Unveiling the origins of work-hardening enhancement and mechanical instability in laser shock peened titanium

Laser shock-peening (LSP) produces complex gradients in microstructures and residual stresses, which enables fabrication of metallic engineering components with superior mechanical properties. Here we use non-destructive and spatially resolved high-energy X-ray diffraction (HE-XRD) to investigate the influences of LSP on microstructure, surface topography, and residual stress for high purity titanium plates. LSP is found to produce large compressive in-plane residual stresses near the peened surface which monotonically decay to zero about 2.5 mm below the surface. These properties were also tracked during in-situ tensile loading, allowing stress partitioning and work-hardening rates to be measured as a function of depth. The surface region is found to have the highest work-hardening rate and remain mechanically stable up to sample failure. In addition, a crystal rigid rotation along a transversal axis of about 27 & nbsp; was observed at large applied strain near the surface region, which is attributed to the formation of denser dispersed shear bands. Furthermore, a sudden drop in tensile stress was observed at a depth of similar to 160 mu m from the LSP surface, indicating the formation of a localized mechanical instability zone (LMIZ). The origin of this LMIZ could be attributed to the increase in shear stress induced by a load transfer from LSP surface due to the formation of denser dispersed shear bands. These observations indicate a localized transition in deformation behavior has occurred from dispersed shear banding to LMIZ and homogeneous deformation. (C)& nbsp;2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Laser shock-peening (LSP) can create complex gradients in microstructures and residual stresses, leading to improved mechanical properties of metallic engineering components. A non-destructive high-energy X-ray diffraction technique was used to investigate the effects of LSP on microstructure, surface topography, and residual stress in high purity titanium plates. LSP was found to generate large compressive in-plane residual stresses near the peened surface, gradually decreasing to zero below the surface. During in-situ tensile loading, stress partitioning and work-hardening rates were measured as a function of depth. The surface region exhibited the highest work-hardening rate and remained mechanically stable until sample failure.