Correlation between mechanical properties and structural changes of the sintered Cu-4 at% Ag alloy during thermomechanical treatment

Abstract

Influence of thermomechanical treatment on micro structure and strength (hardness and microhardness) of the sintered copper based Cu-4 at% Ag alloy was investigated using Vickers hardness and microhardness measurements, and optical microscopy. After sintering at 790°C, samples of Cu-4 at% Ag alloy were subjected to thermomechanical treatment by cold rolling with 20, 40 and 60% deformation degrees, and annealing below and over the recrystallization temperature. It was shown that microstructure of Cu-4 at% Ag alloy changed with thermomechanical treatment, which directly causes changes of mechanical properties. Optical microphotograph of the sintered Cu-4 at% Ag alloy shows relatively homogeneous structure with spherical pores presented. The strength (hardness and microhardness) of the sintered Cu-4 at% Ag alloy during cold rolling increases with deformation degree due to deformation strengthening. Maximum values of hardness and microhardness were for 60% deformation. The porosity still exists in spite of the fact that compacting was carried out during the cold rolling. The hardness and microhardness continue to increase after annealing at temperature bellow recrystallization temperature due to anneal hardening effect which occurs in a temperature range of 160-350°C. It was concluded that solute segregation to dislocations, analogous to the formation of Cottrel atmosphere in interstitial solid solutions, is primarily responsible for anneal hardening phenomenon. Annealing at higher temperatures (higher than 400°C) results in strength decrease due to beginning of alloy recrystallization