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1

Defects in Some Hydrogenated Metallic Materials Studied by Positrons

100%

Mikhalenkov V.

Acta Physica Polonica A

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2001

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vol. 99

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issue 3-4

415-422

EN

The measurements of angular correlation of annihilation radiation and positron lifetime were performed to study defects in commercial stainless steel and nickel subjected to deformation and electron irradiation. It follows from variation of S-parameter derived from angular correlation of annihilation radiation spectra that hydrogen charging of Fe-Cr-Ni-Mn austenite steel results in appearance of modest amount of vacancies which agglomerate into small clusters during annealing at low temperatures. Electron irradiation produces much more defects, so that subsequent hydrogenation does not add much to their concentration. The major part of defects anneals out gradually to 700 K. The residual part is preserved up to 950 K. This fact testifies to bonding state of vacancies. Nickel of 3N purity was prepared in three initial states, i.e. cold-rolled and hydrogenated before and after deformation. In an initial state all samples contain, along with simple defects, vacancy clusters. Their size and concentration are much larger in hydrogenated samples, as compared with merely cold-rolled one. Annealing above 400 K causes growth of cluster size and decrease in their concentration. At 500 K clusters are observed to disappear in cold-rolled sample, while in the sample hydrogenated after deformation they survive to 600 K.

2

Defects in Decomposing Copper Alloys Studied by Positrons

51%

Mikhalenkov V., de Lima A., Lopes Gil C.

Acta Physica Polonica A

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1999

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vol. 95

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issue 4

615-622

EN

The evolution of defect structure during isochronal annealing of water-quenched Cu-4.83 at.% In and Cu-4.94 at.% Sn alloys was studied by measuring positron lifetime and Doppler broadening of annihilation line. The behaviour of annihilation parameters in both alloys is found to be analogous. In as-quenched alloys one component of about 180 ps is detected in the lifetime spectra. It remains intact up to the annealing temperature of 450 K and is attributed to positron annihilation at quenched-in vacancies associated with alloying atoms. When going above this temperature, the short component appears in the lifetime spectra, while intensity of the long component starts to drop giving evidence to the reduction of defect concentration. This process is observed to develop up to 550 K; thereafter all annihilation parameters level off. After crossing the phase separation temperature they begin to vary again since the defect structure comes into dependence on cooling conditions. The obtained results are discussed in terms of defect structure evolution in the course of precipitate formation.

3

Positron Annihilation in γ-Irradiated Amorphous Iron Alloys

51%

Mikhalenkov V., Chernyashevskii A., Shalaev A.

Acta Physica Polonica A

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1993

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vol. 83

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issue 3

359-363

EN

One-dimensional angular correlation of annihilation radiation was measured in a series of amorphous (Fe_{100-x}Cr_{x})_{85}B_{15} alloys (x = 0-32) exposed to γ-irradiation from intensive ^{60}Co source. The relevant shape parameters were compared with those in non-irradiated alloys. Irradiation-induced changes of those parameters were found to depend on Cr contents x. The opposite signs of these changes were observed in x < 4 and x > 4 ranges, while near x = 4 the parameters stayed unchanged. We try to interpret the results assuming that γ-quanta are able to knock out boron atoms from their positions into large cavities, thus preventing positron trapping. The crystalline embryos model of amorphous alloys suggested by Hamada and Fujita is also used for explanation of the observed effects.

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3 Acta Physica Polonica A

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3 Mikhalenkov V.

1 Chernyashevskii A.

1 Lopes Gil C.

1 Shalaev A.

1 de Lima A.

Defects in Some Hydrogenated Metallic Materials Studied by Positrons

Defects in Decomposing Copper Alloys Studied by Positrons

Positron Annihilation in γ-Irradiated Amorphous Iron Alloys