Superhard NbB2 −x thin films deposited by dc magnetron sputtering
2014 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 257, 295-300 p.Article in journal (Refereed) Published
We have deposited weakly textured substoichiometric NbB2-x thin films by magnetron sputtering from an NbB2 target. The films exhibit superhardness (42 +/- 4 GPa), previously only observed in overstoichiometric TiB2 thin films, and explained by a self-organized nanostructuring, where thin TiB2 columnar grains hinder nucleation and slip of dislocations and a B-rich tissue phase between the grains prevent grain-boundary sliding. The wide homogeneity range for the NbB2 phase allows a similar ultra-thin B-rich tissue phase to form between thin (5-10 nm) columnar NbB2-x grains also for films with a B/Nb atomic ratio of 1.8, as revealed here by analytical aberration-corrected scanning transmission electron microscopy. Furthermore, a coefficient of friction of 0.16 is measured for an NbB2-x film sliding against stainless steel with a wear rate of 5 x 10(-7) mm(3)/Nm. X-ray photoelectron spectroscopy results suggest that the low friction is due to the formation of a lubricating boric acid film.
Place, publisher, year, edition, pages
Elsevier, 2014. Vol. 257, 295-300 p.
Boride; Magnetron sputtering; Structure characterization; Mechanical properties; Friction; Tribological properties
IdentifiersURN: urn:nbn:se:liu:diva-112641DOI: 10.1016/j.surfcoat.2014.07.087ISI: 000344423100029OAI: oai:DiVA.org:liu-112641DiVA: diva2:769091
Funding Agencies|Vinnova (Swedish Governmental Agency for Innovation Systems) through the VINN Excellence Centre FunMat; Swedish Foundation of Strategic Research through the Synergy Grant FUNCASE; Knut and Alice Wallenberg Foundation2014-12-052014-12-052016-08-31Bibliographically approved