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

采用Al-B-TiO_2或Al-C-Ti （TiO_2）三组分体系反应烧结的方法，制备了Al_2O_3、TiB_2或TiC陶瓷颗粒增强铝基复合材料。系统地研究了强化相的反应路径、形成机制、微观组织演变、致密化和塑性加工过程。对于Al- b -TiO_2三组分体系，证明了TiO_2被熔融Al还原是一个循序渐进的过程。制备过程中可生成4种缺氧钛氧化物，其中Ti_2O_3为主要中间相。在Al-B-TiO_2粉末混合物的反应烧结过程中，除了存在缺乏氧的氧化钛外，还存在AlB_2、γ-Al_2O_3和Al_3Ti等过渡相。Al_2O_3作为复合材料中的增强物是通过一系列铝热反应形成的，而TiB_2的形成在很大程度上取决于AlB_2过渡相。小尺寸TiO_2粉末在较低温度下更能促进增强相的形成，所形成的增强颗粒尺寸比大尺寸TiO_2粉末要小。对于Al-C-Ti混合粉末，在TiC颗粒生成的同时，反应烧结过程中一般会形成Al_3Ti相。为了避免Al_3Ti相的发生，采用高温烧结、TiO_2置换Ti和添加过量的C是有效的方法。结果表明，多孔烧结试样在热压缩作用下可以致密化到高密度水平。在350 ~ 450℃的温度范围内热轧可获得较好的复合板材。由于亚微米颗粒均匀分布在Al基体中，复合材料具有良好的力学性能，特别是强度和杨氏模量。与传统的粉末冶金技术和各种铸造技术相比，反应烧结技术已被证明是制备细陶瓷颗粒增强铝基复合材料的一种有前途的方法。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