Abnormal softening of Ti-metallic glasses during nanosecond laser shock peening

Abstract

Nanosecond laser shock peening (NLSP) has been proved to be an effective way to enhance the mechanical properties of metallic components through modifying the surface microstructures. However, the micromechanism of structure and property fluctuations induced by shock wave propagation is still limited due to the intrinsic defects in crystalline materials. Here, NLSP treatment has been performed into the Ti-metallic glasses. Owing to the absence of dislocations, grain boundary and phase segregation, the structural signals caused by the shock wave could come into sight. According to grid nanoindentation results, the shock-affected region can be divided into three sections: (I) the rapid softening region, (II) the recovery region and (III) the matrix region. The fronted first pop-in event and the reduced hardness found in the subsurface region provide clear evidence of the release wave-induced structural rearrangement. The abnormal change of the average volume of the shear transformation zone (STZ) could be explained by a two-step transformation mechanism, due to the fluctuations of the "weak spot" induced by the release stress wave. By means of these results, this work provides an opportunity to shed light on the common laser-solid interaction.

Unprecedented hardness of polycrystalline diamond via laser surface engineering

“…4e) might be due to dislocation burst or initiation of cracking. The pop-in events imply a change to plastic deformation and also indicates formation of localised inhomogeneous plastic flow under loading [29]. However, no crystalline defects have been observed from the load-depth graph.…”

“…In the LE/HF-LSPwC, it was observed that above a specific fluence range (19.98 J/cm 2 ) direct ablation occur, which explain a transition As-received LE/HF-LSP (without coating) @19.98 J/cm 2 LE/HF-LSP (without coating) @21.21 J/cm 2 LE/HF-LSP (without coating) @24.14 J/cm 2 LE/HF-LSP (Vinyl + Quartz) @9.025 J/cm 2 LE/HF-LSP (Vinyl + Quartz) @42.12 J/cm 2 LE/HF-LSP (Vinyl + Soda lime glass) @96.27 J/cm 2 LE/HF-LSP (Vinyl + Soda lime glass) @102. 29 from compressive to tensile stresses in the material. Furthermore, this also adds up the reason i.e., the existence of a selective range of energy irradiation with a minimal ablation of matrix which has clearly attributed to the surface topography change and direct ablation where no coatings were used [34].…”