The Effect of Hydrogen on Corrosion of Tb[sub 0.3]Dy[sub 0.7]Fe[sub 1.92]

Abstract

The effect of hydrogen on the corrosion behavior of rare-earth-based magnetostrictive material Tb0.3Dy0.7Fe1.92 was studied after cathodic charging of hydrogen. The aqueous solutions used for understanding electrochemical behavior were 3.5% NaCl and 0.01 N Na2SO4 , in freely aerated and deaerated conditions. The severity of hydrogen attack in the presence of chloride ions increased with increasing hydrogen charging duration. Terraced and cleavagelike faceted features were evident on the surfaces after hydrogen charging and they were related to hydrogen embrittlement of the material. The destabilizing effect of chloride ions on the surface films, resulting in increased hydrogen uptake and consequent lowering of corrosion resistance, was verified by testing in chloride-free 0.01 N Na2SO4 environment in both freely aerated and deaerated conditions. The material was more tolerant to charged hydrogen in the absence of chloride ions. Protective surface film formation in 0.01 N Na2SO4 solution resulted in improved corrosion resistance of Terfenol-D compared to that in 3.5% NaCl solution.

Passivity of Tb0·3Dy0·7Fe1·92in alkaline solution and its breakdown by chloride ions

“…The destabilisation of surface film in the presence of Cl 2 resulted in hydrogen embrittlement of material. 24 The present study showed improved corrosion behaviour in alkaline solutions, due to the formation of protective surface passive film. Therefore, encapsulating the material in chloride free alkaline environment can be advantageously explored as a method of protection for this material.…”

“…32 Therefore, it is more likely at higher potentials of polarisation scan. Thus, it can be anticipated that Previous studies on corrosion behaviour of Tb 0?3 Dy 0?7 Fe 1?92 23,24 revealed its active nature in near neutral aqueous solutions with and without the presence of Cl 2 . Corrosion rates were higher in the former condition, particularly in the absence of oxygen.…”

“…Under active corrosion conditions, a similar behaviour was determined for Tb 0?3 Dy 0?7 Fe 1?92 . 23,24 During the anodic scan, the sample polarised to stable passivity conditions. The stable passive region extended from 2230 mV up to breakdown potential E b of z680 mV in the case of solution without chloride ions, beyond which a rapid increase in current density was obtained with increasing scan potential.…”

“…A preliminary study on corrosion behaviour of Tb 0?3 Dy 0?7 Fe 1?92 22 suggested corrosion mechanism similar to that of Nd-Fe-B magnetic material. A detailed investigation of the corrosion behaviour of Tb 0?3 Dy 0?7 Fe 1?92 23 and hydrogen effects on corrosion behaviour 24 has recently been concluded. These studies indicate that Tb 0?3 Dy 0?7 Fe 1?92 is susceptible to localised corrosion, particularly in chloride environment.…”

On the Mechanism of Corrosion of Terfenol-D (Tb[sub 0.3]Dy[sub 0.7]Fe[sub 1.92])

“…Detailed studies on several aspects of corrosion of commercial-grade Tb 0.3 Dy 0.7 Fe 1.92 ͑commercially called Terfenol-D͒ have recently been concluded. [1][2][3][4][5] Corrosion of these ͑Tb,Dy͒Fe 2 -based magnetostrictive materials is of scientific, commercial, and strategic concerns, as this material is the nextgeneration material for active sonar applications. Apart from this, Terfenol-D finds varied applications, such as in tools for well cleaning in the petroleum, oil, and gas industries, in fuel injection, and in medical appliances.…”