Molecular dynamics simulation and experimental proof of hydrogen-enhanced dislocation emission in nickel

The molecular dynamic simulations indicate that hydrogen solubilized in nickel decreases the critical stress intensity for dislocation emission from K-Ie(theta = 45degrees) = 1.00 MPa(.)m(1/2) or K-Ie(theta = 70degrees) = 0.82 MPa(.)m(1/2) to K-Ie(*)(theta = 45degrees) = 0.90 MPa(.)m(1/2) or K-Ie(*)(theta = 70degrees) = 0.70 MPa(.)m(1/2), respectively. Therefore, hydrogen could enhance dislocation emission. In addition, hydrogen decreases critical stress intensity for cleavage of a Griffith crack along the only slip plane in the quasi three-dimension model from K-IG(theta = 0degrees) = 1.03 MPa(.)m(1/2) to K-IG(*)(theta = 0degrees) = 0.93 MPa(.)m(1/2) and then the surface energy from gamma(111) = 2.20 J/m(2) to gamma(111)(*) = 1.78 J/m(2), resulting in facilitating dislocation emission. In situ observation in a transmission electron microscope (TEM) shows that hydrogen enhances dislocation emission and motion before the initiation of hydrogen-induced crack.