Decrease in hydrogen embrittlement sensitivity of INCONEL 718 by laser surface softening

A Ni-base superalloy, INCONEL 718, has a high sensitivity to hydrogen embrittlement. Hydrogen induced cracking tends to occur at the surface of the stress concentrated regions. Reducing the hardness of such surface regions locally is known to be effective in preventing such cracking. To this end, in the present work, a laser surface solutionizing has been applied to INCONEL 718 using a 2.5 kW CO2 laser. The surface solutionized zones up to approximately 1 mm in depth, where age precipitates of γ and γ′ʹ were dissolved in the matrix; could be obtained without melting the treated zones by optimizing the laser conditions. While the base metal has a hardness of approximately 450 Hv, the hardness of the laser solutionized zones was reduced to below 250 Hv. The ductility of the surface solutionized specimen was almost twice that of the base metal in a tensile test under a 29.4 MPa hydrogen atmosphere at room temperature with hydrogen pre-charging. Thus, the laser surface softening is effective in reducing the sensitivity of INCONEL 718 to hydrogen embrittlement.