Effect of interlayer thermal history on the plasticity for 316L stainless steel fabricated by laser-directed energy deposition

• The melt pool width control method was proposed. • The effect of in-situ melt pool control on temperature gradient was determined. • The effect of heat control on the grain refinement was revealed. • The rules of dislocation density affecting plastic deformation was investigated. The conventional laser directed energy deposition (LDED) technology faces the heat accumulation problem, which affects the microstructural distribution and plasticity between the layers of the component. The melt pool as a direct carrier of LDED heat needs to be monitored in real time. And the width, which is an intuitive parameter to feed back its state, needs to be controlled online to improve the stability. Therefore, this paper proposed a coaxial camera monitoring combined with online feedback control algorithm. The block samples of 316L stainless steel were respectively deposited in the conventional and control modes, and the comprehensive comparisons of melt pool feature, microstructure and tensile properties were made. The heat dissipation models were deduced, and the mechanism of the interlayer microstructure distribution under the heat accumulation influence on the material plasticity was explored. The results showed that the cooling rate of the components was increased by 24 % after control, and the melt pool width was successfully stabilized at 2.5 mm. The accelerated interlayer heat dissipation can promote the grain refinement by 31.4 %, further reduce the dislocation density and improve the plasticity of the material, and the final elongation of the material was increased by 52.8 %.