A Mechanical Study of T91 Embrittlement by Liquid Lead-Bismuth Eutectic
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0981-JJ07-02
A Mechanical Study of T91 Embrittlement by Liquid Lead-Bismuth Eutectic Zehoua HAMOUCHE1,2, Thierry AUGER1, and Ivan GUILLOT1,2 1 CECM-CNRS UPR2801, 15 Rue Georges Urbain, VITRY SUR SEINE, 94407, France 2 University PARIS XII, 61 avenue du Général de Gaulle, CRETEIL, 94010, France
ABSTRACT The susceptibility of liquid metal embrittlement of the T91 martensitic steel is investigated from slow deformation rate (6.67x10-8 m.s-1) to high deformation rate (6.67x10-3 m.s-1), using a Center Cracked in Tension geometry. Brittle fracture, characterized by elongated river cracks on all the fracture surfaces, indicates that T91 is sensitive to the Embrittlement by LBE. This embrittlement effect is very marked at the low deformation rate (~10-5 mm.s-1). A ductile-brittle transition is observed in the high strain rate range investigated. In this transition regime, there is a competition between the growth of dimples and the cracking induced by the liquid metal. Ductility recovery is complete at the highest investigated displacement rate. This dependence of T91/LBE susceptibility to LME on the displacement rate and the brittle to ductile transition at high strain rate is confirmed by a fracture mechanics analysis. 1. INTRODUCTION High chromium martensitic steels (9Cr1MoNbV T91 steel) are presently considered as the most promising candidates structural materials for an Accelerator Driven Systems (ADS), on account of the severe expected in-service conditions, neutron irradiation and contact with the lead-bismuth eutectic (LBE) coolant. The effects of LBE on the materials properties are subject to many research activities worldwide. Besides the corrosion issue, the process of Liquid Metal Embrittlement (LME) is of particular interest as this phenomenon may impair the use of the selected material. LME is the premature brittle failure of a normally ductile material when it is strained in contact with liquid metal. The embrittlement manifests it self as reduction in fracture stress, strain, or both [1]. In many cases the liquid metal adsorption induces a ductile to brittle transition. In addition to plastic deformation, the most critical and mandatory condition for LME is that the liquid should be in intimate contact with the solid surface to initiate embrittlement [2]. It should subsequently be present at the tip of the propagating crack to induce brittle fracture. If the contact between the solid metal and the LM is hindered by the presence of an oxide film, LME does not occur. Due to its natural passive film, wetting of T91 by LBE is a crucial point in LME experiments and has hampered serious study of this phenomenon. By carefully preparing pre-wetted specimens, reproducible results have been obtained, in particular the growth of cracks can be stopped if the supply in liquid metal is limited or interrupted [3]. Embrittlement by liquid Pb or LBE of ferritic/martensitic steels has already been reported [4,5]. In such case, unlike the classical LME example Al/Ga, no intergranular cracking was observed precluding high cra
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