Al含量对高Nb铸造TiAl合金高温强度和室温塑性的影响

HIGH TEMPERATURE STRENGTH AND AMBIENT DUCTILITY DEPENDENCES ON Al CONTENTS OF HIGH Nb CONTAINING TiAl ALLOYS

固定Nb含量在7%(摩尔分数),研究了Al含量变化对高Nb铸造TiAl合金高温强度和室温塑性的影响,并根据铸造组织的差异对不同Al含量合金表现出的性能特点进行分析讨论.结果表明,Al含量为46%—49%的高Nb铸造TiAl合金均具有优异的高温强度.其中,高Al含量合金更具高温强度优势.分析认为,在高Nb合金化产生的固溶强化作用基础上,层片组织处于拉仲硬取向以及应变诱发的形变孪晶强化也有可能是高Al含量高Nb铸造TiAl合金900℃具有优异强度的重要机制.层片组织相对细小的Ti-46Al-7Nb-2.5V-1.0Cr合金室温塑性相对较好,而层片组织处于拉伸硬取向的高Al含量合金室温拉伸塑性很低,但有可能通过后续热处理改善其室温塑性.

The influences of Al contents on the high temperature strength and ambient ductility of cast high Nb containing TiAl alloys were investigated with 7%Nb （mole fraction） addition and Al contents varying from 46%--49%. The macro- and micro-structures were examined. Due to the Nb solid solution strengthening effect, the cast alloy with lowest A1 content consisting of a refined lamellar microstructure in equiaxed macro-grains exhibits excellent strength at 900 ℃that is comparable with the well developed wrought alloys. The alloys with A1 contents higher than 47% contains mostly or fully lamellar colonies with little orientation differences in macro-columnar crystals. Probably because of the lamellar structures with orientation hard to deform and the twining reinforcement, those alloys exhibit the more preponderant strength at 900 ℃ that can be as high as 595 MPa in the alloy with 47.5%Al. While, the effect of Al contents on ambient ductility becomes reversed as the hard-to deform lamellar structures present very poor plastic elongation after tensile fractures.