Failure behaviors of vacuum plasma sprayed tungsten coatings for plasma facing application

About 1 mm vacuum plasma sprayed tungsten (VPS-W) coatings were fabricated on the copper chromium zirconium (CuCrZr) alloys substrate. The failure behaviors were studied by means of the steady state and transient heat load using the electron beam facility and the Nd: YAG laser, respectively. The results indicated that the columnar crystals grew up and then micro-cracks between the lamellar layers were observed. Macro-cracks and delamination appeared with the fatigue cycles increase. Finally, the coating failed. The surface cracks were also observed and propagated during the fatigue tests. The failure behaviors of the transient heat load are as follows: the homogeneous melting and micro-cracks, melting tungsten ejection which enhanced the erosion of tungsten due to the splash and evaporation. In addition, the physical properties of W coatings such as porosity, Vickers hardness were degraded. The roughing phenomenon was not easy to be observed due to the rough surface characteristic of VPS-W coatings.