Characterization of magnetron sputtered Cr-B and Cr-B-C thin films for electrical contact applications
2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 266, 167-176 p.Article in journal (Refereed) Published
We have deposited Cr-B and Cr-B-C thin films by co-sputtering from chromium boride and carbon targets. The binary Cr-B films consist of nanocrystalline and substoichiometric CrB2 - x grains (B/Cr atomic ratio <= 1.5) with a (101)-texture, where B segregates to the grain boundaries forming a B-rich tissue phase. A hardness of 25 GPa is measured for these films. They have a low wear resistance, attributed to a (101)-texture and limited adhesion. As a consequence, wear debris in the CrB2 - x wear track from delaminated film and steel-to-steel contact between the exposed substrate and the counter surface result in a high friction (0.52-0.78 against stainless steel) making the Cr-B films unsuitable as sliding electric contacts. Cr-B-C films, on the other hand, form a two phase amorphous structure at >17 at.% C consisting of an amorphous Cr-rich phase containing both B and C and an amorphous matrix phase containing mainly B and C. The addition of C improves the adhesion and tribological properties and a coefficient of friction of 0.12 is obtained at 38 at.% C. The improved tribological properties are explained by the formation of the matrix phase, which acts as a solid lubricant forming a graphite-like tribofilm during ball-on-disc test. However, the formation of an amorphous structure is not beneficial for the electrical contact resistance, which increases from 0.5 Omega for the Cr-B film to 1.5 and 2.3 Omega for the Cr-B-C films containing 17 and 26 at% C, respectively. Finally, the importance of a chemical analysis of the chromium boride sputtering target composition is discussed.
Place, publisher, year, edition, pages
2015. Vol. 266, 167-176 p.
boride, CrB, CrBC, nanocomposite, amorphous, mechanical properties, electrical properties
Research subject Chemistry with specialization in Materials Chemistry
IdentifiersURN: urn:nbn:se:uu:diva-219033DOI: 10.1016/j.surfcoat.2015.02.037ISI: 000352664600022OAI: oai:DiVA.org:uu-219033DiVA: diva2:698065