Study On In-situ Synthesis Of Al₂O₃ -TiC Particulates Reinforced 45 Steel Matrix Surface Composites

This paper presented a way that combines in-situ synthesis of reinforcement particulates by SHS with V-EPC infiltration technique to make particulates reinforced 45 steel matrix surface composites. First, experimental materials are prepared in a proper proportion and mixed in a ball mill, then certain amounts of binder added. The materials are pressed as a preform in a mold. The preform is then put on a surface of EPS samples. The samples are then placed in a steel made sand box. Molten carbon steel containing 0.45%C is poured into the samples, which triggering SHS reaction within the preforms and forming the Al₂O₃-TiC particulates reinforced 45 steel matrix surface composites. As the particles are in-situ synthesised in the molten steels, they have good wettability with liquid steels. Consequently, the interface between the compound layer and matrix is clean and no obvious defects. Moreover, the reinforced particles distributed evenly in microstructures.The paper carried out investigations on two systems: (1) TiO₂-C-Al-(Ti-Fe) system. The preform in this system is consisted of titanium dioxide, ferro-titanium, aluminum, carbon and iron oxide powders; (2) Ti-C-Al-(Ti-Fe) system. The preform in this system is consisted of titanium, aluminum, carbon and ferro-titanium powders as well as self-fusion alloy powders. The effect of the amounts of ferro-titanium powders, aluminum powders and self-fusion of alloy powders, and the powder size and density of the perform on quality and microstructure of the composites are invesitgated. The microstructures are observed and analysised using SEM, DES, XRD, differential thermal analysis and other modern analytic instruments. The surface hardness of the composite is tested using microhardness tester. On the basis of these test and analysis, the mechanism of the formation of the composites is explored.The results showed that for the TiO₂-C-Al-(Ti-Fe) system, the synthesized Al₂O₃ particulates tends to segregate at grain boundaries and TiC particles to precipitate and mainly distribute in matrix grains. The addition of ferro-titanium powders in preform reduced the SHS reaction temperature, which decreases the number of porosity in the compound layer. The incresse of the amounts of Al powder addition in the perform promoted the reduction of the titanium dioxide and the iron oxide and formation of Al₂O₃ and TiC reinforced particles and enhanced the areas of the strip-like matrix microstructures in compound layer. The reduction of the powder size of experimental materials coarsed the composite. For the Ti-C-Al-(Ti-Fe) system, microstructure observation and analysis found that there are many TiC particles with size of 1～2μm distributed in a compound layer. But the SHS reaction for the system is not complete. When there is not the self-fusion powder addition in preform, the transition layer tends to become thicker and increase grains size. Howeover, the thickness of the transition layer and grains size tend to decrease after the addition of the self-fusion alloy powders and ferro-titanium powders.