Microstructure And Performance Of Ni-base Superalloy Prepared By Laser Direct Deposition

The superalloy with excellent properties such as high strength,good high-temperature oxidation resistance is widely used to manufacture the structural components in aerospace,civil and other fields.The laser direct deposition technology as one of advanced manufacturing technology of the key research in recent years can realize the super alloy with high performance and complex structure formed directly to reduce the waste of materials,shorten the production cycle and obtain the excellent properties.Therefore,the research on microstructure and performance of super alloy prepared by laser direct deposition has important scientific significance and potential application.In this experiment,the Inconel625 sample with few cracks was formed by laser direct deposition through changing the process parameters.In order to reduce the cracks and improve the performance of the sample,the different content Y2O3 was added to the Inconel625 powder.The microstructure,phase,composition and microhardness of the as-deposited layer were systematically studied by using the OM,SEM,XRD,EDS,TEM,micro-hardness tester and other analysis methods.The results show that:The optimal process parameters for the experiment are power of 1400W,scanning speed of 240mm/min,powder feeding rates of 5.7g/min,overlapping of 30%and spot size of 4x4mm.The layers of superalloy without cracks and porosities were prepared successfully.The microstructure is equiaxial crystal and columnar crystal,and the apparent white band appears between the layer and layer.The phase of as-deposited layer is composed of y-Ni solid solution,and the white phase with rich Mo,Nb precipitate in the dendritic crystal.The average hardness is 293HV.The addition of Y2O3 has the effect of grain refinement and reducing cracks in the deposited superalloy layer.Compared with the as-deposited layer with 0%Y2O3,the microstructure is obvious refined and the segregation composition is reduced after the addition of 0.5%Y2O3.The phase of as-deposited layer can't be changed with the addition of Y2O3.A small amount of NbC precipitate in the grain boundary.The hardness of as-deposited layer increases to some degree.The high-temperature oxidation experiment shows that oxide film become more dense and the thickness of oxide film decreases after the addition of 0.5wt.%Y2O3 in the superalloy which illustrate the addition of Y2O3 makes superalloy possess higher oxidation resistance.