Effects of Boron Addition on the Mechanical Properties of Ni-Fe-Al Ternary β Phase

The mechanical properties of the ordered intermetallic Ni-Fe-Al beta phase alloys with and without boron has been studied as a function of composition and temperature by compression testing. The alloys without boron where Al is kept constant at 45 and 40 mol%, whereas that with boron where Al is kept constant at 45 mol% and addition of 0.05 mass% boron. The present work indicated that (1) the temperature dependence of strength behavior of (Ni,Fe)Al; (45 mol% Al) alloys is similar to bcc metals and binary NiAl alloys, characterized by three different stages. The alloys of stochiometry in binary NiAl, FeAl and near the second stoichiometry in ternary (Ni,Fe)Al; (45 mol% Al) show plateaus distinctly and have a wide plateau temperature range, which becomes narrower and less distinct when the composition of the alloy is off stoichiometry. (2) Consisting with the hardness, the ternary alloys of near the second stoichiometry that with the beta phase in the Ni-Fe-Al system show the lowest 0.2% flow stress, and an increase in iron content largely enhances the solid solution strength. (3) The boron improved the strength of (Ni,Fe)Al; (45 mol% Al) alloys, especially at low temperature, and with increasing temperature, the effect becomes weaker and disappears beyond 1250K. (4) The brittle-ductile transition temperatures (BDTT) of (Ni,Fe)Al; (45 mol% Al) alloys were also largely decreased by a small amount of boron addition in comparison to the unalloyed (Ni,Fe)Al; (45 mol% Al) alloys, indicating a better high-temperature mechanical properties with a favorable of strength and fracture toughness.