FIGURE 11 Rapidly solidified Ni-Al-Cr-W superalloy specimens with (left) and without (right) yttrium additions, after a cyclic oxidation test consisting of 300 one-hour heatings in air at 1150°C. From Cox.20

of such phases cannot be predicted yet, one can confidently anticipate that surprises will continue to arise out of this netherworld of metastability.

Ion Implantation and Beam Processing

The advent of processing methods based on the injection of accelerated ions (10 to 500 keV) into solid metals and alloys is leading to a new world

FIGURE 12 Variations of interfacial partition ratio, k, with growth velocity, v, normalized to the diffusive velocity, DL/λ, where DL= liquid diffusivity and λ=diffusion jump distance; k0=equilibrium partition coefficient. From Boettinger, Coriell, and Sekerka.21 Reprinted with permission.

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