Study On Technology And Microstructure-properties Of FeCoCrNi High-entropy Alloy Fabricated Via Selective Laser Melting

It is an important measure to develop the materials and preparation technology of new aero-engine combustion chamber casing to greatly improve the performance of domestic aero-engine.Due to its excellent mechanical properties,high-entropy alloys are expected to be widely used in the manufacture of combustor casings.Selective laser melting technology has broad application prospects in the field of complex component manufacturing because of its two-dimensional manufacturing principle.In this paper,the selective laser melting of FeCoCrNi high-entropy alloy(SLM-FeCoCrNi HEA)was systematically studied.Through process optimization,composition control,mechanism analysis and finite element simulation,its high-quality manufacturing was realized,and the mechanism of strengthening at room temperature and high temperature was clarified.It provides important data support and theoretical basis for the application of SLMFeCoCrNi HEA in the field of combustor casing manufacturing.The research work of this paper is as follows:(1)The process optimization of SLM-FeCoCrNi HEA was analyzed.A polynomial regression model considering the interaction of parameters is designed to realize the preparation of high-density SLM-FeCoCrNi HEA.However,this process optimization method needs a lot of experiments to obtain stable model parameters.A process optimization method based on cross test was designed according to SLM forming principle,and the preparation of high density SLM-FeCoCrNi HEA was realized with less test amount.(2)In situ synthesis of SLM-FeCoCrNi HEA was investigated.The in-situ synthesis of samples with homogeneous composition was realized by reducing the melting point with binary alloy and layer-by-layer remelting.In situ synthesis of SLMFeCoCrNi HEA with different Mo content was realized by controlling the proportion of alloy powder.(3)The mechanical properties of as-printed SLM-FeCoCrNi HEA at room and high temperature were studied.A large number of dislocation networks and high dislocation density hinder the movement of dislocations and form excellent mechanical properties at room temperature;the recovery behavior of dislocation networks at high temperature leads to high temperature softening,and the segregation of elements at grain boundaries leads to high temperature embrittlement.(4)The effect of annealing temperature on the room temperature and high temperature properties of SLM-FeCoCrNi HEA was investigated.The recrystallization behavior leads to the decrease of dislocation and dislocation network density.Therefore,with the increase of annealing temperature,the room temperature strength of the sample decreases and the ductility increases.The results show that annealing at all temperatures does not improve the grain boundary weakening during high temperature tensile process,so it can not improve the high temperature plasticity.(5)The effect of Mo addition on the structure and properties of SLM-FeCoCrNi HEA was revealed.With the increase of Mo content,the σ phase precipitates from the junction of dislocation network and grows along the dislocation network,which has pinning effect on dislocation at room temperature and high temperature;the addition of Mo can strengthen the grain boundary and improve the high temperature plasticity.When Mo content is 11.12 at.%,the SLM-FeCoCrNi HEA has both excellent room temperature properties(tensile strength of 1114.7 MPa and elongation of 15.9%)and high temperature properties(tensile strength of 323.4 MPa and elongation of 14.1% at800 °C).The precipitation behavior of σ phase under complex thermal cycle and the influence mechanism of forming process on it were investigated.