Trends in the Development of Machinery and Associated Technology ” TMT 2010 , Mediterranean Cruise , 11-18 September 2010 ANNEAL HARDENING EFFECT IN SINTERED COPPER ALLOYS DEPENDENCE ON ALLOYING ELEMENTS AND DEFORMATION
This paper reports results of investigation carried out on sintered copper alloys: Cu-8at%Ni, Cu8at %Zn, Cu-8at%Al, Cu-8at%Ag, Cu-4at%Ni-4at%Sn, Cu-4at%Ni-4at%Zn and Cu-4at%Au. For comparison, investigation carried out on the sintered copper. The sintered alloys, as well as pure copper, were subjected to the same thermomechanical treatment. Thermomechanical treatment included cold rolling of 30,50 and 70% in reduction. Isochronal and isothermal annealing up to the recrystallization temperature were performed, followed with hardness and electrical conductivity measuring. This investigation shows that hardness and electrical conductivity of cold deformed copper-alloys increase after annealing in the temperature range of 160 400°C, due to anneal hardening effect. Electrical conductivity decreases with increasing the amount of alloying elements. During the annealing the electrical conductivity slowly increases for both set of the samples copper and alloys due to recovery and recrystallization
The mechanisms of anneal hardening in Cu-Al alloys
The anneal hardening behavior of a Cu-16 at. pct. Al alloy was investigated by tensile testing, measurement of Young’s modulus and electrical resistivity, and electron microscopy. It was shown that three main stages of annealing processes can be distinguished. Stage 1 atT ≤ 150°C is characterized by vacancy annihilation and short-range diffusional processes giving rise to three successive, low maxima in yield and tensile strength. Substages in this temperature range are also evident from resistivity measurements. Stage 2 at 150 ≲ 275°C is essentially associated with solute segregation to dislocations giving rise to the main increase in flow stress. In Stage 3 at 725 ≤T ≤ 350°C recrystallization takes place.
Release of stored energy during low temperature annealing of some cold worked metals
Recovery processes have been studied by measuring the release of stored energy in Cu, Ni, Ag and Au during annealing in the temperature range of stages II and III after deformation at − 195°C. Stage II recovery shows a fine structure, somewhat different for the different metals. In Cu and Ag, the energy released is about 2 per cent of the work done during deformation, practically independent of the degree of cold-work (40–70 per cent compression). Within the accuracy of the measurements (0.2 per cent) no influence of the annealing processes on the lattice specific heat could be observed. Comparison of the energy released to the decrease of electrical resistivity during annealing in stages II and III results in a value of the stored-energy/resistivity ratio for these stages: UΔϱ = 3.0–3.5 cal/g μΩcm. The influence of impurities (0.1 and 1 at.% Au and Ag, 0.1 at.% Be) on the recovery processes in Cu has been investigated. The total energy released between − 195°C and room temperature is not different from that in pure Cu within the accuracy of the measurements. The main effects of the Au and Ag solute atoms are: 
1. 
(a) the release of energy is shifted to higher temperatures. 
 
2. 
(b) the stage II fine structure is gradually vanishing with increasing solute concentration 
 
3. 
(c) the recovery peak II∗, which is weakly present in pure Cu, increases 
 
4. 
(d) some new recovery peaks in the temperature range of stage III are observed. 
 
 
No influence was observed of 0.1 at.% Be in Cu 
 
The recovery processes in stages II and III are discussed in terms of di-interstitials and interaction of interstitials with impurities and dislocations.