STRENGTHENING MECHANISMSIN TiAl BASED ALLOYS

查看全文 作　　者：M. H. Loretto, A.B.Godfrey and D.Hu Interdisciplinary Research Centre (IRC) in Materials for High Performance Applications, The University of Birmingham, Edgbaston B15 2TT, UK 出　　处：《中国有色金属学会会刊:英文版》索引1999年第9卷第S1期,共8页 摘　　要：The influence of heat treatment and of thermomechanical processing on the structure and properties of a range of TiAl based alloys has been assessed and in agreement with other reports it has been found that increased refinement of the microstructure leads to improved mechanical strength at room temperature, both for the lamellar and the duplex structures. In the case of alloys cooled rapidly from the alpha phase field the increased refinement in lamellar spacing leads to significant increases in room temperature strength but thermomechanical processing can lead to far greater increases. The origin of this increase in strength in samples with a lamellar structure has been assessed in terms of the ability of dislocations to cross gamma/gamma and gamma/alpha 2 lamellar interfaces. It was concluded that the alpha 2 gamma interfaces and the alpha itself are important factors in strengthening the lamellar alloys. The stability of the various structures developed either by appropriate heat treatments or by thermomechanical processing has been investigated by exposing samples for a range of times at temperatures between 700 and 1 000 ℃. It has been found that the yield strength and the ultimate tensile strength generally decreased by about 20% during high temperature exposure at 700 ℃ for 3 000 h. The detailed behaviour on exposure at 700 ℃ has been found to be a function of alloy composition, with complex precipitates being formed in some alloys, but in all cases the amount of alpha 2 decreased with increased heat treatment time. It has been found that during exposure the alpha 2 lamellae decomposed to gamma phase by a mechanism that can involve the formation of thin gamma lamellae within the original alpha 2 lamellae. 关 键 词：TIAL BASED alloy strengthening mechanisms LAMELLAR STRUCTURE DUPLEX STRUCTURE ALPHA phase