Investigation On The Forming Mechanism Of M42/45 Steel Bimetal Composites Sintered By Spark Plasma Sintering

M42/45 steel bimetal composites were sintered by spark plasma sintering (SPS) in this thesis, and the sintering process was investigated and optimized. Based on the microstructural characteristics of the composites, the sintering process and principle of SPS and the traditional conection theory, we proposed a bonding mechanism modle and expored the bonding mechanism and formation of the phase interface. It can be conclued as follows.(1) As the sintering temperature increased, the hardness of M42 steel firstly increased then decreased and reached to a maximum at 970℃. Meanwhile, the porous in M42 decreased as well as in the interface, and the microstructure became densified. With sintering time extending, the hardness of M42 steel firstly increased then decreased and reached to a maximum at 12min. Meanwhile, the porous in M42 decreased as well as in the interface, and the microstructure became densified.(2) The best optimized SPS sintering process of M42/45 steel bimetal composites was given. The pressure were 50MPa at the temperature rising period but 70MPa at the soaking stage and the following cooling stage. The sintering temperature and the holding time were 970℃,12min, respectively. The composites were firstly cooled to 800℃at a speed of 100℃/min, then cooled to 400℃at a speed of 20℃/min, and followed with furnace cooling.(3) Prepared from the best sintering process, the composites had no body deformation in the joint. Macro-defects such as cracks and large voids were not observed, namely, the interface combined closely. The carbide particles in M42 were fine and uniform, distributing dispersively in the matrix. In the transition layer, no obvious interface existed, but the composition and the microhardness varied gradiently. In addition, elements in both sides of the interface diffused to each other, and the bonding strength of the interface could reach to 542MPa.(4) The bonding process of the composites can be devided into three stages, namely physical contact stage, formation of fusion region and the diffusion bonding stage, corresponding to three different bonding mechanism, mechanical, fusional and diffusional effect, respectively. However, those stages are not entirely separated but intercrossed, finally resulting in solid-state metallurgical bonding at the joint because of the process such as diffusion and recrystallization.