Micro-scale Laser Shock Peening Method and Fatigue Test of DZ17G Directionally Solidified Superalloy

Aiming at the fatigue fracture fault of aero-engine turbine blades, laser shock peening was conducted on the DZ17G directionally solidified superalloy simulated blades to improve fatigue performance. However, in order to avoid the occurrence of grain refinement in the columnar crystals, an underwater high frequency laser shock method without ablation coating based on micro-scale laser shock peening was proposed. In this method, a short laser pulse width micro-scale laser beam was conducted to decrease the plasticity degree and affected depth, and high frequency shock without ablation coating was conducted to form a uniform plastic strengthening layer. The microhardness and high-cycle fatigue performance of the original sample and the strengthening sample were comparatively examined. The results indicate that there are high density dislocations and dislocation tangles generated in the shallow layer of DZ17G superalloy simulated blades, but no grain refinement occurs, and the density of dislocations decreases sharply with the increase of depth. High density dislocations and dislocation tangles result in a high improvement of hardness, increased by 30%. However, a hardened layer of 180 p.m in thick is generated. The fatigue strength of the DZ17G superalloy simulated blades increases form 257.00 MPa to 302.00 MPa, increased by 17.5%. There is still an improvement of 11.7% in fatigue strength after the thermal insulation at 800 degrees C for 2h. High density dislocations and dislocation tangles are the immanent causes for fatigue performance improvement.