Microstructure and mechanical properties of the heat treated Nb-16Si-22Ti-2Hf-2Cr-2Al alloy prepared by vacuum induction melting
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摘要: 用真空非自耗电弧熔炼法制备了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, 浇注在温度梯度约为4 ℃/mm的模壳里, 制备出Φ 60 mm×170 mm铸锭, 研究了1500 ℃/100 h真空热处理后铸锭的组织特征对室温抗拉强度和高温压缩性能的影响。结果表明, 真空感应熔炼Nb-16Si-22Ti-2Hf-2Cr-2Al合金经过1500 ℃/100 h热处理后, 合金锭的组成相为NbSS枝晶, Nb5Si3层片或不规则颗粒和残留Nb3Si块。块状Nb3Si的尺寸越大, 发生完全共析转变需要的时间越长、温度越高。热处理合金锭的室温抗拉强度在208~355 MPa之间, 室温延伸率变化不大, 均小于0.3%。残留的粗大块状Nb3Si和热处理过程中析出的HfO2是导致合金锭拉伸性能较低的重要原因。合金锭的高温压缩强度受到组织中硅化物相含量的影响, 压缩强度与硅化物含量成正比。Abstract: The master alloy ingot with the nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was prepared by vacuum non-consumable arc-melting and then vacuum induction melting. The melt was poured in a ceramic mould (Y2O3) with the temperature gradient of about 4 ℃/mm. The ingot with the dimension of Φ 60 mm×170 mm was fabricated. Heat treatment was conducted at 1500 ℃ for 100 h. The microstructure, room temperature tensile strength, as well as compression strength at 1250 ℃ of the heat treated ingot were described. Relationship between the microstructure and mechanical properties was also investigated. The results reveal that microstructure of the heat treated ingot is composed of NbSS dendrites, Nb5Si3 particles or lamellae and remaining Nb3Si blocks. Room temperature tensile strength is in the range of 208 to 355 MPa. Both Nb3Si and HfO2 have detrimental effects on the tensile strength. The volume fraction of silicides is in proportion to the high temperature compression strength at 1250 ℃.
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Key words:
- Nb-Si alloy /
- microstructure /
- induction melting /
- tensile strength /
- high temperature compression
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