Surface integrity and fatigue lives of Ti17 compressor blades subjected to laser shock peening with square spots

Abstract

To address the effects of laser shock peening (LSP) on surface integrity and high cycle fatigue (HCF) vibration fatigue lives of Ti17 compressor blades, LSP experiments on the 1st-order bending vibration nodal region of the blades were performed by a Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) laser system with square spots. Surface roughness, in-depth residual stresses both on the pressure and suction surfaces, local bending deformations at the leading and trailing edges, and surface microstructure were analyzed by surface profiles, X-ray diffraction (XRD), three-coordinate measurement and transmission electron microscopy (TEM), respectively. HCF vibration fatigue tests were carried out on a DC-4000 electric vibration system and fatigue fracture morphologies were analyzed by scanning electron microscope (SEM). Results showed that surface roughnesses values were not more than Ra 0.4 μm both on the pressure and suction surfaces of the blades with and without LSP. Compressive residual stresses layers with about 1 mm were generated both on the pressure and suction surfaces of the blade and the maximum values were located at the topmost surface. Two-way local bending deformations induced by LSP were convex bending deformation at the trailing edge and concave bending deformation at the leading edge. High density dislocations, twinning and nano-grains were observed on the surface microstructure. Compared with as-received blades, HCF vibration fatigue lives of the blades with LSP were increased by one order of magnitude. Fatigue strengthening mechanism was implied by establishing the relationship between fatigue fracture morphologies and effects of compressive residual stresses and refined grains.