| With the industry development, more structural materials which can fulfil the high temperature, high wear rate and load bearing needs are largely required. Steels only can not meet this demand. However, particles reinforced steel matrix composites which combine both steels and ceramics of high melting point, thermostability and hardness , have good high-temperature behavior and wear resistance performance.Steels have high melting point and density, addition of particles is difficult using traditional methods, which is limited to local reinforced steel matrix composites. In-situ synthesis can form particles directly in matrix, and obtain unitary composite by shapecasting. However, there is difference between particles and steels density, which leads to segregation. Particles with a close density to steels are preferred.In order to narrow the density difference, we use W element to replace part of Ti atoms to obtain (Ti,W)C, thus reduce segregation. In this study, In-situ (Ti,W)C and TiC particles reinforced steel matrix composites with different volume fractions were fabricated by reaction casting respectively based on thermodynamics calculations. Microstructure and the mechanism of (Ti,W)C formation are investigated. Segregation of particles is analysed qualitatively by vertical Brinell hardness distribution. Friction and wear performance, abrasion mechanisms are studied. In this research, the effects of Cu component on In-situ (Ti,W)C/45#steel composite is investigated.Thermodynamics calculations show that TiC is most likely to be generated. Microstructure and phase analysis indicates that In-situ TiC and (Ti,W)C particles can be obtained, with size of less than 10μm. The composites are mainly composed of ferrite and pearlite matrix and particles. Ti, W, C distribute uniformly in (Ti,W)C, with a Ti/W ratio of 3 to 1.According to the thermodynamics calculations and experiments, the mechanism of (Ti,W)C formation is like this: Ti and C combined first to produce plentiful fine crystal nucleus, while W existed mainly in the melt. As the temperature declined, the TiC nucleus began to unite and grow, since W has the similar atomic radius with Ti, WC and TiC are both interstitial phases, or because TiC has the solubility ability of W, W entered the growing TiC and replaced part of Ti atoms. By repeating this process, (Ti,W)C can be obtained.Vertical Brinell hardness distribution shows that segregation occurred in 15 vol.%TiC/45#steel composite. The hardness distribution is uniform in (Ti,W)C/45#steel composite, and (Ti,W)C can help to reduce segregation. Abrasion test indicates that (Ti,W)C/45#steel has a better performance in wear resistance, the abrasion mechanism of TiC/45#steel can be divided into three stages: abrasive wear and slight adhesive wear, severe delamination wear and oxidative wear, serious adhesive wear companied with oxidative wear. However, In-situ (Ti,W)C/45#steel composite has a stable abrasion performance, the abrasive wear and slight adhesive wear dominates in its initial stage, and oxidative wear, together with adhesive wear are the main mechanism in the later stage.When Cu element is added, the matrix of In-situ (Ti,W)C/45#steel composite transformed from ferrite and pearlite into ferrite mainly. Cu promoted the formation of (Ti,W)C to a certain degree. The hardness of this composite declined, and its wear resistance decreased. The abrasion mechanism converted from abrasive wear, oxidative wear and slight adhesive wear to oxidative wear and severe adhesive wear. And the main abrasion mechanism is adhesive wear. |
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