Experimental Research On Multilayer Structure Of High Nitrogen Steel-316L Made By Robot CMT Additive Manufacturing

Additive Manufacturing based on cold-metal transition technology(CMT-AM)is a manufacturing method of incremental rapid prototyping with welding wires with the welding material and electric arc as the heat source.It is advantageous for its short cycles and high efficiency.Here,through bionic structure of natural nacre shell,an interlaced structure of hard and soft bimetallic multilayers is designed.As for materials,ER316L and HNS were used respectively to study the influence of the additive process on the macroscopic size,microstructure and mechanical properties with proper analysis.Through comparing the performances of samples of multi-layer interlacing manufacturing with different materials through different paths,the process of CMT-AM based composite component manufacturing is studied.The first part of research is a study of ER316L CMT-AM process.It is investigated the influences that cladding heat input and interlayer cooling temperature have on the macroscopic size,microstructure and mechanical properties of the straight wall.The coagulation model of ER316L is therefore determined as a ferrite-austenite model in CMT-AM.Then,the grain growth directions in the bottom,middle,and top of the cladding layer are analyzed from wall samples during additive processes.It turns out that the grain size is negatively correlated to the deposition rate while positively correlated to the heat input.As a result,the best interlayer cooling temperature is calculated.Secondly,HNS CMT-AM forming process is researched.It is studied the influences that heat input has on the element Nitrogen in HNS additive forming;the solidification model with varying Nitrogen levels is then determined with its microstructure confirmed.The hardness and tensile properties of straight walls under different Nitrogen levels are also studied,and the tensile fracture mode is determined by SEM.Thirdly,the bimetallic multi-layer interlaced components were fabricated by CMT-AM to study the overlapping space between adjacent cladding lamellae along with the microstructure and growth direction of the interface.In the bimetallic multilayered interlaced components,the hardness of HNS is distributed around 310HV-320HV,and the hardness of ER316L is near 200HV.In the ER316L and HNS interface junction,the hardness is in the vicinity of 280HV-290HV.The tensile properties of the bimetallic multi-layer interlaced structure consisting of both HNS and ER316L is lower than that of HNS while higher than that of ER316L.Its impact resistance has been greatly improved as well.Finally,according to structural features of the nacre shell,a three-dimensional model of an interwoven structure is established by intertwining soft and hard materials with staggered angles between layers,and the proportion between soft and hard materials is designed.The double-sided additive manufacturing method was used to complete the staggered 30° multilayer-interwoven composite components.As a result,the overall deposition efficiency achieves 0.1097kg/h.