Pulsed laser induced deformation in an Fe-3 Wt Pct Si alloy

Abstract

The plastic deformation produced by laser induced stress waves was investigated on an Fe-3 wt pct Si alloy. The intensity and duration of the stress waves were varied by changing the intensity and pulse length of the high energy pulsed laser beam, and also by using different overlays on the surfaces of the specimens. The resulting differences in the distribution and intensity of the deformation caused by the stress waves within the samples were determined by sectioning the specimens and etching (etch pitting) the transverse sections. The magnitude of the laser shock induced deformation depended on the laser beam power density and the type of surface overlay. A combination transparent plus opaque overlay of fused quartz and lead generated the most plastic deformation. For both the quartz and the quartz plus lead overlays, intermediate laser power densities of about 5×10⁸ w/cm² caused the most deformation. The shock induced deformation became more uniform as the thickness of the material decreased, and uniform shock hardening, corresponding to about 1 pct tensile strain, was observed in the thinnest specimens (0.02 cm thick). 200 ns laser pulses caused some surface melting, which was not observed for 30 ns pulses, the pulse length used in most of the experiments. Deformation of the Fe-3 wt pct Si alloy occurred by both slip and twinning.