Diffusion and trapping of hydrogen due to elastic interaction with η-Ni₃Ti precipitates in Custom 465® stainless steel

Since it is difficult to determine the local distribution of hydrogen in alloys experimentally, it is desired to estimate it theoretically. Here, the effect of elastic stresses around η-Ni₃Ti precipitates in Custom 465® martensitic age-hardenable stainless steel on the distribution of hydrogen and its diffusivity in the matrix is evaluated. A comparison is made to recent experimental data. The calculations are based on the solution of the stresses associated with coherent precipitates in the framework of linear elasticity combined with expressions for hydrogen concentration and diffusion in the presence of stress. Local compressive and tensile hydrostatic stresses form around the η-Ni₃Ti precipitate, resulting in regions of reduced or increased hydrogen concentration, respectively. The integrated effect is an increased average hydrogen concentration, in agreement with the experimental results. The equilibrium concentration of hydrogen due to the elastic stresses decreases with increasing temperature, in conformance with experimentally measured temperature programmed desorption (TPD) data. This quantitatively confirms that the coherency stresses of the precipitate in the peak-aged condition increase the concentration of absorbed hydrogen and decrease its diffusivity.