Hydrostatic pressure annealing more precisely than atmospheric pressure annealing enables the design of microstructure and properties of nanomaterials by slowing down diffusion. However, the influence of impurities on microstructure evolution in nanostructured materials during high hydrostatic pressure annealing has not yet been investigated. Electrolytic tough pitch copper (ETP) and deoxidized high phosphorus (DHP) copper were processed by high-pressure torsion at 4 GPa, at a speed of 0.25 rpm in 5 revolutions. Afterward, the samples were annealed at high hydrostatic and atmospheric pressures at 0.4 Tm for 15 min. Differential scanning calorimetry, X-ray diffraction, transmission, and scanning electron microscopy were applied to analyze the obtained microstructures. High-pressure torsion led to the creation of nanostructures in ETP and DHP copper with grains of 0.19 and 0.15 μm in the average equivalent diameter. After high-pressure annealing, the average equivalent diameter reached 0.38 μm and 0.24 μm for ETP and DHP copper, respectively. However, after conventional annealing, the grain growth was more intense, and grains measured on average 0.90 μm and 1.75 μm for ETP and DHP copper, respectively. Differential scanning calorimetry analysis indicated that stored energy decreased by 71% for ETP and 8% for DHP copper after high hydrostatic pressure annealing. X-ray line profile analysis revealed a 54% decrease in dislocation density in ETP after high hydrostatic pressure annealing, compared to 15% in DHP copper. High hydrostatic pressure annealing enables the production of nanostructured DHP copper with a reduced dislocation density compared to high-pressure torsion-processed DHP copper.
Kerber et al. (Wed,) studied this question.
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