Comparison between the improvements made to the fatigue strength of stainless steel by cavitation peening, water jet peening, shot peening and laser peening

The effects of ultrasonic impact peening (UIP) and laser shock peening (LSP) on 316L stainless steel were compared in terms of surface morphologies, microstructural evolutions and mechanical properties. The grain refinement mechanisms by mechanical and laser shock wave were subsequently analyzed. Experimental results showed that both UIP and LSP produced micro-grooves with the same depth (~48 μm) at the surface of 316L. The nano-grain size induced by double UIP treatment (10–90 nm) was much smaller than that by triple LSP treatment (>70 nm) because the impact numbers and total impact energy of UIP were much higher. The mechanical twinning was almost complete absence in the sample by UIP. On the contrary, the mechanical twinning was frequently observed in samples by LSP. The magnitude of peak pressure determined the transition from dislocation-dominated mechanism (~680 MPa for UIP) to twinning-dominated mechanism (~2200 MPa for LSP). The resultant dislocation cell size by UIP was much smaller than that by LSP due to the difference of dislocation density caused by different shock wave speed and impact numbers. Additionally, the compressive residual stress on the surface by UIP was higher than that by LSP in both measuring direction. Furthermore, both grain refinement and high dislocation density induced by UIP contributed to a significant increase in the hardness (~433 HV) and yield strength (~447 MPa). By contrast, the LSP induced mechanical twins which can act as dislocation blockers significantly improved the yield strength (~423 MPa).

Microstructural characterization and mechanical behavior of ultrasonic impact peened and laser shock peened AISI 316L stainless steel

Laser shock peening (LSP): Electrochemical and hydrodynamic investigation of corrosion protection pre-treatment for a copper surface in 3.5 % NaCl medium

Effect of laser shock peening on high cycle fatigue properties of aluminized AISI 321 stainless steel

It is well understood that the components with holes used in aviation and aerospace industries are generally vulnerable to alternate cycles of working stress during their service, which are weakest parts and highly prone to failure and fracture due to the stress concentration at the edge of hole. To improve the resistance towards fatigue failure of the hole, laser shock peening (LSP) technology is successfully applied to the hole on powder metallurgy (P/M) Ni-based superalloy labyrinth disc in present work and significant 18% increase in high cycle fatigue limit is achieved (from 224 ± 4 MPa to 265 ± 6 MPa). The notable effects of LSP on the residual stress, microhardness and microstructure of the hole with and without LSP is investigated based on experimental and simulation method. It is found the large improvement of fatigue limit is attributed to the comprehensive action of high amplitude compressive residual stress and microhardness, grain refinement and the removement of inclusions caused by LSP. The finding here in promoting the fatigue resistance of hole by LSP are general and flexible, thereby exhibiting a potential application to a wide spectrum of engineering components with hole structures.

Fatigue performance improvement of laser shock peened hole on powder metallurgy Ni-based superalloy labyrinth disc

Laser shock peening studies on SS316LN plate with various sacrificial layers

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.

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

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Laser shock peening studies on SS316LN plate with various sacrificial layers

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