Ti＋48Al＋B合金中硼化物的生长机理

研究了Ti-48Al (0.2～0.8)at%B合金中硼化物的生长机理。结果显示：合金中的硼化物均为C32结构的TiB2相；在加入0.2at%和0.5at%B的合金中只存在带状TiB2相；而加入0.8at%B的合金中除带状TiB2相外，还出现了少量六方形貌的块状TiB2相，块状硼化物是从液相中自由生长的初生TiB2相，其惯习面为（0001）基面和｛10∧-10｝柱面；而带状硼化物则是次生TiB2相，是通过L→β TiB2和L β→α TiB2反应与基体耦合生长的非规则共晶反应产物。两种形貌的TiB2颗粒均以台阶方式生长。

Growth Mechanism of Borides in the Alloys Ti-48Al+B

The growth mechanism of borides in the alloys Ti-48Al+(0.2～0.8)at%B has been investigated. The results show that the borides in these alloys are TiB2 with C32 type crystal structure. The TiB2 particles are flaky in the alloys containing 0.2at%B and 0.5at%B, but there are a few hexagonal blocky borides besides flaky borides in the alloy containing 0.8at%B. The blocky borides are primary TiB2 phase with (0001) basal and {100} prismatic habit plans. The flaky borides are secondary TiB2 phase, which are irregular eutectic reaction products of L→β+TiB2 and L+β→α+TiB2, and coupling growth with matrix. The growth mechanism of blocky and flaky TiB2 is a ledge mechanism.