In 1980, Weber[5] prepared a large amount of mechanically alloyed ODS superalloy (INCONEL MA 754). It is essentially a Ni-20% Cr alloy strengthened by about 1 vol % Y2O3. The Ni, Cr, and Y2O3 powders were milled until a homogeneous Ni-20% Cr alloy was formed in which the Y2O3 particles were uniformly distributed. The fabricated alloy powder was then consolidated by hot extrusion which was followed by hot rolling. A recrystallization step, often directional, followed consolidation that resulted in elongated, high-aspect-ratio grains that were very stable owing to the inert oxide pinning. After the directional crystallization, the grains had typical dimensions of ~ 500 to 700 µm parallel to the working direction and ~ 15 µm perpendicular to this direction. The typical BFI of the fabricated MA 754 is displayed in Fig. 2.1, which shows the oxide distribution in the metallic matrix. Benjamin et al.[6] have suggested that fine particles are a uniform dispersion of stable yttrium aluminates formed by the reaction between the added Y2O3, excess oxygen in the powder, and the aluminum added to getter oxygen. In Fig. 2.1, the larger particles are titanium carbonitrides.
The dispersoids are typically 14 nm in diameter with an average spacing of 0.2 µm. The 1093°C stress rupture properties of INCONEL MA 754 are compared to those of other alloys in Fig. 2.2. The MA 754 alloy, like other ODS materials, has a very fine, flat, log stress-log rupture life slope compared to conventional alloys. The strength of MA 754, about 100 MPa for 100 hours life, is somewhat higher than both of the other ODS alloys and several times greater than conventional materials, MAR-M alloy 509 and alloy 80 A. Thus, while MA 754 alloy is comparable to TD (Thoria dispersed) NiCr, it has a non-radioactive dispersoid and high strength, so it is suitable for applications such as gas turbine vanes.