近净成形Ti-Al多孔金属间化合物的孔隙形成及生长的演变机制

Pore Formation and Growth Mechanism of Near-Net Shaping Ti-Al Intermetallic Compound Porous Material

近净成形Ti-Al金属间化合物多孔材料具有优异的特性,但制备过程中由于Ti,Al元素粉末反应合成及孔隙演变的复杂性,导致这种新型多孔材料的孔结构很难控制。通过对Ti,Al元素粉末在反应合成过程中的显微结构、物相以及孔结构进行观测和分析,揭示了近净成形Ti-Al多孔金属间化合物的孔隙形成及生长的演变过程。结果表明,在Al元素两阶段的偏扩散过程中,在快速扩散组元Al的位置,在Kirkendall效应以及与孔径成反比的张应力的共同作用下,Ti-Al合金多孔材料中的Kirkendall孔隙随着Al元素的快速扩散逐渐长大;Ti-Al合金多孔材料中的Kirkendall孔隙是以生坯中Al颗粒的变形形状为模板进行生长并连通,经烧结驱动力微观调整后随合金成分的均匀化而被稳定下来,形成由大量高度连通孔隙和很少一部分细小闭合孔隙组成的孔结构。

Near-net-shaping Ti-Al intermetallic compound porous material has excellent properties. However, the complexity of pore evolution during the reactive synthesis of Ti/Al elemental powders leads to the deficiency of the pore structure controllability. In order to reveal the pore formation and growth mechanism of near-net-shaping Ti-Al intermetallic compound porous material, the microstructure, phase evolution and pore structure during the reactive synthesis of Ti/Al elemental powders were investigated thoroughly and detailedly. The results show that the Kirkendall pores in porous Ti-AI alloy formed at the site of Al element in both Al metal and TiAl3 phase during two fast diffusion stages of Al. The pores began to grow due to the coactions of the Kirkendall effect and the existence of tensile stress with inverse ratio to the pore diameter. Based on the template of the deformed Al metal in green compacts, the Kirkendall pores in porous Ti-Al alloy grew to connect with each other. After being stabilized with the uniform procedure of alloy composition, the pore structure showed the characteristics of a combination of highly connected pores and a few closed pores.