*Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, U.S.A. #MER Corp., 7960 S. Kolb Road, Tucson, AZ 85706, U.S.A. (Received January 4, 1996) In a recent paper Chen et al. (1) discussed the effect of directional solidification processing at different solidification rates on the structure and mechanical properties of Ni,,Al,,Fe,,. The purpose of the present short nfote is twofold: first, to clarify the phases present in this alloy at or near equilibrium; and second, to point out that mechanical properties superior to those obtained by Chen et al. (1) for direc- tionally-solidified material have previously been reported for the same alloy. Concerning the phases present, Chen et al. (1) describe Ni,,Al,$e,, processed by directional solidi- fication as consisting of various distributions of a y phase and a p phase. (The crystal structures of y and p were undefined by the authors but we assume that these refer to ordered f.c.c., or Ll,, and ordered b.c.c., or B2, respectively based on their reference to the work by Inoue et a1.(4). We will follow the nomenclature of earlier work and refer to these as y and b’, respectively (2-5) and reserve g and b for the f.c.c. and b.c.c. phases, respectively, which are nearby on the phase diagram (5).) Inoue et a1.(4) rapidly-solidified Ni,,,Al,,Fe,, and described the resulting duplex structure as consisting of grains of p’ and v. In contrast, later work by Field et a1.(2) reported a similar microstructure after rapid solidi- fication but instead being p’ and p, the phases present were p’ and of y containing fine y precipitates. In both cases the microstructures are, of course, non-equilibrium. However, the microstructure of Ni,,Al,,Fe,, processed by casting and hot-extrusion in steel cans, followed by air-cooling was also shown by Guha et al. (2) to consist of p’ and y, with the latter again containing fine y precipitates, see Figure 1. Only after annealing at temperatures of 1100 K or above (followed by water quenching) did Guha et al. (3:) observe that the y/y grains became disordered, i.e. they became simply y. The phases observed by Field et al. (6) and Guha et al. (2,3) are consistent with the reported phase diagram (5). Thus, it appears likely that the microstucture of the directionally-solidified NiSoAlzoFe,, studied by Chen et al. (1) consists of grains of p’ and y/v, and not simply p’ and y (p and y in their nomen- clature) as the:y report. Of course, by using only a scanning electron microscope Chen et al. (1) would be unable to observe this. Figure 2 shows the fracture strain as a function of lamellae width (the average of the reported p’ and y widths) for Chen et al’s (1) alloys and includes a datum Tom Guha et al. (2). The data suggest that for aligned eu.tectic lamellar structures, i.e. ignoring the point for the equiaxed grain structure, the fracture strain broadly increases with decreasing lamellar spacing. In other words, it is not directional solidification ,that improves ductility (the point from Guha et al. (1991) is for double-extruded mate- rial) but refining the microstructure. Further, one can suggest that producing an aligned microstructure