Vacancy-induced toughening in hard single-crystal V0.5Mo0.5Nx/MgO(001) thin films
2014 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 77, 394-400 p.Article in journal (Refereed) Published
Using a combination of experiments and density functional theory (DFT), we demonstrate the first example of vacancy-induced toughening, in this case for epitaxial pseudobinary NaCl-structure substoichiometric V0.5Mo0.5Nx alloys, with N concentrations 0.55 ≤ x ≤ 1.03, grown by reactive magnetron sputter deposition. The nanoindentation hardness H(x) increases with increasing vacancy concentration from 17 GPa with x = 1.03 to 26 GPa with x = 0.55, while the elastic modulus E(x) remains essentially constant at 370 GPa. Scanning electron micrographs of indented regions show ductile plastic flow giving rise to material pile-up, rather than cracks as commonly observed for hard, but brittle, transition-metal nitrides. The increase in alloy hardness with an elastic modulus which remains constant with decreasing x, combined with the observed material pile-up around nanoindents, DFT-calculated decrease in shear to bulk moduli ratios, and increased Cauchy pressures (C12-C44), reveals a trend toward vacancy-induced toughening. Moreover, DFT crystal orbital overlap population analyses are consistent with the above results.
Place, publisher, year, edition, pages
Oxford, England: Elsevier, 2014. Vol. 77, 394-400 p.
DFT; Mechanical properties; Toughness; Transition-metal nitrides
IdentifiersURN: urn:nbn:se:liu:diva-106350DOI: 10.1016/j.actamat.2014.06.025ISI: 000340303200035ScopusID: s2.0-84903803295OAI: oai:DiVA.org:liu-106350DiVA: diva2:715540
FunderSwedish Research CouncilKnut and Alice Wallenberg Foundation
The authors gratefully acknowledge the financial support of the Knut and Alice Wallenberg Foundation, the Swedish Research Council (VR), the Swedish Government Strategic Research Area Grant in Materials Science (SFO Mat-LiU) on Advanced Functional Materials, and the Linköping Linnaeus Initiative LiLi-NFM (grant 2008-6572). DFT calculations were carried out on the Neolith and Triolith clusters located at the National Supercomputer Center (NSC) in Linköping, and on the Akka and Abisko clusters located at the High Performance Computing Center North (HPC2N) in Umeå, Sweden. The authors are grateful to E. Broitman and L. Martínez-de-Olcoz for fruitful discussions on nanoindentation2014-05-052014-05-052016-08-31Bibliographically approved