Study On The Microstructure And Mechanical Properties Of Deposited-IN625 Nickel-based Super-alloy By Laser Additive Manufacturing

Laser additive manufacturing(LAM)has been a new type of rapid prototyping technology in recently years.Components with complex shape produced from bottom to top by high energy laser beam scanning metal powder or metal wire,is widely used in areas of national defense,shipbuilding,aerospace,industrial machinery medical care and so on.Super-alloys have much attention in those fields.IN625 nickel-based super-alloy is mainly used for manufacturing high temperature parts of aviation engine,such as turbine blades,turbine disk.Meanwhile,laser additive manufacturing technology has the advantage of fast process,low cost,short cycle,high flexibility,high performance parts,free solid forming,no mold and so on.However,the investigation of IN625 alloy produced by LAM technology is in its start-up step nowadays.It is necessary to have a deep investigation in LAM produced IN625 nickel-based alloys.In this study,IN625 nickel-based super-alloy components are produced by LAM technology,and high temperature annealing treatment is taken on these components.The microstructures,mechanical properties of as-deposited IN625 specimens with different annealing temperatures are detailed analyzed.The microstructure,phases composition,morphology and type of precipitates,mechanical properties and tribological properties are studied by using optical microscope(OM),scanning electron microscopy(SEM),energy dispersive spectrometer(EDS),transmission electron microscopy(TEM),polycrystalline X-ray diffractometer(XRD),Vickers hardness tester,electronic universal tensile test machine,nano-indentation tester and wear test machine as well as other materials analysis and testing equipments.The effect of annealing temperature on the microstructure and properties of IN625 nickel-based super-alloy fabricated by laser additive manufacturing is also analyzed.The results of this study are as follows:Under the optimizing of process parameters,the IN625 alloy block specimens(size: 50 mm×50 mm×13 mm)are produced by laser additive manufacturing,which have high density and fine microstructures,no obvious cracks and pores.The following results are obtained through XRD,SEM,EDS,TEM and so on.The main phase of IN625 nickel-based super-alloy fabricated by laser additive manufacturing is ?-Ni solid solution,and a large amount of Cr dissolve in it.The microstructure of ?-Ni solid solution in deposited specimens is a typical dendritic structure;and the primary dendrite epitaxially grows up along the direction of building.The deposited specimens are composed of a number of deposited layers.The secondary dendrite at the top of each deposited layer is stronger than that at bottom of the layer.From the bottom to the top of the specimen except the overlapping zone,the dendrite morphology changed from the shorter secondary dendrite to the longer dendrite to equiaxed dendrite transition because of the difference of cooling rate and temperature gradient at different zones.The precipitated phase of ?-Ni solid solution in as deposited IN625 alloy fabricated by laser additive manufacturing is mainly composed of thick and irregular Laves phase and nanometer MC type carbide(NbC,Nb(Ti)C).There is no change about the main phase structure in IN625 specimens fabricated by additive manufacturing when annealed between 1000?and 1200?.When the annealing temperature is 1000?,the recrystallization phenomenon occurs in the alloy.Meanwhile,when the annealing temperature reaches 1200?,the dendrite is completely replaced by the recrystallized grains.The following results about as deposited and annealed at three kinds of temperatures specimens by XRD.On the one hand,the orientation of dendrite reduces through high temperature annealing recrystallization.On the other hand,the morphology and size of main Laves phase precipitated at the interdendritic area are changing.The remaining Laves phase is changing from thick and irregular shape to fine rod-like or block-like shape,and more particle dispersion.Meanwhile,the lattice constants of ?-Ni solid solution increase slightly due to more Mo,Nb and other atoms dissolve into ?-Ni.The results of electronic tensile test and hardness test about specimens are as follows.Compared with untreated samples,the tensile strength and elongation increases specimens when specimens annealed at 1000-1200?,and the yield strength and hardness decreases,while the elastic modulus is essentially the same,are 270 GPa.The elongation rate above 26% is obtained under the three kinds of annealing temperatures,which is increasing by more than 100% comparing with as deposited samples.The tensile strength of specimens annealed at 1000? is the highest,increasing from 812 MPa to 915 MPa,and the yield strength decreased slightly from 635 MPa to 564 MPa.The tensile fracture mechanism of all specimens showed typical ductile fracture.The results of hardness are as follows.The micro-hardness of the IN625 alloy fabricated by laser additive manufacturing in cross section is 233 HV,and the longitudinal section is 261 HV.The orientation of the dendrite structure decreases and there is no significant difference about hardness in cross and longitudinal section because of high temperature annealing treatment.The hardness of specimens annealed at 1000?,1100?,1200? is 237 HV,233HV and 228 HV.Meanwhile,The nano-hardness of the as-deposited specimens without treatment and specimens annealed at 1000?/1h,1100?/1h,1200?/1h is 3769 MPa,3375 MPa,3580 MPa,3329 MPa.The improvement of the plasticity of the IN625 specimens may be related to the annealing treatment promoting the of Laves dissolving,finer and uniform distribution.Meantime,more Mo,Nb and other atoms dissolve into the ?-Ni solid solution,which is improving the tensile strength of the alloy.The wear behavior of the specimens is test with atmospheric condition at 400?.The influence of different annealing temperatures on the friction coefficient of the specimens is not significant.The wear resistance of the specimens under different annealing temperatures is adhesive wear and fatigue wear,which is due to the disappearance of dendrite structure,the elimination of internal stress and the local dissolution of Laves phase.The wear debris presents typical slice and small granular structure.This research provides references for the application of IN625 alloy produced by LAM technology in the field of aeronautics and astronautics,petrochemical industry as well as the damaged nickel-based alloy parts repairing and so on.