定向凝固Ti—43Al—3Si合金的组织演化规律 Ⅰ.初始过渡区组织演化规律

STRUCTURE EVOLUTION OF DIRECTIONALLY SOLIDIFIED Ti-43Al-3Si ALLOY Ⅰ. Microstructure Evolution in the Transition Region

对Ti-43Al-3Si(原子分数,%)合金在3—100μm/s的生长速度下进行了系统的定向凝固实验.研究了生长速度对固/液界面形态及初始过渡区组织演化规律的影响.合金在3—60μm/s的生长速度范围内均以胞晶形态生长,胞晶间距随着生长速度的增大而减小;当生长速度达到90μm/s时,开始出现枝晶生长.在定向凝固初始启动阶段,存在清晰的热过渡区,热过渡区内Ti_5Si_3相分布及过渡区组织与定向凝固区组织的关联性对于籽晶材料的引晶效果有重要影响.生长速度在10μm/s以内时.热过渡区内Ti_5Si_3相分布连续,且热过渡区组织与定向凝固区组织的关联性好,有利于该合金的引晶.

Ti-43Ak-3Si （atomic fraction, %） alloys, seeding material used in preparation of TiAI base alloy, were prepared by directional solidification with growth rate range of 3 100 μm/s. The influences of growth rate on interracial morphology and microstructure evolution in transition region were studied. Cellular growth appears in a wide range of growth rate of 3-60 μm/s, and the cellular spacing decreases with increase of growth rate. When growth rate is 90 μm/s, a dendritic growth is observed. During the initial solidification, a thermal transition region can be observed clearly. The distribution of Ti5Si3 phase along transition region and relevance of microstructures between the transition region and directional solidification region have obvious effects on the seeding. When the growth rate is lower than 10μm/s, a good distribution of Ti5Si3 phase and a good relevance appear, which is favourable in seeding for the present alloy.