Chen Tijun, Gao Min, Tong Yunqi
State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050, China.
Materials (Basel). 2018 Jan 15;11(1):138. doi: 10.3390/ma11010138.
To prepare core-shell-structured Ti@compound particle (Ti@compound) reinforced Al matrix composite via powder thixoforming, the effects of alloying elements, such as Si, Cu, Mg, and Zn, on the reaction between Ti powders and Al melt, and the microstructure of the resulting reinforcements were investigated during heating of powder compacts at 993 K (720 °C). Simultaneously, the situations of the reinforcing particles in the corresponding semisolid compacts were also studied. Both thermodynamic analysis and experiment results all indicate that Si participated in the reaction and promoted the formation of Al-Ti-Si ternary compounds, while Cu, Mg, and Zn did not take part in the reaction and facilitated Al₃Ti phase to form to different degrees. The first-formed Al-Ti-Si ternary compound was τ1 phase, and then it gradually transformed into (Al,Si)₃Ti phase. The proportion and existing time of τ1 phase all increased as the Si content increased. In contrast, Mg had the largest, Cu had the least, and Si and Zn had an equivalent middle effect on accelerating the reaction. The thicker the reaction shell was, the larger the stress generated in the shell was, and thus the looser the shell microstructure was. The stress generated in (Al,Si)₃Ti phase was larger than that in τ1 phase, but smaller than that in Al₃Ti phase. So, the shells in the Al-Ti-Si system were more compact than those in the other systems, and Si element was beneficial to obtain thick and compact compound shells. Most of the above results were consistent to those in the semisolid state ones except the product phase constituents in the Al-Ti-Mg system and the reaction rate in the Al-Ti-Zn system. More importantly, the desirable core-shell structured Ti@compound was only achieved in the semisolid Al-Ti-Si system.
为通过粉末触变成形制备核壳结构的Ti@化合物颗粒（Ti@化合物）增强铝基复合材料，研究了Si、Cu、Mg和Zn等合金元素在993 K（720°C）粉末坯体加热过程中对Ti粉末与铝熔体之间反应以及所得增强体微观结构的影响。同时，还研究了相应半固态坯体中增强颗粒的情况。热力学分析和实验结果均表明，Si参与了反应并促进了Al-Ti-Si三元化合物的形成，而Cu、Mg和Zn未参与反应，并在不同程度上促进了Al₃Ti相的形成。首先形成的Al-Ti-Si三元化合物是τ1相，然后逐渐转变为(Al,Si)₃Ti相。随着Si含量的增加，τ1相的比例和存在时间均增加。相比之下，Mg对加速反应的作用最大，Cu最小，Si和Zn的作用相当且居中。反应壳越厚，壳中产生的应力越大，壳的微观结构就越疏松。(Al,Si)₃Ti相产生的应力大于τ1相，但小于Al₃Ti相。因此，Al-Ti-Si体系中的壳比其他体系中的壳更致密，Si元素有利于获得厚而致密的化合物壳。除了Al-Ti-Mg体系中的产物相组成和Al-Ti-Zn体系中的反应速率外，上述大多数结果与半固态状态下的结果一致。更重要的是，理想的核壳结构Ti@化合物仅在半固态Al-Ti-Si体系中实现。
