Structure of duplex CrN/NbN coatings and their performance against corrosion and wear

In tribological applications the coating-substrate combination can be considered as a system, since both greatly influence the properties of that affect the tribological performance. Further, it is often desirable that both high wear resistance and corrosion resistance can be achieved even when low cost and easily machineable substrate materials are considered. Duplex surface treatment combining pulse plasma nitriding and PVD coating can provide solution for excellent wear and corrosion resistance for low alloy and constructional steels. In this work three different pulse plasma nitriding processes were carried out prior to the CrN/NbN PVD coating to attain high surface hardness and enhanced load bearing behaviour for S154 high strength construction steel. The phase composition of the compound layer, formed in the nitriding process, was found to greatly affect the tribological properties of the duplex system. The compound layer with high amount of epsilon-phase contributed to superior corrosion and wear resistance, whereas the ductile gamma'-phase compound layer provided better impact resistance and enhanced. The best duplex treated S154 samples had wear resistance comparable to that of similarly coated HSS. The corrosion resistance was also improved by duplex process. If anodic current at +500 mV vs. SCE is considered as criteria, the best system has almost 3 orders of magnitude lower corrosion current than with the PVD coating alone. (c) 2007 Elsevier B.V. All rights reserved

Microstructure and properties of novel wear and corrosion resistant CrON/NbON nano-scale multilayer coatings

CrN/NbN nano-scale multilayer coatings have found use in a number of commercial applications where wear and corrosion resistance determine the service life of the components. To further improve their performance a novel CrON/NbON topcoat has been developed. The coatings were deposited using an industrial Hauzer HTC 1000/4 UBM-ABS coating machine utilising the Arc Bond Sputtering method where cathodic arc metal ion etching is used to prepare the interface prior to coating deposition by unbalanced magnetron (UBM) sputtering. The oxynitride process was performed in mixture of dry air and argon at bias voltages varying from U-B=-75 V to - 120 Vat total pressures during deposition from 3.5*10(-1) Pa to 4.9*10(-1) Pa. The thickness of the oxynitride film varied between 1.6 and 2.3 mu m, while the total coating thickness varied between 4.6 and 5.3 mu m. The XTEM investigation revealed that the microstructure of the oxynitride layer was dense columnar with a pronounced nano-scale multilayer architecture. By X-ray difraction (XRD), the coatings were identified as crystalline with mixed texture. As the pressure during the oxynitfide deposition stage was increased the crystal structure of the top layer became increasingly amorphous/nano-crystalline. An increase in the bias voltage also caused a shift from {100} texture towards {111} texture. The best performing oxynitride coatings had similar low sliding wear rates as the reference standard coating without affecting their corrosion resistance. However, the wear rate against a 100Cr6 counter body was reduced by a factor of 10 and the friction coefficient from 0.57 to 0.49. The wear rate of both the coating and the counter body was reduced as the bias voltage was increased, while increasing the deposition pressure had adverse effects on the tribological properties. The wear behaviour can be related to the special nano-scale multilayer structure of the oxynitride layer as coating with best tribological properties exhibits a pronounced nano-scale multilayer structure parallel to the coating surface. (c) 2005 Elsevier B.V. All rights reserved

Influence of ion bombardment on the properties and microstructure of unbalanced magnetron deposited niobium coatings

The effect of the ion bombardment to unbalanced magnetron deposited, approximately 1.5 and 4.5 mum thick, Nb coatings have been investigated as the bias voltage was varied from U-B = -75 to -150 V. Increasing bias voltage increased the hardness of the coating from 4.5 to 8.0 GPa. This was associated with residual stress and Ar incorporation into the Nb lattice. Strong {110} texture developed in the samples deposited at low bias voltages, while beyond U-B = -100 V a {111} texture became dominant. However, strong {111} texture was observed only with the thicker 3Nb coatings. Secondary electron microscopy investigation of the coating topography showed fewer defects in the thicker coatings. All coatings exhibited good corrosion resistance, with the thicker coatings clearly outperforming the thinner ones. Excessive bias voltages (U-B = -150 V) was found to lead to poor adhesion and loss of corrosion resistance. (C) 2004 Elsevier B.V. All rights reserved

Towards a 300 WP p-Type HIP-MWT-Module - Simulation, Experimental Results and Costs

In this work we are aiming at the goal of fabricating a cost-effective HIP-MWT module exceeding 300W. In order to accomplish this goal HIP-MWT (high-performance metal wrap through) silicon solar cells [1, 2] are fabricated on industrial PERC (passivated emitter and rear cell) precursors. Simulation of the optimal metallization layout for MWT based on measured parameters show cell efficiencies up to 21.5%. The consequentially fabricated HIP-MWT solar cells reach maximum efficiencies of 21.4%. The in parallel processed H-pattern reference cells reach maximum efficiencies of 21.2%. The cell efficiencies show a reduced advantage for MWT than in similar experiments, which is due to the tapered busbars of the reference cells allowing nearly the same short circuit currents. Anyhow, combined with a module interconnection based on back contact foils a cell-to-module (CTM) loss of 2 % is demonstrated which allows module power over 300 WP. Due to a power advantage of about 15W in comparison to H-pattern modules the cost of ownership calculation shows a cost advantage of the HIP-MWT module of 3.2 %. Simulation, experimental results and cost calculation show an advantage for HIP-MWT technology over the H-pattern reference leading to the conclusion that MWT is a more cost-effective concept