| With the advancement of technology,the performance requirements of materials are becoming severer and severer.Some existing materials can no longer meet the actual service requirements of the components.In practical applications,the service conditions of different parts of the same component may be different.Some components do not work at a constant temperature,but the temperature and usage requirements of different parts of the same component are different.Therefore,gradient functional materials came into being.Among them,the stainless steel-superalloy gradient function materials can be used as a material for high temperature resistance and repeated thermal shock with large temperature differences,which are applied in the petrochemical industry,nuclear reactors,various acid-resistant valves and high-temperature high-pressure valves,as well as engine combustion inner wall,turbine wear-resistant parts,etc.From the current point of view,the use of stainless steel-high temperature alloy gradient materials can achieve different performance requirements of different parts of the components to a certain extent,achieving a certain degree of weight and cost reduction.Laser melting deposition technology,a point-by-point,layer-by-layer additive manufacturing technology,is different from traditional material reduction processing.Due to its high degree of flexibility,it can be successfully applied to the preparation of gradient materials.Currently,stainless steel-superalloy gradient material has been successfully prepared by laser melting deposition technology.In this paper,the effects of line energy density on formability were studied by controlling the process parameters such as laser power,scanning speed and overlap and 5 group of 316L stainless steels/IN625 super alloy gradient materials have been successfully prepared,named 100%316L→80%316L+20%IN625→60%316L+40%IN 625→40%316L+60%IN625→20%316L+80%IN625→100%IN625.The microstructure,phase composition and mechanical properties of gradient layers of gradient materials were prepared,by means of optical microscope,scanning electron microscope,transmission electron microscope,XRD,micro-vickers hardness tester,electronic universal testing machine and other experimental analysis methods.The results show that the prepared gradient material was dense and had no defects,and the microstructure tends to penetrate the multi-layers continuous epitaxial growth of columnar crystal plus cell crystal mixed structure along the deposition direction.With the gradual increase of IN625 content in the designed gradient components,the content of interdendritic precipitation phase gradually increased.The overall hardness change of the gradient material does not vary along the designed composition,but decreases in the gradient of the IN625 content of 20%and 40%,and then gradually increases along the hardness.According to the deposition direction,the line energy of the gradient materials prepare by the process energy density of 77.8 J/mm is the highest,reaching 568.1 MPa,while the sample with the line energy density of 111.1 J/mm has the highest elongation,reaching 47.2%.The gradient material with the line energy density of 88.9J/mm along the scanning direction has the highest tensile strength,reaching 641.2 MPa.The as-deposited samples were heat treated.The heat treatment system was solid solution at 980℃ for 1 hour,and 720℃ for 12 hours.After heat treatment,the microstructure of the sample from the deposited columnar dendrites plus cellular dendrites transformed into equiaxed crystal structure with different grain sizes,and white precipitate is precipitated along the grain boundary,which improves segregation of sedimentary dendrites after heat treatment.Compared with the deposited state,the hardness after heat treatment is lower than the as-deposited state.After heat treatment,the tensile strength of the sample with line energy density of 66.7 J/mm decreased slightly,but the elongation increased to 23.1%. |
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