Laser Repair With Addition of Nano-WC on Microstructure and Fracture Behavior of 304 Stainless Steel

Abstract

Precracked 304 stainless steel (304SS) compact tension (CT) specimens repaired by laser with addition of different weight fractions of nano-tungsten carbide (nano-WC) were studied to investigate the effects of nano-WC on the fracture behavior and microstructure. Crack open displacements (CODs) measured by a digital image correlation (DIC) system were compared among specimens with different treatments. Microstructures were examined by scanning electron microscopy (SEM) equipped with an energy dispersive spectrometer (EDS). The results indicate an overall improvement of microstructure and fracture behavior. The specimen repaired by the addition of 5% nano-WC shows the most significant improvement from the current study. Both metallurgical bonding at the interface and fine equiaxial grains in the repaired layer are observed. The densification process of the repaired layer is also improved. In addition, an approximately 10–30% reduction of COD values was observed as the applied load varied from 1 to 20 kN. However, excessive addition of nano-WC led to the agglomeration and inhomogeneous distribution of WC nanoparticles in the repaired layers, resulting in the formation of microcracks. The fracture parameter COD shows a close relationship with the microstructure in laser repaired specimens with different powder ratio addition.