Nb-Mo-Si共晶合金的定向凝固组织特征

Microstructure Characterization of the Directionally Solidified Nb-Mo-Si Eutectic Alloys

采用光悬浮区熔定向凝固技术制备了Nb-Mo-Si三元共晶合金,研究了试棒旋转速度和抽拉速度对Nbss-β(Nb,Mo)5Si3共晶组织形态的影响。结果表明籽晶棒的旋转对组织形态有显著影响,而料棒的旋转对组织形态的影响并不明显。当抽拉速度是5mm/h,籽晶棒不旋转时,得到了规则的Nbss-β(Nb,Mo)5Si3片层结构;而当籽晶棒旋转时,试棒中心处为先析出的球状Nbss和规则片层组织,沿径向向外,规则的片层组织逐步转变成不规则的碎块状组织。当籽晶棒不旋转,抽拉速度是1mm/h时,组织为不规则共晶组织,Nbss倾向于连成网状;当抽拉速度是3～5mm/h时,形成典型的规则片层组织;当抽拉速度是10mm/h时,具有片层组织的柱状晶和胞状晶共存。此外,从液/固界面特性及过冷度的角度对组织多样性进行了讨论。

The Nb-Mo-Si eutectic alloys were prepared using Optical Floating Zone （OFZ） directional solidification method. The effects of rod rotation speed and withdrawal rate on the eutectic morphology were examined. Results show that the rotation speed of seed rod has an obvious effect on structure morphology, while the rotation speed of starting sample rod has unobvious effect. When the withdrawal rate is 5 mm/h, and the seed rod doesn＇t rotate, a regular Nbss-β（Nb,Mo）5Si3 lamellar structure can be obtained. When the seed rod rotates, some spherical particles and regular lamellar structure firstly appear in the center area of the sample, and then expand outwards along radius direction. Afterwards, the regular lamellar structure is gradually transferred into irregular and broken lamellar structure. When the withdrawal rate is between 3 and 5 mm/h, it is regular lamellar structure. At 10 mm/h, columnar and cellular structures co-exist. At 1 mm/h, the lamellar structure is degenerated and Nbss tends to form a net-work structure. The variety of microstructure was discussed in terms of liquid/solid interface characterization and undercooling.