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

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/M2 (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.