Ti-40Al-2B合金微观组织和初生TiB2生长特征

用原位自生法制备了Ti-40Al-2B(wt%)复合材料,并用XRD、SEM对复合材料的相组成和微观组织,特别是TiB₂的形貌进行了研究。结果表明:该合金由TiAl和TiB₂两相组成。其中TiB₂颗粒以初生的块状和共晶的片状或细棒状形式共存。初生TiB₂呈六面棱柱体,端面有清晰的生长台阶,其显露晶面分别为(0001)和｛101 - 0｝。结合晶体生长理论分析认为:TiB₂的生长单元为一个硼原子和六个钛原子组成的三棱柱,硼原子位于三棱柱的中心,生长方式以台阶式生长为主。其中｛112 - 1｝面生长速率最快,｛101 - 0｝面生长速率最慢,导致TiB₂形成以｛101 - 0｝面为棱柱面的六面棱柱结构。 

MICROSTRUCTURE OF Ti-40Al-2B AND GROWTH CHARACTERISTIC OF PRIMARY TiB2

Ti 40Al 2B(wt%) alloy was produced successfully by an in situ method. The microstructure and the phase constitution, especially the morphology of the primary TiB 2 of this alloy were investigated by XRD and SEM. The results show that this alloy is composed of TiAl and TiB 2. TiB 2 mainly exists in the matrix with block primary TiB 2 and plate or fine bar shape eutectic TiB 2.The primary TiB 2 is hexagonal prism morphology. Clear growth steps were observed at the top of the primary TiB 2, and the crystal faces were determined to be (0001) and {101-0}. Based on the crystal growth theory, it was considered that the growth element of the primary TiB 2 is the trigonal prism of six Ti atoms with one B atom at the center, and the primary TiB 2 grows mainly in a step growth method. The growth rate of {112-1} faces is the fastest and that of {101-0} is the slowest, which results in a hexagonal prism TiB 2 with {101-0} as prismatic faces.