| Traditional subtractive manufacturing is the preparation of workpieces through casting,forging,milling,milling,and other processes.It involves long cycles,cumbersome processing techniques,and waste of raw materials.3D printing can not only shorten the preparation cycle signicantly and save materials,but its special processing method makes the materials Obtain a fine and uniform structure and excellent performance.In this paper,focusing on a typical superalloy hard-to machine,laser selective melting(SLM)is used to form IN 718 alloy and WC reinforced IN 718 alloy,and it is subjected to 720?/8h+620?/10h direct two-stage aging treatment to study SLM molding and direct two-stage aging process and WC The effect of the addition on the microstructure,mechanical properties and high-temperature stability of the alloy,as well as the evolution of each precipitated phase in the alloy.The following main results based on simulation and experiements were obtained as the followings:The structure of IN 718 superalloy formed by SLM is long in the direction of the scanning track in the XY direction,ish-shaped in the Z direction and there anisotropic long columnar grains passing through the printed layer,and the structure is anisotropic.There are mainly dendritic matrix ? phases,intergranular granular ? 'reinforced phases,long rod-shaseaped ? phases at grain boundaries and irregular and hard and brittle Laves harmful phases in the alloy.Sub-cells in the remelting zone can produce sub-structure strengthening.Provide nucleation sites for the precipitated phase,improve the mechanical properties of the alloy.The two-stage aging process promoted the precipitation of ?',?",and the dissolution of Laves phase,and the structure is homogenized more,the phase difference of the grain boundary decreases and the subcell increases;the room temperature TS of the IN 718 alloy after aging increases from 1162MPa to 1608MPa Increased by 38.4%,PS increased from 834MPa to 1472MPa increased by 76.5%,elongation after fracture increased from 7.9%to 9.2%increased by 16.50/n.and ductile fracture occurred;thermogravimetric analysis experiment at 1000?/8h+air In the meantime,the weight loss before and after aging is reduced from 0.15?0.20mmg/cm2 to 0.08?0.15mmg/cm2.The dense oxide film formed by lumpy Cr2O2,flake NiCr2O4 and rice granular NiFe2O4 is more uniform and fine,and the high temperature stability can be further improved.In the WC-reinforced IN 718 superalloy formed by SLM,the added WC particles react wtith the matrix to produce MC carbides such as W1-xC,W2C,CrNiFeC,CoCx,NbC,and Ni2W4C.forming a chemical interface with a certain strength and high melting point.WC hinders the movement of grain boundaries during solidification to refine the grains.WC with lower thermal conductivity produces a heat seal during solidification and heat dissipation,which promotes the precipitation of more ?,Laves phase and MC carbides in the grains.The two-stage aging process promotes the diffusion of Nb element in the WC-reinforced IN 718 alloy to form NbC between grains.This consumption of Nb element reduces the formation of ?and Laves phase.Under the SLM+direct two-stage aging process with a scanning speed of 800mm/s,the alloy has insufficient input energy density to cause brittle fracture,TS is 731.7MPa,PS is 472MPa,and the elongation is only 0.9%.In the SLM process with a scanning speed of 600mm/s,the WC-reinforced IN 718 alloy has a good rigidity under the SLM forming process with a scanning speed of 600mm/s,a tensile strength of 1071.9MPa,a yield strength of 872.5MPa,an elongation of 4.5%.the weight loss before and after aging is from 0.15?0.17mmg/cm2 is reduced to 0.12?0.15mmg/cm2.In the oxide film layer with Cr2O2,NiCr2O4,NiFe2O4 and new phases of WO3 and CrWO4 as the main components,the loosely structured sheet-like WO3 phase is not conducive to the improvement of high temperature stability,dense Cr2O2,NiCr2O4 And the NiFe2O4 phase is the real reason for the high temperature corrosion resistance of the alloy. |
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