Phase transformations in Fe-Mn alloys with nanosecond iodine laser pulses

摘要

Abstract: If a short laser pulse with high intensity is focused on the surface of a target in vacuum, it causes a nearly instantaneous vaporization of a limited volume of material. The rapid expansion of this material vapor produces an impact at the surface. The shock wave propagates and is absorbed in the material. In certain alloys, this causes work hardening, an increase in dislocation density, and phase transformations. While most material is vaporized, some surface melting occurs. The rate of re-solidification of the molten material is such that an almost completely amorphous structure results. The martensitic transformation in the solid target has been confirmed by using optical and transmission electron microscopy and by electromagnetic detection techniques. An iodine photodissociation laser emitting at the wavelength of 1315 nm was used for the experiments. The pulse length was typically 1 ns and the pulse energy could be varied between 1 and 30 Joules. The energy and power density in the focused spot were larger than 3 $MUL 10$+3$/ Jcm$+$MIN@2$/ and 3 $MUL 10$+12$/ Wcm$+$MIN@2$/, respectively. Calculations of impact/momentum, peak pressure, and peak temperature were performed using the finite difference method with moving boundaries. The effects of the iodine laser pulses are compared with those of Q- switched Nd:YAG and ruby laser pulses. !25