Analysis of the brazeability of W–W joints using a high temperature Ni-based alloy

Tungsten is considered in fusion technology as structural material in divertor for future application in DEMO. Helium cooled divertor design includes joints between W and W alloys. Present study analyzed the brazeability of pure tungsten using a commercial high temperature nickel-based alloy in vacuum furnace. Although nickel application of interlayers in the W–W joints of the structural zone is not desirable, as it can promote helium accumulation under irradiation and a subsequent embrittlement enhancement of the brazed joint, this experimental study could help to define conditions of the braze application inside the W–W joints, besides obtaining useful information to control the brazing conditions and avoid undesirable brazeability problems (cracking, dilution, W recrystallization, grain growth, etc.). High vacuum brazing tests have been carried out at temperatures higher than the liquidus one of the braze alloy. Characterization studies, both microstructural and mechanical, of the W–W brazed specimens demonstrated the development of new brazing fillers which meet requirements such as strength and flexibility for adaptation to the shape of the joint.