The effects of pressure and pressure routes on the microstructural evolution and mechanical properties of sintered copper via SPS

Spark Plasma Sintering (SPS) is a pressure-assisted sintering process in which high density and mechanical properties are usually reached. This study applied the SPS to consolidate copper powder using different sintering pressures and pressure routes during holding time or heating. In the first route, the pressure was maintained (around 15 MPa) during the heating up to the sintering temperature (650 ^ºC), and the pressure was increased during the holding time. In the second route, the pressure was raised during the heating and kept constant during holding time at 650 ^ºC. Three different pressure levels were applied on each route: 110, 65, and 50 MPa. Microstructural evolution was investigated using densification (Archimedes method), scanning electron microscopy (SEM), hardness, and X-ray diffraction (XRD). The increase in pressure improves the microstructural features. In addition, in the first route, in which higher pressure rates were found, grain growth inhibition was observed, and densification was also improved significantly. The smallest crystallite size and highest microstrain were also observed at higher pressures. The increase in pressure also led to a rise in microhardness (17%), a decrease in pore volume fraction (10.5%), and an increase in pore circularity, causing substantial variations between the microstructures of samples. A finite element method (FEM) analysis was conducted using a thermo-mechanical approach to evaluate the stress distribution in the two different sintering routes. The results agree with the experimental results, and more pronounced effects were found in the first route because of higher compressive stresses, corroborating the results of microstrain and hardness.