deformation and fracture behavior have been studied and reported in these alloys; however, most of the works were carried out under static loading conditions.[2,7,8] The behavior of the material at high loading rates is still not well understood. One possible application of the alloys is as engine parts. Due to the service conditions, the load and deformation experienced by the material are either from mechanical impact or from thermal shock. Therefore, unZ.M. SUN, formerly Research Fellow of Japan Society for the Promotion of Science (JSPS), Department of Production Systems Engineering, Toyohashi University of Technology, is Staff Scientist, Materials Engineering Division, Tohoku National Industrial Research Institute, Sendai 983, Japan. T. KOBAYASHI, Professor, and H. FUKUMASU, Graduate Student, are with the Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi 441, Japan. I. YAMAMOTO, formerly Assistant Professor, Department of Production Systems Engineering, Toyohashi University of Technology, is Associate Professor, Osaka University of Education, Osaka 582, Japan, K. SHIBUE, Head, is with the Research and Development Center, Sumitomo Light Metal Ind. Ltd., Nagoya 455, Japan. Manuscript submitted March 17, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A
derstanding the deformation and fracture behavior of the material at high loading rates is imperative to assure material performance and to extend its application as a new type of high-temperature material. The reports on the mechanical properties of TiAl alloys at high loading velocities, though limited, are mainly from the experimental work using the split Hopkinson pressure bar technique[9] for compressive loading at strain rates ranging from 102 to 104/s for measuring strength and deformation[10–14] and the pendulum type impact tests for the fracture toughness test.[15] Maloy and Gray[10] have studied a g-base TiAl alloy at strain rates of 1023, 1021, and 2 3 103/s. The strain rate sensitivity exponent of strength was found to be 2 3 1022, and the work hardening rate was found to increase from 2.8 to 4.5 GPa with increasing strain rate. It was also found that deformation twinning tends to occur with increased propensity at higher strain rates. Conducting compressive tests at high loading rates, Ogawa et al.[11] have also
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