Abstract
Owing to the special layer-by-layer deposition process of directed energy deposition(DED),columnar coarse grains,produced by cyclic reheating with intrinsic directional heat flow along the building direc-tion,are difficult to avoid.These grains result in strong anisotropic characteristics with poor mechanical properties,which restrict the application of DED products.This work proposes a novel fabrication strat-egy based on the cyclic-phase-transformation behavior,which can reduce the anisotropy and improve the mechanical properties of DED-printed stainless steel.Using this fabrication strategy,316 L powder(austenitic stainless steel)and 17-4PH powder(martensitic stainless steel)were mixed in different mass ratios to fabricate five types of DED-printed stainless steels.Among the five samples,P70(mixture of 70 wt％17-4PH powder and 30 wt％316 L powder)showed the weakest anisotropy and the best mechanical properties,which can be attributed to the cyclic phase transformation under cyclic reheating treatment and the transformation-induced plasticity(TRIP)effect over a wide range of strains,respectively.Com-pared with the pure 316 L printed material,the tensile test results of P70 showed that the yield strength(YS)and ultimate tensile strength(UTS)increased by 35.4％and 34.5％,respectively,whereas the uniform elongation(UE)and total elongation(TE)were improved by 63.9％and 31.4％,respectively.In addition,the strength-ductility balance(UTS × UE)increased by as much as 120.4％.The proposed fabrication strategy is expected to reduce the anisotropy in other materials that undergo cyclic-phase-transformation phe-nomena during additive manufacturing.
基金项目
Key Program of National Natural Science Foundation of China(52235005)
Natural Science Foundation of Hunan Province,China(2023JJ30137)
NETL
NSTL
万方数据