Influence of the Chromium Content in Low-Alloyed Cu–Cr Alloys on the Structural Changes, Phase Transformations and Properties in Equal-Channel Angular Pressing

Abstract

The quantitative concentration of alloying elements in low-alloyed copper alloys is an important factor in forming electrical and mechanical characteristics. It is known that severe plastic deformation is accompanied by both a substantial refinement of the structure and changes in the kinetics of phase transformations during the deformation and the post-deformation thermal treatment. This paper presents the results of a comparative analysis of the Cu–0.2Cr and Cu–1.1Cr alloys subjected to equal-channel angular pressing at room temperature. The analysis was performed for the grain structure, solid solution, and second-phase particles using transmission electron microscopy, scanning electron microscopy, X-ray crystal analysis, and the small-angle diffraction method. It was found that the level of structure refinement and mechanical characteristics after equal-channel angular pressing was almost the same for both studied alloys. Post-deformation aging of the Cu–0.2Cr alloy leads to the development of polygonization and re-crystallization within it. The aging of the Cu–1.1Cr alloy shows a better thermal stability than that of the Cu–0.2Cr alloy. In the Cu–1.1Cr alloy, after aging, in comparison with Cu–0.2Cr, a denser-packed ensemble of fine particles with an average size of 54 ± 2 nm is formed. In this case, the average size of fragments is 270 ± 15 nm and the ultimate tensile strength reaches 485 MPa.

Parallel Tubular Channel Angular Pressing (PTCAP) Processing of the Cu-20.7Zn-2Al Tube

“…The difference between the maximum and minimum hardness values across the different samples did not increase above 5 HV in all cases, proving the homogenized distribution of the hardness through the tube thickness. Therefore, the PTCAP process produced homogenous tubes with a higher degree of homogeneity than the TCAP and ECAPed specimens, which suffer from the formation of a corner gap, as noted in various materials [22,60,61].…”

Electrical Conductivity of Ultrafine-Grained Cu and Al Alloys: Attaining the Best Compromise with Mechanical Properties

“…The microstructure examination revealed nanosized banded grains (200300 nm) with Cr-rich particles uniformly precipitated at grain boundaries and within grains. The tensile strength and electrical conductivity reached 587 MPa and 69% IACS after aging at 698.15 K for 1 h. Aksenov et al 57) also studied the CuCr alloy with 0.2 and 1.1 mass% Cr by ECAP and then aged at 723.15 K. Cu 1.1%Cr experimented higher thermal stability than Cu 0.2%Cr, mainly attributed to banded grains with slightly finer nano-sized widths and higher degree of fragmentation of second phase particles. Cu1.1%Cr microstructure also exhibited more non-equilibrium boundaries between bands, mostly dislocation cell walls and a higher fraction of second phase particles, which provided a UTS of 485 MPa and maximum electrical conductivity of 76% IACS.…”

“…SPD technologies change the kinetics of phase transformations and precipitation in both binary and ternary systems, such as CuCr, CuZr and CuCrZr alloys, inducing nucleation of precipitates at lower temperatures than expected from their CG counterparts. 57) In addition, Zr additions improve thermal stability, reduce the diffusion activity of Cr in the alloy and contribute to the formation of smaller particles. 57) Vinogradov et al 40,65) showed by detailed DSC studies in a Cu0.44Cr0.21Zr alloy, that the precipitation of Cr at 713.15 K and Cu 3 Zr at 793.15 K became affected by ECAP processing, reversing the sequence of precipitation.…”

“…57) In addition, Zr additions improve thermal stability, reduce the diffusion activity of Cr in the alloy and contribute to the formation of smaller particles. 57) Vinogradov et al 40,65) showed by detailed DSC studies in a Cu0.44Cr0.21Zr alloy, that the precipitation of Cr at 713.15 K and Cu 3 Zr at 793.15 K became affected by ECAP processing, reversing the sequence of precipitation. The Cu 3 Zr nucleated at 643.15 K and Cr at 698.15 K. In both cases, the temperatures were lower than in the non-deformed state, suggesting that the presence of high density of dislocations could promote the atomic mobility for nucleation of precipitates.…”