真空感应熔炼Nb-16Si-22Ti-2Hf-2Cr-2Al合金的组织和性能

来源期刊：金属学报2011年第1期

论文作者：贾丽娜 高明 盖京茹 郑立静 沙江波 张虎

文章页码：88 - 94

关键词：Nb-Si合金； 真空感应熔炼； 微观组织； 抗拉强度； 高温压缩

Key words：Nb-Si base alloy； vacuum induction melting； microstructure； tensile strength； high temperature compression strength

摘    要：用真空非自耗电弧熔炼制备了Nb-16Si-22Ti-2Hf-2Cr-2Al母合金锭,用Y₂O₃坩埚真空感应熔炼对母合金锭重熔,浇入温度梯度约为4℃/mm,底部有铜板的Y₂O₃模壳,制备出直径60mm,长170mm的合金锭.考察了合金性能与组织特征的关系,探讨了硅化物对室温抗拉强度和高温压缩性能的影响.结果表明,Nb-Si双相复合材料中两相的组织特征对冷却速率非常敏感,初生相的选择和相组成均与冷却速率有关.大的冷却速率容易导致生成Nb₃Si相.随着冷却速率的减小,板条状Nb₃Si相的体积分数逐渐减少,有消失的趋势,初生相将变成块状Nb₅Si₃;共晶组织含量明显增加,Nbss枝晶尺寸增大,尤其是二次枝晶臂尺寸增大.细小均匀的两相共晶组织有利于提高合金的室温拉伸性能,板条状初生Nb₃Si相明显降低合金的室温拉伸性能,但适当数量、大小和形态的硅化物有利于提高合金的高温压缩强度.当铸锭由细小共晶组成时,其抗拉强度为449 MPa,相应的延伸率可以达到0.3%;当Nb₃Si含量在50%,宽度在80μm且平行于压缩方向时,合金在1250℃的高温压缩强度最高,为650 MPa.

Abstract: The melt with a nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was poured in a ceramic shell mould with a temperature gradient of about 4℃/mm, and the ingot with the dimension of 60 mm×170 mm was obtained. The relationship between the microstructure and mechanical properties was measured, and the effects of the silicide on fracture toughness at ambient temperature and compression strength at high temperature were analyzed. It is revealed that the microstructure of the alloy consists of Nb solid solution and silicides, and the cooling rate can obviously change primary phase and constituent phases. The volume fraction of Nb₃Si formed at rapid cooling rate is significantly increased, and Nb₅Si₃ phase is formed with decreasing in cooling rate, whereas the volume fraction of the eutectic colonies and Nbss dendrites increase evidently, especially the second dendrite arm. Fine and uniform eutectic colonies are contributed to the ambient tensile strength, while the coarse primary Nb₃Si decreases the tensile strength but improves the compression strength of the alloy. When the microstructure is mainly composed of fine (Nb_SS+Nb₅Si₃) eutectic colonies, the tensile strength and elongation of the alloy reach 449 MPa and 0.3%, respectively. When lath-like Nb₃Si phase has 80μm in width and 50% in volume fraction as well as its long axis is parallel to compression direction, the compression strength of the alloy at 1250℃ is about 650 MPa.