Effect of thermal cycles on microstructure of reduced activation steel fabricated using laser melting deposition

Reduced activation steel was successfully fabricated by laser melting deposition employing a Gaussian and a ring-shaped laser. The microstructure evolution of the reduced activation steel was investigated using the scanning electron microscope, transmission electron microscope and electron backscatter diffraction. The experimental results showed that the grains close to the substrate were smaller than the grains in the upper layers. Compared to those deposited using a Gaussian laser, the samples deposited using a ring-shaped laser showed a more homogeneous microstructure. Furthermore, a finite element analysis (FEA) model was applied to reveal the thermal history during laser melting deposition. The simulation results were well validated with the experimental results. FEA results indicate that the peak temperature increases and the cooling rate decreases, as the layer gets further from the substrate. Additionally, the temperature and the cooling rate resulting from the Gaussian laser model were higher at the midline of the samples and lower around the edges, whereas those of the ring-shaped laser model were consistent with both at the center and around the edges.