Grain refinement and boundary misorientation transition by annealing in the laser rapid solidified 6FeNiCoCrAlTiSi multicomponent ferrous alloy coating

A 6FeNiCoCrAlTiSi multicomponent ferrous alloy coating with simple BCC solid solution phase has been prepared by laser cladding on a low carbon steel substrate. Grain boundary misorientation transition and abnormal microstructure refinement in the coating after annealing at 500 °C have been studied by electron backscatter diffraction (EBSD) observation. Before annealing, the microstructure of the coating is mainly composed of directionally solidified columnar grains with low angle grain boundaries distributed as networks. After annealing, the main phase and microhardness of the coating almost remain unchanged. However, the columnar grains transform to equiaxed refined grains with the grain boundary misorientation transition from low to high angles. This result supports such an argument that the reheating process in post-stage of solidification plays a key role on the grain refinement during rapid solidification process.

Research Highlights
► Lots of low angle grain boundaries are found in the 6FeNiCoCrAlTiSi coating.
► Abnormal grain refinement is taken place in the coating after annealing.
► Fracture toughness decreases with the grain boundaries transition after annealing.