Structure and Properties of Hard Nanostructured Coatings in Cr-B-N System

Abstract

The CrB 2 thin coatings are of interest because of their high hardness, wear-and corrosion resistance [1,2]. Incorporation of nitrogen in transition metal-boron systems (TiB 2 , ZrB 2 etc.) often leads to enhancing of chemical, mechanical and tribological characteristics [3,4]. The objective of the present study is the investigation of structure and properties of Cr-B-N coatings.The CrB 2 targets were synthesized from exothermal powder mixtures by means of selfpropagating high-temperature synthesis [5]. The Cr-B-N coatings were obtained using DC magnetron sputtering of CrB 2 target in an argon atmosphere or in a gaseous mixtures Ar+N 2 (Table 1). The total pressure was maintained at 0.2 Pa. The diameter of the targets was 12.5 cm and the distance from the target to substrate was 9 cm. During deposition, the applied bias voltage was kept constant at -250 V and the substrate temperature was controlled at 250-300 0 C. Coatings were deposited on single crystal Si (100), Ni foil, and cemented carbide substrates for various times to obtain 1.0-2.5 m thick coatings.The structure, phase, and chemical composition of coatings were studied by means of transmission and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA). To evaluate the oxidation resistance and thermal stability, the samples were annealed at 500, 700 and 900 0 C in air for 1 hour. The elemental depth profiles for oxidized coatings were obtained by second ion massspectrometry (SIMS). Adhesion (critical load Lc 2 ), hardness (H), Young's modulus (E) friction coefficient (f) and wear rate (Vw) were evaluated by means of scratch-tester, nanohardness tester, and pin-on-disk tribometer (CSM Instruments). The electrochemical tests of the Cr-B-N coatings were carried out in 5N H 2 SO 4 using three-electrode cell and VoltaLab 50 potentiostat (Radiometr analytical).

Thermal Stability of Nanostructured Coatings

“…The first layer (L1) was characterized by the presence of Al and O (as detected by EDS). This suggested that Al 2 O 3 crystallites formed as a consequence of the outward Al diffusion to the free surface [75,76]. Preferential oxidation of Al with respect to Ti at high temperature was reported by A. Joshi et al in [81].…”

“…Finally, coarse grains with an average size of 500 nm constitute the layer directly in contact to the substrate (L5). EDS indicates a large content of Cr and some Ti, N and B [73][74][75].…”

Advanced Ceramic Target Materials Produced by Self-Propagating High-Temperature Synthesis for Deposition of Functional Nanostructured Coatings - Part 1: Four Elements and Less Systems

“…The SHS targets passed successful tests in various types of installations, namely, dc magnetron systems (MS) [1, 9, 12-14, 15-17, 18-24], high-frequency [25] and pulsed MS [11], MS with additional inductively coupled plasma [26], and arc evaporators [27]. Over the last several years, using the magnetron sputtering of SHS targets, hard coatings were obtained in the systems Ti-Si-N [9,12,28], Ti-B-N [10,13,29,30], Ti-Si-B-N [4,13,29], Ti-Si-C-N [13,29], Ti-Al-C-N [13,29], Ti-C-N [31], Ti-Mo-C-N [31], Ti-Al-B-N [32], Ti-Al-Si-B-N [17,18,30], Ti-Cr-B-N [10,12,14,17,30], Cr-B-N [10,12,33,34], Ti-Zr-C-O-N [19], Ti-Ta-Ca-P-C-O-N [23,24], Ti-Cr-Al-C-N [35,36], etc. Taking into account the increase in demand for various compositions of composite targets, we decided that it is important to present the data on the features of the synthesis of the most interesting and necessary classes of SHS targets differing in regards to their combustion mechanisms and structure formation in the form of the review.…”