TiAl-B合金凝固过程中初生TiB_2的固-液界面形态演变特征

Evolution Characteristic of Primary TiB_2 Solid-liquid Interface Morphology in Solidification in TiAl-B Alloys

用原位自生法制备了 Ti Al- B合金 ,并用 XRD、SEM对材料的相组成、微观组织和初生 Ti B2 晶体的界面结构特征进行了研究。结果表明 :该合金主要由 Ti Al和 Ti B2 两相组成 ;初生 Ti B2 呈六面棱柱状 ,在其 (0 0 0 1)面存在清晰的生长台阶、凸台状或柱棒状分枝 ,它们的各晶面取向与母体的取向一致。分析表明 ,在 Ti Al- B合金凝固过程中初生 Ti B2 晶体的固 -液界面是不稳定的 ,使固 -液界面由一完整光滑的界面逐渐演变为由多个相互独立的次级界面构成的复杂界面 ,次级界面亦为小面结构。

TiAl B alloys have been produced by an in situ method The microstructure, phase institution and the surface morphology of primary TiB 2 of these alloys were investigated by XRD and SEM The results showed that the alloy is composed of TiAl and TiB 2, and the primary TiB 2 exhibits hexagonal prism shape There are pyramidal protrusion or rod shape dendrites on (0001) face of the primary TiB 2 , and the protrusions or rods exhibit facets parallel to the primary TiB 2 from which they protrude The structure of TiB 2 solid liquid interface during solidification has been investigated It was indicated that solid liquid interface of the primary TiB 2 crystal evolve from single and homogeneous faceted face to a few or more separated solid liquid faceted faces, which are parallel with the original faceted face Therefore, dendrites are resulted at primary TiB 2 crystal solid liquid interface and grow in the same direction with the original TiB 2 crystal