Mechanical Activation - A Total Restore The Preparation Of Nano-molybdenum-copper Composite Powder And Its Sintering Behavior

Mo-Cu composites are important candidate materials for many kinds of electrical material because of their good thermal and electrical conductivity combined with low thermal expansion coefficient. Mo-Cu composites produced by infiltration, liquid phase sintering and hot pressing do not have satisfactory complex properties for their wide use. Therefore, it is necessary to study the manufacturing methods of Mo-Cu composites in order to improve their complex properties.In the investigation, preparation of ultra-fine Mo-Cu nanocomposites by the technique of coreduction of mechanical-activated CUMoO4-MoO3 mixtures was studied with the aid of differential scanning calorimetry and thermal gravimetric analysis (DSC-TG), X-ray diffraction (XRD), scanning electron microcopy (SEM), transmission electron microcopy (TEM). The influence of the ball-milling time and reduction temperature on the microstructure of the Mo-Cu powders was studied and the thermodynamical conditions at different stages of hydrogen reduction of Mo-Cu nanocomposite powders were analyzed. The possible mechanism of reduction at low temperature was also proposed. Finally, the technique of Mo-Cu composite powders sintering and influence of sintering temperature on properties of Mo-Cu composites were researched.CUMoO4-MoO3 mixtures can be obtained by calcinating of MoO3 and CuO mixtures milled for 12 hours. In other words, the ball-milling treatment of MoO3 and CuO mixtures reduced the preparation temperature of CUMoO4-MoO3 mixtures. The mechanochemical treatment of the CUMOO4-MOO3 powder mixtures caused a substantial increase of both the reduction activity of powder mixtures in hydrogen and the refinement of powders. It was accompanied by a transformation from CuMoO4 to CU3Mo2O9, which can decompose into MoO2 at a low temperature (200℃) during the H2 reduction process, giving rise to the Mo-Cu nanocomposites with particle size ranging from 100 nm to 200 nm at a low temperature (680℃). The prepared Mo-Cu powders have a coating structure, which causes a homogeneous distribution of Mo and Cu phases and controls the growing of Cu phase effectively.Sintering temperature has critical effects on the microstructures and properties of Mo-25Cu composites. It is shown that specimens sintered at 1050℃for 90 min obtained good complex properties. The density, hardness, electrical conductivity, thermal conductivity and coefficient of thermal expansion are 9.31 g·cm-3,214 MPa, 22.4 MS·m-1,147 Wm-1K-1,8.5×10-6K-1 respectively.The liquid sintering method was not ideal way to fabricate the Mo-Cu composite materials, because after liquid sintering the phenomena of copper exudation was observed, which has a negative effect on properties of Mo-Cu composites.