Effects of micro-scale laser shock peening on surface integrity of DZ17G alloy

Micro-scale laser shock peening is a surface treatment technology, which utilizes laser pulse with spot-size in micro-scale, low energy and short duration to induce shock wave acting on the metals. In order to improve mechanical properties of DZ17G directionally-solidified alloy without effects on the columnar crystals, micro-scale laser shock peening was suggested. The surface morphology, microstructure and micro-hardness were studied to analyze the effects on surface integrity by X-ray diffractometer, scanning electron microscope, transmission electron microscope and micro-hardness tester. The experiment showed that the alloy surface was ablated and melted by micro-laser shock peening underwater without ablating layer. There was smooth region generated with one laser impact, but the ablation degree increased with laser impacts, generating lots of ablation holes and infusible particles. The material still consisted of phases of γ and γ'. High-density dislocations and dislocation tangles were generated in material surface after μLSP, but without grains refined. The micro-hardness decreased with depth, with an affected depth of 100 μm and a maximal value 503 HV in the surface, increased by above 20%, under one laser impact. The micro-hardness and hardened layer depth increased with laser impacts.