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14. Influence of Severe Plastic Deformation on Microstructure, Strength and Electrical Conductivity of Aged Al–0.4Zr(Wt.%) Alloy

Author

Orlova T.S., Mavlyutov A.M., Latynina T.A., Ubyivovk E.V., Murashkin M.Yu., Schneider R., Gerthsen D., and Valiev R.Z.

Subjects
Technology, Chemical technology, TP1-1185
Abstract

Microstructure evolution of an Al-0.4Zr(wt.%) alloy after isothermal aging (AG) and subsequent high pressure torsion (HPT) and its impact on strength and electrical conductivity has been investigated. Microstructure was characterized by X-ray diffraction, electron backscatter diffraction, transmission electron microscopy (TEM) and electron energy-dispersive X-ray spectroscopy in TEM. The initial Al-0.4Zr(wt.%) alloy obtained by combined casting and rolling presents solid solution of Zr in Al matrix. Aging at 375 °C for 60 h leads to formation of uniformly distributed metastable Al3Zr precipitates with the average diameter of 13 nm, resulting thereby in a decrease of strength sUTS from 128 to 95 MPa and in increase of conductivity from 50.7 to 58.8% IACS at ambient temperature. The subsequent HPT processing leads to grain refinement and partial dissolution of the Al3Zr precipitates that is accompanied by enrichment of solid solution by Zr atoms and by coarsening of the remaining Al3Zr precipitates. The combination of AG and HPT provides the strength and the conductivity at ambient temperature which do not decrease under annealing up to 230 °C. Moreover, additional strengthening accompanied by an increase in conductivity was found for AG-HPT samples after annealing at Tan=230 °C for 1 h, that provides the best combination of the strength of sUTS=142 MPa and the conductivity of 58.3% IACS. Contribution of different possible mechanisms into strength and charge scattering are analyzed on the basis of specific microstructural features. The analysis indicates a suppression of strengthening by the Orowan mechanism in AG and AG-HPT samples. In all the studied states, i.e. initial, after AG, and subsequent HPT, grain boundary strengthening is found to be the main strengthening mechanism.

Published
2018
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36. Low-temperature superplasticity in nanostructured nickel and metal alloys

Author

McFadden, S.X., Mishra, R.S., Valiev, R.Z., Zhilyaev, A.P., and Mukherjee, A.K.

Subjects
Superplasticity -- Research, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Research into low-temperature superplasticity in nanocrystalline nickel, a nanocrystalline aluminium alloy and nanocrystalline nickel aluminide indicates that mechanistic details of superplasticity in nanocrystalline materials differ very significantly from those in microcrystalline materials. The most important observation in this research was the large reduction in superplastic temperatures. With nickel, a very low normalized temperature was achieved. It appears that it is not possible to obtain superplasticity in pure metals with a grain size of 100 nm or less, as the fall in superplastic temperature is balanced out by a reduction in the grain-growth temperature.

Published
1999

44. Microstructural features of failure surfaces and low-temperature mechanical properties of Ti-6Al-4V ELI ultra-fine grained alloy

Author

Tabachnikova, E.D., Podolskiy, A.V., Smirnov, S.N., Csach, K., Miskuf, J., Saitova, L.R., Semenova, I.P, Valiev, R.Z., and Bengus, V.Z.

Subjects
Научно-технический раздел
Abstract

Microstructural regularities of failure surfaces and low-temperature mechanical characteristics in quasistatic uniaxial tension and compression have been studied for ultra-fine grained structural states of Ti-6Al-4V ELI alloy processed by equal channel angular pressing. Values of the yield stress and uniform strain at 300, 77, and 4.2 K have been compared for structural states of the Ti-6Al-4V ELI alloy that differ in the average grain size and the morphology of α and β phases. Statistical distributions of dimple sizes on the failure surfaces have been studied for different structural states and temperatures. Исследованы особенности микроструктуры поверхностей излома и низкотемпературные механические свойства сверхмелкозернистого ELI-сплава Ti-6Al-4V, обработанного методом равноканального углового прессования, при квазистатическом одноосном растяжении и сжатии. Проведено сравнение значений предела текучести и однородной деформации, полученных при температурах 300, 77 и 4,2 К для разных структурных состояний ELI-сплава ТІ-6А1-4У с различным средним размером зерна и морфологией α- и β-фаз. Исследовано статистическое распределение размеров ямок на поверхностях излома при различных структурных состояниях и температурах.

Published
2008

45. Superplastic behavior of ultrafine-grained Ti−6Al−4V ELI alloy produced by severe plastic deformation

Author

Semenova, I.P., Saitova, L.R., Raab, G.I., and Valiev, R.Z.

Abstract

This paper reports the results of investigation of mechanical behavior of the ultrafinegrained (UFG) Ti-6Al-4V alloy processed by equal-channel angular pressing (ECAP) and extrusion at temperatures in a range of 500−800°C. The UFG alloy reveals superplastic behavior at relatively low temperatures down to 600°C (elongation 240%). The features of microstructure change of the UFG alloy under superplastic straining conditions that contribute to additional strengthening of the alloy are shown.

Published
2006

46. The new trends in SPD processing to fabricate bulk nanostructured materials

Author

Valiev, R.Z.

Abstract

During the last decade severe plastic deformation (SPD) has become a widely known method of materials processing used for fabrication of ultrafine-grained materials with attractive properties. Nowadays SPD processing is rapidly developing and is on the verge of a transition from lab-scale research to commercial production. This paper focuses on several new trends in the development of SPD techniques for effective grain refinement, including those for commercial alloys, and presents new SPD processing routes to produce bulk nanocrystalline materials.

Published
2006

47. Backpressure at ECAP as a way for decreasing grain size and increasing ductility of UFG materials

Author

Raab., G.I, Krasilnikov, N.A., and Valiev, R.Z.

Abstract

The investigation of the backpressure effect during equal-channel angular pressing (ECAP) on formation of ultrafine-grained (UFG) structure in pure copper has revealed that the increased hydrostatic pressure can contribute to formation of a more homogeneous microstructure with finer grains. ECAP with backpressure also exerts a favorable effect on strength and ductility characteristics of the UFG material.

Published
2003

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