Grain Boundary Segregation in Zr-, B- and C-Doped Mo

Abstract Molybdenum-based alloys possess a unique combination of physical properties including high strength at elevated temperatures, high thermal conductivity, low coefficient of thermal expansion, and excellent performance in neutron flux environments. However, welds in commercial grade molybdenum alloys typically exhibit low (∼3%) ductility which limits their application. Bryhan has shown that controlled additions of substitutional and interstitial alloying elements can provide almost 20% elongation from gas-tungsten arc welds in 6.35-mm-thick material. Therefore, molybdenum alloys may be considered for use in fusion reactors and other high temperature applications. The molybdenum alloy was vacuum arc-cast with 0.16 at % Zr intended to getter the O (250 appm) and N (178 appm) impurities together with 53 appm B and 96 appm C intended to strengthen the grain boundaries. The 4-pass welding process was performed on a 6.35-mm plate in a controlled atmosphere chamber where the O, N and water vapor impurity levels were < 10 wppm each.