New insights on the formation of supersaturated solid solutions in the Cu–Cr system deformed by high-pressure torsion

Abstract

In the Cu-Cr system, the formation of supersaturated solid solutions can be obtained by severe plastic deformation. Energy-dispersive synchrotron diffraction measurements on as-deformed Cu-Cr samples as a function of the applied strain during deformation confirm the formation of supersaturated solid solutions in this usually immiscible system. Due to evaluation of the diffraction data by a newly developed energydispersive RIETVELD-program, lattice parameter and microstructural parameters like domain size and microstrain are determined for as-deformed as well as annealed samples. The obtained information is used to deepen the understanding of the microstructural evolution and the formation of supersaturated solid solutions during severe plastic deformation. Complimentary transmission electron microscopy investigations are furthermore performed to characterize the evolving microstructure in detail. After annealing at elevated temperatures, the formed solid solutions decompose. Compared to the as-deformed state, an enhanced hardness combined with a high thermal stability is observed. Possible mechanisms for the enhanced hardness are discussed. Published inActa Mater Volume 69 (2014), Pages 301-313 http://dx.

Deformation‐Induced Supersaturation in Immiscible Material Systems during High‐Pressure Torsion

“…Another mechanism, which takes the large amount of applied strain into account, is a fracture and rebonding process. [59] In Cu-W and Cu-Cr, it appeared that the harder particles fracture repeatedly, and the softer phase fills the gap in between the broken particles. This Cu in between is deformed under high pressure, and could eventually dissolve in the other phase.…”

“…With ongoing deformation, these dislocations arrange to new grain A. Bachmaier studied materials science and is currently doing her Post-doc at the Erich Schmid Institute, Austria. Grain size in saturation [nm] Cu-Ag (fcc-fcc) [53,54] Cu-6/9Ag %355 %30-50 nm Cu-16/22Ag %380 %20-40 nm Cu-37/46Ag %340 %10 nm Cu-26/25Co %280 %100 nm Cu-Co (fcc-hcp) [55][56][57][58] Cu-54/50Co %400 <50 nm Cu-76/75Co %450 <50 nm Cu-17/17Fe %330 <50 nm Cu-Fe (fcc-bcc) [49] Cu-53/53Fe %440 <50 nm Cu-73/73Fe %445 <50 nm Cu-87/87Fe %640 <50 nm Cu-Cr (fcc-bcc) [32,59] Cu-47/47Cr %450 %10-20 nm Ni-6/9Ag %700 %30-50 nm Ni-Ag (fcc-fcc) [60] Ni-19/26Ag %600 %10-20 nm Ni-35/46Ag [61][62][63] Cu-51/58W %550 %5-15 nm boundaries, which subdivide the initial grains and finally transform the material into an UFG structure.…”

Phase separation of a supersaturated nanocrystalline Cu–Co alloy and its influence on thermal stability

“…For example, severe plastic deformation (SPD) by high-pressure torsion (HPT) deformation has been used to produce bulk, nanocrystalline (nc) solid solutions in a variety of binary Cu-based alloy systems with a positive heat of mixing (for instance: Cu-Fe, Cu-Cr, Cu-Co, Cu-W [4][5][6][7][8][9][10][11][12][13]) by extending the solid solubility level during deformation. As expected, these metastable solid solutions are not in the equilibrium state after HPT processing and during subsequent annealing treatments, decomposition of the metastable solid solutions is reported [4,9,10,12]. Tailoring material properties for potential technological applications requires an understanding of the thermal stability, the structural changes (phase decomposition, nucleation and growth) during annealing after HPT processing and the atomic-scale processes underlying elemental decomposition.…”

Liquid Phase Separation and the Aging Effect on Mechanical and Electrical Properties of Laser Rapidly Solidified Cu100−xCrx Alloys

“…Great research interest has been devoted to Cu-Cr alloys in the past few decades as the alloys are the most commonly used contact materials in medium-voltage and high-current vacuum interrupters [1][2][3]. It has been well known that a liquid miscibility gap exists in the Cu-Cr binary phase diagram, due to a large positive mixing heat between Cu and Cr in the liquid state.…”

“…It has been well known that a liquid miscibility gap exists in the Cu-Cr binary phase diagram, due to a large positive mixing heat between Cu and Cr in the liquid state. Once the Cu-Cr melt achieves a sufficient undercooling and cools into the liquid miscibility gap, the Cr-rich strengthening phase will nucleate through the liquid phase separation (LPS) process and form particulates to disperse in the Cu-rich matrix [1][2][3]. Numerous explorations, mostly by the containerless solidification, have been made to investigate the undercooling effect in Cu-Cr alloys and it has been proved that the properties of Cu-Cr alloys are strongly dependent on their solidification behavior, compositions, aging effects, and also the morphology of the Cr phase [3][4][5].…”