Positron trapping at grain boundaries

Dupasquier, A.; Romero, Ricardo; Somoza, A.

doi:10.1103/physrevb.48.9235

Cited by 70 publications

(75 citation statements)

References 29 publications

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“…The sample may exhibit inhomogeneity, like point defects, grains and grain boundaries or small precipitations across the diffusion length which is about 0.1 µm [5,14]. Let us consider first small, homogeneous spherical particles of radius R being immersed in the uniform and homogeneous region, Fig.…”

Section: Inhomogeneity Across the Diffusion Lengthmentioning

confidence: 99%

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Positron annihilation studies of recrystallization in the subsurface zone induced by friction in magnesium—effect of the inhomogeneity on measured positron annihilation characteristics

Dryzek

2013

Appl. Phys. A

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The discussion of the positron annihilation studies of crystal structure defects, like vacancies, dislocations, grain boundaries and the defect depth profile, is presented. The role of the positron implantation depth and positron diffusion in such studies has been considered in detail. For description of the measured annihilation characteristics the proposed theoretical models take into account both effects. The annealing studies of defects created in pure magnesium by compression or dry sliding-wear were used for demonstration of the discussed thesis. The positron lifetime measurements were applied for monitoring open volume defects behavior. It was demonstrated that annealing at the temperature of about 300°C removes the defects created by compression. Application of the proposed model to description of the data obtained allows to determine the activation energy of the grain boundary mobility in pure magnesium equal to Q = 0.56 ± 0.18 eV. However, defects created by the dry sliding are not completely annealed up to the temperature of 500°C. The defect depth profile induced by dry sliding evolves with the annealing temperature in such a way that at the worn surface concentration of defects gradually decreases but at the depth between 60 and 100 µm the generation of new defects takes place at temperature of 150 and 225°C. Above 300°C the defects still are extended up to the depth of about 80 µm.

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Section: Inhomogeneity Across the Diffusion Lengthmentioning

confidence: 99%

“…This problem was attacked theoretically and experimentally by many authors; some of them are listed in Refs. [4][5][6][7][8]. The size of the scanned volume depends on the positron diffusion length which is equal about 0.1 µm.…”

Section: Introductionmentioning

confidence: 99%

Positron annihilation studies of recrystallization in the subsurface zone induced by friction in magnesium—effect of the inhomogeneity on measured positron annihilation characteristics

Dryzek

2013

Appl. Phys. A

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“…Hence, positrons trapped at dislocations are finally annihilated at vacancy-like defects. It is known [7] that positrons trapped at GBs exhibit lifetime comparable to a vacancy. Thus, in all Pd samples studied positrons are confined in similar kind of defects characterized by open volume comparable to a monovacancy.…”

Section: Resultsmentioning

confidence: 99%

Structural studies of thin Pd films loaded with hydrogen

Melikhova

Čı́žek

Vlček

et al. 2014

J. Phys.: Conf. Ser.

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Abstract. In this work variable energy positron annihilation spectroscopy was employed for investigation of defects created in Pd films electrochemically charged with hydrogen. The development of hydrogen-induced defects in nanocrystalline, polycrystalline and epitaxial Pd films were compared. It was found that absorbed hydrogen causes plastic deformation and increases defect density in all Pd films studied. Moreover, buckling was observed in nanocrystalline and polycrystalline films loaded above certain critical hydrogen concentration.

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“…This model assumes that the material is formed by identical spherical domains of radius R and that open-volume defects only concentrate in a distorted region (DR) of constant thickness (d) at the surfaces of the domains. This model was used for the analysis of positron lifetime spectra of a fine-grained Al-Ca-Zn alloy [33]. However, the assumption of defect-free grain interiors (non-distorted region (NR)) is inconsistent with observations in UFG materials [9,34].…”

Section: Discussionmentioning

confidence: 99%

“…This indicates that the STM cannot be directly applied to these samples. Dupasquier et al [33] have developed a diffusion trapping model (DTM), which considers the positron diffusion from grain interiors to grain boundaries. This model assumes that the material is formed by identical spherical domains of radius R and that open-volume defects only concentrate in a distorted region (DR) of constant thickness (d) at the surfaces of the domains.…”

Section: Discussionmentioning

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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Positron trapping at grain boundaries

Cited by 70 publications

References 29 publications

Positron annihilation studies of recrystallization in the subsurface zone induced by friction in magnesium—effect of the inhomogeneity on measured positron annihilation characteristics

Positron annihilation studies of recrystallization in the subsurface zone induced by friction in magnesium—effect of the inhomogeneity on measured positron annihilation characteristics

Structural studies of thin Pd films loaded with hydrogen

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

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