Liquid metal embrittlement occurrence: phenomena and prediction – applied to the Cu-alloys/Ga-In system – GauguIn

In-situ observations at the MET will be carried out to validate phenomena occurring at the crack tip induced by a liquid film of Ga-In (dislocation emission or interfacial crack propagation). In-situ tests in SEM will complete these measurements by focusing on the initiation and propagation of a crack in weakening cases. In-situ observations in AFM during liquid metal bending tests will be implemented as a first of its kind to quantify the deformation in the presence of liquid metal and with the aim to study the existence of brittle crack propagation threshold stress. The interface conditions will be analyzed (AFM, ToF-SIMS). Mechanical measurements will attempt to measure critical stress intensity factors for fracture in weakening cases. Feeded by DFT atomic scale simulations, the emission of dislocations and brittle fracture in the presence of liquid metal will be evaluated in a continuous-atomistic mixed approach from energy balances. This requires simulating a solid-liquid brass/GaIn interface and friction stresses in the Cu-Zn alloy in a Peirls-Nabarro type model. The results of this theoretical approach will be compared with the experimental data from the project in order to validate this predictive tool of sensitivity to LME. We will focus in particular on the zinc threshold from which it should be possible to observe LME as a discriminating criterion on the predictive character of such an approach.

The aim of the GauguIn project is to develop a generic predictive methodology for liquid metal induced brittle cracking that could be applicable to any metallic system. The approach proposed is on the one hand to experimentally study crack initiation and dislocation emission at the crack tip and on the other hand the simulation of the phenomena. The model system under consideration (copper and brass in contact with Ga-In liquid) offers a ductile to brittle transition in the LME behavior as a function of the alloying of the solid metallic alloy that has to be reproduced by the predictive approach that will be used. With this system a strong coupling between experiments and simulation is possible. Dedicated in-situ mechanical tests in presence of liquid metal and in AFM, SEM and TEM will allow to measure and quantify the effect of the presence of liquid metal on the plasticity and crack propagation at nano-scale. These approaches have never been considered in the field of LME in a same project with an objective towards a predictive framework. The project dedicated to in-situ tests in presence of liquid metal in TEM, SEM and AFM presents a significant challenge from the technology and microscopy points of view. The modelling part is also using state of the art modelling techniques (DFT and AIMD).

In progress

In progress

Liquid Metal Embrittlement (LME) is a phenomenon taking place according to two modes: the best known is explained by a spontaneous wetting at the level of the grain boundaries (Al/Ga, Cu/Bi); a second mode requires a deformation plastic in the presence of liquid metal. Cases of LME such as steels in contact with liquid metals are to be taken into account in the safety of installations using liquid metals (nuclear reactors, solar thermal energy) or for galvanized steels. It is this last mode concerning a priori any metal alloy in the presence of a liquid metal which is the object of the proposed study. Indeed, the objective is to determine a methodology on a model system able to predict the propagation conditions of a brittle fracture in the presence of liquid metal. Recent observations have shown that fracture occurs mostly at interfaces in the presence of liquid metal for many systems of industrial interest. It is therefore considered that working on a "model" system will bring decisive progress towards improved modelling applicable to the many industrial systems. We settled on studying brasses (copper alloys containing different levels of zinc) in contact with a liquid Ga-In alloy. This model system will allow to couple analyzes, experimental observations and modeling of the initiation or propagation of a crack in liquid metal. In this system, a ductile-brittle transition is observed when the zinc solution content is increased. Thus, the objectives of this proposal are, in addition to a standard study of susceptibility to liquid metal embrittlement, to gain a better understanding of the mechanisms of LME through in-situ tests and electron microscopy observations. In-situ mechanical testing (AFM, MET, MEB) down to nanoscopic scales and a new numerical approach to LME able to predict brittle fracture in the presence of liquid metal will be confronted. In-situ observations at the MET will be carried out to validate phenomena occurring at the crack tip induced by a liquid film of Ga-In (dislocation emission or interfacial crack propagation). In-situ tests in SEM will complete these measurements by focusing on the initiation and propagation of a crack in weakening cases. In-situ observations in AFM during liquid metal bending tests will be implemented as a first of its kind to quantify the deformation in the presence of liquid metal and with the aim to study the existence of brittle crack propagation threshold stress. The interface conditions will be analyzed (AFM, ToF-SIMS). Mechanical measurements will attempt to measure critical stress intensity factors for fracture in weakening cases. Feeded by DFT atomic scale simulations, the emission of dislocations and brittle fracture in the presence of liquid metal will be evaluated in a continuous-atomistic mixed approach from energy balances. This requires simulating a solid-liquid brass/GaIn interface and friction stresses in the Cu-Zn alloy in a Peirls-Nabarro type model. The results of this theoretical approach will be compared with the experimental data from the project in order to validate this predictive tool of sensitivity to LME. We will focus in particular on the zinc threshold from which it should be possible to observe LME as a discriminating criterion on the predictive character of such an approach. The ambition of the project is therefore to predict the mechanical behavior in FML of a model system and thus be able to propose as well for the first time a predictive approach for industrial systems.