Research On Densification And Properties Of TiC/316L Composites Prepared By Powder Metallurgy

TiC is responsible for the hardness and abrasive resistance increase while 316L stainless steel ensures the toughness and better corrosion resistance. Such combination of properties make the TiC/316L stainless steel composites very attractive for numerous applications like in mechanical, chemical, petroleum and oceanic fields. Compared with other preparation methods, powder metallurgy (P/M) is thought to be a more suitable preparation technique for particles reinforced stainless steel composites because it has many advantages, such as accurate component proportion, lower process temperature, and higher production efficiency. However, P/M materials have relatively high porosity and low densification. Thus, how to improve the densification of P/M materials is the problem that is concerned by the researchers. Therefore, this thesis researches on the densification and properties of TiC/316L stainless steel composites obtained by P/M technology. In order to improve the densification of P/M stainless steel composites, new densification methods were also investigated.In this study, microstructure characteristics of the TiC/316L composite powders obtained through different ball-milling modes were performed by means of scanning electron microscopy (SEM). Huang Pei-yun's log-log powder compacting theory and relevant sintering theory were used to analyze the compactability and sintering behavior of those powders, respectively. The results indicated that TiC/316L composite powders prepared by the ball-milling mode of dry ball milling and then wet grinding exhibited a more small grain size, lower activation energy of sintering, and it has a beneficial effect on their subsequent compression and sintering.In order to discuss the P/M composites densification factors, a study on effect of conventional compaction and warm compaction on densification of composite powder was performed. The analysis show that warm compaction process results in the increased the plastic deformation capability of TiC/316L composite powder, which had helped to improve the particle rearrangement. As a result, the densification increases. And based on this, a new densification method for TiC/316L composites by using warm compaction and microwave sintering (WM) is put forward. It is found that the composites prepared by WM not only has high relative density, but also better distributing of TiC particles in matrix, and diminishing agglomeration of the particles than the composites prepared by conventional P/M.The effects of reinforcement particles of different shapes on the stress and strain behaviors of composites were investigated by using the ANSYS software. The simulation results indicated that the composites in which the particles are assumed all in round shape produce a better strengthening for its more uniform dispersions of stress and strain, as compared with the composites which adopt the hexagon or square particles.The factors affecting the tensile properties, abrasion resistance and high temperature oxidation behavior of TiC/316L composites were analyzed in this paper. The results show that the addition of TiC is effective in improving the tensile properties, abrasion resistance and high temperature oxidation resistance of the composites. Furthermore, the tensile strength and abrasion resistance of TiC/316L composites were increased with the increase of the pressing pressure. The experimental results demonstrate that the composites with 10wt.%TiC addition exhibited a higher tensile strength and better oxidation resistance; 5wt.% TiC/316Lcomposites exhibited a better abrasion resistance. The tensile property of the composites is better under the pressure of 500MPa than other case. A better abrasion resistance property was obtained when the pressure was 400MPa.Research on the friction and wear behavior of TiC/316Lcomposites suggests that improving the densification of composites and dispersion of TiC particles in matrix can effectively promote the loading of TiC particles during wear sliding, resist the wear deformation, and reduce volume loss of composites. The sample prepared by warm compaction and microwave sintering exhibited significantly superior densification, higher hardness and better abrasion resistance when compared with conventionally processed counterpart. Research on the high temperature oxidation behavior of TiC/316L composites show that the composites obtained by MW because of the improving of TiC particles dispersion, and thereby increment of the densification, which causes a decrease in oxidation rate.The thesis also discusses the effect of Mo content on the densification and properties of TiC/316L composites. Results show that Mo addition contributes to enhancing the densification of the composites during sintering and thus to promoting the tensile strength and abrasion resistance of the composites. Moreover, the addition of Mo is beneficial to improve the resistance to pitting in 3.5wt.%NaCl solution, and the corrosion rate of composites could appreciably decrease.