Effects of shot peening on microstructure evolution and mechanical properties of surface nanocrystal layer on titanium matrix composite

Shot peening (SP) was employed to modify the surface microstructure and mechanical properties of (TiB +TiC)/Ti-6Al-4V titanium matrix composite (TMC). And the microstructure evolution and mechanical properties were characterized and analyzed in detail. Transmission electron microscopy (TEM) results illustrated that the surface nanograins were introduced by the effect of SP and the hindering of reinforcements to the matrix deformation. The nanograins were formed near the reinforcement/matrix interface because the matrix was squeezed by both the shots and the reinforcements. Moreover, with increasing the volume fraction of reinforcements, the smaller nanograins were introduced near the interfaces due to the severe deformation between the matrix and reinforcements, which were caused by the decrease in average distance between two reinforcements. Under the same intensity of SP, the deformation of TiC was more severe than that of TiB, and more dislocations were introduced around TiC. The results were influenced by both the different shapes and distribution of reinforcements, and the impact direction of shots. After SP, the compressive residual stress (CRS) and the hardness in the peened surface layer were improved, which was due to the surface deformation, nanograins and high dislocation density in the nanocrystal layer. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

Shot peening was used to modify the surface microstructure and mechanical properties of (TiB + TiC)/Ti-6Al-4V titanium matrix composite. Transmission electron microscopy revealed the introduction of surface nanograins after shot peening, with smaller nanograins formed near the interfaces due to severe deformation between the matrix and reinforcements. The deformation of TiC was found to be more severe than that of TiB, affecting the distribution of dislocations in the composite. The compressive residual stress and hardness in the peened surface layer were improved, attributed to surface deformation, nanograins, and high dislocation density in the nanocrystal layer.