Investigation of Cu5Zr particles precipitation in Cu-Zr and Cu-Cr-Zr alloys subjected to quenching and high strain rate deformation

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 (10 5 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 Cu 5 Zr 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 Cu 5 Zr 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.

Realizing ultrafine grain structure of Cu-Cr-Zr alloy via friction stir welding / processing

“…3 a demonstrate massive particles distributed in the base material. The dark rounded particles 1-5 µm in size are pure chromium precipitates with bcc lattice [17,18], while light rod-shaped particles up to 1 µm in size are Cu 5 Zr with a complex face-centered cubic lattice of the Be 5 Au type [19,20]. On the other hand, high magnified TEM (Fig.…”