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1

Effect of 2% at. of alloying elements: Si, V, Nb, Mo, Ti, Zr or Cu on the corrosion behavior of sintered Nd-Fe-B under conditions of prolonged atmospheric exposure

Bala H., Szymura S., Dymek M., Rabinovich Y. M., Kucharska B.

Ochrona przed Korozją

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2014

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nr 4

111--115

EN

The Nd-Fe-B type sinters were exposed to long-term (10 years) atmospheric corrosion which brought about their partial pulverization. The destruction process is markedly inhibited by partial (2 at.%) substitution of Si for Fe but it is strongly accelerated by Ti, Zr or Cu substitutions. A galvanic nature of the sinter damage is postulated. Due to contact with humidity the sinters absorb reversibly hydrogen and there is evident correlation between hydrogen uptake ability and pulverization susceptibility of the Nd-Fe-B based sinters.

PL

Długotrwała (10-letnia) ekspozycja atmosferyczna spiekanych materiałów na bazie Nd-Fe-B prowadzi do częściowej pulweryzacji spieków. Podstawienie żelaza niewielką (2% at.) ilością Si wyraźnie hamuje zaś podstawienie za pomocą Ti, Zr lub Cu – znacznie przyśpiesza degradację. Powstałe zniszczenia korozyjne sugerują ich galwaniczny charakter. W wyniku oddziaływania z wilgocią spieki na bazie Nd-Fe-B odwracalnie pochłaniają wodór, przy czym widoczna jest korelacja pomiędzy zdolnością do absorpcji wodoru a podatnością spieków na pulweryzację.

2

Behaviour of nitrided layers subjected to influence of hydrogen

Ćwiek J., Baczyńska M.

Archives of Materials Science and Engineering

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2010

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Vol. 43, nr 1

30-41

EN

Purpose: of this paper is evaluation of behaviour of plasma nitrided layers subjected to influence of internal and external hydrogen. Properties of nitrided layers like: hydrogen permeation and trapping, fracture mode, and plasticity were examined. Design/methodology/approach: Structural low-alloy steel was nitrided at glow discharge in the gas mixture of various N2, H2, and Ar content. Samples with nitrided layers were subjected to cathodic hydrogen charging in acid solution simulating the aged engine oil hydrogenating environment. The effect of the nitrided layers on the hydrogen transport and on the irreversible trapping was evaluated by the measurements of the hydrogen permeation rate and by the vacuum extraction, respectively. Surfaces with modified layers were examined with the use of a scanning electron microscope (SEM) before and after hydrogen permeation tests. Slow strain rate test (SSRT) on samples with and without nitrided layers was carried out in hydrogen generating environment. After SSRT fracture mode and plasticity of nitrided layers were examined with SEM. Findings: In the presence of the not defected compact nitride layer, no hydrogen permeation through the steel has been stated under the experimental conditions. Influence of hydrogen content in working atmosphere, i.e. internal hydrogen, was found. Absorbed hydrogen, i.e. external hydrogen, was accumulated within this layer. Research limitations/implications: There is no possibility to perform direct observations of exact mechanism of hydrogen-assisted cracking so far. Further research should be taken to reveal the exact mechanism of increased plasticity of nitrided layer with absorbed hydrogen. Practical implications: Plasma nitrided layers are effective barriers to hydrogen entry into structural steel utilised in aggressive environments, which is especially important in the case of possible hydrogen charging of exploited steel. Originality/value: Using the atmosphere of the higher nitrogen to hydrogen ratio at plasma assisted nitriding provides the formation of thin compact nitride zone, highly protective against corrosion and hydrogen degradation. Evidences of a likely increased plasticity of nitrided layers with absorbed hydrogen was observed.

3

Effect of steel microstructure on bacteria-assisted hydrogen effects at cathodic polarization in sea water

Łunarska E., Domżalicki P., Birn J.

Advances in Materials Science

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2007

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Vol. 7, nr 1(11)

160-165

EN

The effect of the SRB action on mechanical properties and hydrogen uptake by the steels of quite similar chemical composition but different microstructure bas been studied at cathodic polarization in synthetic sea water. Susceptibility of sorbite steel to the SRB action, as seen from the plasticity los s and hydrogen uptake was higher than that of ferrite-pearlite steels. The sorbite steel revealed also the highest polarization current, highest amount of S.2 in solution and the highest amount of S on the surface of metal tested in the presence of SRB. The made pronounced detrimental effect of SRB produced on sorbite steel was mostly accounted for the presence of Mn, Fe sulfides in the steel microstructure.

4

Hydrogen charging of plasma nitrided steel in acid solution

Sobieszczyk S., Łunarska E., Ćwiek J., Zieliński A., Nikiforow K.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 17, nr 1-2

205--208

EN

Purpose: Purpose of this paper is evaluation of susceptibility of plasma nitrided structural steel to hydrogen absorption. Design/methodology/approach: Structural steel, nitrided at glow discharge in the gas mixture of various N2, H2, Ar content was subjected to cathodic hydrogen charging in acid solution simulating the aged engine oil. The effect of the nitrided layers on the hydrogen transport and on the irreversible trapping was evaluated by the measurements of the hydrogen permeation rate and by the vacuum extraction, respectively. Findings: In the presence of the not defected compact nitride layer, no hydrogen permeation through the steel has been stated under the experimental conditions. Absorbed hydrogen was accumulated within this layer. Research limitations/implications: Further research should be taken to evaluate the influence of compact nitride zone on hydrogen degradation under tensile stress. Practical implications: Plasma nitriding treatment could improve the properties of the low-alloy high-strength structural steels exploited in aggressive environments, which is especially important in the case of possible hydrogen charging of exploited steel. Originality/value: Using the atmosphere of the higher nitrogen to hydrogen ratio at plasma assisted nitriding provides the formation of thin compact nitride zone, highly protective against corrosion and hydrogen degradation.