Study of precipitates formation in Al-4.5Wt%Cu and Al-4.5Wt%Cu-0.1Wt%In alloys using creep measurements and positron annihilation technique

Abstract

The transient and steady state creep deformation of Al-4.5 wt%Cu and Al-4.5 wt%Cu-0.1 wt%In alloys were studied using a constant stress in the aging temperatures range 403 to 703 K for various aging times under different working temperatures. Positron annihilation studies using Doppler−broadening measurements were carried out on the specimens used in creep measurements. The subsequent decrease and increase in the creep parameters n, β and ε st as well as in Doppler lineshape parameter with increasing aging temperatures and aging times were explained on the basis of structure transformations occuring in Al-Cu alloys. The mechanical creep measurements are very well correlated with positron annihilation characteristics.

Transformation characteristics of Al–Ag and Al–Ag–Ti alloys

“…At high temperatures the microstructure changes and coarsens allow the operating of thermally activated processes such as interface-dislocation interaction, reduction of interface density and dislocation glide. The value of 51.7 ± 0.4 kJ/mol for the high temperature region agrees well with that quoted [23] for dislocation glide as dominant mechanism.…”

Effect of cyclic stress reduction on high temperature creep characteristics of solid solution Al−2·9 wt-Mg alloy

“…2 that: (i) all the creep curves exhibit normal creep behaviour while the strain level increases as either the magnitude of s cy or n of CSR increases (ii) the creep rate is enhanced under CSR as compared with static stress of same peak stress (iii) the sequence of curves with respect to working temperatures is regular. The transient creep stain e tr can be represented by the relation 22,23 In the present investigation, a threshold cyclic stress amplitude, (s cy ) th for CCA is defined as the steady state CSR amplitude applied to peak stress to initiate the CCA. To obtain the value of (s cy ) th , extrapolation of each line in Fig.…”

“…The transient creep stain ϵ tr can be represented by the relation 22,23 where β and n are the transient creep parameters, and t is the transient creep time in seconds. The transient creep parameter n , was calculated from slopes of the straight lines relating ln ϵ tr and ln t .…”

“…The value of 171 kJ mol 21 for activation energy of the steady state stage can be attributed to dislocation climb controlled process. 40 The relation that relates the transient and steady state creep stages is 15,23…”

“…The relation that relates the transient and steady state creep stages is 15,23 where β o is a constant and α is the steady state creep exponent measuring the contribution of the transient mechanism to the steady state creep behaviour, in other words, α shows to what an amount the effect of mechanisms controlling the transient creep extends to the steady state creep in this alloy. Figure 9 shows the relationship between ln β and ln ░ st , a linear dependence is obtained with a mean value of α = 0·55 is obtained for different working conditions.…”