Thermal stability of submicrocrystalline copper strengthened with HfO2 nanoparticles in the temperature range 20–500 °C
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- Lebedev, A.B., Pul’nev, S.A., Vetrov, V.V. et al. Phys. Solid State (1998) 40: 1155. doi:10.1134/1.1130509
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The thermal stability of the yield stress and Young’s modulus was investigated in ultrafinegrained copper (99.98%) and a Cu-HfO2 composite obtained by intensive plastic deformation using the method of equichannel angular pressing. It is shown that both the pure copper and the composite strengthened with HfO2 nanoparticles demonstrate in this state a high yield stress (σ0.2≈400 MPa). When the two-hour annealing temperature Ta is increased above 200 °C, the yield stress in pure copper decreases to 40 MPa at Ta=400 °C, whereas in the Cu-HfO2 composite, high yield stresses are conserved up to Ta=500 °C. A recovery stage of Young’s modulus is found at around 200 °C both in pure copper and in the Cu-HfO2 composite. It is concluded that this stage reflects the transition of the grain boundaries from a nonequilibrium to an equilibrium state, and the high-strength properties of the materials are determined mainly by the grain size and depend weakly on the grain-boundary structure.