Key Engineering Materials Vols. 373-374

Abstract: Cr-Al-N coatings with the thickness of about 2 μm have been prepared by a reactive magnetron sputtering method. The effects of substrate negative bias voltage (VB) on the microstructure and critical failure load have been investigated as the VB varied from 0 to –150 V. With VB increasing, grain size, lattice parameter and microstrain increase. (111) preferred orientation dominates in the coatings deposited under 0 and –50 V, while a (200) preferred orientation developed when VB further raised. The reasons for these variation caused by VB are discussed.

Abstract: This article summarizes briefly our recent research on low-temperature synthesis of TiN, TiN/Cu and TiN/Si films by using inductively coupled plasma assisted magnetron sputtering method. It is shown that the incorporation of high-flux low-energy ion irradiation during deposition strongly affects film growth, structure evolution, morphology and mechanical properties. A main attention is devoted to the synthesis of superhard nanocomposite films at a low deposition temperature. In both TiN/Cu and TiN/Si films the maximum hardness reaches a value higher than 40 GPa.

Abstract: CrNx film was widely used in mechanical engineering field because of its excellent anti-wear and corrosion resistance properties. While most of research was focused on mechanical properties, little attention had been paid to the corrosion resistance and residual stress of CrNx film . In this paper, CrNx films were deposited on silicon wafer (100) and iron substrate by unbalanced magnetron sputtering system (UBMS) at different N2 flow. Then the structure, thickness, residual stress, micro-hardness, wear-resistance and anti-corrosion properties of CrNx films were investigated. The results showed that the phase composition of CrNx films transformed from Cr, single phase Cr2N, Cr2N and CrN coexist to single CrN with the N2 flow rate increasing. The CrNx films composed with Cr2N phase, which deposited at 6 sccm N2 flow, had the highest microhardness and had higher compressive residual stress. Whereas the CrNx films with CrN and Cr2N phase coexist had the best wear and corrosion resistance.

Abstract: Protective TiC coating was produced on Cr-Zr-Cu electrode by vibrating electrospark deposition. Microstructure of the functional coating with pre-treatment (clean) and post-treatment (diffusion) were tested respectively. The deposition parameters on the structure of the substrate is discussed. The results indicate that as-deposited substrate consists of four layers. There are many micro-porous and micro-cracks in transition layer where mutual diffusion of Ti and Cu occurs, which provides atomic bonding between the coating and the substrate. Pre-treatment modifies the coating structure with small influence on its hardness whereas post-treatment modifies it and reduces its hardness and thickness. The service time of the specimens with TiC coating 2.4 times exceeds that of the uncoated ones.

Abstract: A 2D kinetic Monte Carlo (KMC) simulation has been applied to study the microstructure of Ni-Cr film deposited by physical vapor deposition (PVD) for variable incident angle. In the KMC method, two phenomena were incorporated: adatom-surface collision and adatom diffusion, the interaction between atoms was described by embedded atom method and jumping energy was calculated by molecular statics calculations, initial location of adatom was located by Momentum Scheme. The results reveal that there exists critical incident angle, which is 35˚ for Ni-Cr thin film. When incident angle is less than 35˚, incident angle have less affect on surface roughness factor and packing density, compact films with smooth surface are obtained, their surface roughness factor is bellow 1.12 and packing density is more than 99.6%. However, when incident angle is more than 35˚, surface roughness factor increases quickly and packing density decreases sharply with incident angle increasing: surface roughness factor increase to 1.5 and 2.3 for incident angle of 45˚ and 60˚ respectively, packing density is below 99% and 96% accordingly. Which reveal that the self-shadowing effect emphasizes with incident angle increasing when the incident angle is more than 35˚.

Abstract: Series Ti-Si-C-N coatings with different carbon were deposited on a high-speed-steel substrate by means of pulsed direct current plasma enhanced chemical vapor deposition (PECVD). The structure and hardness were subsequently investigated using X-ray diffraction, transmission electron microscopy and microindentation measurements. It was found that the carbon content had a profound effect on the microstructure and hardness of the Ti-Si-C-N coatings. The results indicated that these coatings consisted of the dominant nanocrystalline Ti(C, N), accompanying with a small amount of silicide (TiSi2, Si3N4 or SiC) dispersed within the dominant phase. An increase in C content resulted in the decrease in the grain size and the increase in fcc-structure lattice parameter. A maximum hardness of 48 GPa was achieved for a two-phase {Ti (C N) + SiC} structure at the C content of 38.6 at.%.

