| The thesis consists of two parts:The first part is preparation of SiC whiskers and the second part is preparing SiC/Cu composites with homemade SiC whiskers through powder metallurgy (PM).SiC whiskers with length of 10-120 μm and particles were fabricated with rice husk by reaction sintering at the temperature from 1400℃ to 1700 ℃. It was found that high temperature could attribute to nucleation and growth of SiC whiskers, for one thing increasing the aspect ratio and dispersion of SiC whiskers, for another maintaining smooth surface and reducing defects. Purer SiC whiskers could be obtained after decarburizing and pickling. Based on results of X-ray diffraction (XRD), α-SiC and β-SiC were found in two kinds of SiC crystal structure. Growth mechanism of SiC whiskers was in the manned of vapor solid(VS) mechanism below1450℃ in temperature while SiC whiskers formed and grown in the manned of more efficient vapor lipuid solid(VLS) mechanism at 1550℃. The best temperature for SiC whiskers preparation was 1550-1600℃.SiC/Cu composites with different content of SiC(1wt%,3wt%,5wt%) could be obtained by hot pressing(HP) or hot isostatic pressing(HIP) with Cu powders and SiC (whiskers and particles).Optical microscopy (OM),X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM) and electron spectroscopy (EDX) were used to systemly investigate characteristics of SiC/Cu composites. Relative density, hardness, tensile strength, electroconductibility, compression strength, shear strength and wear properties of SiC/Cu composites were tested respectively. Influence of process and composition with SiC content on microstructure and performance of SiC/Cu composites were studied systematically.Under technological conditions of 900℃×27.7MPa×1h, SiC/Cu composites with good density were successfully fabricated by hot pressing. When the weight fraction of SiC was 1%, relative density of SiC/Cu composites was more than 95.4% with highest tensile strength and homogeneous structure. There was no surface reaction between the second phase and Cu matrix by TEM analysis, while α-SiC and β-SiC were found by SAED (Selected Area Electron Diffraction) and HRTEM (High Resolution Transmission Electron Microscopy).With increasing of SiC content in SiC/Cu composite material system, relative density was decreased but the porosity of composite, the identity of enhancement phase agglomerations, hardness and compression yield strength were increased. The highest hardness (95 HV) and highest compress yield strength (143 MPa) were both attained at 5wt%SiC. The relationship model between porosity and tensile strength was found by the conclusion through carrying on curve fitting.Fully densed SiC/Cu composites could be fabricated by hot isostatic pressing (800℃×120MPa×1h) with good conductivity and better mechanical properties than that of composites made by hot pressing. With the increase of SiC content, the fracture mechanism of composite materials gradually changed from ductile fracture to brittle fracture. Results showed that addition of SiC reinforced phase have effect of dispersion strengthened, and increasing plastic deformation resistance of materials. SiC whisker in SiC/Cu composite had whisker pull-out, crack deflection, crack ridge and hind plastic deformation to strengthen SiC/Cu composites.The wear performance of the fully dense SiC/Cu composites was tested; the researches showthat the wear rates of SiC/Cu composites were increased with increasing of speed under constant loading and were increased with increasing of the load at same speed. The mechanical mixing layer was formed in the wear process. With increasing of the load, friction and wear mechanism of SiC/Cu composites changed from abrasive wear gradually to adhesive wear and oxidation wear, and the SiC could improve the wear resistance of the SiC/Cu composite materials. |
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