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
Influence of Alloying on the Anneal Hardening Effect in Sintered Copper Alloys
Copper and copper alloys were prepared by a powder metallurgical method. Sintered copper and copper alloys were subjected to cold rolling with different degrees of deformation. The alloy in the cold-rolled state was isochronally annealed up to the recrystallization temperature during which the hardness was measured. These investigations show that anneal hardening effect occurs in a temperature range of 473-673 K.
Energetic and kinetic evaluations conducted in Cu-3.34 at % Sn through differential scanning calorimetry
Microcalorimetric enthalpy measurements associated with the different peaks appearing during linear heating of Cu-3.34 at % Sn were made in a 50% cold-rolled alloy. Unlike the situation in the deformed material, quenched and furnace-cooled alloys do not exhibit thermal events at any of the heating rates employed in the temperature range scanned. In the cold-rolled condition, from the energetic and kinetic analysis of the first exothermic peak, designated Stage 1, and of the endothermic peak, designated Stage 3, it was consistently inferred that they correspond, respectively, to the growth on dislocations of a metastable phase ε′ and to its subsequent dissolution prior to recrystallization. Such inference was also supported by Vickers microhardness and yield-stress determinations. The calculated volume fraction for ε′ after Stage 2 goes to completion, is about 0.02. A suitable expression previously developed for enthalpy release due to the pinning of solute atoms to partial dislocations was applied to compute dislocation density from the exothermic peak (Stage 2). The calculated value is in excellent agreement with those obtained from the analysis of the recrystallization trace (Stage 4) and from tensile tests, thus confirming that the second DSC trace actually corresponds to the solute segregation process. It is also suggeseted that additional dislocation-induced formation of ε′ might take place as a consequence of the enhanced solute concentration around partial dislocations. The non-isothermal dissolution kinetics of ε′ was adequately described by an integrated kinetic model function essentially appropriate for application in one-dimensional diffusion situations.