Combining high strength and moderate ductility in wear resistant coatings: a MO2BC study
October 1-6, 2017
Wear resistant coatings employed in cutting and forming applications usually require the combination of high stiffness and high hardness, as these properties often enable low wear rates. Moreover, moderate ductility is often desirable as crack formation can lead to early service failure. Traditionally, the combination of high stiffness and high ductility has been considered as self-excluding. However, recent investigations based on correlative experimental and theoretical research suggest that this empirical relationship can be overcome by a new generation of hard coating materials.
For example, ab initio calculations have predicted Mo2BC to exhibit a high stiffness in combination with moderate ductility . The material crystallizes in an orthorhombic structure (space group Cmcm), in which B atoms are positioned in Mo6B trigonal prisms and C atoms are at Mo6C octahedral sites in alternating sequence (unit cell is shown in Fig. 1a). The calculated bulk modulus of 324 GPa for Mo2BC surpasses the one of Ti0.75Al0.25N (178 GPa) , often referred as benchmark coating, by more than 50%. In addition, Mo2BC has been also predicted to be moderately ductile based on its ratio of bulk to shear moduli (B/G) and the calculated positive Cauchy pressure .
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Rafael Soler, Stephan Gleich, Christoph Kirchlechner, Christina Scheu, Gerhard Dehm, Hamid Bolvardi, and Jochen M. Schneider, "Combining high strength and moderate ductility in wear resistant coatings: a MO2BC study" in "Nanomechanical Testing in Materials Research and Development VI", Karsten Durst, Technical University of Darmstadt, Germany Eds, ECI Symposium Series, (2017). http://dc.engconfintl.org/nanomechtest_vi/59