The effect of aging heat treatment on microstructure and mechanical properties of laser welded joints of alloy GH909

In this study, we describe the effect of aging heat treatment on the microstructural response in laser welded joints of low thermal expansion superalloy GH909. This investigation was conducted using an optical microscope, scanning electron microscope, energy diffraction spectrum and other methodologies. The results demonstrated that part of strengthening phase γʹ was transformed into ε phase in the interior of the grains and more precipitated particles were formed in the grain boundary after aging heat treatment of the welded joint, resulting in bending of the grain boundary. Laves phase formed in the grain boundary is rich in Si and Nb elements, which helps to restrict grain growth. The second-phase particles generated at the bottom of dimples enhance the mechanical properties of the welded joint. Microhardness and strength of the welded joints can be significantly improved due to the occurrence of the precipitated phase in the grain boundary and interior of the grains. However, the occurrence of liquated GB can weaken binding between the grains, with the result that the heat affected zone becomes the weakest zone in the joint.