Development of Niobium Based Coatings Prepared by Ion-Plasma Vacuum-Arc Deposition

Abstract

Comparative studies of niobium carbide and niobium carbonitride coatings deposited on AISI 430 stainless steel have been presented. The NbC and NbCN coatings have been deposited by vacuum-arc evaporation in Bulat-type device by using the pulsed biasing mode with repetition frequency 50 kHz, allowing decreasing the micro-arcs formation. An additional magnetic coil for plasma flow focusing was used, allowing one to enhance deposition rate up to 35 μm/h. The phase composition of the obtained coatings was analyzed via X-ray diffraction. The surface morphology was monitored by scanning electron microscopy; whereas, chemical composition was examined by using energy dispersive X-ray analysis. X-ray fluorescent analysis was used to evaluate the thickness of the coatings. The reflectance R(λ) of the obtained coatings in the wavelength 300–625 nm at normal incidence was measured. The XRD data from NbC coating revealed the existence of the niobium carbide phase with a NaCl-type lattice with fine-crystalline grains ranging from 14 to 16 nm. For the NbCN coating, the two-phase state with c-NbC and hexagonal NbN0.95 phases was monitored. The average grain size for c-NbC phase comprised 16–17 nm; whereas, for NbN0.95 the average grain size was only 1–2 nm, confirming formation of a nanocrystalline structure. Surface nanomechanical behavior under nanoindentation of NbC and NbCN was studied. It was revealed that nanohardness for a NbC coating was varied from 30 to 43 GPa; whereas, for NbCN the data spread comprised 30–48 GPa. It was established that the surface of the grown coatings was very smooth with an extremely low amount of macroparticles.