Papers by Keyword: PVD

Abstract: This work is part of a publicly funded project called ReffiMaL (resource efficient material solutions for power electronics), which aims to substitute electroplated Nickel (Ni) as contact material in power electronic modules. The baseplates of these power electronic modules are based on the metal matrix composite material AlSiC, which needs to be coated to become solderable. Today, it is state-of-the-art technology to coat the baseplate with electroplated Ni to form an adhesive layer to the system solder. In this paper we present a performance comparison of physical vapor deposited (PVD) Ni and electroplated Ni. The main advantage of PVD Ni is a significant reduction of layer thickness compared to the electroplating process. Second advantage of PVD Ni is the limitation of the deposition to areas that get soldered, in contrast to a non-selective electroplated coating. When deposited by PVD at room temperature, Ni exhibits columnar growth patterns, whereas electroplated Ni tends to form a laminar layer. The columnar growth leads to an increase in interface area affecting phase formation behavior. To compare both adhesion layers, we investigate the phase formation after soldering with a Sn based soft solder-copper composite material. The baseplates are reflow-soldered at different temperatures and process times. Temperature varied between 270°C and 400°C. The corresponding process time ranged from 10 to 40 minutes. We inspect the samples optically to determine the phase formation. Intermetallic phase (IMP) composition is evaluated using energy dispersive X-ray analysis (EDX). ReffiMaL is funded by the German Federal Ministry of Education and Research (BMBF).

Abstract: In this study we determined average residual stresses in hard nitride PVD AlCrN, TiAlN and TiCN coatings through simultaneous measurement of length variation in thin-walled tubular substrates and of the curvature of plate substrates. A device for measurement of the length of the tube was developed. Inside the depositing chamber the tube and the plate were fixed parallel in the relation to the axis of the rotating cathode. One batch of plate samples was produced by deposition on front surface (facing the cathode) and the other batch, by deposition on back surface (with back to the cathode). The cross-sectional microstructure and thickness of the coatings were investigated by means of scanning electron microscopy (SEM). The thicknesses of the coatings deposited on front and back surfaces of the plates and on the tube were significantly different. The values of average compressive residual stresses, determined by both methods, were very high irrespective of coating thickness. It was found that the values of compressive residual stresses in the coating were dependent on the shape of the substrate and on its position in the relation to the axis of the rotating cathode.

Abstract: The DC magnetron sputtering is often used for fabricating thin hard coatings for a wide range of industrial applications. The technique allows using DC power for deposition low or non-conductive films from metal target without using expensive RF power for insulation target. However, the performance of DC reactive sputtering is affected significantly by a phenomenon namely target poisoning. When the target poisoning occurs, coating is formed not only on substrate surface but also on target surface, which results in the reduction of deposition rate and coating properties. This paper presents a study on poisoning of Ti target during TiN coating deposition in the Ar + N₂ atmosphere. Results showed that the target poisoning state is impressed dramatically by partial pressure and flow rate of nitrogen gas. In poisoning mode, the deposition rate was reduced significantly compared to that in the metal mode. In addition, the formed TiN coating exhibited a non-stoichiometric and low adhesion to the substrate.

Abstract: To reduce maintenance and to increase the corrosion protection and lifetime of maritimestructures while complying with environmental standards, multilayer coatings are applied to protectsteel sections. A new generation of hybrid sol-gel and/or HiPIMS Ni-based thin films appear toconstitute an efficient pre-treatment before the anti-corrosion paint application. However, increasingthe number of coatings and associated interfaces may lead to coating failure due to stresses inducedby the different deposition processes. Therefore developing smart models to assess the stressdistribution along these multilayers appears of significant importance. The well-known Stoneyformula cannot be used for multilayers and owing to the large dimensions of the object to be protected.To assess an easily measurable curvature after deposition, thin steel sheets are used but do not respectany more the Stoney hypotheses. So we set up an analytical thermo-elasto-plastic model to evaluatethe stresses induced by depositions in each layer. This model is based on the various thermalexpansion coefficients of every coat. After extrapolation along the complete thickness, combiningsol-gel and PVD deposition smoothens the stress difference between steel and paint. The shearstresses at interface seems thus to be reduced. The evolution of the stress difference between layerswith the imposed deflection can predict the mechanical strength and the interface failure. In order toevaluate the quality of the model, in-situ four-point bending in SEM was performed to study of theadhesion between the various layers. The results deduced from the model are in good agreement withSEM images.

