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Catastrophic brittle failure of ductile materials by liquid metal embrittlement (LME) is a widely documented phenomenon but the fundamentals of its initiation mechanism are poorly understood. The widespread use of Zn-coated advanced high strength steels in the automotive industry has been plagued by Zn-induced LME which is frequently observed in high-temperature forming and welding applications. In this study, numerical modeling and an atomic-scale experimental investigation are used in order to gain insight into the atomistic events that lead to the onset of LME cracking. The results showed that the formation of a stress-induced diffusion wedge (SIDW) at the exposed grain boundary (GB) due to the interdiffusion of Zn-embrittler atoms was the trigger for LME. The formation of the SIDW facilitated the diffusion of the Zn-embrittler atoms into the GBs, which compromised their mechanical integrity. The results show that LME initiation entails several steps: (i) solid-state GB diffusion, (ii) formation of the SIDW, (iii) eventual melting of the SIDW, and (iv) opening of the liquid wedge due to interdiffusion and the application of externally applied stresses. [ABSTRACT FROM AUTHOR]

The ultra-low elastic modulus (~34 GPa), high strength, and low density of Ti-Zr-Al-V series alloys show a great application potential as implant materials. However, their surface properties need to be studied and improved before clinical applications. In this work, nanocomposite coatings are deposited on the surface of the Ti-30Zr-5Al-3V alloy through the magnetron sputtering technique at various N2 flow rates. X-ray diffractometer, scanning electron microscope, and electrochemical workstation are employed to investigate the effect of the N2 flow rate (NFR) on the phase constitution, microstructure, and corrosion resistance in a simulated body fluid of the nanocomposite coatings. The phase constitution of the nanocomposite coating changes from α-Ti + Ti2N to α-Ti (inner layer) + Ti2N + TiN (outer layer) as the NFR increases from 6 × 10-5 to 4.8 × 10-4 m3/h. The tiny nanograins (~30 nm) cluster together and then coarsen into lumpy grains of an average size of 117.2 nm with the increase of the NFR. Analyses of potentiodynamic polarization curve and electrochemical impedance spectroscopy prove the obvious enhanced corrosion resistance of specimens with the nanocomposite coating. And the specimen, after deposition at the NFR = 2.4 × 10-4 m3/h, has the best corrosion resistance. The formation of TiN and the cluster of tiny nanograins are the major reasons for affecting the corrosion resistance of the nanocomposite coating. [ABSTRACT FROM AUTHOR]