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Abstract: Although electroless Ni–P–SiC is a well known industrial coating used for wear resistance, there appears to be little information pertaining to its effectiveness to resist cavitation erosion. In this study, electroless Ni–P composite coatings are formed on AISI 1045 steel through the addition of nano- and micro-scale SiC particles to the plating bath. The influence of a post-heat treatment on both the conventional electroless Ni–P and composite coatings is examined. The cavitation erosion test is carried out on stationary specimens in accordance with the ASTM G32-98 standard. It is found that the best cavitation erosion resistance, in either distilled water or a 3.5wt.% NaCl solution, is achieved through both the incorporation of nano-SiC particles and the application of a post-heat treatment. [Copyright &y& Elsevier]

Abstract: There has been interest for some years now in the development of duplex treatments involving plasma nitriding coupled with the deposition of a hard coating. Although this coating system has in service use for various applications, there are still however many underlying uncertainties with regard to how treatment parameters affect coating performance, for example the deposition temperature and the related substrate softening. Different duplex treatments are applied to SKH 51 and SKH 2 steel by changing the nitriding atmosphere and TiN deposition temperature. The nitride layers with the ε-Fe3N phase are more prone to denitriding than those consisting of either an α or γ′-Fe4N phase during deposition of the hard coating. The black layer formed through denitriding of the SKH 51 alloy is thinner than that of the SKH 2 alloy. This is considered to be a result of the presence of nitride forming elements. Regardless of the nitride phases that are formed, the diffusion of nitrogen atoms is enhanced at increased substrate temperatures, induced by ion bombardment characteristics during coating growth, causing a significant decrease in the nitrogen content of the original prenitrided layer. The composite surface hardness of the treated specimens is found to be most dependent on substrate softening effects, as opposed to factors such as black layer formation. The adhesion of the TiN coating to the underlying nitrided layer again appears to be influenced more by softening of the substrate during higher temperature deposition as opposed to the formation of a black layer. This is indicated by the fact that the adhesion to the samples with an initial ε-Fe3N nitrided surface is greater than those with an α phase, even though the black layer is only present for the former. These studies reveal that avoiding substrate softening is essential in producing high performance hard coating/nitride duplex coatings. [Copyright &y& Elsevier]

Abstract: In this work, a novel arc ion plating (AIP) system, consisting of a centrally configured multi-arc source array (CCMA), is developed. This system is aimed to satisfy the present industrial demands for the large-scale production of multicomponent, multilayered, and superlattice coatings. The central array is made up of three flat, independently powered, arc sources. These form a triangular pillar. The newly developed CCMA AIP system is used to deposit TiN/ZrN coatings, in order to evaluate its performance. The surface hardness of the specimens is measured by micro Vickers indentation. A scratch test is used to determine the adhesive strength of the coatings. Scanning electron microscopy (SEM) is used to observe the cross-sectional morphology and to measure the film thickness. An energy dispersive spectrometer (EDS) is used to characterize film composition. The crystal structures of the coatings are characterized by an X-ray diffractometer and transmission electron microscope (TEM). The deposited coatings range from a micro- to nano-layered (TiN/ZrN) structure as the rotation speed of the substrate table was increased. Each layer exhibits a (111) preferred orientation. At rotating speeds in excess of 10 rpm, a nano-multilayered Ti(Zr)N structure is formed, again with each layer having (111) preferred orientation. At the highest rotation speeds the greatest surface hardness and film adhesion strength are attained. This is attributed to the maximized stress accommodation of the nano-multilayer structure, through the different shear elastic modulus of each layer. This research demonstrates that this novel CCMA AIP system is highly flexible in coating material design and capable of mass production. [Copyright &y& Elsevier]

Abstract: Arc ion plating is known to be capable of producing crystalline ceramic films at low deposition temperatures and therefore lends itself to the production of functional zirconia films which are commonly used for thermal barrier coatings, fuel cells and gas sensors. In this study, yttria-stablized zirconia (YSZ) films were deposited on Alloy 600 nickel-based superalloy by an arc ion plating system utilizing a single 84Zr–16Y alloy cathode. The working pressure, substrate bias and substrate-to-cathode distance were varied systematically in order to reveal their effects on the growth behavior and microstructure of the YSZ films, which is important when considering future applications. In this study YSZ films with mixed crystalline cubic and tetragonal structures were synthesized at temperatures of about 400 °C without in situ substrate heating. The influence of total pressure was examined by changing the argon pressure whilst maintaining a constant oxygen pressure of 0.6 Pa. Arc motion was found to be stable on the cathode up to a working pressure of 4.0 Pa and the optimum film quality was achieved for deposition in pure oxygen at 0.6 Pa. Film growth rates ranged from 11 to 18 μm/h for all deposition conditions. For both source to substrate distances (12 and 18 cm) the film growth rate increased with negative substrate bias, reaching similar maxima at −400 V, which subsequently decreased on further increase of the bias. By taking account of process parameter effects such as these, it may be possible to optimize the film quality for specific requirements. [Copyright &y& Elsevier]