定向凝固对Nb-14Si-22Ti-2Hf-2Al-4Cr合金组织和高低温力学性能的影响

采用光悬浮炉在氩气环境下制备了成分为Nb-14Si-22Ti-2Hf-2Al-4Cr的定向凝固试棒，研究了凝固工艺对合金相组成、组织形貌和高低温力学性能的影响，并与电弧熔炼态的合金进行了比较。结果表明，定向凝固试样相组成与电弧熔炼态相比没有发生变化，均由Nb基固溶体(Nb solid solution, NbSS)和Nb/Si化合物Nb5Si3组成，定向凝固合金NbSS呈枝晶状，硅化物呈板条状沿着生长方向分布。与电弧熔炼态相比，定向凝固速度为15和10 mm/h的合金在1250 ℃的抗压缩强度从电弧熔炼态的290 MPa分别提高到约442和493 MPa；15 mm/h的定向凝固后，合金的室温断裂韧性从电弧熔炼态的12 MPa·m1/2增加到15 MPa·m1/2。通过光悬浮定向凝固法制备的该合金具有优良的高低温力学性能

Effects of Directional Solidification on Microstructure and Mechanical Properties of Nb-14Si-22Ti-2Hf-2Al-4Cr Alloy

The samples cut from the arc-melted Nb-14Si-22Ti-2Hf-2Al-4Cr alloy were directionally solidified in an optical imaging floating zone furnace under argon atmosphere with different growth rates. The effects of directional solidification (DS) technique on phase composition, microstructure characteristics and the mechanical properties at room and high temperatures were investigated with those of arc-melted alloys for comparison. Results show that compared with the arc-melted alloys, the DS samples are still composed of NbSS (Nb solid solution) and Nb5Si3, without any change. Nbss of DS alloys is dendritic, and the lath-like Nb5Si3 distributes along growth direction. The compressive strength of the samples at the DS speeds of 15 and 10 mm/h increase to 442 and 493 MPa at 1250 oC respectively, from 290 MPa of arc-melted alloys. After DS at 15 mm/h, the fracture toughness of the samples increases to 15 MPa·m1/2 from 12 MPa·m1/2 of the arc-melted alloys. The alloys prepared by the optical floating DS method possess good mechanical properties at room and high temperature