Mechanical performance of Mo2BC coatingsThursday (29.09.2016) 09:45 - 10:00 Part of:
The lifetime of applied hard coatings (e.g. CrN, TiN, TiAlN) is often limited by brittle failure. Future material systems should concomitantly show high strength and resistance to brittle fracture. One possible candidate identified via DFT calculations is Mo2BC, showing a positive Cauchy pressure and Pugh´s criterion which are indicative for a moderate ductility . The mechanical performance of Mo2BC nanocrystalline coatings deposited on Cu substrates by magnetron sputtering were investigated compared to the bench-mark TiAlN, and other reference coatings . The coatings were subjected to uniaxial tensile loading and the crack density with increasing strain was determined using scanning electron microscopy. The Mo2BC coatings were found to have the highest resistance compared to the bench-mark coatings.
In the present study, in situ tensile tests were conducted using synchrotron based X-ray diffraction at the KMC-2 beamline of the BESSY synchrotron source. The aim of this study was to investigate the crack-onset strain, as well as the maximum lattice strains at crack onset of the Mo2BC coatings. It was shown that the lattice strains increase to a maximum applied strain of ~8% irrespective of film thickness. Subsequent straining does not lead to a decrease in lattice strain but to a stresses plateau at high level. The results will be discussed with respect to the damage tolerance in this new type of hard coating, the formation of channel cracks and interface delamination.