A full-field model for hydrogen diffusion and trapping in two-phase microstructures: Application to thermal desorption spectroscopy of duplex stainless steel

We present a fully kinetic, full-field model for hydrogen diffusion and trapping in two-phase microstructures. Trapping is described by a flux directed toward the center of trapping sites, spatially and temporally resolving the trapping kinetics. The model is used to analyze thermal desorption spectroscopy (TDS) in duplex stainless steel (DSS) under different charging times, showing good agreement with experimental results. We found that the charging time has a substantial effect on the shape of TDS curves and the underlying desorption kinetics. The 1-day charging condition resulted in accumulation of hydrogen at the edges compared to the bulk. The TDS curve for this condition is characterized by a main peak followed by a high-temperature tail. Analyzing the simulation results showed that the majority of the hydrogen accumulated at the edges desorbed, creating the main peak. The remaining fraction of this hydrogen diffused inward toward the center before desorbing, generating the tail. The 15-day charging and fully saturated conditions resulted in a shoulder preceding the main peak. Our analysis showed that in the low-temperature range of the TDS curve, fast desorption from the ferrite phase creates the shoulder. At higher temperatures, diffusion in the austenite phase accelerates, increasing the overall desorption rate and resulting in the main peak. The study concludes that the diffusion-based description provided by the presented model offers key details on desorption kinetics, particularly when the trapping phase is governed by diffusion, as in the case of DSS.