Effects of process parameters on the crystallographic orientation and elemental segregation behavior of a novel Ni-based superalloy in laser additive manufacturing

The effect of process parameters of DED technology on elemental segregation and crystallographic orientation of alloys was investigated. The results show that the degree of elemental segregation decreases with the increase of scanning rate, and the degree of segregation rather increases with the increase of deposition height. The microstructure of all specimens consists mostly of columnar grains grown epitaxially along the build direction, showing a clear [001] orientation. The increase in scanning rate weakens the effect of epitaxial growth of crystals, leading to a significant weakening of the strength of the weave in the [001] direction texture. In addition, the actual growth direction of the dendrites is not strictly parallel to the building direction, but is tilted towards the laser scanning direction, resulting in a large deflection angle from the building direction. Based on the synergistic effect of the local temperature gradient and the optimal grain orientation, a composite temperature gradient model is established in combination with the numerical simulation of the temperature field, which reasonably explains this phenomenon. The fundamental reason for the deflection of the dendrite growth direction is that the direction of the composite temperature gradient deviates from the build direction, and the transverse temperature gradient is larger after the scanning rate is increased, resulting in a larger deflection angle.