Study On Preparation, Hot Deformation Behavior And Processing Map Of W-Cu Composite

Based on its well properties of high density, high strength, high hardness, high density, as well as good electrical and thermal conductivity, W-Cu composite has been widely used as electronic contactors, EDM electrode materials, and electronic packaging materials, etc. According to its better performances and lower cost, W-Cu composite has been used with a broad application prospect with great potential. At present, the study of W-Cu composite mainly deals with two aspects, the density and manufacturing technology, while the hot compression behaviors of W-50%Cu composite have not been widely investigated on a national and international.This paper focuses on grain-refining W-Cu composite with high performance which prepared by vacuum hot-pressing sintering. The effects of different Cu content on the microstructure and properties of W-Cu composite were analyzed, its hot deformation behavior was investigated, and then its constitutive equation was established. Based on dynamic materials model (DMM), the processing map was established which would provide a theoretical basis for the production.Reached fully dense W-Cu50%, W-Cu75% composites and pure Cu substrate were prepared by means of vacuum hot-pressing sintering of W-Cu composite powder with different Cu content under the condition of sintering temperature at 950°C for 2 hours, compaction pressure of 30MPa, and vacuum degree of 5×10-3Pa in this paper. The microstructure, density, microhardness and electrical conductivity of W-Cu50%, W-Cu75% composites and pure Cu were investigated. The effects of different Cu content on the microstructure and properties of W-Cu composite and densification mechanism are discussed. The results showed that the densification mechanism of vacuum hot-pressing sintering was achieved by grains rearrangement, plastic deformation and relative slipping. The flow-ability and plastic deformation of powder were rising by increasing the copper content, so that the density and electrical conductivity increased. Tungsten hindered the growth of Cu grains. With the increasing of W, the grains were finer, and the hardness was higher. The relative density, microhardness and electrical conductivity of W-Cu50%, W-Cu75% composites and pure Cu substrate were 99.12%, 99.63%, 99.81%; 133HV, 110HV, 80HV; 68.90%IACS, 86.10%IACS, 92.80%IACS, respectively.Using the uniaxial compression test, the hot compression behaviors of the three materials were studied. The results showed that the flow stress-true strain curves of W-Cu50%, W-Cu75% composites had dynamic recrystallization character under the present deformation conditions. The dynamic recovery occurred when the curves of pure Cu were at the temperature of 650°C and the strain rate of 1s-1, 5s-1, while the dynamic recrystallization occurred in other conditions. The increasing of temperature and decreasing of strain rate were in favor of the occurrence of dynamic recrystallization. The higher the strain rate, the higher the flow stress, the finer the grains. The higher the temperature, the lower the flow stress, and the rougher the grains. Tungsten provided the nuclei of inhomogeneous nucleation for the dynamic recrystallization and decreased the dynamic recrystallization temperature of Cu. The hyperbolic sine equation can be used to describe the relationship of flow stress, deformation temperature and stain rate of these three materials under all stress. According to the calculations of the thermal deformation activation energy, the relative constitutive equation of W-Cu composite was established.The processing map of the three materials was established, based on dynamic materials model (DMM). And their variation laws of the processing map, and microstructure were analyzed. The results showed that the key factor of the instability of W-Cu composite was the micro-cracks as a result of W-Cu interfacial debonding at high strain rate. Meanwhile, the instability mechanism of pure Cu was the flow localization during the hot deformation process. The optimized hot deformation process was achieved by synthesizing the processing map and microstructure.