Predicting brittle fracture in presence of liquid metal involves understanding the phenomena leading to fracture and their quantification. This is why mechanical tests in presence of liquid metal with in situ observations at different scales are fundamental for continuous visualization and analysis of the phenomena during the test: by a scanning electron microscope for macroscopic and microscopic observations, with a transmission electron microscope for nanometric scales. To better interpret the experimental results, mechanical simulation of mechanical tests at the different observation scales must be correlated with experimental results, with the aim to quantify and predict the embrittlement due to liquid metal. As the LME sensitivity of various materials would be based on similar failure modes, quantification is possible, and prediction could be as well. So, the study of “simple” model systems (here copper alloys in presence of liquid gallium-indium eutectic) can make it possible to develop a predictive framework of LME sensitivity for model systems, and then applicable to more complex industrial materials.

Major results of the project

During the project, original mechanical testing methodologies, in presence of indium-gallium eutectic (EGaIn) liquid at room temperature, ex-situ and in-situ in scanning and transmission electron microscopy as well as simulation approaches at different scales were developed. The LME sensitivity conditions of copper and different brasses by liquid EGaIn as well as the intergranular cracking paths were observed. The LME sensitivity was quantified at microscopic and nanoscopic scales experimentally and by simulation by the determination of a critical fracture stress intensity factor in presence of liquid metal.

sensitivity, we transfer the results obtained during the GauguIn project to other conditions especially to better understand the galvanization (zinc deposition) of steels, a process used to improve the corrosion resistance of steels.

Results of Marco Ezéquiel's thesis work (28/02/2023)

The work concerned a study of the liquid metal embrittlement (LME) phenomenon at room temperature on alpha brasses with different Zn content in contact with the liquid eutectic Ga-In (EGaIn). The liquid EGaIn wets pure Cu partially with a relatively low contact angle of 49 ± 5 °, which is lower for the alpha brasses and decreases with the Zn content alloy down to 36 ± 5 ° for the Cu-30%Zn alloy. Moreover, the CuGa2 intermetallic forms whenever the liquid EGaIn is in contact with Cu and the alpha brasses, independently of the Zn content. Testing with the 3-point bending test showed that the LME sensitivity by the EGaIn increases at higher strain rates, higher Zn content, and higher hardness. Whenever there is LME, the liquid EGaIn does not affect the fracture initiation but the fracture propagation; hence the samples systematically presented a ductile fracture initiation followed by a brittle intergranular fracture propagation. The CuGa2 intermetallic impedes the brittle fracture initiation by blocking the contact between the EGaIn and the alpha brasses from the early stages of the test. Later, when the intermetallic breaks, the liquid EGaIn comes into contact with the alpha brass making the LME possible if the brass is under sufficient plastic deformation. Due to the ductile fracture initiation, the Cu-30%Zn alloy does not present LME when tested using the standard Small Punch Test (SPT). In contrast, using pre-notched SPT samples enables the observation of this alloy's embrittlement in contact with the liquid EGaIn. Furthermore, due to the ductile fracture initiation, it is impossible to use the bending tests or the SPT to measure the fracture toughness related to the LME phenomenon. In contrast, in-situ micro-bending tests with a W protective layer were suitable for the fracture toughness measurement of Cu-30%Zn in contact with the EGaIn; for instance, a fracture toughness value of 1.57 ± 0.08 MPa m1/2 was measured with the double clamped beam test.

Results of Antoine Clément 's thesis work (20/12/2022)

This PHd-thesis deals with the plasticity and liquid mercury embrittlement of α-brass. Different properties such as Peierls stress or critical stress intensity factors for dislocation emission at the crack tip were studied as a function of the zinc concentration of the alloys. This study was performed by developing an EAM potential which was then used in a QM/MM approach to combine the advantages of ab-initio calculations and interatomic
potentials. Different grain boundaries were modeled and their behavior in contact with liquid metal was observed. A new mechanism of embrittlement by liquid metal has been revealed with the creation of subsurface cavities.