Structure and fatigue of titanium alloy samples under laser impact treatment

The effect of laser shock peening on the level and depth of residual stresses, microstructure and fatigue life in titanium alloy samples is considered. At present, shot peening and hydro shot peening are most widely used in the aircraft engine industry. Such methods create a favorable residual stress diagram to a depth of 0.2mm, which is insufficient to ensure the required level of fatigue strength of parts when they are damaged by foreign objects to a depth of 1 mm. Laser shock peening is considered to increase the durability of samples. A flat sample of 50×40×2 mm was selected for testing the laser shock peening technology. To study the physical mechanisms of residual stresses occurrence, structural studies of samples after laser shock peening were carried out using the electron backscatter diffraction (EBSD) method. The data obtained include the distribution of grain orientation, average grain disorientation, and grain size distribution. From the analysis of microstructure maps it follows that the change in the predominant orientation of grains significantly affects the depth of laser action. After laser shock peening, three layers with different orientations were formed: a near-surface layer with a depth of up to 130 μm, a transition layer – up to 240 μm, and then the main layer. The use of laser shock peening led to an increase in the resource under low-cycle fatigue up to 1ˑ105 cycles (initial 2ˑ104 cycles) for the selected deformation value.