Research On Microstructure And Properties Of Hastelloy X Prepared By Selective Laser Melting

Selective Laser Melting(SLM),as a kind of metal material additive manufacturing technology,has many advantages,such as no need of mold,saving of raw materials and high precision,so it shows great application potential.Hastelloy X is a kind of Ni-based superalloy,with Cr and Mo as the solution strengthening elements,it has a high Fe content.The current processing method is difficult to realize the overall forming of complex components.SLM technology provides a new solution for the rapid manufacturing and integral forming of Hastelloy X complex components.Since the plasticity of SLM formed workpiece is often unsatisfactory,it is necessary to improve it after processing.The austenite structure of Hastelloy X is extremely stable,and it is difficult to enhance its properties by inducing phase transformation.The composite material reinforced by ceramic particle dispersion is easy to cause crack defects and thus lead to poor ductility of the material.Therefore,it can be considered to prepare the composite material by adding metal additives.The main application environment of Hastelloy X determines the importance of its mechanical properties,especially the mechanical properties at high temperature.With the wide application in the field of energy and chemical industry,new requirements are put forward for its corrosion resistanceFirst of all,the residual stress levels of SLM generally higher,heat treatment is required to improve,to improve the plasticity and security of the material,after heat treatment,the tensile strength and strain increased from 28.2%to 43.3%lower,showed decreased,after heat treatment of materials in has a lot to improve the mechanical properties of medium temperature,at 400℃ and 550℃,while maintaining the high strength,the elongation after fracture is much higher than that before heat treatment.At 800℃,the tensile strength of the specimen decreases obviously after reaching the ultimate tensile strength,and the dynamic softening is dominant.The corrosion resistance of samples after heat treatment decreases,and the uneven formation of passivation film caused by large amount of chromium element precipitation is the reason for the deterioration of corrosion resistance.In situ heat treatment refers to the laser forming of the powder layer and then sweep the solidified layer,after the in-situ heat treatment of the material fracture increased about 4%,is expected to improve the metal materials prepared by SLM is not ideal plasticity shortcomings.Secondly,the Fe-based amorphous powder is mixed into the Hastelloy X powder as a metal additive for forming,and the metal matrix composites are prepared.With the addition of Fe-based amorphous powder,the mechanical properties of the material are greatly improved.The yield strength is significantly increased from 637 MPa to 902 MPa,the tensile strength is increased from 827 MPa to 1120 MPa,the elongation is maintained above 12%,and the Vickers hardness is increased from 231.6 HV to 307.8 HV.The size and shape of the subgrains change greatly.In the high temperature environment,the Fe-based amorphous reinforced composites show great advantages in strength and plasticity.The strength is more than 100MPa higher than that of Hastelloy X,and the effect of strain improvement after fracture is also obvious.Therefore,the Fe-based amorphous reinforced Hastelloy X composites are very suitable for high temperature applications.In addition,Fe-based amorphous reinforced Hastelloy X composites have better surface quality and smaller roughness.Fe-based amorphous reinforced composites have better corrosion resistance,which is attributed to Cr and Mo elements in Fe-based amorphous powders.Enhanced corrosion resistance will broaden the application of materials in marine ships.Finally,it is studied that the mechanical properties and corrosion resistance of Hastelloy X are enhanced by Ti6A14V.The increase of the content of Ti element and Al element is conducive to the formation of ordered precipitate phase Ni3(Ti,Al)of Hastelloy X,and then the ordered strengthening and precipitation strengthening of the alloy are enhanced.Therefore,the mass fraction of 5%Ti6A14V is added to Hastelloy X for SLM forming.Compared with pure Hastelloy X,the molten pool boundary of TC4/Hastelloy X composite is dissolved,and it has a subgrain structure with obvious angular cell characteristics,and the size is refined to a certain extent.After Ti6A14V powder is added,the yield strength,tensile strength and Vickers hardness are increased to about 900 MPa,1075 MPa and 304.2 HV.The corrosion resistance of TC4/Hastelloy X composite is greatly improved,which is closely related to the disappearance of molten pool boundary and grain refinement.