Superelastic Fullerene-like Carbon Nitride Coatings Synthesised By Reactive Unbalanced Sputtering Magnetron

Abstract

The present paper presents the results of in depth process characterisation and microstructural investigation of fullerene-like carbon nitride (FL - CNx) coatings combined with deformation analysis, such as indentation testing, in order to assess its performance. Unbalanced reactive magnetron sputtering of graphite in a nitrogen containing atmosphere is essential for the growth of FL - CNx structures due to CxNy molecules, which are preformed in the process and may act as precursors or growth templates. The deposition process is best described as a hybrid of plasma vapour deposition and chemical vapour deposition. The fullerene-like (FL) structure leads to extraordinary mechanical properties which are assessed by nanoindentation. It exhibits a low work of indentation (usually a property associated with superhard materials) and also a low to moderate resistance to penetration. Therefore, deformation energy is predominantly stored elastically and released after unload giving it a tough and resilient character. In addition, the relatively low modulus leads to a spreading of the contact stresses over a larger volume and consequently to low stress gradients at the substrate/film interface. This hinders substrate/film delamination under load and therefore results in a high load bearing capability, while the coating asperities behave elastically with no tendency to brittle fracture in tribological contact. This characteristic combined with the low coefficient of friction reveals a coating which may be suitable for many tribological applications.