V. I. Kopylov

Structure and properties of ultra-fine grain Cu–Cr–Zr alloy produced by equal-channel angular pressing

Abstract The structure, thermal stability and properties are investigated of a Cu–Cr–Zr alloy with ultra fine grains (UFG) of 160 nm diameter produced by severe plastic deformation through equal-channel angular pressing (ECAP). Special attention is paid to optimization of multi-functional thermal, electrical and mechanical properties of this alloy by aging after ECAP. Fatigue life and cyclic response under strain-controlled experiments are investigated aiming at clarification of mechanisms of plastic deformation and fracture in the precipitation hardened ECAP materials. It is shown that the precipitation strengthened UFG structure remains stable both under elevated temperatures as high as 500°C and under cyclic loading at room temperature. Substantial improvement of fatigue life is evidenced in comparison with conventional coarse-grain materials. The appearance of cyclic softening is noticed and its nature is discussed in terms of dislocation–particle interaction and possible dissolution of precipitates during fatigue.

Enhanced strength and fatigue life of ultra-fine grain Fe–36Ni Invar alloy

Abstract The mechanical behavior and fatigue life of ultra-fine grain (UFG) Fe–36%Ni Invar alloy fabricated by severe plastic deformation (SPD) is investigated in both high-cyclic and low-cyclic regimes. A significant enhancement of mechanical properties has been achieved via equal-channel angular pressing (ECAP); the yield stress and the fatigue limit are increased by a factor of three and two, respectively, when compared with those of ordinary Invar alloy with conventional grain size. The fatigue characteristics are determined and tabulated in terms of cyclic stress–strain curves (CSSC), endurance limit, Coffin–Manson and Basquin parameters. It has been shown that the notable improvement of both low-cyclic and high cyclic properties is possible after SPD depending on the processing route.

Fatigue life of fine-grain Al /Mg /Sc alloys produced by equal-channel angular pressing

The effect of severe plastic deformation through equal-channel angular pressing (ECAP) on the fatigue life of Al � /Mg � /Sc alloys with different concentration of magnesium is discussed. Both high-cyclic and low-cyclic fatigue properties have been assessed in terms of the fatigue strength, fatigue ductility, cyclic stress � /strain curves, etc. It is shown that the addition of Sc significantly increases the thermal stability of the fine-grain structure formed during ECAP. However, only modest improvement of tensile and cyclic mechanical properties have been achieved via ECAP of Al � /Mg � /Sc alloys in comparison to their ordinarily fabricated counterparts. The results of present investigation show that the grain refinement of precipitation hardenable Al-alloys through severe plastic deformation can not be effective for enhancement of their static or cyclic strength. It is argued that early shear banding play an important role in cyclic degradation of ECAP Al � /Mg � /Sc alloys. # 2002 Elsevier Science B.V. All rights reserved.

Softening of the elastic modulus in submicrocrystalline copper

Abstract Youngs modulus of copper polycrystals with an ultrafine-grained structure synthesized by two independent methods (compacting and heavy plastic deformation) has been measured within a temperature range from 20 to 200–300°C. It has been concluded that there is a component of the Youngs modulus softening which is peculiar to metals with nano- and submicrocrystalline structures, irrespective of the presence of porosity.

Thermal stability of submicrocrystalline copper and Cu: ZrO2 composite

Ultrafine-grained (UFG) polycrystals are very attractive subjects for both theoretical and experimental research due to their unusual physical and mechanical properties. In recent years much attention has been paid to UFG polycrystals produced by heavy plastic deformation techniques, which allow one to obtain poreless materials with a grain size of about 0.1--0.2 {micro}m. A large number of investigations have been done in copper. Heavily deformed (HD) copper with UFG structure exhibits a high value of the yield stress and microhardness, and a softening of elastic moduli. However, annealing at temperatures of about 150--200 C for 20--60 min considerably increases the grain size, reduces the yield stress and microhardness, and increases the elastic constants. In the present communication the effect of annealing on the yield stress and Young`s modulus in HD Cu and precipitate hardened Cu:ZrO{sub 2} composite with UFG structure is reported. Good thermostability of the yield stress for HD Cu:ZrO{sub 2} within a temperature range 20--500 C is demonstrated.

Developing high strain rate superplasticity in Al-Mg-Sc-Zr alloys using equal-channel angular pressing

Abstract The processing of metallic alloys through the procedure of equal-channel angular pressing (ECAP) provides an opportunity for achieving superplastic ductilities at very high strain rates. This paper reports experimental data from an investigation of a series of AlMgScZr alloys processed by ECAP. The results show the occurrence of high tensile ductilities at testing strain rates above 10 −2 s −1 .

Fracture and Fatigue Resistance of Ultrafine Grain CuCrZr Alloy Produced ECAP

Anisotropy of mechanical properties, fatigue and fracture resistance of precipitation hardened CuCrZr alloy ultrafine (UFG) grained by equal-channel angular pressing (ECAP) is in focus of the present communication. Fracture toughness was estimated in terms of J-integral and the fatigue crack growth rate was quantified. It was found that although the estimated JIC-value appeared lower than that reported in the literature for a reference alloy, the ductility, fracture and crack growth resistance remained satisfactory after ECAP while the tensile strength and fatigue limit improved considerably. The stable crack growth rate did not differ very much for ECAP and reference conventional CuCrZr and no remarkable anisotropy in the stable crack growth was noticed.

APPLICATION OF ECAP - TECHNOLOGY FOR PRODUCING NANO- AND MICROCRYSTALLINE MATERIALS

Conditions for producing nano- and microcrystalline structures (NMC) by ECAP technology are described. The concept of “clear ECAP” for describing uniform ECAP deformation is introduced. A model of grain refinement and temperature-strain rate conditions of effective refinement is described.

Resistance of alloy Zr – 2.5% Nb with ultrafine-grain structure to stress corrosion cracking

The effect of severe plastic deformation of commercial alloy Zr – 2.5% Nb by the method of equal-channel angular pressing on the mechanisms and kinetics of stress corrosion cracking in a 1% “iodine – methanol” medium is studied. Quantitative comparative data on corrosion resistance of the alloy with ultrafine-grain structure after equal-channel angular pressing and with coarse-grain structure after the traditional treatment are obtained.

Formation of High-Angle Grain Boundaries in Iron upon Cold Deformation by Equal-Channel Angular Pressing

At present, the possibility of the formation of high-angle grain boundaries upon severe cold deformation, in particular, equal-channel angular (ECA) pressing is reliably proved. The structure formation upon multi-cycle ECA pressing substantially depends on the route determining the shear plane in the sample upon repeated passes. The route is defined by the rotation of the sample around its axis upon the multi-cycle ECA pressing. There are four main routes: route A, in which the sample is deformed by many passes without any rotations; route Ba, in which the sample is rotated by ± 90°; route Bc, in which the sample is sequentially rotated in the same direction by 90°and route C, in which the sample is rotated by 180° about its axis before each subsequent pass. By the methods of SEM, TEM and EBSD analysis it was shown that the fraction of high-angle boundaries in a-Fe upon cold ECA pressing with an angle of 90° between the channels and N=4 depends on the deformation route and increases according to the route sequence: Ba-C-Bc.