The distortion of β -brass and iron crystals

Experiments on the distortion of metal crystals having cubic face-centred or hexagonal lattices have given very consistent results, and in every experiment the slip-plane has proved to be the crystal plane of greatest atomic density, which is subjected to the maximum shear stress. The direction of shear on this plane is represented by the line of atoms in closest formation nearest to the line of maximum slope. there is still conquerable diversity of opinion concerning the actual mechanism of distortion in crystals having a body-centred cubic lattice. Goucher,* using tungsten crystals in the form of a line wire (maximum diameter 0·195 mm), concluded that planes of type {112} were the most probable slip-planes, the direction of slip being [111]. Distortion combined with X-ray measurements on iron indicated that the pole of the slip-plane was usually nearest to a {112} plane, but tended to lie on the great circle perpendicular to the direction of slip, which was a [111] direction, between a {110} and {112} plane. The slip plane was determined by stress considerations. This work was confirmed by Taylor's similar invalidation of the distortion of β-brass crystals; but with this material the slip-plane tended to be closer to a {110} plane.