Study on phase transition and ablation characteristics of metal target irradiated by pseudo-spark pulsed electron beam

Pseudo-sparking electron beam (PSEB) has been demonstrated as a unique technique in ultra-fast, efficient and controllable surface modification in the field of materials processing and preparation and has recently received widespread attentions. A combined experimental and simulation method was used in this study to explore the phase transition and ablation and the surface morphology formation of PSEB irradiated metal target. A dual-temperature model describing the interaction between PSEB and the target was established to reveal the temperature effect at different time scales. The modelling results show the dual-temperature effect occurs in the initial Ps time scale, so the classical Fourier heat conduction law can still be used to describe the high power-density and super-fast heat transfer process in nanosecond pulsed PSEB irradiated target. A phase transition and ablation model of PSEB irradiated target was then established, and the temperature change and phase distribution in the target were calculated. The results reveal the complex phenomena including melting, vaporization, solid–liquid coexistence, thermal stress and sub-surface overheating caused by PSEB irradiation. An experiment of PSEB irradiated AISI1045 steel sample for surface modification was carried out. The XRD and SEM characterization results show that due to the extremely fast heating and cooling, the austenite structure can stably exist at room temperature, and the corrosion resistance of the AISI1045 steel sample surface can be significantly improved. The characterization results further show the grain sizes in the sub-surface layer are smaller than that in the surface layer due to the combined effects of the elastic-stress wave, impact stress wave and temperature gradient. The experimental characterization has a good agreement with the numerical models, jointly demonstrating the phase transition and ablation characteristics and morphology formation of the metal target irradiated by PSEB.