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  • Laser shock peening studies...
    Yella, Pardhu; Venkateswarlu, P.; Buddu, Ramesh K.; Vidyasagar, D.V.; Sankara Rao, K. Bhanu; Kiran, P. Prem; Rajulapati, Koteswararao V.

    Applied surface science, 03/2018, Letnik: 435
    Journal Article

    •Effects of various sacrificial layers on the surface characteristics of SS316LN are examined.•Influence of laser energy and pulse width have been comprehensively studied.•Laser induced texturing in 111 direction is observed.•Absorbent tape results in no surface damage while simultaneously inducing required surface residual stresses.•XRD and TEM results suggest increased dislocation densities in the laser peened surfaces contributing to lattice microstrain. Laser shock peening (LSP) has been utilized to modify the surface characteristics of SS316LN plates of 6mm thickness. Laser pulse widths employed are 30ps and 7ns and the laser energy was varied in the range 5–90mJ. Peening was performed in direct ablation mode as well as with various sacrificial layers such as black paint, transparent adhesive tape and absorbing adhesive tape. The surface characteristics were greatly influenced by the type of sacrificial layer employed. The average surface roughness values are about 0.4μm when the black paint and transparent adhesive tape were used as sacrificial layers. In contrast to this, using absorbent adhesive tape as a sacrificial layer has resulted in an average surface roughness of about 0.04μm. Irrespective of pulse durations (30ps or 7ns), absorbent adhesive tape has always resulted in compressive residual stresses whereas other layers appear to be not that effective. In case of 30ps pulse, as the laser energy was increased from 5mJ to 25mJ, there was a texture observed in (111) reflection of X-ray diffractograms and the center of the peak has also gradually shifted to left. X-ray line profile analysis suggests that with the increase in laser energy, lattice microstrain also has increased. This lattice microstrain appears to be resulting from the increased dislocation density in the peened sample as evidenced during transmission electron microscopic investigations. Cross-sectional scanning electron microscopy performed on peened samples suggests that absorbing adhesive tape brings no surface damage to the samples whereas other sacrificial layers have resulted in some surface damage. Based on all these structural and microstructural details, it is recommended that absorbent tape could be used as a sacrificial layer during LSP process which induces surface residual stresses with no damage to the sample surface.