EFFECT OF STRESS ON BETA'-]ZETA DEGREES TRANSFORMATION IN EQUIATOMIC AGZN

The growth of the trigonal ζ° phase from the CsCl β′phase in AgZn is accompanied by a homogeneous change of shape. An increase in length along 〈0001〉ζ° ∥〈111〉β′, a decrease in length normal to this direction, and an increase in volume are associated with the lattice transformation. Measurements of the length change parallel to 〈0001〉ζ° have been made on ζ° particles formed from β at 265°C. Single crystal discs of β′having faces (100), (110) and (111) were transformed at 140°C under compressive loading. In the (111) crystals the nucleation frequency of that variant having 〈0001〉ζ° parallel to the compression axis was markedly reduced with respect to the other three variants. The effect was less pronounced for the (110)β′ crystals and did not occur in the (100)β′ crystals. The growth rate parallel to the stress axis was reduced in all cases, but showed no apparent acceleration normal to this direction, compared with unstressed specimens. The overall transformation rate was substantially increased as a result of an increase in the nucleation rate. In (111)β′ crystals the growth rate of the few particles formed with the trigonal axis parallel with the stress axis was not reduced relative to the growth rate of the three remaining equally inclined variants. It is suggested that the nucleation of ζ° particles from β′ requires the deformation of the matrix in a 〈111〉β′ direction, but that growth is controlled by a deformation of the matrix in the 〈100〉β′ directions. © 1969.