Study On Microstructures And Mechanical Properties Of TiN/Inconel 718 Composites Fabricated By Selective Laser Melting

Inconel 718 alloy was a precipitation-hardened nickel-based superalloy,which has important applications in aerospace,nuclear energy and chemical industries.With the rapid development of modern industries,higher requirements have been imposed on the structural complexity,dimensional accuracy and mechanical properties of Inconel 718alloy parts.Selective laser melting（SLM）technology overcomes the problems of geometric limitations and low accuracy in traditional manufacturing methods.However,SLM technology was currently limited to the formation of several metal powders.And the fabricated parts have problems such as spheroidization,low density,and high porosity.Therefore,it’s great theoretical significance to study the microstructures and mechanical properties of Inconel 718 composites fabricated by SLM.In this paper,pure Inconel 718 alloy and TiN/Inconel 718 composite specimens were successfully prepared by SLM technology.The influences of TiN particle addition and heat treatments on the microstructures and mechanical properties of the specimens were studied.The results show that the parameters have a significant influences on the forming quality and microstructures of the specimens fabricated by SLM.The densityρof the specimens increases first and then decreases with the increases of the laser energy density E.The relationship was:=-2.65072×10^-42+9.447×10^-2+90.9399.The scanning pitch can be change by the overlap rates,which affects the orientation of the microstructures.The laser power and scanning speed will affect the width and depth of the melting track.The shape of the melting track obtained by high laser power and low scanning speed was wide and deep,while the shape of the melting track obtained by low laser power and high scanning speed was narrow and shallow.Combining the forming quality and microstructure analysis,the optimized laser process parameters are:overlap rate was 45%,scanning speed was 550mm/s,and laser power was 150W.In the TiN/Inconel 718 composites specimens fabricated by the optimized process,TiN particles are tightly bonded with the matrix and formed a transition layer.There are no holes and cracks in the specimens,and the microstructure shows an epitaxial columnar along the direction of heat flow.Compared with the pure Inconel 718 alloy specimens,the microhardness of the composite specimens was increased by 39HV0.2,the wear resistance was improved by 41.6%,and the tensile strength was increased by 114MPa.The microstructures have obvious differences after different heat treatments.After double aging（DA）heat treatment,the microstructure has not changed significantly.The solid solution aging（SA）heat treatment can make the material precipitate a large number of needle-likeδphases and ultrafine sphericalγ’/γ’’phase inside the grain.After HSA heat treatment,the‘fish scale structure’of pure Inconel 718 alloy and TiN/Inconel 718composite material completely disappeared.An appropriate amount of ultrafine sphericalγ’/γ’’precipitated inside the grain.The difference was that the needle-likeδphase appears only at the grain boundaries in pure Inconel 718 alloy.While more needle-likeδphase appeared around the grain boundaries and TiN particles in TiN/Inconel 718 composite materials,and theδphase size was finer and longer.The mechanical properties of these materials can also be changed by heat treatment.The microhardness and wear resistance of TiN/Inconel 718 composites was higher than that of pure Inconel 718 alloy under the same heat treatment conditions.And the tensile properties were significantly improved after heat treatment.The tensile strength of pure Inconel 718 alloy and TiN/Inconel 718 composites after HSA heat treatment were1570MPa and 1430 MPa,respectively.The elongations were 27.3%and 21.0%,respectively.Its comprehensive tensile properties reach the best,i.e.the comprehensive mechanical properties of HSA heat treated composite specimens are outstanding.Based on the results of this study,the microstructures and mechanical properties of the fabricated-specimens can be improved by optimized SLM laser parameters,TiN ceramic particles,and heat treatment.For TiN/Inconel 718 composites,the HSA heat treatment was benificial to improve the microstructures and mechanical properties.