Effect of the Small Punch Test sample geometry on the Liquid Metal Embrittlement of Cu-30 wt% Zn by the eGaIn

Liquid metal embrittlement (LME) is the embrittlement or the modification of the fracture behaviour of a metal or alloy when it undergoes plastic deformation while in contact with a liquid metal or liquid alloy. LME occurrence depends strongly on the properties of the metals involved and on the conditions of the mechanical stresses applied to the solid. The Small Punch Test (SPT) on flat specimens is very sensitive to identify the conditions of LME occurrence. Moreover, there are alternative SPT notched specimen geometries that have the potential to screen solid/liquid couples for sensibility to LME in different conditions. To study the apparition of the LME on an alpha brass with 30 wt% Zn in contact with the eGaIn (Ga-In eutectic), SPT at room temperature were carried out at different displacement rates and using three specimen types: the standard flat geometry and two notched geometries. While the flat specimens did not present LME, the presence of a notch and a high strain rate induced LME on the other specimen geometries. For these last specimens, the eGaIn modifies the SPT load-displacement curves at the crack propagation stage and changes the fracture to a partially ductile fracture followed by a brittle fracture

Mechanical reliability of T91 and 316L steels in liquid Lead-Bismuth Eutectic

International audienc

A Review of the Surface Modifications for Corrosion Mitigation of Steels in Lead and LBE

International audienceThe review paper starts with the applications of liquid metals and then concentrates on lead and lead–bismuth eutectic used in Gen IV nuclear reactors and accelerator-driven systems. Key points of degradation modes of austenitic stainless steels and ferritic-martensitic steels, candidates for the structural components, are briefly summarized. Corrosion and liquid metal embrittlement are critical issues that must be overcome. Next, the paper focuses on the strong efforts paid to the mitigation of corrosion and reviews the different solutions proposed for the protection of steels in lead and lead–bismuth eutectic. There exist promising solutions based on protection by deposition of protective coatings or protection by “natural” oxidation resulting from optimized chemical composition of the steels. However, the solutions have to be confirmed especially by longer-term experiments and by additional mechanical testing

Compréhension de la fragilisation de l’acier T91 par l’eutectique Plomb-Bismuth liquide : analyses par ToF-SIMS pour évaluer l’absorption du Plomb et du Bismuth.

