Abstract
The paper studies the decomposition of a supersaturated solid solution with a precipitate of particles of the copper-zirconium phase in the Cu-0.06 wt.% Zr and Cu-0.21 wt.% Cr-0.20 wt.% Zr alloys in two initial states, i. e. after solid-solution quenching and after high strain rate deformation (105 s−1) by the method of dynamic channel-angular pressing (DCAP). It has been shown that the decomposition of the supersaturated solid-solution of zirconium in copper in the quenched micro-alloyed Cu-Zr and low-alloyed Cu-Cr-Zr alloys occurs in two stages. At the first stage, nanoparticles of a metastable copper-zirconium phase are formed. The crystal structure of the nanoparticles is close to the structure of the copper matrix. At the second stage, particles of the equilibrium Cu5Zr phase are formed in the form of rods. Annealing (aging) of the alloys deformed by DCAP is characterized by the predominance of heterogeneous precipitation of Cu5Zr nanoparticles at sub-grain boundaries and dislocations, and the decomposition begins at a lower temperature. The particle size is less by an order of magnitude than that in the quenched state. The precipitation of nanoparticles at dislocations retards the formation of recrystallization centers. It has been shown that the treatment including DCAP and annealing at 450°C for 1 h substantially increases microhardness of the micro-alloyed Cu-0.06 %Zr alloy by a factor of 2.7 as compared to the initial quenched state. This behavior is related to substantial structure refinement during DCAP and decomposition of the supersaturated α-solid solution of copper.
Highlights
Copper alloys with small additions of chromium and zirconium belong to the group of precipitation-hardenable micro- and low-alloyed alloys, characterized by a good combination of strength and electrical conductivity [1,2,3,4,5]
We used a new method of severe plastic deformation (SPD), namely, the dynamic channel-angular pressing (DCAP) [10 –12], which is a high-strain-rate variant of equal-channel angular pressing (ECAP)
It is important to emphasize that, in the case of DCAP, the simple shear deformation, which produces the structure upon ECAP, is a high-strain-rate process; upon DCAP, a high-speed shock-wave compressive strain takes place, which creates an additional source of deformationinduced work hardening
Summary
Copper alloys with small additions of chromium and zirconium belong to the group of precipitation-hardenable micro- and low-alloyed alloys, characterized by a good combination of strength and electrical conductivity [1,2,3,4,5]. To obtain a submicrocrystalline (SMC) structure in copper alloys, methods of severe plastic deformation (SPD), such as high-pressure torsion, equal-channel angular pressing (ECAP), multidirectional forging have been used [5 – 9] In this investigation, we used a new method of SPD, namely, the dynamic channel-angular pressing (DCAP) [10 –12], which is a high-strain-rate (with strain rates of 104 – 105 s−1) variant of ECAP. It was established that the strengthening phase in Cu-Zr alloys is the intermetallide phase Cu5Zr, which participates in the eutectic reaction with an α-solid solution copper-based at 967°C [1, 4,15]
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