Fabrication And Properties Of Tungsten-Copper Three Layers Heat-Sink Gradient Material

W-Cu composite has been regarded as a good heat sink of the high power microwave apparatus, but with the development of microwave apparatus towards miniaturization, high integration and high power, which results in highly thermal generation. The present homogeneous W-Cu composite can't meet the requirement of electronic board on heat radiating properties. W-Cu FGM is a potential method to solve this problem. In this paper, the feasibility that W-Cu FGM is fabricated by combining mechanical alloy technique and traditional powder metallurgy technique is mainly investigated.Three gradient layers were designed after calculating the physical parameters of W-Cu FGM layers according to Kerner-law and determining the composition gradient in the FGM by powder-law equation: f_cu= (z/t_FGM)^p.The composition in the three layers is in the order of W-20Cu,W-35Cu and W-50Cu.W-20Cu, W-35Cu and W-50Cu nano-crystallite composite powder were obtained by MA technique. The composite powders were characterized by XRD, SEM, TEM and the mechanism of W-Cu solid solution was studied. The results show that Cu dissolved in W lattice entirely forming W(Cu) solid solution after W-20Cu and W-35Cu were high-energy ball milled while W(Cu) and Cu(W) solid solution were both formed after W-50Cu were milled. During the high-energy milling, much nano-sized crystallite boundary and defects such as dislocation, stacking fault were produced , which made Cu dissolve in W lattice forming W(Cu) solid solution. Crystallite size of W-Cu composite powder decreased with the increasing milling time and stayed steady at last. Crystallite size of W(Cu) in W-20Cu, W-35Cu and W-50Cu were 6.6nm,6.5nm and 8.0nm respectively.The effect of milling time on the microstructure and properties of W-Cu composite was also investigated in order to obtain the optimal milling time. The results show that with increasing milling time, microstructure of W-Cu composite become more homogeneous and tungsten crystallite size become smaller; Relative density, shrinkage, hardness and bending strength of W-Cu composite increased. The value of thermal conductivity peaked when milling time was 20h. Considering all factors, the optimal milling time for producing W-Cu nano-crystallite composite powder was 20h in this paper.W-20Cu, W-35Cu and W-50Cu nano-crystallite composite powder obtained after 20h high-energy ball milling were stacked layer by layer in the die to form a green compact. Then the green compacts were sintered at different temperature to form the W-20Cu/W-35Cu/W-50Cu FGM. The effect of sintering temperature on the microstructure and properties of the FGM was studied. The results show that FGM sintered at 1200℃had perfect microstructure and better physical and mechanical properties. In the FGM sintered at 1200℃, copper formed continuous network distribution to the framework of W and defects were less and crystal size were smaller. The composition had graded distribution in the cross-section .Composition and microstructure around the interface changed continually through element diffusion in high temperature, thus reducing thermal stress. The relative density of three layers FGM sintered at 1200℃was all above 95%. And the value of its hardness and whole bending strength were the largest. Its whole thermal conductivity is 151.4 w·m^-1k^-1 and the thermal conductivity of sealing layer and radiating layer were 127.6 w·m^-1k^-1 and 212 w·m^-1k^-1 respectively. The thermal shock and thermal cycle tests were conducted on FGM sintered at 1200℃with the cooling temperature difference 800℃. After the thermal shock test, no cracks were found at the interface. The FGM survived up to 83 thermal cycle tests. Cracks were found at the interface between W-20Cu and W-35Cu , but the FGM didn't break. These results indicated the FGM had excellent heat resistance and exhibited good properties of reducing thermal stress.