冷轧Ti/Al层状复合材料固-液反应过程中的界面微观组织演变

Interfacial Microstructure Evolution During Solid-Liquid Reaction in Cold-Rolled Ti/Al Laminated Composites

将冷轧Ti/Al层状复合材料在675~750℃下进行不同时间的退火处理,退火过程中钛和铝都保持过剩,研究了Ti/Al层状复合材料的界面微观组织演变。结果表明:Ti和Al的界面层由2个亚层组成,其中一个为紧密的TiAl_(3)亚层,其微观结构为紧密的TiAl_(3)层,其中分布着随机取向的充满Al的裂纹,另一个为颗粒状的TiAl_(3)亚层,其微观组织结构是颗粒状的TiAl_(3)分布在Al基体中。在不同的退火温度和时间条件下,紧密TiAl_(3)亚层的厚度几乎没有变化,但是颗粒状亚层的厚度随着退火温度及时间的增加而增加;另外,界面层中的TiAl_(3)颗粒的体积分数在不同的温度下均随着退火时间的延长而下降。因此提出了反应扩散模型来描述界面层的形成机理,在此模型中,TiAl_(3)相是化学反应和扩散的结果,并且也考虑了TiAl_(3)相的溶解。计算结果表明TiAl_(3)相的形成与生长由化学反应控制,其等效厚度与退火时间之间遵循线性规律,这主要是因为Ti和Al原子能够快速地通过紧密的薄TiAl_(3)亚层。

Cold-rolled Ti/Al laminated composites were annealed at 675~750 ℃ for different time with superfluous Ti and Al, and the interfacial microstructure evolution in Ti/Al laminated composites during annealing was investigated. The results indicate that the interfacial layer between Ti and Al consists of two sub-layers: a compact TiAl_(3) sub-layer with the microstructure of many randomly oriented cracks filled with Al, and a granular TiAl_(3) sub-layer with the microstructure of granular particles distributed in Al matrix. The thickness of the compact TiAl_(3) sub-layer is stable at different annealing temperatures for different durations, but the thickness of the granular sub-layer increases with increasing the annealing temperature and duration. Furthermore, the average volume fraction of TiAl_(3) phase in the interfacial layer at different temperatures decreases with increasing the duration. A reaction diffusion model, in which the TiAl_(3) phase is regarded as the result of diffusion and chemical reaction, was established to evaluate the formation mechanism of the interfacial layer. Additionally, the dissolution of TiAl_(3) phase into liquid Al was considered in the model. The calculated results indicate that the formation of TiAl_(3) phase is governed by the chemical reaction, and the equivalent thickness of TiAl_(3) phase in the interfacial layer obeys a linear relationship with annealing time, which is attributed to the rapid diffusion of Ti and Al atoms through the thin TiAl_(3) compact sub-layer.