Joining of self-passivating W-Cr-Y alloy to ferritic-martensitic steel by hot isostatic pressing

Abstract

The use of self-passivating tungsten alloys for the blanket first wall armor of future fusion reactors is advantageous concerning safety issues compared to pure tungsten because in case of a loss-of-coolant accident with simultaneous air ingress, a stable protective scale at high temperatures in presence of oxygen will be created, preventing the formation of volatile and radioactive WO3. Bulk W-10Cr-0.5Y alloy manufactured by mechanical alloying and hot isostatic pressing (HIP) exhibits a high oxidation resistance compared to pure tungsten. For the production of plasma-facing components, a tungsten alloy layer of a few millimeters has to be joined to reduced activation ferritic-martensitic steel. In this work, diffusion bonding by HIP of W-10Cr-0.5Y alloy to P91 steel was successfully performed, using a 50 μm thick copper interlayer at temperatures of 700 and 980 °C. The joints at 980 °C show good metallic continuity at both interfaces and a high shear strength of 354 MPa. A drop of shear strength to 174 MPa is observed after the tempering required to recover the initial properties of steel. The high shear strength values obtained at 980 °C and the observed fracture mechanisms are indications of the good adhesion obtained both with and without tempering.