| Copper and its alloys played a important role in the human history. Along with the rapid development of modern science and technology, copper and its alloys with excellent electrical conductivity, thermal conductivity, good corrosion resistance and processing properties increasingly become an integral role of the process of industrialization. However, the low hardness, strength, poor wear resistance of copper limits its further application. With the development of materials science and technology, new materials continually appear and develop towards the composite, high functional or intelligentized direction. In general, there are two ways to improve the mechanical strength and wear properties of copper base materials, method of composite and alloying. Some studies suggest that hard particles reinforced composite with copper matrix can maximum keep the thermal conductivity and electrical conductivity of copper. The rapid development of new powder metallurgy technology provide effective new ways for preparation of high-performance copper-based particulate reinforced composite materials, and greatly expanded the selection of strengthening particles of copper matrix composite. As the hardest pure metal carbide, TiC was often used as reinforcement in composite materials. However, it is difficult prepared TiC by traditional methods, but preparation methods, such as mechanical alloying, self-propagation high-temperature synthesis provide new ways of application and preparation of TiC and its reinforcement composites. The TiC reinforcement copper matrix composite material has both excellent thermal conductivity copper matrix performance, but also has good wear resistance. In this paper, mechanical alloying, cold pressing-sintering and spark plasma sintering was used to prepare TiC, Ti-C powders and TiC reinforcement copper matrix composites, and the evolution of the microstructure, mechanical properties and tribological properties were analyzed.In this paper, the relationship between the milling balls diameter and synthesis process of TiC was first analyzed by mathematical method. In the Ti-C mechanical alloying process, the small milling balls is better on the fragmentation for powder particles than big milling balls, but the big milling balls can transfer more energy to powder particles in the collision process, therefore, when the small milling balls were used to mill Ti-C powders, it can obtain TiC in within a shorter time than using big milling balls, but the TiC synthesis process can not be complete in a short time. However, when big milling balls were used in the Ti-C mechanical alloying, the TiC synthesis process may be complete in a short time by MRD reaction. Furthermore, the Ti-C compound powder with highly activated which can synthesis TiC at lower temperature were prepared by mechanical alloying in this study. The microstructure and morphology evolution of Cu-Ti-C compound powders with different content during mechanical alloying process was studied and analyzed in this paper. In the mechanical alloying, the particle size of Cu-Ti-C compound powders decreased at first, and then increased as increasing of milling time, and the Cu-Ti-C compound powders with higher copper content agglomerated observably in mechanical alloying process. It can be found that Ti as solid solute into Cu matrix with different milling times, while C gone into Cu matrix as sub-solution. It can be observed small mechanical twins in the milled Cu-Ti-C compound powders after mechanical alloying. The milled Cu-Ti-C compound powders with high activity which can synthesis TiC at a low sintering temperature.In this paper, cold pressing-sintering method was used to prepare TiC reinforcement Cu matrix composites from Cu-Ti-C powders which mixed with milled Ti-C powders and Cu powders, and microstructure evolution and wear behavior of the composites was studied in this paper. TiC was synthesized during sintering, and the content of TiC increased as increasing of sintering temperature, however, the hardness and density of the composites increased first and then decreased as increasing of sintering temperature. Significantly between the heat-affected zone which was caused by heat released from TiC synthesis reaction can be observed in the microstructure between the TiC and Cu matrix which can improve interfacial bonding between TiC and Cu matrix, enhance the performance of the composites. The content of TiC decreased following increasing of intensity of mixed for the Cu powders and Ti-C powders (mixing time and mixing speed). The TiC reinforcement Cu matrix composites which were prepared by cold pressing-sintering method show third-body wear in the wear test. The wear rate of the composites decreased as increasing of milling time of Ti-C powders; The wear rate of the composites decreased first and then increased as increasing of sintering temperature and intensity of mixed for the Cu powders and Ti-C powders. The composites prepared by cold press-sintered show excellent wear resistance, the lowest wear rate of the composites is 1.96×10-4mm3/NmThe spark plasma sintering method was first to prepare TiC reinforcement Cu matrix composites from two Cu-Ti-C compound powders, milled Cu-Ti-C powders and added milled Ti-C powders to Cu powders, and microstructure evolution and wear behavior of the composites was studied in this paper. Results show that TiC synthesis reaction occurred in the sintering process of two kinds of powders, the composites sintered from the added milled Ti-C powders to Cu powders content Cu, TiC and C which gradually decreased and disappeared as increasing of sintering temperature, and the composites sintered from the milled Cu-Ti-C powders content Cu, TiC, C and Cu3Ti2. TiC in the two composites shown different synthesis mechanism, TiC in the composites sintered from the added milled Ti-C powders synthesis by direct synthesis reaction, and TiC in the composites sintered from the milled Cu-Ti-C powders synthesis by direct synthesis reaction and diffusion reaction. Two kinds of composites sintered from different powders show different wear behavior and wear mechanism in the wear test. The composites sintered from the added milled Ti-C powders show third-body wear in the wear test, mechanical mixed layer increased and was broken as rising of normal load. The composites sintered from milled Cu-Ti-C powders show adhesive wear, as well as abrasive wear and delamination wear at higher normal load, and the composites show lower friction coefficient and wear rate, the friction and wear behavior is more stable than the composites sintered from the added milled Ti-C powders. The composites sintered by SPS show better wear resistance than the composites prepared by cold press-sintered.The composites for high-speed trains brake materials which content milled Cu-Sn alloy powder, milled Ti-C compound powders, and graphite, Fe, Ni, Cr, Al2O3 were first prepared by cold pressing-sintering method in this paper. TiC synthesis reaction released heat which can improve interfacial bonding between the matrix phase, grinding phase and lubrication phase, enhanced the mechanical properties and wear resistance of the composites. The composites show third-body wear in the wear test, the friction coefficient of composites can be controlled by composition ratio and sintering temperature. The composites which contained Al2O3 were broken at higher normal (over 200N), and addition of Ni and Cr benefit to improve the stability of the friction coefficient of the composites. The composites for high-speed trains brake materials show good wear resistance in the wear test, the wear rate is significantly lower than the standard (0.63cm3/MJ) of International Union of Railways.
|
PDF Full Text Request