Positron annihilation investigation for an estimation of the dislocation density and vacancy concentration of plastically deformed polycrystalline Ni of different purity

Dlubek, G.; Brümmer, O.; Hensel, Edward

doi:10.1002/pssa.2210340239

Cited by 80 publications

(22 citation statements)

References 22 publications

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“…An agreement between σ w and S/W confirms that residual stresses origin is an increase in defect density. Analogous rise of S parameter was observed for cold rolled nickel [14]. In this case the saturation of S value was explained as positron trapping in vacancies only.…”

Section: Resultssupporting

confidence: 71%

Positron Annihilation in Steel Burnished by Vibratory Shot Peening

Zaleski

2006

Acta Phys. Pol. A

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A series of C45 steel samples was burnished by shot peening with varying time of treatment. The samples were investigated by nondestructive positron annihilation techniques: angular correlations of two-quantum annihilation radiation and positron annihilation lifetime spectroscopy. To determine residual stresses present under burnished surface the same samples were studied by destructive Davidenkov method. Change of absolute value of the weighted average of residual stresses over positron range in the series of the samples is in good agreement with change of S/W ratio obtained by angular correlations of two-quantum annihilation radiation. Both parameters increase during first 10 minutes of shot peening and then stabilize. Positron annihilation lifetime spectra allowed to identify two types of structural defects: smaller ones like vacancies or dislocations and bigger -probably clusters of vacancies. Increase in shot peening time causes reduction of positron trapping rate and lifetime rise in bigger defects.

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Section: Resultssupporting

confidence: 71%

Positron Annihilation in Steel Burnished by Vibratory Shot Peening

Zaleski

2006

Acta Phys. Pol. A

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“…Then, the mean lifetime saturates at the value about 210 ps. This is characteristic feature, occurring for instance for Ni [14], Cu [15] and also other metals exposed to the compression. The saturation can be explained by so large defect concentration, usually about 10 3 , that after termalization all positrons are trapped at open volume defects where they annihilate.…”

Section: The Sample Exposed To Compression the Calibration Testmentioning

confidence: 89%

Formation of Subsurface Zone Induced by Sliding Wear in Zirconium Studied by Positron Lifetime Spectroscopy

Dryzek

Siemek

2016

Tribol Lett

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The zone below the surface in pure Zr exposed to dry sliding is the subject of studies using positron lifetime methods. New type of the defect depth profile is observed. The zone contains dislocations and vacancy clusters which occur only at a certain depth from the worn surface. The size of the vacancy clusters decreases with the depth increase. The total depth of the subsurface zone is about hundreds of micrometers and depends on the applied load. The estimated effective strain in the subsurface zone decreases exponentially with the depth increase. The similar kinds of defects and their depth profiles are observed also for the Zr samples exposed to sandblasting. This indicates the common origin of formation of the subsurface zone during dry sliding and sandblasting. Results of the theoretical calculations of the positron lifetime in vacancy clusters in Zr are also presented.

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“…where k f is the positron annihilation rate in the bulk (free) state; l v is the specific positron trapping rate into defects (for monovacancies in Ni l v = 2.2 Â 10 15 s À1 [19]); S f and S v are the S-parameters characteristic of the positron annihilation from the bulk (free) and monovacancy-trapped states, respectively. The value S f = 0.520 ± 0.001.…”

Section: Methodsmentioning

confidence: 99%