Role of sacrificial layers on surface characteristics of laser shock peened SS304 plates

Laser shock peening (LSP) has been used to modify the surface characteristics of SS 304 plates using various sacrificial layers (transparent tapes, absorptive tapes, and paints). The laser energy has been varied in the range 5-90 mJ and adapted pulse widths are 30 ps and 7 ns. The average surface roughness of the untreated sample was 0.046 ± 0.02 and it has increased to1.018 ± 0.01 µm for direct ablated condition. Further it appears to be influenced by the applied laser parameters and the sacrificial layers laid on the SS304 targets. Among the sacrificial layers used in the present study, the absorbent adhesive tape has resulted in low surface roughness value of about 0.04 µm. Depending on the sacrificial layer laid on the surface, the nature of the stresses has changed i.e., tensile residual stresses (+676 ± 20 MPa with 7 ns, 90 mJ) for transparent tape and compressive residual stresses (−805 ± 45 MPa with 7 ns, 90 mJ) for absorbent tape respectively. The X-ray line profile analysis showed that the microstrain (ranging from 1.1 × 10−3 to 4.1 × 10−3) and the dislocation densities (ranging from 28 × 1013 m−2 to 298 × 1013 m−2) have increased with increase in laser energy at 30 ps and 7 ns pulse durations. From the X-ray diffractograms of the samples adhered with a transparent tape as a sacrificial layer, the (1 1 1) reflection shows texture with an increase in laser energy from 5 mJ to 25 mJ. The absorbing adhesive tape has shown no surface damage which has been confirmed through cross-sectional micrographs. Altogether, the absorbent adhesive tape as a sacrificial layer for stainless steel targets showed an excellent performance to achieve high compressive residual stresses, lower surface roughness. Based on the comprehensive study presented in this manuscript, adaption of absorbent tape is recommended while doing LSP of SS304 surfaces to be used in complex structural engineering applications.