Abstract: The Multi-Sources of Cathode Arc (MSCA) were installed in the vacuum chamber in order to increase the substrate temperature and to provide a plenty of Ti plasmas from titanium plate inside the chamber. The increase rate of the substrate temperature of the SKD11 substrate against the deposition time for two thicknesses of the substrate by operations with both single ion source and MSCA was obtained. It was known that MSCA were useful for the film synthesis for the larger substrate both in size and in number. A wider diffusion interface between TiN film and SKD11 substrate was formed by dissolution of both TiN and Ti₂N into the substrate more actively due to plenty Ti ion numbers supplied by MSCA. Due to the thick diffusion interface the adhesion of the film increased and thus the hardness increased up to twice. The peaks of Ti₂N(111) and Ti₂N(211) which are indicators of high hardness were observed in XRD pattern. The pseudo-diffusion interface between the outer TiN film and substrate formed and it improved the film adhesion. By using MSCA the hardness of SKD11 surface was improved up to 126 from 58 in Rockwell-C scale by the TiN deposition in this study.

Abstract: By newly adopting of a two-step bias voltage-sustained nitrification of the plasma process the titanium nitride films which applied to the mold base steel KP-1 are manufactured. The two-step process of biased voltages was introduced in order to consider microscopic kinematics of Ti ion bombardments which lead to a deep study on the plasmas including surface temperature of substrates associated with nitrification the KP-1 surface. For supplying of the additional biased voltage to the conventional coater, an anode-biased ring was installed near the plasma source and it ultimately upgraded the typical method of physical vapor depositions which uniquely adopted one bias voltage applied to the substrates because the additional ring controlled both ions and electrons effectively in order to improve surface smoothness and to increase surface hardness with various values of surface temperatures of substrate and deposition times. The discharge ionic current of titanium flux was measured as functions of both the ring bias voltage and the substrate voltage using single probe. By using plasma physics for the two-step bias voltages the discrete mean-free-times, due to cyclonic motions of ions by magnetic field, were studied to show the effects of two bias voltages. The maximal hardness increase of Ti/TiN films deposited on KP-1 was 370% when the surface temperature was 370 °C, the substrate bias voltage of 800volts, and the deposition time was 55 minutes after ring bias was applied. The 2000 times-magnified cross-sectional morphologies of TiN films deposited on the carbon mold base KP-1 were taken as a function of the ring anode bias. The 1000 times-magnified photograph of the TiN-filmed surface deposited on KP-1 mold base was taken to investigate the surface morphology. In order to examine the two-step bias test with respect to both the corrosion problem and the surface hardness, the 2000 times-magnified morphological photograph of a cross-sectional Ti/TiN film which was deposited on the KP-1steel mold was taken.

Abstract: 7075-T6 aluminium alloy is under investigation in the last decades because of its sensitivity to corrosion and its poor surface behaviour. The alloy is widely used in many mechanical, aeronautical and structural engineering appliances because of its high strength-to-weight-ratio. Notwithstanding its strength and light weight advantages, its applications in corrosive environments, with fatigue applied loads, is still under research. The mechanical and chemical driving forces have still to be accurately evaluated and the role of each one identified. Results of tests on rotating bending fatigue (R = -1) 7075-T6 uncoated and PVD DLC coated specimens are reported in this paper under various stress levels and number of cycles to failure. Fracture surfaces were observed via SEM characterization in order to assess the role of the chemical aggressive environment, the residual stress field and the applied load.

Abstract: In order to improve surface smoothness and increase its surface hardness of the PK-4 steel mold the dependencies of the surface temperatures of substrate, deposition times, and bias voltages applied to the substrate on the TiN film made by the physical vapor deposition were studied. Six main steps of the synthesis process were introduced to improve the robustness. Double applications of the bias voltages increased the surface hardness. The rotating substrates increased the uniformity of the films. 1000 times-magnified pictures were taken to analyze the micro-grains of TiN. SEM pictures were taken to confirm the surface smoothness. Both the surface temperature of substrates and deposition time were affecting factors. The maximal hardness of TiN film deposited on KP-4 was increased by 20%. The surface temperature of substrates contributed to 13% in the increase of hardness. The deposition time also contributed to 6% in the increase of hardness respectively.

Abstract: TiCN and TiAlN gradient coatings were deposited on the AISI 316L stainless steel substrates by lateral rotating cathode arc (LARC) physical vapour deposition (PVD) technology. Corrosion and tribocorrosion behaviour was studied in 3.5 wt. % NaCl solution. The thickness of coatings was about 3 μm. For both coatings the corrosion potential shifted to more positive values as compared to the uncoated substrate. The corrosion current density decreased for TiCN and TiAlN coatings indicating up to 40 folds higher polarization resistance. The coefficient of friction value of TiCN coating is three times lower and durability is six times higher than that of TiAlN coating under the same tribocorrosion conditions.

Abstract: This work presents a photolithographic rapid prototyping process for producing thin films ("Rapid Phototyping"). This process allows a quick and cost-effective generation of scalable thermopile microstructures using commercial equipment and materials. Structural widths of 100x250μm can be produced reproducible in a lift-off process with an accuracy of 5 microns vertically and 30 microns horizontally.