| Copper is closely related to human production and living activities. The consumption of copper is second only to alumina in the consumption of nonferrous metal materials in our country. Copper and its alloys have excellent mechanical properties, thermal conductivity, electrical conductivity and corrosion resistance. They are used to manufacture multiple electrical contact materials, structural materials, corrosion-resistant materials and wear-resistant materials which are used in electronics, automobile, aerospace, shipbuilding industry and other fields. Copper based friction materials are an important kind of metal-based friction materials. The main two ways of developing copper based friction material are alloying with other elements and making composite materials with second phases. The copper based composite materials can keep good electric eonductivity as well as small friction coefficients and low wear rates. It is a promising kind of current-carrying friction materials. Titanium carbide is one of the hardest carbide. It has high melting point, high Young's modulus, stable chemical nature, electrical conductivity and thermal conductivity. Copper based composite materials with second phase of Titanium carbide have great deal of research prospects in the field of friction and wear.The purpose of this research is to prepare TiC strengthened copper composites, and to study the microstructures, hardnesses, densities and tribological properties of the composites which are effected by processing conditions. The contents of this research are included in the following aspects:1. Prepare Cu-Ti-C composite powders with copper content of 50wt% and 70wt% by mechanical alloying (MA). Analyze the ball milling process by XRD, SEM and TEM. The results show that with the increase of milling time, the powers take a serious plastic deformation. By the constantly circulation of cold welding– breaking, the powder particle size decreases continuously by the effects of strong mechanical force. Milled After 50 hours,the powder becomes equiaxed small particles. Keeping milling, the particles begin to reunite, and their size begin to grow. At last, the final average size of particles is maintained by the dynamic balance of reuniting, cold welding and breaking. Mechanical milling makes the wetting property between C and Cu improved effectively. The supersaturated solutions of Ti, C in Cu are successfully prepared by mechanical alloying. Mechanical milling makes a high density of dislocations inside the grains. So part of the grains turns into nanocrystallines. At the same time, the high-speed loading shear stress makes lots of small size mechanical twins which can strong the copper matrix without reducing its electric conductivity.2. Prepare 50wt%Cu-TiC and 70wt%Cu-TiC composite materials (marked as Cu-TiC(A) materials) by Cu-Ti-C composite powders useing spark plasma sintering (SPS). Analyze the microstructures, densities and microhardnesses of the composites to find out the effects of different copper contents, milling times and sintering temperatures. In the process of sintering, new phases of TiC and Ti2Cu3 are produced. Some copper grains are melted and interconnected to form a mesh matrix. The TEM photos indicate that TiC dispersed in the copper matrix and the gaps of the original power particles. Some C atoms precipitate from the copper matrix and become graphite phase. With the increasing of sintering temperature, the original powder particle morphology disappears gradually from the microstructure of the composites. The composites sintered at 1000℃have the finest microstructure. When the sintering temperature raises to 1050℃, the microstructures of the composites become coarse. The densities of the Cu-TiC(A) composites first increases and then discreases when the sintering temperature raises from 850℃to 1050℃. When the sintering temperatures are low, some copper melts and fills in the gaps of power particles. So the densities increase. When the sintering temperatures are too high, the copper melts rapidly and is extruded out of the die. And the densities decrease. The microhardnesses of the Cu-TiC(A) composites also first increases and then discreases when the sintering temperature raises. The TiC produced in the sintering process strengthens the copper matrix and make the microhardness increases greatly. The influence on the microhardness of the density is first increase and then discrease when the sintering temperatures raises.3. Prepare another kind of composite powders by adding Ti-C powder into copper base. And then sinter this powder into Cu-TiC composite materials (marked as Cu-TiC(B) materials) by spark plasma sintering. Phase analysis shows that Ti and C are not reacted to TiC after 10 hours milling. But the ball milling process increases the activity of Ti-C powder. So the sintering temperature needed to the reaction of TiC decreased observably. After SPS, composites have a microstructure that copper particles are surrounded by fine titanium carbide particles. As the sintering temperature raises, Ti and C react to TiC gradually. So the content of residual graphite decreases. When the sintering temperature raises, the wettability between TiC and copper is improved, and the reinforcement of TiC raises. When sintered at 1000℃, copper extruded out of the die and the density of composite decreases.4. Test the the friction and wear properties of this two kind Cu-TiC composites. Analysis the wear mechanisms of the two composites. The friction coefficients and the wear rates of 70wt%Cu-TiC(A) composites both decrease slightly when the normal load increases. It has very low friction coefficients and excellent wear-resistance. Its abrasion mechanism is adhesive wear. The friction coefficients and the wear rates of 70wt%Cu-TiC(B) composites first dicreases steeply and then dicreases slightly when the normal load raises. Its abrasion mechanism is three-body abrasion, and the third body is mechanical mixed layer that formed by accumulation and compaction of the debris which come from the composites and corresponding disk.
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