Key Engineering Materials Vols. 373-374

Abstract: Molybdenum has many prominent properties, such as high melting point, good thermal properties, low erosion rate and so on, which make it promising candidate materials for plasma facing materials in the next fusion reactor. In the present work, molybdenum coatings were deposited onto the oxygen-free copper substrates by atmospheric plasma spraying. Different interlayers were introduced between the coatings and substrates. SEM, EDS and XRD were used to investigate the photographs and compositions of these coatings. The bonding strength of the coatings was tested to investigate the effect of interlayers on adhesion of the coatings at room temperature and it was found that the coating without interlayers showed the highest bonding strength. Water quenching method was used to evaluate the adhesion of the coatings under thermal cycling conditions and the results showed that the molybdenum coating with two interlayers possessed of the highest resistance of thermal cycling wrack.

Abstract: The coatings for elevated temperature erosion resistance in circulating fluidized bed (CFB) boilers were fabricated by high velocity arc spraying process and CrB powder wire. The microstructure and phase component of the coating were examined by optical microscopy(OM) and Transmission electron microscopy (TEM). The properties including microhardness, adhesion strength and in-situ erosion rate of the coating were measured. The failure mechanism was also discussed based on the experimental data. The OM results showed that the coating consisted of individual flat lamella, thin oxide layer, porosity and very small amount of particle which characterized as different shape and color respectively. TEM results indicated that the phases within the lamella were mainly composed of α phase, amorphous phase and other nanosized particle phase of Fe23(C,B)6, Cr23C6 etc.. The amount of amorphous phase near the substrate was more than that in the other area indicating that the appearance of amorphous phase was related to the high cooling rate of the coating. The microhardness was about 860~1100HV0.2. The coating exhibited high erosion-corrosion resistance, which was about six times as 20G steel. The advantage of the coating with excellent performance, simple process and low cost made it possible to find potential application in power plants.

Abstract: A new automatic high velocity arc spraying system was developed. The system was consisted of five units, i.e. central control unit, operating machine, positioner, touching screen and high velocity arc spraying equipment. The central control unit is controlled by a program, controlling other four units. Spraying parameters could be input and modified on the touching screen during spraying. The moving of spraying gun was carried out by motion arm of the operating machine. The rotational velocity and angle of components to be sprayed was controlled by positioner. The spraying process for a cylinder body of automobile engine with the system was introduced in detail. The auto and manual arc spraying have been used to fabricate coating. The microstructure of the coatings prepared by the two spraying processing was analyzed. The result shows that the auto sprayed coating has a more uniform and compact structure than that of the manual sprayed coating.

Abstract: After reviewing most of the recent developments performed on hybrid processes, basic physical phenomena of PVD-PECVD processes are detailed with the help of a model showing the different influences of main process parameters. Ti-Si-O and Zn-Si-O thin films are synthesized as possible examples of composite thin films. Limitations of the model developed are also discussed with respect to the composition and structure of deposited thin films.

Abstract: TiN coatings were produced by depositing a series of Ti layers and subsequently ion implanting 80 keV nitrogen ions. TRIDYN FZR software simulation was used to estimate the maximum Ti layer thickness which could be successfully transformed to TiN by ion implantation. The chemical profile of these coatings was achieved by conducting a series of EDS measurements across coatings, sectioned at shallow angles. It was found that the structure of the RIBAD TiN films produced changes significantly with the implanted nitrogen ion dose. Their hardness and wear resistance were found to increase rapidly as the post implantation time was increased up to 230 minutes, reaching a maximum of 27GPa and 2.5x10-12 mm3m-1N-1 respectively. On the other hand, the electrochemical corrosion resistance of TiN coated magnesium substrate was inferior to that of the untreated substrate material. The results suggest that the coating developed is attractive as a topcoat of a duplex coating; having as underlay a corrosion protective film. In a separate study, it has been shown that such coatings could be ion beam sputtered titania or alumina.

Abstract: Fe/Cu nanometer-scale multilayers with nominal modulation wavelengths ranging from 5 to 40 nm are deposited by direct current magnetron sputtering on Si (100) substrates. Modulation structures of the multilayers are examined by small angle / wide angle x-ray diffraction (SA/WAXRD) and cross-sectional transmission electron microscopy (XTEM). Hardness of the multilayers is measured by using nanoindentation. All the multilayers have Fe (110) and Cu (111) textures. Interface coherency is observed in the multilayers with designed modulation wavelengths of 5 and 10 nm. The hardness increases firstly and then deceases with increasing the modulation wavelength, and reaches peak value of 7.29±0.29 GPa in the multilayers with nominal modulation wavelength of 10 nm. The evolution of the hardness of the mulitlayers is explained by interface width and modulus difference between sublayers.