For the development of ADS and Generation IV reactors cooled by liquid lead-bismuth eutectic (LBE) or liquid lead, the sensitivity of structural materials to liquid metal embrittlement (LME) or to liquid metal assisted damage has been studied since several years. For one of them, the T91 martensitic steel, a very selective set of parameters including test temperature, strain rate, oxygen content in LBE, surface roughness, microstructure state of the steel promotes brittle fracture in LBE or an accelerating damage instead of ductile fracture in neutral environment (argon or air) under monotonic and cyclic loading [1-4]. The mechanisms that explain this embrittlement are generally based on the adsorption of the liquid metal atoms on the surface of the steel, which results in the local reduction of the shear stress and the reduction of the cohesion. Furthermore, LBE is not a pure metal but an alloy. Thus, it is not easy to estimate which between lead and bismuth contribute the most to LME. Moreover, the literature does not report at the moment any evidence of the penetration of Pb or Bi atoms in the iron networks even after long term pre-immersion in LBE. Thus, we studied if atoms of LBE can penetrate the lattice of T91 steel, and even segregate, during immersion under plastic deformation. Then, if so, it aims at determining if lead and bismuth produces the same degree of LME.Cyclic loading in LBE was applied on a notched flat specimen to obtain large value of cumulated plastic deformation at notch root. After test, ToF-SIMS (The time of flight secondary ion mass spectroscopy) analyses were performed to study the presence of the bismuth and lead in depth of the steel, under the surface. It is shown that both Pb and Bi can penetrate the steel network only in plastically deformed material. No microstructural interface (lath boundaries, grain boundaries ….) was found to be preferential site for trapping Pb and Bi but clustering with molybdenum has been identified. Pb seems to be easier adsorbed than Bi because of, we suppose, its higher affinity with oxygen. A mechanism based not only on adsorption but also on the absorption of Pb-Bi is proposed.References[1] G. Nicaise, A. Legris, J-B. Vogt, F. Foct, Embrittlement of the martensitic steel 91 tested in liquid lead, J. Nucl. Mater. 296 (2001) 256-264.[2] I. Serre, J.-B. Vogt, Heat treatment effect of T91 martensitic steel on liquid metal embrittlement, J. Nucl. Mater. 376 (2008), 330-335.[3] C. Ye, J-B. Vogt, I. Proriol Serre, Liquid metal embrittlement of the T91 steel in lead bismuth eutectic: The role of loading rate and of the oxygen content in the liquid metal, Mat. Sci. Eng. A 608 (2014) 242-248.[4] A. Verleene, J.-B. Vogt, I. Serre, A. Legris, Low cycle fatigue behaviour of T91 martensitic steel at 300 °C in air and in liquid lead bismuth eutectic, Int. J. Fatigue 28 (2006) 843-851.Dans le cadre du développement des ADS et des réacteurs de génération IV refroidis par l’eutectique plomb-bismuth (Pb-Bi) liquide, il a été étudié, si la présence du Pb-Bi induit une fragilisation par les métaux liquides (FML) ou une accélération de l’endommagement par métal liquide de l’acier martensitique T91. Des essais ont été menés à l’air et en métal liquide, suivis d’analyses approfondies des faciès de rupture, des chemins de fissuration, des surfaces et sous-surfaces. Il a été mis en évidence des conditions expérimentales et microstructurales menant à la FML de l’acier par Pb-Bi liquide. Un endommagement accéléré par métal liquide sous sollicitation cyclique est aussi observé. Les mécanismes expliquant ces phénomènes sont généralement basés sur l’adsorption des atomes de métal liquide à la surface de l’acier ce qui entraîne la réduction locale de la contrainte de cisaillement et la réduction de la cohésion.Cependant, à partir d’analyses ToF-SIMS de la surface et sous surface de l’acier déformé en présence de Pb-Bi, il est observé que Pb et Bi peuvent pénétrer au niveau de la couche d’oxyde et dans l’acier, ceci sous déformation plastique en présence de métal liquide. Les interfaces microstructurales de l’acier n’apparaissent pas comme des sites d’absorption privilégiés, cependant qu’une affinité de Mo et Pb-Bi est notée. Pb semble être plus facilement absorbé que Bi. Un mécanisme basé pas seulement sur l’adsorption mais aussi sur l’absorption de Pb-Bi est proposé

Tenue des matériaux de structure en contact avec un métal liquide : fragilisation de l’acier T91 par l’eutectique Plomb-Bismuth

National audienc

Mechanical properties of austenitic and martensitic steels in contact with liquid lead bismuth eutectic and liquid lead : influence of dissolved oxygen in liquid metal and of strain rate.

International audienceThe mechanical behaviour assessment of structural alloys is crucial for the durability and safety of ADS. Moreover, it is well-known that the presence of a liquid metal may compromise the good performances of a metallic alloy due to liquid metal corrosion or liquid metal assisted mechanical damage. Though tough and ductile metallic alloys are selected, they may become brittle when stressed in liquid metal exhibiting thus the so called Liquid Metal Embrittlement (LME).The paper summarizes the results obtained in our lab on the mechanical behaviour of martensitic and austenitic steels in liquid lead and in liquid lead-bismuth (LBE) eutectic. Attention was paid on the influence of two parameters: the oxygen content in the liquid metal and the strain rate. Indeed, the chemistry of the liquid metal, especially oxygen content affects the interface between the steel and the liquid metal by formation of an oxide layer (high oxygen) or decreasing the possibility of protective oxide layer to form (low oxygen). Furthermore, variation in oxygen content or chemistry of the liquid metal (Pb, Pb-Bi) could lead to a modification of adsorption or absorption mechanisms. The mechanical properties in inert environment depend on the strain rate as the effect of liquid metal on the time immersion in the liquid metal. So, the strain rate could be considered as an important parameter concerning the mechanical behaviour of the steel in contact with lead and LBE.The mechanical behaviour of martensitic steel and austenitic steels were investigated in a temperature range from 200°C to 500°C by performing monotonic tests (Small Punch Tests and tensile tests) and low cycle fatigue tests in air and in liquid LBE or/and liquid lead. After tests, cracking and fracture surfaces were analysed by SEM, EDX-SEM, EBSD or ToF-SIMS to characterize and understand the effect of the liquid metal.The effect of the presence of liquid metal will be discussed according to the microstructure of the steels as well as the strain rate and chemistry of liquid metal