Microstructure evolution and EBSD analysis of a graded steel fabricated by laser additive manufacturing

Abstract

This paper demonstrates the successful fabrication of a graded steel with successive 15 layers by direct laser metal deposition. The phase evolution, microstructure and grain growth of the as-built graded steel were investigated by X-ray diffraction (XRD), optical microscopy (OM), and electron back-scatter diffraction (EBSD), respectively. Experimental results showed that the crystal structures of the graded steel evolved from FCC (Austenite) in the first two grades to BCC (Ferrite) with a small trace of Austenite phase. Columnar dendrites are observed in the first and second grade with the growth orientation horizontal to the direction of the laser deposition. The third grade has a finer microstructure with equiaxed grains. Preferred texture was dominant in the microstructure for the first two grades with low-angle grain boundaries (about 2°). No preferred texture was observed in the third grade. Large-angle grain boundaries are available in the third grade with distribution from 50° to 60°. Our findings suggest that a graded steel with microstructure and grain growth orientation evolution can be obtained by direct laser metal deposition. The evolution of microstructure and grain growth was not changed by different scanning rate.