Synthesis and Secondary Processing of High-Strength Aluminum Matrix Composites by Reactive Sintering

采用Al-B-TiO2或Al-C-Ti(TiO2)三元系反应烧结法制备了陶瓷颗粒(Al_2O_3、TiB_2或TiC)增强铝基复合材料。系统地研究了Al-B-TiO2三元系的反应途径、增强相的形成机理、组织演变、致密化和塑性加工。对于Al-B-TiO2三元系，熔融Al还原TiO2时是一个分步过程。生成了四种缺氧型钛氧化物，其中Ti2O_3是主要的中间相。在Al-B-TiO_2混合粉末的反应烧结过程中，除缺氧钛氧化物外，还存在AlB_2、γ-Al_2O_3、Al_3Ti等过渡相。Al_2O_3是由一系列铝热反应生成的，而TiB_2的形成在很大程度上依赖于Alb_2过渡相。小颗粒二氧化钛助剂…Al-C-Ti混合粉末在反应烧结过程中，在生成TiC颗粒的同时，一般会生成Al_3Ti相。为了避免Al_3Ti相的产生，采用高温烧结、用二氧化钛置换钛和添加过量的C是有效的方法。结果表明，采用热压的方法可以使多孔烧结体致密化。此外，在350~450℃的温度范围内热轧可获得良好的复合板。由于亚微米颗粒的存在，使复合材料具有良好的力学性能，尤其是强度和弹性模量。与传统的粉末冶金和各种铸造工艺相比，反应烧结法是制备陶瓷颗粒增强铝基复合材料的一种很有前途的方法。较少

Aluminum matrix composites reinforced with ceramic particulates (Al_2O_3, TiB_2 or TiC) were synthesized via reactive sintering of Al-B-TiO_2 or Al-C-Ti (TiO_2) three-component systems. The reactive paths, formation mechanism of reinforcing phases, microstructural evolution, densification, and plastic processing have been investigated systematically.For Al-B-TiO_2 three-component system, the reduction reaction of TiO_2 by molten Al has been proved to be a stepwise process. Four oxygen-deficient titanium oxides could be formed, and Ti_2O_3 was a main intermediate phase. In addition to the oxygen-deficient titanium oxides, there also existed several transitional phases, such as AlB_2, γ-Al_2O_3, and Al_3Ti during the reactive sintering process of Al-B-TiO_2 powder mixtures. As the reinforcements in the composites, Al_2O_3 was formed by a series of aluminothermic reactions, while the formation of TiB_2 depended to a large extent on AlB_2 transitional phase. Small-sized TiO_2 powder promot … More ed the formation of the reinforcing phases at lower temperatures, and the resultant reinforcing particulates exhibited smaller sizes, compared to large-sized TiO_2 powder.With regard to Al-C-Ti mixed powder, concurrent with the generation of TiC particulates, Al_3Ti phase was generally formed during the reactive sintering. In order to avoid the occurrence of Al_3Ti phase, sintering at a higher temperature, displacement of Ti by TiO_2, and addition of excess amount of C have been proved to be effective methods.It was shown that porous sintered specimens could be densified to a high-density level by hot compression. Furthermore, sound composite sheet could be obtained by hot rolling in a temperature range of 350-450℃. Because of the existence of submicron particulates which were homogeneously dispersed in Al matrix, the composites exhibited good mechanical properties, especially in strength and Young's modulus. In comparison with conventional powder metallurgy and various casting techniques, the reactive sintering process has been shown to be a promising approach to fabricate aluminum matrix composites reinforced with fine ceramic particulates. Less