Papers by Keyword: Liquid Metal Embrittlement LME

Abstract: The models of liquid –metal embrittlement (LME) which explore the concept of fast stress/strain induced liquid phase diffusion as the major factor responsible for acceleration of subcritical cracks are overviewed and refined. The models are used for further analysis of several focus issues in the LME kinetics.

Abstract: Thermodynamic conditions for spontaneous grain boundary wetting (GBW) and stress driven liquid metal embrittlement (LME) are related to each other. Kinetic mechanism responsible for fast GB penetration (GBP) under small stress is described. Dissolution–condensation mechanism of LME and linear fracture mechanics for calculation of crack profile are applied to the classical system “Al-liquid Ga”. The results tend to support the idea that the recently observed fast linear penetration of Ga along 150° tilt <110> GB of Al should be considered as propagation of LME crack under small residual stress rather than as spontaneous GBW. With the residual tensile stress σ≈ 0.5MPa acting normal to the GB plane, all major findings reported for this model system are explained in semi quantitative way assuming that GB spreading coefficient is extremely small by its absolute value, i.e. that the system is near the threshold of spontaneous GBW.

Abstract: The consequences of the contact between liquid bismuth and a copper bicrystal are investigated at 500°C. Atoms of bismuth are shown to penetrate and embritlle the copper grain boundary. Grain boundary concentration profiles of bismuth are obtained on fracture surfaces by both Auger electron spectroscopy and He4+ Rutherford backscattering spectroscopy. The maximum bismuth intergranular concentration is calculated from experimental data to be about 1.7 monolayers (near the liquid bismuth / solid copper interface). The overall profiles are significantly different from typical erfc profiles and an interpretation is proposed, based on the coupling effect between grain boundary diffusion and non-linear segregation. These results allow us to conclude on the absence of grain boundary wetting for the Cu / Bi system at 500°C.

Abstract: A model Ni-Bi system has been used to investigate intergranular penetration (IGP) phenomenon. All experiments have been done on Ni 26°<110> bicrystal at 700°C using bismuth vapour condensation as a source of liquid bismuth. Such a procedure results at room temperature in either partial or total Liquid Metal Induced Embrittlement (LMIE) of a unique grain boundary, depending on the duration of liquid Bi / solid Ni contact at 700°C. Auger Electron Spectrometry (AES) and Rutherford Backscattering Spectrometry (RBS) have been used to measure the Bi concentration profile between the source of liquid bismuth and the penetration front. Two zones have been clearly identified : the first one of almost constant Bi concentration called nanometrethick film which is interpreted in terms of Fowler-Guggenheim multi-layer segregation under local equilibrium conditions and the second one with a progressive decrease of Bi concentration over a distance of the order of 20-200µm. Such a long transition zone, together with parabolic diffusion kinetics indicates diffusion-based mechanism of intergranular penetration as opposed to the direct grain boundary wetting.