The Research Of TiB₂ Paticles Reinforced The 45 Steel Matrix Surface Composites

This paper presents a way that combines in-situ synthesis of reinforcement particulates by SHS with V-EPC infiltration technique to make TiB₂ particulates reinforced 45 steel matrix surface composites. Firstly, alloy powders mixed with certain amounts of binder and lacquer solvent, and then the powers were pressed as a 30mm diameter×5mm thickness preform in a mold with a pressure of 40MPa. When the preform is dried, it was attached on a surface of EPS template, then painted a layer of anti-sand burning coatings with thickness of 1², and dried again at the temperarure below 50℃. Secondly the EPS templates were placed in a steel made sand box. Molten carbon steel containing 0.45%C was then poured into the box, which triggering the SHS reaction within the preforms and forming the TiB₂ particulates reinforced 45 steel matrix surface composites. As the particles were in-situ synthesised in the molten steels, they had good wettability with liquid steels. Consequently, the interface between the compound layer and matrix was clean and no obvious defects. Moreover, the reinforced particles were distributed evenly in microstructures.The paper carried out investigations on two systems: (1) (B-Fe)-(Ti-Fe)-(Cr-Fe) system. The preform in this system is consisted of ferro-boron, ferro-titanium and high-carbon ferrochrome powders; (2) Ti-B₄C-(Ti-Fe) system. The preform in this system is consisted of titanium, boron carbide and ferro-titanium powders. The effect of the amounts of ferro-titanium powders and relative thickness(δ) on quality and microstructure of the composites were investigated in (B-Fe)-(Ti-Fe)-(Cr-Fe) system. The effect of the amounts of ferro-titanium powders, powder size of titanium and boron carbide, relative thickness (δ) and heat-treatments on quality and microstructure of the composites were also conducted in Ti-B₄C-(Ti-Fe) system.The microstructures were observed and analysised using SEM, DES, XRD and other modern analytic instruments. The surface hardness of the composite was tested using microhardness tester. On the basis of these test and analysis, the mechanism of the formation of the composites was explored.The results showed that in the (B-Fe)-(Ti-Fe)-(Cr-Fe) system, TiB₂ particles are well distributed in the matrix, but the amouts of the particles are less. The addition of ferro-titanium powders in preform rised the SHS reaction temperature. With increase of the amounts of ferro-titanium powders, the qualitiy of the compound layer and transition layer has improved significantly. With the increase of relative thickness (δ), the surface qualitiy of the composite was improved and macro-defect reduced obviously. When theδequales to 9, the best surface quality is obtained. In the Ti-B₄C-(Ti-Fe) system, after observation and analysis of the structure, it showed that there are many TiB₂ and TiC particles with size of 1²Î¼m distributed in matrix of the compound layer. The effect of the amounts of ferro-titanium powders and relative thickness(δ) on quality and microstructure of the composites in the Ti-B₄C-(Ti-Fe) system and in the (B-Fe)-(Ti-Fe)-(Cr-Fe) system is similar. The size of titanium has a great influence on the formation process of Fe-Ti liquid phase, but has a litte influence on the size of TiB₂ and TiC particles. The size of B₄C has a great influence on the SHS reaction. The bigger B₄C is , the more difficult SHS reaction is ignited and the lower reaction temperature SHS reaction is. After the heat-treatment, the amout of TiB₂ and TiC particles reduced and the size of these particles increased slightly and the morphology of the particles changed.