Development of high-grade VPS-tungsten coatings on F82H reduced activation steel

Vacuum plasma sprayed tungsten (VPS-W) coating formed on F82H steel kept at about 873 K in conventional plasma spray conditions has inhomogeneous texture; it is a mixture of disorganized areas composed of large unmelted grains, fine randomly oriented grains and pores, and well-ordered areas composed of columnar grains. Heat load tests indicate that elimination of the disorganized area is necessary to improve the heat load resistance of VPS-W. One can get W coating with a texture of homogeneous columnar crystal grains by eliminating the unmelted large particles. Optimization of the W powder size was also effective to reduce the number of randomly oriented fine grains and pores.