금속간화합물 TiAl의 미세조직과 기계적 성질에 미치는 탄소 및 질소의 영향

Abstract

Effects of carbon and nitrogen additions on microstructure and mechanical properties of Ti-48.5Al-1.5Mo (at.%) alloys were investigated. The alloys added with 0.3%, 1.0% and 2.0%C or N were prepared by vacuum arc melting, and heat-treated at 1390℃ for lamellar microstructure and then aged at 900℃. Tensile tests were performed in air with the strain rate of 2×10-4S-1 at room temperature and 800℃. It was found that C (or N) addition decreased the grain size of lamellar structure. Especially, 1.0%C(or N) and 2.0%C(or N) addition refined the grain size to 1/10 of that of the mother alloy. Only fine Ti3AlN precipitates were formed at the lamellar boundaries for the alloy containing 0.3% N, but Ti2AlN precipitates of a few micrometers in size were also formed in the matrix in addition to Ti3AlN precipitates for the alloys with 1.0 and 2.0% N. Tensile elongation at room temperature decreased markedly for the alloys with 0.3%C or N but recovered for the alloys with 1.0% and 2.0% addition compared to the value of the mother alloy. Yield strength at room temperature for the alloys containing 1.0% and 2.0% C or N increased up to two times of the value of the mother alloy, and the high strength was maintained up to 800℃. The aged alloys showed much higher tensile elongation at room temperature than the alloys only heat-treated to obtain the lamellar microstructure.