TiAl金属間化合物の焼結に関する研究

Abstract

通常の無加圧焼結により、高密度で健全なTiAl焼結材を製造することを目的として、焼結性の優れた原材料粉の探索を行うとともに、有望と思われる原材料粉を用い、TiAl、TiAl-CrおよびTiAl-Nb系の焼結特性を調べた。また、焼結材については、一層の高密度化を図るために、無封缶のHIP(ホットアイソスタティック成形)処理を施し、高密度化の状況を調べた。原材料粉としては、Ti+Al母合金混合粉が、TiAl粉、Ti+Al混合粉などの従来粉に比べ優れた焼結性を有し、有望であることを明らかにした。この粉末を用いることにより、相対密度が95%以上の高密度焼結材が容易に得られた。TiAlの焼結は組成に依存し、(γ+α(sub 2))組成のTiAlがγ単相のものに比べ優れた焼結性を有していた。また、TiAl-Cr系では、Cr量が1?5at%の範囲ではCr量の増加に伴い焼結性は向上し、TiAl-Nb系では、Nb量が1?15at%の範囲ではNb量の増加により焼結性は低下した。HIP材の密度は、焼結密度の増加に伴い増加し、一定の密度以上で飽和した。飽和に達したHIP材の密度は真密度に匹敵していた。TiAlは難焼結性の金属間化合物であるが、本研究で開発した反応焼結-HIP法により、容易に高密度材が得られることが判明した。

Along with the research on raw material powders having a superior sinterability, aiming at producing high density and quality TiAl sintered body by an conventional pressureless sintering, the examination on the sintering properties of TiAl, TiAl-Cr and TiAl-Nb was made by using selected raw material powders. Furthermore, in order that sintered body may be more densified, HIP (Hot Isostatic Pressing) treatment was carried out without containment in a can and the realized extent of densification was examined. It was clarified that Ti+Al mother alloy mixed powder showed a promising characteristics having a better sinterability than conventional powder such as TiAl powder and Ti+Al mixture powder. A high density sintered body of which relative density is 95 percent or higher was easily obtained by using this powder. The sinterability of TiAl depended on the composition, and (gamma + alpha (sub 2)) TiAl showed better sinterability than gamma single phase TiAl. The sinterability of TiAl-Cr system was improved with increase in Cr content in the range of 1-5 atomic percent, and that of TiAl-Nb system was decreased with increase in Nb content in the range of 1-15 atomic percent. The density of HIP material increased with increase in the density of sintered body, and was saturated above a definite density. The saturated density of HIP material was nearly equal to real density. Though TiAl is a sintering resistant intermetallic compound, it was shown that a high-density sintered body could be easily obtained according to the reactive sintering-HIP method developed in this study.