Research On The Thermoformabilities Of ?Sr,Ba? TiO₃ Particle Reinforced Copper Matrix Composites

Barium strontium titanate ceramic particles with negative thermal expansion properties were choosen as the reinforcement while copper with high heat conductivity were choosen as matrix of composites. Different Sr/Ba ratio of barium strontium titanate particles reinforced copper matrix composites were prepared by Spark Plasma Sintering. After coated rolling, the morphology and interfacial characteristics of reinforcement and matrix of composites were observed by several methods of microstructure analysis(XRD, SEM, etc.). Using thermal expansion instrument and thermal conductivity equipment to test and analyse the thermal expansion ability and thermal conductive of the composites. Using Electronic Universal Testing Machine to test the compress yield strength of composites.XRD and microstructure observation results prove that the high density SBT/Cu composites were obtained by SPS method. SBT reinforcement also shows good dispersion in whole matrix. Interface is smooth and clear while no impurities were observed. In the coated rolling process, the SBT/Cu composite material is in a three-direction-stress situation, sometimes the low internal stress is insufficient to drive the grain to form high strength texture. There are quite strong <100> texture and weak <112> texture, <122> texture and <210> texture in rolling state composite. In rolling direction, texture intensity is much higher than both normal direction and transverse direction.Compare to martix metal, the thermal expansion coefficient(CTE) of sintered composite material have fallen sharply, but the coefficient of thermal expansion of rolling state composite rises up. Mainly because of the appearance of texture and the interface were destroyed in rolling. Thermal cycle and heat treatment can improve the thermal expansion stability of the rolling state composite, which made SBT/Cu composites become a new copper matrix composites with low expansion, thermal stability and excellent physical properties in great range of temperatures. Moreover, the higher texture intensity is, the more obvious the grain preferred orientation shows, and the smaller the effect of heat treatment.Relationship between the thermal expansion behavior and stress of rolling state SBT/Cu composites is discussed. As a reinforcement, SBT particles with high elastic modulus is quite differ from any other reinforce paticles. Its elastic modulus even higher than the matrix metal. So when composite material is under room temperature, matrix metal is under tensile stress, reinforcement particle is under compressive stress. With the increase of temperature, phase transformation of reinforcement particle cause great negative thermal expansion during 60?~120?, which confined expansion of matrix within interface. As a result, the whole composite expansion is deviated from the linear increase.