| AVS 64th International Symposium & Exhibition | |
| Advanced Surface Engineering Division | Wednesday Sessions |
| Session SE+2D+NS+SS+TF-WeA |
| Session: | Nanostructured Thin Films and Coatings |
| Presenter: | Daniel Edström, Linköping University, University of Illinois at Urbana-Champaign |
| Authors: | D. Edström, Linköping University, University of Illinois at Urbana-Champaign D. Sangiovanni, Linköping University, University of Illinois at Urbana-Champaign L. Hultman, Linköping University, University of Illinois at Urbana-Champaign I. Petrov, Linköping University, University of Illinois at Urbana-Champaign J. Greene, Linköping University, University of Illinois at Urbana-Champaign V. Chirita, Linköping University, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
Enhanced toughness in hard and superhard thin films is a primary requirement for present day ceramic hard coatings, known to be prone to brittle failure. Density Functional Theory (DFT) investigations predicted significant improvements in the toughness of several B1 structured transition-metal nitride ( TMN ) alloys, obtained by alloying TiN or VN with MoN and WN. The calculations reveal that the electronic mechanism responsible for toughness enhancement stems from the high valence electron concentration (VEC) of these alloys, which leads to the formation of alternating layers of high/low charge density orthogonal to the applied stress, and allows a selective response to deformations. This effect is observed for ordered and disordered ternary TMN alloys. The essential feature in the disordered alloys, as reported for ordered alloys, is the increased occupancy of electronic d-t2g metallic states, which allows the selective response to tensile/shearing stresses, and explains the enhanced toughness confirmed experimentally for VMoN films.
Recently, these results have been validated experimentally. Single-crystal VMoN alloys, grown by dual-target reactive magnetron sputtering together with VN and TiN reference samples, exhibit hardness > 50% higher than that of VN, and while nanoindented VN and TiN reference samples suffer from severe cracking, the VMoN films do not crack.
New DFT calculations suggest similar toughness improvements may be obtained in pseudobinary NaCl structured transition-metal carbide (TMC) compounds by alloying TiC or VC with WC and MoC. A comprehensive electronic structure analysis, as well as stress/strain curves DFT-based calculations, carried out for the newly formed ternary TMC alloys, reveal similar trends between shear-stressed TMN and TMC compounds, and predict VMoC as the best candidate alloy with enhanced ductility.
KEYWORDS: nitrides, carbides, toughness, hardness, ductility.