Non-reactively sputtered ultra-high temperature Hf-C and Ta-C coatings
2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 309, 436-444 p.Article in journal (Refereed) Published
Transition metal carbides are known for their exceptional thermal stability and mechanical properties, notably governed by the carbon content and the prevalent vacancies on the non-metallic sublattice. However, when using reactive deposition techniques, the formation of amorphous C-containing phases is often observed. Here, we show that non-reactive magnetron sputtering of HfC0.89 or TaC0.92 targets lead to fully crystalline coatings. Their C content depends on the target-to-substrate alignment and globally increases from HfC0.66 to HfC0.76 and from TaC0.69 to TaC0.75 with increasing bias potential from floating to - 100 V, respectively, when using a substrate temperature T-sub of 500 degrees C. Increasing T-sub to 700 degrees C leads to variations from TaC0.71 to TaC0.81. All HfCy films are single-phase face-centered cubic, whereas the TaCy films also contain small fractions of the hexagonal Ta2C phase. The highest hardness and indentation modulus among all coatings studied is obtained for TaC0.75 with H = 41.9 +/- 03 GPa and E = 466.8 +/- 15 GPa. Ab initio calculations predict an easy formation of vacancies on the C-sublattice, especially in the Ta-C system, and a temperature driven stabilization of defected structures at high temperatures, with fewer vacancies on the C sublattice for Hf-C than for Ta-C The predicted phase stability is proven up to 2400 C for both systems by annealing experiments in vacuum.
Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA , 2017. Vol. 309, 436-444 p.
HfC, TaC, Non-reactive sputter deposition, Vacancies, UHTC, Density Functional Theory (DFT)
Condensed Matter Physics
IdentifiersURN: urn:nbn:se:uu:diva-319134DOI: 10.1016/j.surfcoat.2016.11.073ISI: 000396184400051OAI: oai:DiVA.org:uu-319134DiVA: diva2:1086257