Nb rich precipitates of Inconel 718 produced by selective laser melting

R.V. Shakhov, K.S. Mukhtarova

Abstract

TEM of Inconel 718 produced by SLMStructure investigation of nickel-based superalloy Inconel 718 produced by selective laser melting was carried out by transmission microscopy. Multiple cycles of heating and rapid cooling during manufacturing lead to the formation of a complex microheterogeneous structure of the alloy. Nevertheless, a chemical analysis of such a structure showed high homogeneity. Structure consists of the γ grains with size of about 1-0.5 μm banded, probably, with δ phase particles or small carbides. Intermetallic phases Ni3Nb were homogeneous precipitated. Volume fraction of this precipitates is about 13%. Carbides typical for this wrought alloy with dimensions of 2-10 μm were not detected. Such an unusual structure is due to manufacturing technology and chemical homogeneity of the powder. The data of the calculation of the maximum volume fraction of the hardening intermetallic phases γ′′, δ Ni3Nb) in the alloy are shown. The calculated volume fraction of the Nb containing phases is not more than 13.61%. However, previously carried out studies give data of a higher (up to 25%) content of this phases. It has been suggested that other metals, for example Ti, Cr, Fe, Mo, Co, can be included in the intermetallic phases that lead to an increase in its volume fraction in the alloy.

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