Study On The Preparation And Properties Of Particulate Reinforced Copper Matrix Composites Fabricated By Composite Electroforming

With the rapid development of aerospace, electronic, automobile and mechanical industry, increase in performance for copper have been required, such as high strength, especially excellent mechanical performance at high temperature, low coefficient of thermal expansion and nice wear resistance, apart from its outstanding conductivity. Consequently, particulates reinforced copper matrix composites (PRCMC) have been arisen. The mechanical performance and tribological behavior at room and high temperature are markedly improved duo to the addition of particles with high hardness, high strength and modulus, resistance to high temperature and low density within the copper matrix. Besides, the electrical conductivity of PRCMC doesn't decrease sharply with the addition of particles, which covers the shortage, such as the deterioration of conductivity, low wear resistance and poor strength under high temperature condition, existed in the copper alloys.At present, some traditional methods (such as powder metallurgy, fusion casting) are employed to prepare particle reinforced metal matrix composites and present many shortages such as high temperature, complicated processing, severe interface reaction duo to the high melting point of metal such as copper and nickel. Meanwhile, with the increasing application of nano particle in metal matrix composites, the traditional methods face many difficulties in solving the agglomeration of nano particle and uniform distribution of particles, which can limit the application range of nano-particle reinforced copper matrix composites.In this work the composite electroforming technology, combining the composite electrodeposion and electroforming technology, is brought forward to prepare PRCMC. The composite electroforming technology owns the merits of simple processing, low operating temperature, none reaction in the interface and uniform distribution of particles. The product can be prepared at one time, which simplify the production course. The composite electroforming technology has been optimized and the properties of PRCMC have been studied systematically in this thesis. The main works are shown as follows:Firstly, surfactants aiding to the codeposition were investigated for SiC particles and Al₂O₃ particles. The results showed the fluorocarbon surfactant (FC-4) and the dodecyl thrimthyl ammonium chloride was in favor of the codeposition of SiC particles and Al₂O₃ particles with copper ion respectively. Cu/SiC and Cu/Al₂O₃ composites were successfully fabricated and presented a microstructure of uniform dispersion of particles and compact and good bonding between the particles and copper matrix, and also presented a finer and smoother surface.Secondly, many important processing parameters, such as particles concentration, particle size, agitating rate, current density and electrolyte temperature, were investigated carefully and the main conclusions were shown in follows:1. The content of SiC particles and Al₂O₃ particles in composite reached the maximum as the concentration of SiC particles and Al₂O₃ particles reached a value.2. There existed an agitating rate, which obtained a maximum content of particle respectively for micro-sized SiC and Al₂O₃ particles in composites. But the content of nano-sized SiC, Al₂O₃ particles in composites increased with the increasing agitating rate.3. Increasing the current density was helpful to the increase in content of SiC particles with different particle size in composites. However, the content of micro-sized Al₂O₃ particles in composite decreased with current density increasing and the change of current density had little influence on the content of nano-sized Al₂O₃ particles in composites. Both the content of SiC particles and Al₂O₃ particles in composite decreased with the increase in electrolyte temperature. For both codeposition system of SiC and Al₂O₃ particles, the optimal current density and temperature of electrolyte was 8A/dm2 and 30℃respectively.4. For both codeposition system of SiC and Al₂O₃ particles, the electroforming rate decreased with the concentration of particle in electrolyte increasing and also decreased with the particle size decreasing.The mechanical performance of Cu/SiC and Cu/Al₂O₃ composites and the strengthening mechanism of particles in composite were then studied after composites were successfully fabricated. The results indicated that the hardness and the strength of composites increased duo to the addition of SiC and Al₂O₃ particles, but the ductility decreased. The larger micron-sized particles reinforced composites presented higher hardness, but the smaller micron-sized particles reinforced composites displayed more remarkable increase in hardness and strength though and still maintain good ductility with above 9%. The improvements of nano-sized particles to the mechanical performance of composites are superior to that of micron-sized particlesThe strengthening mechanisms of micro-sized SiC and Al₂O₃ particles in composites were mainly the dispersion strengthening and dislocation strengthening. But the strengthening mechanisms of nano-sized SiC and Al₂O₃ particles in composites were mainly the Orowan dislocation strengthening and the grain refining. The final failure is associated with a sequence of microcracks initiating from the interface, propagation and coalescence through the matrix. Composites presented a characteristic of the ductile failure with numerous microscopic voids and shallow dimples spreading on the fracture surface.The electrical conductivity and coefficient of thermal expansion of composites were also discussed. The results indicated that the composites reinforced by micro-sized SiC and Al₂O₃ particles presented a decrease in electrical conductivity with the content of particle increasing but still maintain nice conductivity, and the coefficient of thermal expansion (CTE) reduced as the content of particle increased. CTE of composite increased after heat treatment was employed. The electrical conductivity and CTE of composites reinforced by nano-sized particle decreased a little with the increasing nano-sized particle content in composite, which provided a way to gain the copper matrix composite with high strength and high electrical conductivity.Friction and wear properties of the composites were tested using a wear tester in the dry conditions at room temperature. The results showed that the wear mechanism of the electroformed copper mainly depended on the adhesion mechanism and the wear mechanism of composite was mainly the abrasion mechanism. The addition of particles enhanced the hardness and plastic stress of composite, and the hardness and strength of mechanical mixing layer (MML) were increased with the addition of particle, which reduced the abrasion of the counterpart to the matrix and resulted in better wear resistance.When the wear load was below 100N, the wear resistance enhanced as the particle content and particle size increased. Under higher load condition (greater than 100N), the severe abrasion was slowed up and reduced effectively with the addition of particle. But increase in content of particle with larger size was harmful to the wear resistance. Composites containing smaller particles, especially nano-sized particles, presented more stable tribological behavior and more excellent wear resistance under higher wear load condition (greater than 100N).In this paper, the composite electroforming technology was put forward to prepare the particulate reinforced copper matrix composite. Based on the investigation of the process, composites owning compact texture and smooth surface were fabricated successfully, and particles disperse uniformly in matrix and the content of particles is controllable. The mechanical performance of composite was examined systematically, and the strengthening mechanism of micro-sized and nano-sized particle was determined, which can make guide for the real application. Nano-particles reinforced copper matrix composites present excellent mechanical property, nice wear resistance and electrical conductivity, which provided a way to gain the copper matrix composite with high strength and high electrical conductivity.