چكيده به لاتين
In the present study, the hot deformation behavior of pure copper prepared by mechanical grinding, cold pressing, and sintering was investigated. For this purpose, pure copper powder was mechanically ground with stearic acid for 240 minutes at a grinding speed of 300 rpm and a ball-to-powder radius ratio of 10:1 in an argon gas environment. The ground powder was subjected to a 7-ton hydraulic press for 10 minutes, and then the cylindrical samples were sintered at 850°C for thirty minutes to increase strength. Then, hot compression tests were performed on the samples at temperatures of 300, 500, 700, and 900°C and a strain rate of 10.001 s-1 to a true strain of 0.8. The hot flow stress diagrams and the hardening/softening behavior of the alloy were investigated based on the Jonas-Polyak method. Accordingly, the maximum stress at temperatures of 300, 500, 700, and 900 °C was 190, 97, 19, and 6 MPa, respectively, indicating a significant decrease in the stress level with increasing temperature. At all deformation temperatures, the flow curve, after the work hardening stage and reaching the maximum stress, experiences a significant softening fraction until reaching a stable state, and the samples were deformed without cracking up to an applied strain of 0.8. Microstructural studies indicate an insignificant change in grain size in the deformed microstructures at temperatures of 300 and 500 °C (4.8 and 5.9 μm, respectively) compared to the initial structure (4.9 μm). The occurrence of softening under these conditions was attributed to the mechanical penetration of the matrix phase into the voids (pre-existing pores), resulting in rotation and change in grain morphology. The results show that the fraction of pores in the initial structure (about 4-6%) has decreased significantly (less than 1%). The grain size in the deformed sample structure was 3.6 μm at 700 ℃ and 8.7 μm at 900 ℃. The significant decrease at 700 ℃ compared to previous temperatures is attributed to the occurrence of dynamic recrystallization phenomenon and the increase in the average size at 900 ℃ is attributed to grain growth. In this study, the hot flow behavior of the copper-graphene composite prepared by mechanical grinding, cold pressing and sintering was also compared with the flow behavior of the pure copper sample at 500 °C.
