Research On The Technology Of Lost Foam-liquid Forging For The Fabrication Of Particle Reinforced Steel Matrix Composites

To resolve the two key technique issues of particle uneven distribution and weak interface bonding during the fabrication of particle reinforced steel matrix composites (PRSMCS), a novel technology named Lost Foam Liquid Forging(LFLF) was proposed in this paper. The technology makes particles getting into molten steel equably come true by the interaction of foam carrier with molten steel, then solidified under applied pressure, and finally obtains the PRSMCS with the uniform distribution of particle, compact structure and excellent interface bonding.This paper researched the preparation process of PRSMCS with uniform distribution of reinforced particle. Distribution of particle in steel matrix was characterized with the mean dispersion coefficient, which was gained by use of image analysis software and Matlab statistical software. The smaller of mean dispersion coefficient, the more equably distribution of particle in steel matrix. The orthogonal experiment for preparing composite of TiC/ZG55SiMn was carried out. When the specific pressure is at80MPa, cooling velocity at24.5K.s-1, filling velocity at107.6mm.s-1and TiC particle volume fraction at10%, the most uniform distribution of TiC particle in steel matrix was gained. Specimens were sampled from the composite of TiC/ZG55SiMn fabricated by the above optimal technical parameters, and to be subjected to tensile test, wear test and hardness test successively. The experimental results show that tensile strength of TiC/ZG55SiMn is525-560MPa, which is smaller than that of steel matrix without TiC particle reinforced; Hardness of TiC/ZG55SiMn is58.1HRC, which is improved by60%～70%compared with that without TiC particle reinforced; wearing capacity of unit length is3.57X1O-9Kg.m-1, which is only20%-25%of that without TiC particle reinforced; specific modulus is6.84MPa.m3.Kg-1, which is improved by5%compared with that without TiC particle reinforced.The gasification behaviors of foam carrier with particle-reinforcement was studied in LFLF, and the computational formula of airflow pressure and airflow velocity in metal cavity were established; The interaction behavior of particle with molten steel was studied, the conditions for particle getting into molten steel, distributing equably in molten steel, and being captured by solidification interface were discussed; In addition, the influence rules of technical parameters on particle distribution and interface bonding were also investigated. Effects of different cooling velocity(2K.s-1,6K.s-1,15.8K.s-1,24.5K.s-1), different particle volume fraction(2%,5%,10%,15%), and different specific pressure(40MPa,60MPa,80MPa,100MPa) on TiC particle distribution were analyzed in the case of the above optimal technical parameters for fabricating TiC/ZG55SiMn. Distribution of TiC particle in steel matrix was investigated by optical microscope(OM) and scanning electron microscope(SEM). The experimental results show that it’s easy to make TiC particle aggregation in the direction of mold filling of molten steel, and the concentration of TiC particle in the subsequent full of part is greater than that in the first full of part. TiC particle distributes more equably with the increase of cooling velocity; when particle volume fraction is lower than10%, TiC particle distributes more equably with the increase of particle volume fraction, but the situation is opposite when particle volume fraction exceeds10%. TiC particle distributes more equably with the increase of specific pressure, but the change trend is not obvious when specific pressure exceeds100Mpa.Effect of different specific pressure on interface bonding was analyzed by means of observing fracture morphology of tensile sample and surface appearance of wearing sample by SEM. The experimental results show that on the condition of low specific pressure, there are micro-pores on the interface, and TiC particles on the fracture which is separated or pulled out from steel matrix. It proves that the unbound region of interface leads to cracks, then grow up and hold together, which causes brittle fracture of composite, so the interface bonding is poor on the condition of low specific pressure. With the increase of specific pressure, cracks come from TiC particle fragmentation but not interface, and there are lots of strain energy will be consumed during the crack propagation process, which causes local plastic deformation in steel matrix. So it’s achievable for excellent interface bonding as specific pressure increases and composite can bear more applied load.Effect of TiC particle coated with8%Ni on interface bonding was analyzed by means of EPMA and XRD. The experimental results show that the main phase on the interface between TiC particle coated with8%Ni and steel matrix is Fe3Ni2, the combination of interface is not simply mechanical setting but metallurgical bonding with a certain of reactions. The addition of Ni accelerates diffusion of alloying element from steel matrix to TiC particle, increases the surface energy of TiC particle, reduces the wetting angle of TiC particle between steel matrix, and forms the continuous interface in the form of Fe-Fe3Ni2-TiC, so the wettability and bonding strength of interface were enhanced, and the mechanical performance was improved accordingly.