Investigation Of Oxidation And Fatigue Properties Of IN 718 Superalloy Manufactured By Selected Laser Melting

Inconel 718,a nickel-base superalloy,has been widely used to make components such as turbine disk for gas turbines due to its excellent mechanical properties at elevated temperature,corrosion resistance,and good weldability.Compared with traditional casting and forging manufacturing ways,additive manufacturing technique has many advantages such as efficient productive cycle,higher precision in forming size,energy-conservation and environment-protection.However,the difference in the microstructure of the additive-manufactured components and the cast and forged components has been a general concerning issue,and also the oxidation resistance of the selected laser melted components of the IN718 alloy,and the reliability of service,especially its fatigue performance.Therefore,in this study,samples of Inconel 718 superalloy formed by using selected laser melting(SLM)technique and the heat-treated ones through regimes of homogenization and two-stage aging were employed to investigate the microstructural characteristics.The oxidation resistance at 650? and the oxidation mechanism of the alloy before and after heat treatment were comparatively studied,and the bending fatigue properties were also studied at room temperature.The effect of the cavities on the fatigue life of the materials was also analyzed and discussed.Results were obtained as follows:Coarse columnar crystals were formed along the building direction of the as-bulit samples by using SLM technique and the grains revealed a strong<001>texture.The density of the as-built sample was?99.993%.After the heat treatment,Laves phase was dissolved into the matrix completely,and ? phase,carbide,?' phase and ?" phase precipitated from the matrix.A densely packed oxide film formed on the surfaces of the SLM samples after 650? for 500 hrs oxidation,which was more uniform than that on the surfaces of the cast and forged samples.The SLM samples had a better oxidation resistance,and the surface roughness had little effect on the oxidation resistance property.The fatigue properties of the heat-treated samples were better than those of the as-built ones.Cavities in the samples had less effect on the fatigue life at the higher stress amplitude of fatigue loading,while having more effect at the lower stress amplitudes.The cavities distributed on the surfaces of samples decreased the fatigue life a lot.The cavities located in the cores of the samples had little effect on the fatigue life of both the as-built and the heat treated samples,while the holes located between the cores and the surfaces had a great more influence on the fatigue life of the as-built samples,and had less effect on the heat-treated samples.