Mechanical and Fatigue Properties of Tungsten Heavy Alloy Prepared by RF-plasma

Tungsten heavy alloys (WHA) are composite materials containing spherical tungsten particles embedded in a Ni-rich matrix. Today, WHAs are being considered as materials for the first wall of nuclear fusion devices. The feasibility of depositing thick WHA coating using RF-ICP technology (thermal spray in a protective atmosphere) was investigated. Thick deposit of WHA (RF-WHA, W-Ni) was fabricated on a graphite substrate at substrate temperature of about 1200 °C. For that, a blend of W and Ni thermal spray powders was used as feedstock. During the relatively short spray time, the two-phase particle-matrix structure typical for WHA fully developed and a high density material was obtained. The sprayed WHA was mechanically tested in pure bending and fatigue bending at R = -1 and compared with reference powder metallurgy-produced material (PM-WHA, W-Ni-Co). While the elastic moduli of the two materials were almost identical, the fatigue crack growth rates of RF-WHA coatings were slightly higher. The fatigue crack growth took place exclusively in the solid solution matrix for both RF-WHA and PM-WHA materials; conversely, the static failure was mainly caused by cracking of the W particles. These early results indicate that RF-plasma spray is an efficient way of manufacturing good quality WHA deposits.