Luo Laima

Fabrication of W/Cu Graded Heat-sink Materials by Electroless Plating and Powder Metallurgy

Abstract The W/Cu graded heat-sink materials with high density were fabricated by electroless plating and powder metallurgy. The microstructure, interface and fracture of the graded heat-sink materials were observed using the field emission scanning electron microscope (FESEM). The mechanical properties of the materials such as bending strength and hardness were determined. The results show that the structure of each layer is uniform and dense. The components of the cross-section present a graded distribution. There is no obvious interface among layers. The relative density of three-layer W/Cu graded heat-sink materials reaches 99.2%. The average values of microhardness HV of the radiating layer, the transitional layer and the sealing layer are 2000, 2100, 2400 MPa, respectively. It is indicated through the experimental results of bending strength that the bending strengths of the sealing layer and the radiating layer as the load-bearing surfaces are 428.5 and 480.7 MPa, respectively.

Preparation and Properties of W-15Cu Composite by Electroless Plating and Powder Metallurgy

Abstract W-15Cu composite samples were prepared by electroless plating (for composite powder) and powder metallurgy (for sintering samples). Starting W powder was activated by a chemical pretreatment first, and then the pretreated W powder was electroless plating to get Cu-cladded W powder, which was pressed into green compacts at different pressing pressures. Afterward, the composite was sintered into W-15Cu composite samples, and Cu-cladded W powder was characterized. The relative density, hardness, compressive strength and electrical conductivity of the composite samples were tested. The morphologies of the Cu-cladded W powder and the samples were investigated. Results show that the prepared powder has good compaction behavior with high purity, uniform particle size and a dense Cu cladding layer. W particles still remain sole ones and no obvious grain coarsening appears in the sintering samples, while 3D Cu network is all over the structure of the samples. The electrical conductivity and the compressive strength of the sample change with pressing pressure and sintering temperature.

Thermal Performance and Microstructure of Vacuum Plasma Sprayed Tungsten Coatings under Cyclic Heat Load

Abstract Tungsten coatings on copper substrate were prepared by vacuum plasma spraying (VPS). NiCrAl and W75Cu25 materials were selected as intermediate layers. The experiment result of cyclic heat load of electron beam with 5 MW/M 2 (heat flux) and 2 s pulse duration indicates that NiCrAl interlayer improves the thermal conduction of the coatings and reduces their thermal and residual stress. The specimen with W75Cu25 interlayer fails with a bad thermal performance because of fabrication problems. The microstructure characterization of the VPS-W coating shows that erosion crater and fine microcracks appear on the tungsten coating after cyclic heat load tests. And erosion crater has a coarse and loose microstructure. Local plastic deformation occurs in the coating because of thermal stress. Cracks originate from debonding of molten tungsten particles at high temperature. However, the crack propagation is constrained by local plastic deformation and pores in the tungsten coating.