EFFECTS OF BORON ADDITION ON THE MECHANICAL-PROPERTIES OF NI-FE-AL TERNARY BETA-PHASE

The mechanical properties of the ordered intermetallic Ni-Fe-Al beta p hase alloys with and without boron has been studied as a function of c omposition and temperature by compression testing. The alloys without boron where Al is kept constant at 45 and 40 mol%, whereas that with b oron where Al is kept constant at 45 mol% and addition of 0.05 mass% b oron. The present work indicated that (1) the temperature dependence o f strength behavior of (Ni, Fe)Al; (45 mol%Al) alloys is similar to bc c metals and binary NiAl alloys, characterized by three different stag es. The alloys of stoichiometry in binary NiAl, FeAl and near the seco nd stoichiometry in ternary (Ni, Fe)AI; (45 mol%Al) show plateaus dist inctly and have a wide plateau temperature range, which becomes narrow er and less distinct when the composition of the alloy is off stoichio metry. (2) Consisting with the hardness, the ternary alloys of near th e second stoichiometry that with the beta phase in the Ni-Fe-Al system show the lowest 0.2% now stress, and an increase in iron content larg ely enhances the solid solution strength. (3) The boron improved the s trength of (Ni, Fe)Al; (45 mol%Al) alloys, especially at low temperatu re, and with increasing temperature, the effect becomes weaker and dis appears beyond 1250 K;. (4) The brittle-ductile transition temperature s (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 (N i, Fe)Al; (45 mol%Al) alloys, indicating a better high-temperature mec hanical properties with a favorable of strength and fracture toughness .