Abstract: TiN/CrN nanoscale multilayered coatings have been deposited using cathodic arc evaporation system. The coatings were deposited using one Ti target and one Cr target with a fixed power output in the processes, whilst the bi-layer thickness was varied by rotation of the substrate holder to obtain different nanoscale multilayered period thickness. The texture structure, residual stress and nanoscale multilayer thickness of the coatings were determined by X-ray diffraction using both Bragg-Brentano and glancing angle parallel beam geometries. Hardness and adhesion strength of the coatings were measured by Vicker's and Rockwell-C indentation methods. It has been found that the structural and mechanical properties of the films were correlated with nanoscale bi-layer thickness and crystalline texture. The maximum hardness of nanolayered TiN/CrN multilayer coatings was approximately 28 GPa, which the bi-layer thickness was 4 nm.

Abstract: In the paper the microstructure and properties of surface coating for Cr12MoV steel treated by TD (Thermal Diffusion) salt-bath vanadizing process are investigated. The research results indicate that after treated by the TD salt-bath vanadizing at 1223K for 5h and followed by oil quenching, and aged at 453K for 2h, the Cr12MoV steel could obtain a surface coating whose thickness is about 11.4um. The coating is mainly composed of vanadium carbide, and its thickness and microstructure are uniform and compact, respectively. At the same time, the coating obtained exhibits super-high surface microhardness, 2586HV. Then the wear resistance property of Cr12MoV steel is improved drastically. In addition, the research results reveal that the effect of TD salt-bath vanadizing treatment on the surface roughness of Cr12MoV steel is not obvious.

Abstract: Hard chromium deposits were prepared from a trivalent chromium plating bath as an alternative to conventional hexavalent chromium deposits. The influences of bath composition on the trivalent chromium electrodeposition process and deposited coating properties were studied. The effects of plating parameters such as current density, bath pH and plating time on structure and morphology of deposited coatings were investigated. Results show that the hard chromium deposits exhibited amorphous structure with thickness of 50-100μm and acceptable quality for functional coatings. The hard chromium deposits exhibited better wear resistance as well as corrosion resistance than that of hexavalent chromium deposits. The hardness of as-deposited chromium coatings is about 600-700HV. Heat treatment could improve the wear resistance and hardness of the hard chromium deposits. The formation of polynuclear coordination compounds from hydroxyl complex ions at high pH is the main disadvantageous factor for the sustained trivalent chromium plating process.

Abstract: Aluminized coatings prepared on nickel-based superalloys can provide good protection against high temperature oxidation and hot corrosion. This study investigated the simple aluminized and silicon-aluminized coatings on nickel-based superalloy K4104. The simple aluminized coating was prepared by pack cementation and the Al-Si coating was prepared by slurry aluminizing, respectively. The microstructure of simple aluminized and Al-Si coatings was analyzed by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA). And the formation mechanism of simple aluminized and Al-Si coatings was discussed. The results showed that the simple aluminized coating was about 49 um thick and consisted of three layers. The outer layer mainly consisted of Al-rich β-NiAl. The intermediate layer consisted of Ni-rich β-NiAl and Cr-rich. The inner diffusion layer consisted of Cr-rich and γ’-Ni3Al. The microstructure of Al-Si coating showed that the coating was about 70 um thick and consisted of five layers. The Al-Si coating consisted of CrxSiy, Al-rich β-NiAl, Ni-rich β-NiAl, Cr-rich and γ’-Ni3Al. The microstructure of simple aluminized coating was compared with that of Al-Si coating in order to find out the effect of Si. Owing to the effect of Si, there was a Transition layer in Al-Si coating. The Al-Si coating was thicker than simple aluminized coating. The declining trend of the aluminum concentration in the Al-Si coating was smoother than that of the simple aluminized coating.