Study On Severe Plastic Deformation Processed Cu-Cr-Zr In-situ Composites

With the rapid development of the science and technology, and modern industry, the copper-based composites must have higher strength and higher electrical conductivity. In this paper, it has been used that the thermodynamic calculation, finite element simulation, and relevant studies to design and prepare a low cost Cu-10Cr-XZr (X= 0,0.2,0.4,0.6) wires and plates with high-strength and high conductivity. The processes of severe plastic deformation (including drawing and accumulative roll-bonding (ARB)) were simulated and analyzed by using software ABAQUS6.5. It was studied that microstructural evolution and mechanical properties of the matirx and reinforced fibers, the influence of strengthening and toughening phase with Zr contents on the microstructures and properties of the composites, the effect of accumulative roll-bonding (ARB) on microstructure, mechanical properties, electrical properties, surface texture, and the bonding strength, the interface diffusion principle and failure model of Cr fiber at high temperature with optical microscopy, scanning electron-microscopy (SEM), transmission electro-microscope (TEM) and X-ray diffraction (XRD). The conclusions were obtained as follows:(1) The results of the finite element simulation of drawing process showed that the plastic deformation was inhomogeneous, elastic deformation or plastic deformation rounded in the drawing-link surface in the process of drawing. With the increasing of drawing rates, the maximum equivalent stress reducesd, but only a little influence affected on the equivalent strain. The friction coefficient had a larger influence on the total energy of deformation. When the friction coefficient was 0～0.1, the total energy increasing would decrease during deformation. And when the friction coefficient increased to more than 0.1, with increasing of the friction coefficient increases, the value of the total energy would raise increasing rapidly during deformation.(2) The results of the finite element simulation of ARB process showed that ARB process would produce a uniform plastic deformation all over tha sample, and only a little stress centration in the parts of accessing to the roller. But as the deformation increased, the grid would have some serious compression and tension in the parts of accessing to the roller, the distribution of stress and strain would have extremely un-uniform. It would be easily to create stress concentration in the experiment, resulting in cracks. In addition, it also found that the process of one-pass with deformation of 75% would not complete, which should be avoided in the actual experiment.(3) The addition of Zr could refine the Cr phases. In Cu-10Cr-0.4Zr and Cu-10Cr-0.6Zr alloys, the typical Cr dendrites could not be found. The average width of Cr phases were 15.8μm,14.4μm,6.3μm and 4.7μm individually in Cu-10Cr-XZr (X= 0,0.2,0.4,0.6). After a large plastic deformation, the thinner and smaller Cr phases would generate small and homogeneous fibers more easily than the thicker and larger Cr phases. When the strain ratio reached 6.2, the average width of Cr in Cu-10Cr would be about 0.5μm～1μm, and in the Cu-10Cr-0.4Zr composite, the average width be about 250nm.(4) During the cold drawing process, Cr fibers in Cu-10Cr-XZr (X= 0,0.2,0.4,0.6) composites at the vertical sections contained the following four main steps:free orienting→rotating and thinning→overlapping and merging→homogenizing; but at the horizontal sections contained four different steps:free orienting→rotating and thinning→bending, twisting and folding→irregul arizing.(5) Between fiber thickness D and deformation ratioη, there was a relationship in the composite Cu-10Cr-0.4Zr:D=9.77396 exp(-2.8η). In the composites Cu-10Cr-XZr(X=0,0.2,0.4,0.6), there were piecewise functions between the strength and fiber thickness:whenη<4.2, the Incremental of strength could be expressed as and whenη≧ 4.2, The calculated values by this model had a good agreement with the experimental values.(6) The failure process of stability about Cr fibers in the aging process included five steps:secondary fibers adhibitting to the surface of the primary fibers, spheroidizing of secondary fibers, further spheroidizing of secondary fibers and the spheroid moving to the boundary, spheroid of secondary fibers combining with the edge of the main fibers, column transitting. Which was the model of the failure process of stability about high-temperature fibers in the deformation composite Cu-Cr-Zr—fiber-induced mechanism of migration and merge. There were three kinds of resistances to prevent migration of grain boundaries in the Cu matrix:obstruction from the Cr/Cu phase interfaces, deformation textures and twin boundaries(7) The interface features of composites and the pure metals in the ARB processes were quite different. Under the deformation ratio of 50%, the interfaces of Cu-Cr-Zr composites were composed of Cu matrix; when the deformation ratio increased to 55%, the interfaces composed of Cu matrix and Cr phases; and when the deformation ratio increased to 60%, the combination of interfaces become straight. The interlayer bonding tests showed that:if the deformation ratios increased to 60%～70%, the maximum bonding stress would be more than 600N, so the best deformation ratio 60% of one-pass ARB was recommened in Cu-Cr-Zr composites.