Microstructural analysis of selective laser melted Ti6Al4V modified by laser peening and shot peening for enhanced fatigue characteristics

The increased availability of additively manufactured materials provides a new extended design freedom for innovative products and applications, especially with view to high-tech demands as in the aerospace industry. Current microstructural challenges relevant for fatigue life like internal processing defects and tensile macro stresses still require innovative post processing methods, where laser peening shows some potential, but with need of more understanding of materials modification and fatigue outcome. This study aims at giving for the first time a thorough microstructural insight of selective laser melted Ti6Al4V, modified by both, laser peening and conventional shot peening. The results for the laser peened state highlight an outstanding depth of residual macro and micro stresses (similar to 2.3 mm zero level-crossing), whereas deformation characteristics are accompanied by a low level however characteristic dislocation structure preferably close to the lath grain boundaries, as well as an orientation dependent grain deformation at the surface. Differences compared to shot peening become clearly obvious, whereas initial roughness is shown to play a substantial role along with both post process effects. Fatigue results prove the usefulness of both processes with significant benefits for laser peening by a minimum of a factor of 10 number of cycles.

Automated summary

Laser peening in additive manufactured materials shows great potential for significantly increasing fatigue life. Differences between laser peening and traditional shot peening are clearly evident, with initial roughness playing a substantial role in post-process effects.