M. S. Sakr

Microstructure changes and steady state creep characteristics in Pb-Sn alloys during transformation

The steady state creep of Pb-10 wt.% Sn and Pb-61·9 wt.% Sn alloys have been investigated under different constant stresses near the transformation temperature. The temperature dependence of steady creep rate has shown two different transition points; at 423 K for Pb-10 wt.% Sn alloy and at 403 K for Pb-61·9 wt.% Sn (the eutectic composition). The strain rate sensitivity parameter (m) has been found to increase by raising the working temperature and to reach 0·45 and 0·85 for the first and second alloy, respectively. The activation energies of steady state creep of Pb-10 wt. % Sn have been found to be 46·2 kJ/mole and 88·2 kJ/mole in the low and high temperature regions (below and above 423 K) referring to dislocation and self diffusion mechanisms. While activation energies of steady creep in Pb-61·9 wt.% Sn have been found to be 42 kJ/mole and 63 kJ/mole in the low and high temperature region (below and above 403 K), characterizing grain boundary diffusion in Sn and Pb respectively. X-ray analysis and microscopic investigations of the test alloys have confirmed the above mentioned mechanisms.

Effect of ≡ precipitates on creep deformation in Al2.5wt.%Cu

Abstract The change in the transient and steady state creep deformation of aluminium alloy containing 2.5 wt.% Cu was studied under various constant stresses ranging from 30 to 36 MPa in the temperature zone of ≡ precipitates. From the transient creep results, the peak values of the transient creep parameters β and n found in this temperature zone can be ascribed to dissolution of ≡ precipitates. The transient creep parameter β is related to the steady state creep rate ϵ st through the exponent γ. γ was found to range from 0.75 to 0.95. At the dissolution temperature (733 K) of ≡ precipitates, the steady state strain rate sensitivity parameter was 0.3 ± 0.01 at the steady state strain peaks which were characteristic of dislocation climb along ≡ grain boundaries. Microstructural analysis confirmed that the above-mentioned mechanism took place in the dissolution region of ≡ precipitates.

Microstructure dependence of yielding and fracture in Cd-Zn alloys

The coefficient of logarithmic work-hardening, the yield stress and the fracture stress of Cd-2 wt. %Zn alloy of different grain diameters and of Cd-17·4 wt. %Zn alloy decrease with increasing working temperature. Two relaxation temperature regions have been found, the low-temperature region of relaxation (below 483 K) and the high-temperature region (above 483 K). The fracture surface energy for Cd-2 wt. % Zn alloy has been calculated and found to be 1·2 J/m2 at the two temperature regions of relaxation. X-ray investigations show that the residual internal strains in the deformed samples increase with increasing working temperature and exhibit a peak value at 483 K.

Transient creep during transformation in Cd-Zn alloys

AbstractTransient 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 equationɛtr=Btn, whereɛtr 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

Effect of transformation on the steady creep characteristics of Zn−Al alloys

\dot \varepsilon _{st}

Transient and steady state creep of Al-4.5 wt % Mg during phase transformation

through the equation

Recovery behaviour after stress reductions during the steady state creep of Al-14wt.%Zn

B = B_0 \dot \varepsilon _{st}^\gamma