Abstract: The novel frictional properties of hydrogenated DLC (Diamond-like Carbon) films have been reported for nearly ten years. But up to now, researchers still haven’t known the exact mechanism resulting in the super-low frictional performance of hydrogenated DLC films. Especially they have little knowledge on the molecular configuration and structural properties of these kinds of films. In this paper, CH3 radicals with different impact energies are selected as source species to deposit DLC films on diamond (100) by molecular dynamics simulation. Results show hydrogenated DLC films can be successfully obtained when impact energy is in an appropriate scope that is no less than 20eV. The depositing processes involve impinging diamond surface and bonding procedure. Some atoms, instead of bonding with substrate atoms, fly away from the diamond surface. Only suitable impact energy can improve the growth of the film. Within 30eV to 60eV, the maximum deposition ratio is attained. In addition, when carbon atoms act as the deposition sources, the deposition ratio is relatively higher. Furthermore, the authors find that species with higher concentration of carbon atoms in deposition sources lead to a better deposition rate. Carbon atoms are more reactive than hydrogen atoms. Then the relative densities of DLC films are calculated. The density curves indicate that the structures of the films vary obviously as the impact energy augments. The average relative density is generally monotone increase with the increment of impact energy. The hybridization of carbon atoms greatly affects the properties of hydrogenated DLC films. The transition between sp2 and sp3 will result in the graphitization and reduce the frictional coefficient when DLC films are used as tribo-pair in friction.

Abstract: Repeated impact test is an appropriate way to evaluate coating properties of metal cutting tools since the cyclic impact loading applied in the test simulates the interrupted cutting process. For hard CVD coatings with multi-layered structure, the alumina is usually of the lowest toughness and adhesion, and relatively easy to fail in the metal cutting. In the present paper, multilayered coatings consisting medium temperature TiCN, Al2O3 and TiN were deposited by chemical vapor deposition (CVD) on the tungsten carbide/cobalt substrate and evaluated using scratch adhesion test and repeated impacted test. The phase structure of alumina layers are α or )κ as usually applied in cutting tools, and the grain size for the α phase one is varied from one micron to four microns. The scratch and indentation test results show that the alumina layer of κ phase is easy to remove under the quasi-static loading, implying brittleness and low adhesion. The repeated impact test results reveal lower impact resistance for the κ phase alumina, and only adhesive failure can be found, which differs to that of the α phase one. The coarse grained α-Al2O3 layer shows similar adhesion compared to the fine grained α- Al2O3 in scratch test. The failure mode of the coating with coarse grained α-Al2O3 layer in the repeated impact test is primarily impact wear. No cohesive failure can be found at all load levels, and this leads to higher impact life than that of the fine grain one. It was shown that the relatively low adhesion of bottom TiCN layer may not affect the impact resistance.

Abstract: To overcome the low adhesion of hydrogen-free DLC films on metal substrates, in this studying, DLC films (0.9μm) were prepared with 3 types of interlayer (2 types of Ti/TiCx/DLC interlayer and 1 type of Ti/TiNx/TiNxCy/DLC interlayer) on different substrates (W18Cr4V, Cr12, GCr15, TC4, 40Cr, 9Cr18 and Cr18Ni9Ti). The internal stress of the films was calculated by the bending of substrate (Si(100)). It was found that it is as high as 3.9GPa, and part of the high residual stress of the DLC films was dissipated through a compound interlayers, and the thick films achieved, and the pull tests found that the adhesion has been highly strengthened with a proper interlayer. The films structure qualities were investigated by Raman spectroscopy and the results indicate that the films have the same structure properties which suggests that the properties of the DLC films can not been affected by substrates. The hardness is about 5000HV, defined by nanoindentation techniques. The frictional properties were investigated by reciprocal sliding tests and the friction coefficient was about 0.1, independent of their substrates. Thus our DLC films may have great potential applications in precision parts tribological application.

Abstract: Cr-Me-N-O (Me; Ni, Cu and Mg) thin films have been designed and successfully prepared by the pulsed laser deposition (PLD) method. It was found that Me, which form the monoxide MeO, are effective for hardening the Cr(N,O) thin films.