مهندس رضا عباسی

The present study focuses on optimizing the mechanical properties and microstructure of laser welding in Haynes 25 (L-605) cobalt-based superalloy. Initially, the influence of laser welding variables such as laser power, pulse frequency, welding speed, and pulse width on the mechanical and metallurgical properties of the weld joints is investigated. By examining the welding variables, the values of G (thermal gradient) and R (cooling rate) are calculated, and their ratio (G/R) and cooling rate (G×R), which predominantly affect the solidification microstructure, are determined. The structural correlation with the mechanical properties resulting from welding is examined.  In this research, it is considered to obtain the welding variables to create a high percentage of the structure in the form of equiaxed dendrite. Microstructural analysis reveals the growth of equiaxed grains and dendritic structures in the weld zone. The high cooling rate in the weld pool leads to dendritic solidification starting from columnar dendrites at the weld walls and ending in equiaxed dendrites at the center of the weld. The microhardness value in the weld zone is HV 328, which is very close to the microhardness of the base material. The tensile strength of the weld samples reaches about 93% to 94% of the base metal tensile strength. Tensile testing of the weld samples indicates a ductile-brittle fracture. Examination of the scanning electron microscope confirms the presence of dimples, intergranular cracks, and microvoids in the fracture zone.