Ultra Fine-Grained Metals Prepared by Severe Plastic Deformation: A Positron Annihilation Study

Čı́žek, Jakub; Procházka, I.; Kužel, R.; Matěj, Zdeněk; Cherkaska, V.; Cieslar, Miroslav; Smola, Bohumil; Stulı́ková, Ivana; Bräuer, G.; Anwand, W.; Исламгалиев, Р. К.; Kulyasova, Olya B.

doi:10.12693/aphyspola.107.745

Cited by 19 publications

(5 citation statements)

References 13 publications

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“…2328) For instance, after 1/4 turn of HPT in an interstitial-free steel the vacancy clusters comprise of 9 vacancies which value was enhanced to 14 when the number of turns increased to five. 24) Similar result was obtained for pure Fe and W. 25,27) In 316L steel, the vacancy concentration increased to about 5 © 10 ¹4 after 10 turns of HPT. 26) In Ti6Al7Nb alloy processed by 1/4 turn of HPT, the average number of vacancies in the clusters was four and the vacancy concentration was estimated as 3 © 10 ¹5 .…”

Section: Vacanciessupporting

confidence: 70%

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Lattice Defects and Their Influence on the Mechanical Properties of Bulk Materials Processed by Severe Plastic Deformation

Gubicza

2019

Mater. Trans.

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Processing of metallic materials by Severe Plastic Deformation (SPD) leads to the formation of many lattice defects (e.g., vacancies, dislocations, twin faults and grain boundaries). In this paper, the characteristic features of the defect structure in SPD-processed bulk metallic materials are overviewed. The influence of the material properties, such as the melting point, stacking fault energy and solute content, as well as the SPD-processing conditions (e.g., SPD route and applied hydrostatic pressure) on the type and densities of defects is discussed in detail. In addition, the effect of lattice defects on the mechanical strength of SPD-processed materials is oveviewed.

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Section: Vacanciessupporting

confidence: 70%

“…Figure 8 illustrates the combined effect of SFE and grain size for UFG fcc metals and alloys processed by ECAP and HPT at RT. 11,25,41,45,46,58) The dashed and solid arrows indicate that twin fault probability increases with decreasing SFE and grain size, respectively. The points in Fig.…”

Section: Twin Faultsmentioning

confidence: 99%

Lattice Defects and Their Influence on the Mechanical Properties of Bulk Materials Processed by Severe Plastic Deformation

Gubicza

2019

Mater. Trans.

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“…The vacancy-Gd pairs are stable at room temperature. Indeed, an enhanced amount of Gd in the vicinity of vacancies was proved by coincidence Doppler broadening measurements [9]. A typical TEM image of HPT-deformed Mg10Gd alloy is shown in Fig.…”

Section: Resultsmentioning

confidence: 84%

“…A possible explanation of this surprising effect is that contrary to pure Mg, the Mg10Gd alloy contains predominantly partial dislocations, which exhibit reduced specific positron trapping rate, i.e. their capability of positron trapping is lower compared to dislocations in Mg [9]. alloy, the metastable phases do not precipitate in HPT-deformed Mg10Gd.…”

Section: Resultsmentioning

confidence: 99%

Microstructure and Thermal Stability of Ultra Fine Grained Mg-Based Alloys Prepared by High Pressure Torsion

Čı́žek

Procházka

Smola

et al. 2006

MSF

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In the present work we studied microstructure of ultra fine grained (UFG) pure Mg and UFG Mg-based alloys. The initial coarse grained samples were deformed by high pressure torsion (HPT) using pressure of 6 GPa. Such deformation leads to formation of UFG structure in the samples. The severe plastic deformation results in creation of high number of lattice defects. Therefore, we used positron annihilation spectroscopy (PAS) for defect characterizations. PAS represents a well developed non-destructive technique with high sensitivity to open volume defects like vacancies, vacancy clusters, dislocations etc. In the present work we combined PAS with TEM and XRD to obtain complete information about microstructure of the UFG samples studied. We have found that microstructure of HPT-deformed Mg contains two kinds of regions: (a) ”deformed” regions with UFG structure (grain size 100-200 nm) and high number of randomly distributed dislocations, and (b) ”recrystallized” regions with low dislocation density and grain size of few microns. It indicates some kind of dynamic recovery of microstructure already during HPT processing. On the other hand, homogenous UFG structure with grain size around 100 nm and high density of homogeneously distributed dislocations was formed in HPT-deformed Mg-9.33 wt.%Gd alloy. After characterization of the as-deformed microstructure the samples were subsequently isochronally annealed and the development of microstructure with increasing temperature and recovery of defects were investigated.

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“…Defects were identified and their concentrations and spatial distributions were investigated. Vacancies situated in distorted regions along grain boundaries and small vacancy clusters distributed homogeneously inside dislocation-free grain interiors were observed [6][7][8][9][10]. Divinski et al also conducted PALS on UFG Cu-1 wt.% Pb alloy, which revealed the existence of vacancy-type defects, presumably related to grain boundary states, and vacancy clusters in this material [11].…”

Section: Introductionmentioning

confidence: 99%

Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures

Lü

et al. 2012

Acta Materialia

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. (2012).Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures.Acta Materialia, 60 (10), 4218-4228. Abstract Commercial-purity aluminum was processed by equal-channel angular pressing (ECAP) at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) with liquid nitrogen cooling between two successive passes. It was found that the RT-ECAPed samples showed equiaxed microstructure after 4 and 8 ECAP passes, while the CT-ECAPed samples displayed slightly elongated microstructure and slightly smaller grain size. Moreover, the CT-ECAPed samples had higher hardness values than the RT-ECAPed samples subjected to the same amount of deformation. Positron annihilation lifetime spectroscopy (PALS) was used to investigate the evolution of vacancytype defects during the ECAP deformation process. The results showed that three types of defects existed in the ECAPed samples: vacancies associated with dislocations, bulk monovacancies and bulk divacancies. The CT-ECAPed samples had a higher fraction of monovacancies and divacancies. These two types of defects are the major vacancy-type defects that can work as dislocation pinning centers and induce hardening, resulting in higher hardness values in the CT-ECAPed samples. A quantitative relationship between material hardness and the defect concentration and defect diffusion coefficient has been established. Authors

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Ultra Fine-Grained Metals Prepared by Severe Plastic Deformation: A Positron Annihilation Study

Cited by 19 publications

References 13 publications

Lattice Defects and Their Influence on the Mechanical Properties of Bulk Materials Processed by Severe Plastic Deformation

Lattice Defects and Their Influence on the Mechanical Properties of Bulk Materials Processed by Severe Plastic Deformation

Microstructure and Thermal Stability of Ultra Fine Grained Mg-Based Alloys Prepared by High Pressure Torsion

Study of vacancy-type defects by positron annihilation in ultrafine-grained aluminum severely deformed at room and cryogenic temperatures

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