Effect of temperature on hydrogen embrittlement susceptibility of alloy 718 in Light Water Reactor environment

A 718 superalloy, presenting a standard microstructure, was mechanically tested under uniaxial tensile loading at 80 °C and 300 °C in Light Water Reactor environment after an exposure at 300 °C for 200 h. Hydrogen embrittlement mechanism was clearly observed. In order to identify the most influent metallurgical parameters on hydrogen embrittlement, three “model” microstructures were synthesized to test the efficiency of carbides, δ, γ′ and γ” precipitates to trap hydrogen at different temperatures. Results showed that γ′ and γ” played the major role on the hydrogen embrittlement susceptibility of the alloy even though carbides and δ precipitates could also act as hydrogen traps and influence the final rupture mechanism. Results also characterized the influence of temperature on the fracture modes.