On the Precipitation of Intermetallic Compounds in Selected Solid-Solution-Strengthened Ni-Base Alloys and Their Effects on Mechanical Properties

We have investigated the susceptibility of selected solid-solution-strengthened Ni-base alloys of commercial grades to precipitating intermetallic compounds during aging at elevated temperatures and the corresponding effects on mechanical properties. Depending upon the exact chemical composition and aging temperature as well as the precipitate morphology, some alloys are found to be susceptible to precipitating detrimental intermetallics, particularly Ni₃Mo, Ni₄Mo, mu, sigma, δ Ni₃Nb and Laves phase. However, in some cases, it is found that certain intermetallics can produce a good combination of strength and ductility such as the Ni₂(Mo, Cr) with Pt₂Mo-type superlattice as well as the γ″ phase of Ni₃Nb with DO₂₂-type superlattice. Also, it is demonstrated that in some cases, small addition of an alloying element such as Fe to a given alloy can decelerate the kinetics of forming detrimental intermetallic compounds; however, a similar addition to another alloy can produce an opposite effect.