Abstract
The dislocation model for the mechanism of diffusion-less transformation from the f. c. c structure β to the c. p. h. _??_ in cobalt-nickel alloys has been studied and examined by means of electron-microscopic observation of relief markings on the crystal surface formed by the transformation. It can be considered that the transformation from β to ε proceeds through the motion of types of half-dislocations (α/6) [121]_??_, (α/6) [211]_??_, and (α/6) [121]_??_ in the {111} plane of an f. c. c. crystal. When these half-dislocations move in all directions over the crystal surface, tilts having three different inclinations to the surface are formed, which can be estimated as 19°28', -10°2' and -10°2' respectively if the surface is parallel to the (112) plane, while under an applied stress only one type of half-dislocations similar in direction to the stress can be considered to move. and then only one sort of the tilts is preferred. These ourface tilts result in the relief markings on the crystal surface. The above results predicted theoretically were confirmed by means of electron-microscopic observation of markings, and it was found that the width of the zone of homogeneous displacement in marking (about 0.1_??_1μ for 25%, nickel alloy) decreased slightly with decreasing nickel content, but for alloys having less than a few percent of nickel it decreased abruptly and for pure cobalt it was of an order of 100Å.
