Abstract
High purity copper and pure iron were melted to form an alloy by arc melting. Cu-Fe alloy and pure copper single crystal bars were grown with the Bridgman method. Their difference in microstructures and hardness after different strain and annealing was compared. TEM samples were used to study the size and morphology of precipitates in the alloy. With 25% compression and 300 oC annealing, there is no recrystallized new grain observed. For the copper/1.25% iron alloy with 25% compression and 700 oC /2 hours annealing, only small new grains were found in isolate narrow strips in the specimen. Therefore, a large strain of 75% compression is selected in this work to study the recrystallization phenomenon and the grain size in whole bulk specimens. Generally, higher heat treatment temperature results in an increase in the grain size and a reduction of the hardness in a material. However, due to the influence of iron precipitate particles that formed and grew along with the recrystallization process, the recrystallization was impeded and the decrease in hardness was also counter affected by the iron precipitate particles. The recrystallization was not completed even after 512 hours annealing at a temperature as high as 800 oC that is lower than but very close to the solid solution temperature (about 820 oC). Because the starting specimens are single crystal with no grain boundary and very low dislocation densities, the precipitates are believed to nucleate at dislocations formed in cold work. At 75% strain, the dislocation density is very high and the precipitates can nucleate more evenly. TEM observations indicate that with increasing annealing temperature the precipitates can grow with accompanying phase transformation.