Study On Electric Characteristics Of SiC_p/Cu Composites

SiC/Cu composites combine both the superior ductility and toughness of copper and the high strength, hardness and high modulus of SiC. These advanced materials also exhibit high thermal, electrical conductivity and low CTE. SiC/Cu composite shows extensive applications in many industrial fields. It is one of the expected "structural-functional" composites. It can be used in the aerospace vehicles, electric contact materials in semi-conductive devices, heat exchangers, abrasive plates, etc. SiC/Cu composites have received considerable attentions for their mechanical and functional applications. No open literature was reported on SiC/Cu composites before 1996. The preparation and properties were studied for SiC_f/Cu, SiC_w/Cu and SiC_p/Cu composites. However, most of the studies on SiC_p,/Cu composites have been focused on the preparation methods and interfacial bond in order to improve their mechanical properties. In fact, the electrical properties of SiC_p/Cu composites are very important for their electrical applications. And no convinced theory about the electrical properties of SiC_p/Cu composites was reported thus far.In this study, the industrialα-SiC particles (in average diameter of 10μm) were commercially available. The electrical properties of SiC were systemically studied. Admixture, coating and hot pressing technique was carried out to prepare SiC_p/Cu composites. Theoretical model for improving the densification of SiC_p/Cu composites containing high content of reinforcement was proposed. SiC-Cu interface and the influential aspects were analyzed. XRD, SEM, TEM, EDS techniques were used to characterize the samples. The electrical properties of SiC_p/Cu were measured. The electrical conduction mechanisms of SiC_p/Cu were analyzed.It was found that SiO₂ film on the surface of SiC particle made great effects on the electrical resistivity of SiC particle. The electrical resistivity of SiC particle increased with increasing SiO₂. The sintered SiC exhibited negative TCR behavior in the range from 225 to 600℃. SiC_p/Cu composites were fabricated at 700℃and under 40 MPa for 10 min by hot pressing. No reaction is detected in the sample. The densification of SiC_p/Cu composites by hot pressing might possibly proceed via the plastic deformation of the softened Cu under applied pressure. The electrical resistivity of SiC_p/Cu composites increased with increasing SiC_p. The percolation threshold occurs when SiC volume fraction reaches about 55%. The variations of electrical resistivity of the composites with 20-35 vol% SiC_p with temperature exhibited a linear relationship, with electrical resistivity increasing as the temperature increased. When the fraction of SiC_p, exceeded 50 vol%, the variations of electrical resistivity of the composites with temperature deviated the linear relationship in the range from 225℃to 500℃. SiC_p/Cu composites prepared by both coating and admixtre methods had the same electrical properties. However, the mechanical properties of the composites made by coating method is better than that of the composites made by admixture method. This resulted from the improved Cu matrix. Theoretical model for improving the densification of SiC_p/Cu composites containing high content of reinforcement was proposed, which suggested that great densification of the composites can be obtained by using proper proportion of two SiC particles with the ratio of the radii of 10:1. The composites made by original SiC and acidetched SiC particles had the same electrical conduction behavior at high temperature due to their similar interfacial structure. There existed glass phase on the interface of the composites made by oxidized SiC particles. The glass phase led to the increase of the electrical conductivity of the composites at high temperature because of the accumulating of the space charge. The beginning temperature of accumulating of the space charge was about 225℃. And the critical temperature of high conductivity was about 400℃.