We have developed several solutions to provide a convenient tool for the studying of dislocation structure and dislocation motion in ordered Ni3Al. The solutions have been applied for for chemical polishing, orientation etching, and selective dislocation etching .
The solutions have several important advantages: (a) they do not require electrolytic techniques for either etching or polishing; (b) the selective dislocation etchant reveals dislocations of various kind (new, aged, individual, in grain boundaries); (c) the contrast of the dislocation etch pits is high enough to distinguish between mobile and immobile dislocations; (d) the polish dissolves all the crystallographic planes uniformly; and (e) the "orientation" etching allows a simple identification of sample orientation by the characteristic shape of "non-dislocation" etch figures.
So far we have tested the solutions on boron-free samples of only one composition (Ni77Al23) and on boron-doped samples of only one boron concentration (Ni76Al23.5B0.5). We have observed no considerable difference in their action, and the dislocation etchant reveals the dislocations in both types of samples by etch pits of practically the same size and contrast. On the other hand, at different stoichiometry and doping, the dissolution rates may be considerably different, and the dislocations can not be revealed anymore in such cases.
The tree different compositions are summarized below. Each solution corresponds to completely different dissolution processes occurring on the surface of Ni3Al samples:
uniform dissolving leading to uniform polishing of a given crystallographic plane (Solution #1, HNO3 + H2SO4 + H2O, 1:1:1, vol. parts);
anisotropic dissolving of the surface, with macroscopic defects serving as nucleation centers and leading to the formation of the orientation figures (Solution #2, HNO3 + H2SO4 + H2O, 1:1:1, vol. parts, + 0.02 M FeCl3.6H2O);
anisotropic selective dissolving of the {001} crystallographic planes, with dislocations serving as permanent nucleation centers and leading to the formation of the dislocation etch pits (Solution #3, HNO3 + HCl + H2O, 1:3:3, vol. parts, + 0.05 M FeCl3.6H2O).