Investigation of microstructures and residual stresses in laser peened Incoloy 800H weldments

• Dislocation slipping and twinning matrix are observed in peened 800H weldments.
• The effect depth of LSP for 800H weldments is about 1.2 mm.
• LSP is effective to refine grain and rebalance residual stress of 800H weldments.

Laser Shock Peening (LSP) is an advanced surface enhancement technique to improve the mechanical properties of engineering materials. In the present study, LSP was performed on Incoloy 800H laser weldments. The microstructure and residual stress, two key factors for application of weldments, were investigated via optical and transmission electron microscopy and crystallographic and residual stress X-ray diffraction analysis. Micro-hardness tests were also used to evaluate mechanical properties. Results show that significant grain refinement occurs in the LSP-treated zone where original lath structures are refined to equiaxed grains, and dislocation density increases significantly. Because of the high strain rates produced by LSP, grain deformation by slip is limited, and therefore deformation by grain twinning occurs. The micro-hardness of weld joint increased after LSP with a hardened depth of about 1.2 mm. LSP processed welded joints exhibited high compressive residual stress, and the residual stress distribution was uniform. It is shown that LSP is an effective way to refine microstructure, increase strength and rebalance residual stress which will improve fatigue life and corrosion cracking resistance of Incoloy 800H weldments.