Strength and toughness of L1_0-type intermetallic TiAl with duplex structure.

Research Project

Project/Area Number	02650521
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	金属材料(含表面処理・腐食防食)
Research Institution	Kyushu University
Principal Investigator	SANO Takeshi Kyushu Univ., Fac. Eng., Research Associate, 工学部, 助手 (70037810)
Co-Investigator(Kenkyū-buntansha)	DEN Bunnkai Kyushu Univ., Fac. Eng., Research Associate, 工学部, 助手 (50223631) HORITA Zenji Kyushu Univ., Fac. Eng., Associate Professor, 工学部, 助教授 (20173643) NEMOTO Minoru Kyushu Univ., Fac. Eng., Professor, 工学部, 教授 (90005265)
Project Period (FY)	1990 – 1991
Project Status	Completed (Fiscal Year 1991)
Budget Amount *help	¥1,900,000 (Direct Cost: ¥1,900,000) Fiscal Year 1991: ¥600,000 (Direct Cost: ¥600,000) Fiscal Year 1990: ¥1,300,000 (Direct Cost: ¥1,300,000)
Keywords	Titanium aluminide / Intermetallic compound / High temperature structural material / Microstucture-control / Age precipitation / Carbide / Nitride / Perovskite / 炭素添加合金 / 窒素添加合金 / 時効析出硬化 / ペロブスカイト型炭化物
Research Abstract	Experimental studies were made on microstructure-controlled L1_0-TiAl mainly by means of transmission electron microscopy. Results are as follows. 1. Microstructural variations of L1_0-ordered TiAl with Al contents. TiAl compounds ranged from 47 to 52 at% AI at intervals of 0.25 at% AI were solution heat treated at 1373 K. The structure was nearly single-phase gamma by optical microscope(OM)examination. During aging at 973 K, transmission electron mocroscope(TEM)revealed that no precipitates were found in the matrix gamma. TiAl compounds ranged from 56 to 62 at% Al at intervals of 2.0 at% AI were solution heat treated at 1473 K. The structure was the single-phase gamma by OM. TEM observation that TiAl_2 precipitate, which was not so fine, was formed during aging at temperatures in the range of 973 to 1173 K. 2. Microstructural variations of stoichiometric L1_0-ordered TiAl containing 0.1 to 2.0 at% C or N. Fine needle-shaped Ti_3AlC and Ti_3AlN of perovskite type were formed only [001] direction of the L1_0 matrix during aging. The cross-section of the needle was not circular but square. In the carbon containing alloys, precipitates with the similar morphology and the same crystal structure was formed. The selected area electron diffraction analyses suggested that the precipitates had a perovskite-type crystal structure and had the orientation relationship(100)-Ti_3AlC/Ti_3AlN parallel to(100)TiAl and[001]-Ti_3AlC/Ti_3AlN parallel to [001]-TiAl. At higher temperatures, Ti_3AlC/Ti_3AlN precipitates were replaced by Ti_2AlC and Ti_2AlN with hexagonal lattice structure. 3. Room temperature compression strength. The strength increase might be not so anticipatated by the precipitation of perovskite phase. The alloy containing 0.5 at% N indicated higher strength than that containing 0.5 at% C.