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Experimental studies on Zr–1%Nb alloy properties in technological conditions of cold pilger tube rolling process

Dyja H., Kawałek A., Ozhmegov K.

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 1

268--273

EN

The paper presents the results of research on the rheological properties of the Zr–1%Nb alloy, obtained for the strain parameters corresponding to the cold rolling tube process in a pilger mill. The studies were carried out under conditions of continuous, discontinuous and variable load in the GLEEBLE 3800 metallurgical processes simulator, according to the program developed on the basis of conditions occurring in the actual technological process. The influence of the strain, strain rate, plastic deformation thermal effect and the Bauschinger effect on changes in the flow stress was determined. Recommendations for division of the alloy strain distribution over the length of the deformation zone in the pilger roll grooves is presented.

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Oxidation and hydrogen behaviur in Zr-2Mn alloy

Zienkiewicz N., Paradowska J., Serbiński W., Gajowiec G., Hernik A., Zieliński A.

Advances in Materials Science

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2018

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Vol. 18, nr 2(56)

37--48

EN

The purpose of the present research was to determine the oxidation and hydrogenation behavior in the new Zr-2Mn alloy. The oxidation of alloy was performed at temperatures between 350°C and 900°C for 30 minutes. The hydrogen charging was made for 72 h at a current density 80 mA/cm2. The charged samples were heat treated at 400°C for 4 h to obtain a uniform hydrogen profile content across the sample. The oxidation resulted in an appearance of non-uniform oxide layers of thickness increasing with temperature. The surface damage was observed at higher temperatures 700 and 900°C. After charging with hydrogen followed by annealing no hydrides were found. The observed effect is evidence that the oxide layers may form effective barriers against hydrogen diffusion even if they are partially degraded. The absence of hydrides or hydride cracking may be caused by an absence in Zr-Mn alloys of such phase precipitates, which may trap diffusive hydrogen and initiate the hydrides. The positive influence of manganese on the formation of the thick oxide layer and relative resistance to delayed hydride cracking may be attributed to its affinity of oxygen, the ability to form thick and compact oxide layers during oxidation, the formation of solid solution in zirconium and no precipitates enhancing nucleation of hydrides.

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Hydrogen degradation of pre-oxidized zirconium alloys

Szoka A., Gajowiec G., Zieliński A., Serbiński W., Olive J. M., Ossowska A.

Advances in Materials Science

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2017

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Vol. 17, nr 1(51)

5--21

EN

The presence of the oxide layers on Zr alloys may retard or enhance the hydrogen entry and material degradation, depending on the layer features. This research has been aimed to determine the effects of pre-oxidation of the Zircaloy-2 alloy at a different temperature on hydrogen degradation. The specimens were oxidised in laboratory air at 350°C, 700°C, and 900°C. After, some samples were tensed at 10-5 strain rate and simultaneously charged with hydrogen under constant direct voltage in 1 N sulfuric acid at room temperature. Other specimens were charged without any tension, then annealed at 400°C for 4 h and finally tensed at above strain rate. The SEM examinations were performed on the cross-sections and fracture faces of specimens. The obtained results demonstrate the effects of the oxide layer on the cathodic current and hydrogen entry, mechanical properties and the appearance of hydrides and fracture behaviour.

4

Modification of zirconium alloy surface using high intensity pulsed plasma beams

Sartowska B., Starosta W., Barlak M., Walis L.

Archives of Materials Science and Engineering

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2016

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Vol. 77, nr 2

53--57

EN

Purpose: The aim of the research was to identify possibility of extending the life time of zirconium claddings. Materials used in nuclear reactors work in extremely hard conditions: irradiation, corrosion, stress. Zirconium alloys, due to their good water corrosion and radiation resistance at normal working conditions of nuclear reactors are used as cladding material for fuel elements. In the case of loss-of-coolant accident (LOCA), the extremely fast oxidation of zirconium at steam or air/steam mixture at temperatures above 800°C results in intense hydrogen generation and possible hydrogen-oxide mixture explosion. The development of the solution to minimize the risk of the accidents mentioned above is urgently needed. The concept of Accident Tolerant Materials (ATM) has been developed recently. Design/methodology/approach: Zirconium surface were treated with 30 high intensity pulsed plasma beams (HIPPB) Cr+Ar, Y+Ar or Al+Ar, with energy density of 4.0 J/cm2. Oxidation tests: autoclave (water, 360°C, 19.50 MPa) for 7 and 40 days and oven (700°C and 800°C/1000 s/air) followed by cooling in water were performed. Samples were characterised with: SEMs, EDS and GXRD. Findings: Zirconium samples with modified surface layer showed the higher resistance for oxidation in simulated conditions of normal work of PWR reactor and in elevated temperatures. Originality/value: Carried out work was connected with new concept of development accident tolerant materials - ATM.