Mechanism of high-cycle fatigue enhancement of TiAl alloys via shot peening

Abstract

This work comprehensively investigates the enhancement mechanism of shot peening (SP) from multiple perspectives, aiming to provide a systematic approach to improving the high-cycle fatigue performance of TiAl alloys. Experimental results demonstrate that SP treatment of 0.45 mmN increased the fatigue life by up to 2.8 times at a high stress of 800 MPa. At the macroscopic level, stress concentration factors and surface roughness were quantitatively analyzed to evaluate the surface quality of TiAl alloys. Fatigue fracture analysis indicated that cracks originated exclusively subsurface in SP samples due to the introduction of residual compressive stress (RCS). Furthermore, the beneficial effects of residual compressive stress were found to outweigh the adverse effects of increased surface roughness at higher SP intensities. At the microstructure level, this study reports for the first time that the long-period stacking ordered (LPSO) structure in TiAl alloys subjected to SP originates from severe plastic deformation caused by high-velocity projectile impact. Two distinct LPSO phase distributions were identified: (i) 6H-type laths within equiaxed α grains, and (ii) 9R/18R-type laths in the γ phase. When the strain increases, the complex crystal defect networks formed by intersection nanotwins and LPSO phases acts as an effective “pinning” mechanism and worked synergistically with RCS, enhancing fatigue resistance.