Residual Stress Distribution and Microstructure Characterization of Particle Reinforced Titanium Matrix Composite After Shot Peening Treatment: A Review

Shot peening (SP) can modify the surface properties of titanium alloys and titanium matrix composites (TMCs). Based on our previous work in the last ten years, the microstructure and mechanical properties of SP treated Ti-6Al-4V (TC4) and (TiB+TiC)/TC4 are summarized in this review. The compressive residual stress (CRS) was formed on the surface after SP. At different SP intensities, the thickness of the surface CRS layer was improved with increasing SP intensities. During the stress peening, the CRS increased evidently, and the increment was proportional to the prestress. Besides, CRS’s thermal relaxation was investigated, which showed that the CRS in the whole deformation layer was relaxed. The relaxation mechanism could be explained by the Zener-Wert- Avrami model. The microstrain, the domain size, and the dislocation density of the peened layer were investigated using the Voigt method. The domain size of TC4 was smaller than the composite, and the microstrain of the TC4 was higher than the composite. The average dislocation density was increased after SP due to the existence of reinforcements. Utilizing the Rietveld method to analyze the microstructure after SP, the variations were similar to the Voigt method’s results. Also, the composite’s stability was higher than TC4 because of the existence of reinforcements. Hardness analysis revealed that the existence of reinforcements raised the hardness. In the peened layer, the surface’s hardness was maximum, and it decreased with the increase in depth. At the same temperature, the hardness of the TC4 was smaller than the composite counterpart. Finally, the strengthening mechanism of SP was discussed and summarized based on the above analysis.