Transient creep during transformation in Cd-Zn alloys

Abstract

Transient creep of Cd-2 wt. % Zn and Cd-17·4 wt. % Zn alloys has been studied under different constant stresses ranging from 6·4 MPa to 12·7 MPa near the transformation temperature. The results of both compositions showed two transient deformation regions, the low temperature region (below 483 K) and the high temperature region (above 483 K). From the transient creep described by the equationɛ _tr=Bt ⁿ, whereɛ _tr andt are the transient creep strain and time. The parametersB andn were calculated. The parameterB was found to change with the applied stress from 0·3×10⁻⁴ to 3×10⁻⁴ and from 0·6×10⁻⁴ to 18×10⁻⁴ for Cd-2 wt. % Zn and Cd-17·4 wt. % Zn, respectively. The exponentn was found to change from 0·8 to 0·95 for both alloys. The parameterB was related to the steady state creep rate$\dot \varepsilon _{st}$ through the equation$B = B_0 \dot \varepsilon _{st}^\gamma$, the exponentγ was found to be 0·5 for Cd-2 wt. % Zn and 0·6 for the eutectic composition. The activation energies of transient creep in the vicinity of the transformation regions (above 483 K) were found to be 50·2 kJ/mole for Cd-2 wt. % Zn and 104·7 kJ/mole for the eutectic composition characterizing the mechanisms of grain boundary diffusion and volume diffusion in Cd, respectively.