| Incone1718(IN718)alloy is a precipitation reinforced nickel base superalloy,which is widely used in various fields because of its excellent mechanical properties and corrosion resistance and oxidation resistance.Selective laser manufacturing(SLM)is widely used in the forming of high temperature alloy parts because it overcomes the problems in traditional manufacturing processes.Heat treatment,a common method to improve the performance of nickel base superalloy,is also used to improve the performance of SLM-IN718 alloy.According to the TTT curve of IN718 alloy,solid solution treatment,solid solution+aging treatment and aging treatment were carried out in this study.(1)In order to study the influence of heat treatment on the tissue evolution of SLM-IN718,three heat treatments were carried out for IN718 alloy made by selective laser melting:dual-aging treatment at 72℃/3h+620℃/3h,solid solution aging treatment at 950℃/1h+720℃/3h+620℃/3h,and solid solution aging treatment at 1050℃/1h+720℃/3h+620℃/3h.It was found that the SLM-IN718 alloy in the as-built state presented the boundary of the molten pool formed by the superposition of "fish scale" circular plates,and columnar grains were observed to grow across several molten pool layers.After double aging treatment,the fish-scale pool trace in the selected laser-made IN718 alloy disappeared,and the grain morphology did not change significantly,but secondary phase began to separate out among columnar crystals.After the alloy was treated by solid solution+dual aging at 950℃,the grain boundary became clearer,and spherical and spiculate secondary phases were precipitated on the grain boundary.After 1050℃ solid solution+dual aging treatment,the columnar crystals recrystallized,fine and uniform isometric crystals formed,a large number of twins were generated.The secondary phase was precipitated in grain boundary and crystal.(2)In order to study the influence of temperature and time changes of solid solution treatment on the hardness of SLM-IN718 alloy,the solid solution treatment of SLM-IN718 alloy was conducted between 950℃ and 1250℃,and the solid solution time was set as 0.5h or 1h.It was found that when the solid solution temperature was the same,the longer the solid solution treatment time was,the lower the hardness of slm-in718 alloy was.When the time of solid solution treatment is the same,the higher the temperature of solid solution treatment is,the lower the hardness of slm-in718 alloy is.(3)in order to study the effect of single aging treatment on the impact toughness and hardness of SLM-IN718 alloy,the alloy was subjected to single aging at 720℃ for 3～6h.It is found that the impact toughness of the alloy decreases rapidly and then becomes stable with the extension of the aging time.The impact toughness of IN718 alloy aged 4-6 hours decreased by 26%-28%compared with that of 718 alloy aged 3 hours.However,the hardness of the alloy increases rapidly first and then tends to stabilize.The hardness of IN718 alloy aged 4-6 hours increased by 22%-29%compared with that of IN718 alloy aged 3 hours.(4)The effect of 720℃/8h+620℃/8h dual-aging treatment on the anisotropy of mechanical properties of SLM-IN718 alloy in vertical plane and horizontal plane was studied.It is found that SLM-IN718 alloy has anisotropy in vertical plane and horizontal plane.The columnar grains grow preferentially on the vertical plane and present a honeycomb equiaxed structure on the horizontal plane.The tensile properties of the horizontal plane and the vertical plane of SLM-IN718 alloy are different,the strength of the horizontal plane is higher,and the plasticity is lower than that of the vertical plane.After the double aging treatment,the strength of the horizontal and vertical printed samples increased and the plasticity decreased.The difference between the yield strength and tensile strength of the vertical and horizontal planes decreased,but the difference in elongation increased.It shows that double aging treatment can reduce the strength anisotropy of SLM-IN718 alloy but not the plastic anisotropy. |
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