Single Slip Plane Research Articles

Frictional stress on dislocations in α-brass single crystals deformed in simple tension

The frictionial stress, τ F , which has to be overcome by moving dislocations, has been determined by means of micro stress-strain measurements. A modification of the cyclic hysteresis method is being described, and this technique has been applied to α-brass crystals deformed into stages I and II. It was found that τ F remains constant throughout stages I and II. This result is in marked contrast to the behavior of copper where τ F rapidly increases from stage I through stage II. It is concluded that the constancy of τ F in α-brass is related to the motion of dislocations on single slip planes well into stage II.

Contribution to Internal Friction from a Dislocation Pileup with Application to Deformed Single Crystals

The contribution to the internal friction resulting from a group of dislocations confined to a single slip plane, and forced against a barrier, is calculated. Application of the result to the long-range-stress theory of work hardening, in conjunction with the Seeger theory of the Bordoni peak, suggests that, in deformed single crystals, an internal friction peak of constant magnitude should be observed throughout stage II of the stress-strain curve.

The different behaviour of hexagonal and cubic metals in their friction, wear and work hardening during abrasion

The mass wear per centimetre M and the friction coefficient μ of metals during abrasion on a relatively rigid hard rough surface are studied experimentally at 1 kg load and a speed of a few centimetres per second. `Smooth-cut' steel files were used as the abrasive surface, cleaned carefully by scratch-brushing rather than by etching, between consecutive experiments. In the mean, linear relations were observed, as expected theoretically, between the reciprocal of the volume-wear rate and the microhardness HD of the filed surface (thus work-hardened to the maximum extent), but the loci were widely different for the cubic metals (Pb, Ca, Al, Ag, Cu, Pt, Fe, Ni, Mo, Cr) and the hexagonal metals (Cd, Mg, Zn, Zr, Ti). For a given surface hardness, the volume-wear rate for the hexagonal metals was about half that for the cubic metals, hence for the hexagonal metals a larger proportion of the metal is displaced by plastic flow (slip) from the groove volume instead of being removed as wear; and this is evidently because of easier slip, mainly on a single slip plane (0001), instead of multiple slip and the associated heavy work hardening as occurs in cubic metals. A single linear locus was obtained when the reciprocal of the volume-wear rate was plotted against the hardness of the annealed metals. For the cubic metals μ decreased mainly linearly with increasing HD of the (work-hardened) filed surface, but for the hexagonal metals μ was practically constant, independent of HD. The relatively rapid surface oxidation of Mg and Ca caused a decrease in μ relative to that of the other metals of similar structure and hardness. These results establish clearly that there is a fundamental difference in wear and friction behaviour of hexagonal and cubic metals.

The fundamental slip process in the torsion of a crystal having a single active slip plane

The hitherto particularly obscure process of deformation of a single crystal by torsion is elucidated in the general case where the slip plane is inclined to the torsion axis. It is shown to consist primarily, in zinc crystals about 0⋅8 cm in diameter, of a new type of slip which will be called ‘flexural’ rotational slip. In this slip process the slip lamellae are rotated relative to adjacent lamellae, about the common normal at any point of the interface, but with simultaneous development of pronounced saddle-like flexure. This flexure results in a variation in the amount of relative rotation of neighbouring lamellae over their interface, and also causes a cylindrical crystal to develop a rounded-triangular cross-section. Optical examination shows S-shaped (0001) slip bands about 0⋅05 to 0⋅1 mm wide. Electron diffraction shows that at the saddle-shaped ( 0001 ) cleavage face the lattice is mainly practically undistorted (apart from the macroscopic flexure) to a depth of 200 Å or more, thus the slip lamellae are at least 200 Å thick. An expression defining the shape the slip lamellae must take up is deduced assuming that the elastic deformation is negligible, and this gives good quantitative agreement with most regions of the observed (0001) surfaces. The very minor role of twinning in the range examined (up to 66°/cm torsion) is demonstrated by this agreement of the calculated and observed (0001) surface shape. Experiments on torsion of a model made of a hundred lead lamellae illustrate well the development of the saddle-like flexure, the rounded-triangular rod section, and the non-uniformity of rotation of the lamellae over their interface.