| Selective Laser Melting(SLM)is an advanced manufacturing technology that combines precision forming with high performance integration.But until now,SLM technology has focused on shaping single materials.With the continuous development of aviation,aerospace,automobile,mold and other industrial fields,the performance of parts made of a single material has been difficult to meet the functional requirements of specific products,in order to meet the performance requirements of specific products such as oxidation resistance,corrosion resistance and high temperature resistance.In this thesis,IN718 alloy and 316L stainless steel powder were taken as the research objects to carry out the process test and interface performance study of SLM forming IN718/3 16L,so as to obtain the optimal SLM forming process parameters and excellent IN718/316L interface performance.The main research contents and conclusions are as follows:(1)The single-factor and full-factor process tests of SLM forming IN718 alloy were carried out,and the influences of different process parameters(scanning power,scanning speed,scanning interval)and physical strength density on the densification of formed parts were analyzed.Based on the comprehensive analysis of various factors,the optimal process parameters for forming IN718 alloy are as follows:the scanning spacing is(0.05-0.08)mm,the scanning power is(350-450)W,the scanning speed is(600-1000)mm/s,and the energy density is(95-150)J/mm3.Under this process,the highest density is 99.52%.(2)The single-factor and full-factor process tests of SLM forming 316L stainless steel were carried out to analyze the influence of various process parameters on the density of forming parts,and the relationship between the energy density and the density of forming parts was analyzed.Based on the analysis of various factors,the optimal process parameters for forming 316L stainless steel are as follows:the stroke spacing is(0.06-0.08)mm,the scanning power is(240-360)W,the scanning speed is(850-1150)mm/s,and the energy density is(85-135)J/mm3.Under this condition,the highest density was 99.65%.(3)On the basis of the above research,process parameters for processing IN718/316L formed parts were selected:scanning interval of 316L stainless steel was 0.07mm,scanning power was 300W,and scanning speed was 850mm/s.The scanning interval,scanning power and scanning speed of IN718 alloy are 0.07mm,400W and 1000mm/s respectively.Under the condition of this process parameter,the sandwich structure of 316L/IN718/316L was prepared,and the micro structure at the interface was observed and analyzed.The results showed that the forming sequence of materials would have an impact on the interface bonding.First,316L stainless steel powder was formed.There were fewer pore defects at the interface of IN718 alloy formed on 316L stainless steel.(4)Tensile tests in different directions were carried out on IN718/316L formed parts.The results of longitudinal tensile test show that the specimen breaks in 316L zone,and the interfacial bonding strength of heterogeneous materials is greater than that of 316L zone.and the interfacial bonding strength of heterogeneous materials is greater than that of pure 316L formed parts.Transverse tensile test results show that the IN718/316L forming parts with tensile strength between pure 316 1 stainless steel and pure IN718 alloy forming parts,between the tensile strength of IN718/316L and elastic modulus of forming parts was obviously higher than that of pure 316L stainless steel and pure IN718 alloy forming parts,the low elongation of tensile sample,conforms to the characteristics of SLM technology of high strength and low toughness,tensile test showed that the preparation of SLM IN718/316L forming parts with good mechanical properties.The microscopical morphology of the transverse tensile section was observed.The transverse tensile section had both stepped area and dense dimples,and the fracture mode of in718/3161 forming part was a mixed fracture.(5)The microhardness of samples treated with heat treatment(solid solution+double aging heat treatment)and those without heat treatment were measured and analyzed.The results showed that the microhardness of the 316L stainless steel zone without heat treatment was(230±6)HV0.3,the microhardness of the IN718 alloy zone was(325±5)HV0.3,there was a hardness transition zone between the IN718 zone and the 316L zone,and the hardness value of the transition zone gradually increased from 316L side to IN718 side.After heat treatment,the hardness of 316L stainless steel near the interface decreased to(191±3)HV0.3,and the hardness of IN718 alloy near the interface increased to(495±10)HV0.3.The strengthening phase of IN718 was dispersed in the heat treatment process,and the austenization of 316L stainless steel internal structure was observed.Therefore,the hardness of IN718 region significantly increased and that of 316L region decreased.(6)Laser remelting was performed on the first layer IN718 formed on 316L stainless steel matrix.The results show that the laser remelting can effectively reduce the roughness of the surface of the forming layer,and the smaller peaks and valleys are beneficial to the powder spreading and processing of the lower layer.The width of the transition zone of the interface without laser remelting is about 300?m,and the width of the transition zone after laser remelting is about 450?m.Because the laser remelting process increases the diffusion degree between IN718 and 316L,the width of the transition zone at the interface increases,thus strengthening the metallurgical combination between IN718 layer and 316L layer. |
PDF Full Text Request