Effect of Remelting and Standard Heat Treatment on Microstructure ‎and ‎Mechanical Properties of IN738LC Superalloy

In the present study, IN738LC superalloy ingot was re-melted and cast, then heat treated under ‎standard conditions. Microstructural studies with field emission scanning electron microscopy ‎‎(FESEM) equipped energy dispersive spectroscopy (EDS) showed that after re-melting and ‎controlled casting, the amount of porosity and size of γ' precipitates decreases. Also, with ‎applying the standard heat treatment cycle, the primary γ' precipitates less than 1µm in size and ‎cubic morphology and nano‏spherical‏ ‏secondary γ' precipitates appeared and eutectic γ-γˈ ‎regions were completely eliminated. Vickers hardness test results under a load of 10 Kg showed ‎that the lowest hardness is related to the solutionized sample due to remove the coarsened γ' ‎precipitates and the highest hardness (833 H.V.) is obtained after aging. According to the results ‎of the tensile test at ambient and 750◦C temperatures, by re-melting and applying the standard ‎heat treatment due to structural modification, strength and elongation increased at both ambient ‎temperature and 750◦C. Also, with applying the standard heat treatment, failure mechanism of ‎IN738LC superalloy was transferred from brittle trans-dendritic failure to brittle inter-dendritic ‎failure with little footprints of ductile fracture.‎