The Research Of TiB₂Paticles Reinforced The45Steel Matrix Surface Composites

This paper presents a way that combines in-situ synthesis of reinforcement particulatesby SHS with V-EPC infiltration technique to make TiB₂particulates reinforced45steel matrixsurface composites. Firstly, alloy powders mixed with certain amounts of binder and lacquersolvent, and then the powers were pressed as a30mm diameter×5mm thickness preform in amold with a pressure of40MPa. When the preform is dried, it was attached on a surface ofEPS template, then painted a layer of anti-sand burning coatings with thickness of1², and driedagain at the temperarure below50℃. Secondly the EPS templates were placed in a steel madesand box. Molten carbon steel containing0.45%C was then poured into the box, whichtriggering the SHS reaction within the preforms and forming the TiB₂particulates reinforced45steel matrix surface composites. As the particles were in-situ synthesised in the moltensteels, they had good wettability with liquid steels. Consequently, the interface between thecompound layer and matrix was clean and no obvious defects. Moreover, the reinforcedparticles 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-carbonferrochrome powders;（2） Ti-B₄C-（Ti-Fe） system. The preform in this system is consisted oftitanium, boron carbide and ferro-titanium powders. The effect of the amounts offerro-titanium powders and relative thickness（δ） on quality and microstructure of thecomposites were investigated in （B-Fe）-（Ti-Fe）-（Cr-Fe） system. The effect of the amounts offerro-titanium powders, powder size of titanium and boron carbide, relative thickness （δ） andheat-treatments on quality and microstructure of the composites were also conducted inTi-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 wastested using microhardness tester. On the basis of these test and analysis, the mechanism ofthe formation of the composites was explored.The results showed that in the （B-Fe）-（Ti-Fe）-（Cr-Fe） system, TiB₂particles are welldistributed in the matrix, but the amouts of the particles are less. The addition offerro-titanium powders in preform rised the SHS reaction temperature. With increase of theamounts of ferro-titanium powders, the qualitiy of the compound layer and transition layer hasimproved significantly. With the increase of relative thickness （δ）, the surface qualitiy of the composite was improved and macro-defect reduced obviously. When the δ equales to9, thebest surface quality is obtained. In the Ti-B₄C-（Ti-Fe） system, after observation and analysisof the structure, it showed that there are many TiB₂and TiC particles with size of1²μmdistributed in matrix of the compound layer. The effect of the amounts of ferro-titaniumpowders and relative thickness（δ） on quality and microstructure of the composites in theTi-B₄C-（Ti-Fe） system and in the （B-Fe）-（Ti-Fe）-（Cr-Fe） system is similar. The size oftitanium has a great influence on the formation process of Fe-Ti liquid phase, but has a litteinfluence on the size of TiB₂and TiC particles. The size of B₄C has a great influence on theSHS reaction. The bigger B₄C is, the more difficult SHS reaction is ignited and the lowerreaction temperature SHS reaction is. After the heat-treatment, the amout of TiB₂and TiCparticles reduced and the size of these particles increased slightly and the morphology of theparticles changed.