Investigations of MX and γ'/γ'' precipitates in the nickel-based superalloy 718 produced by electron beam melting

Samples with a composition similar to the nickel-based superalloy Inconel alloy 718 were produced by electron beam melting of prealloyed powder and investigated with respect to type and composition of the strengthening precipitates. The matrix consists of γ grains orientated in nearly the same direction, almost like a single crystal. Coarse precipitates (<2 μm), mostly of the (Ti,Nb)(C,N,B) type with B1 structure, are aligned along the growth direction. TEM and APFIM investigations of the γ matrix revealed very fine γ'' precipitates of around 5-10 nm in size. Additionally, at small angle grain boundaries, coarser γ'' precipitates of 50-100 nm in size have been observed. The <0 01> γ//<0 0 1> γ'' and {1 0 0} γ//{1 0 0} γ'' orientation relationship between γ and γ'', known from literature [M. Sundararaman, P. Mukhopadhyay, Mater. Charact. 31 (1993) 191-196], was confirmed. Some γ' precipitates of 2-5 nm in size were observed by means of FIM