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

Abstract: 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 (<2μm), 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 5–10nm in size. Additionally, at small angle grain boundaries, coarser γ″ precipitates of 50–100nm in size have been observed. The 〈001〉 γ//〈001〉 γ″ and {100} γ//{100} 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 2–5nm in size were observed by means of FIM. [Copyright &y& Elsevier]