Plasma nitriding is an established process for increasing the corrosion and wear resistance of steel. However, the possibilities of modern developments in the field of high-voltage plasma power supplies have been hardly investigated. For example, modern plasma generators allow improved arc management, which enable plasma nitriding at higher voltages.In the present work, the influence of increased voltage (up to 800 V) on the nitriding of a ferritic steel X38CrMoV5-1 was investigated. It was found that the thickness of the compound layer increases with increasing voltage. Especially at short process times the increased voltage leads to increased growth. An increase in the nitriding depth was also observed.Furthermore, the increased voltage has an effect on the composition of the compound layer too. A moderate increase in epsilon-nitride in the compound layer was observed.One explanation for the observed behavior is the over proportional increase in power with increasing voltage, indicating an increased ionization rate of the plasma. Due to this, more diffusible species would be available for nitriding.The presented results could be used to reduce process times, particularly where the formation of a compound layer is the aim of the process. An example of such a process is oxy-nitriding. Das Plasmanitrieren ist ein etabliertes thermochemisches Verfahren zur Verbesserung der Korrosions- und Verschleissbestandigkeit von Stahlen. Moderne technologische Entwicklungen auf dem Gebiet der Hochspannungsplasmastrom-Versorgung und die Erforschung ihres Potenzials sind kaum untersucht worden. So ermoglichen moderne Plasmageneratoren ein deutlich verbessertes Arc-Management, das Plasmanitrierprozesse bei hoheren Spannungen ermoglicht. In der vorliegenden Arbeit wurde der Einfluss einer erhohten Spannung (bis zu 800 V) auf das Nitrieren eines ferritischen Stahls (X38CrMoV5-1) untersucht. Es wurde festgestellt, dass die Dicke der Verbindungsschicht mit steigender Spannung zunimmt. Insbesondere bei kurzen Prozesszeiten fuhrt die erhohte Spannung zu einem deutlich erhohten Wachstum. Daruber hinaus wurde auch eine Zunahme der Gesamtnitriertiefe beobachtet. Daruber hinaus scheint die erhohte Spannung einen Einfluss auf die Zusammensetzung der Verbindungsschicht zu haben. Mit zunehmender Spannung wurde eine moderate Zunahme von epsilon-Nitrid in der Verbindungsschicht beobachtet. Eine Erklarung fur das beobachtete Verhalten ist der uberproportionale Anstieg der Leistung mit steigender Spannung, was auf eine erhohte Ionisierungsrate des Plasmas hinweist. Dadurch stehen mehr diffusionsfahige Spezies fur die Nitrierung zur Verfugung. Die vorgestellten Ergebnisse konnen genutzt werden, um die Nitrierprozesszeiten zu verkurzen, insbesondere wenn die Bildung einer Verbindungsschicht das Ziel des Prozesses ist. Ein Beispiel fur solche Prozesse ist das Oxy-Nitrieren. Modern power supplies allow plasma nitriding at high voltages. To date, nearly no studies have been published on this topic, but the results show that it is worth studying. The thickness of the composite layer increases as the voltage increases, especially at short process times. At 800 V/2 h a similar compound layer thickness was achieved as at 500 V/2 h.image

Nitriding is a common thermochemical treatment to improve surface properties of steels with focus on corrosion and wear resistance as well as hardness. To meet the requirements of specific application fields, surface properties can be adjusted in a wide range by varying the process parameters such as nitriding temperature, processing time and atmosphere. Aim of this work is the numerical description of a plasma-nitriding process for a high-alloy tool steel X153CrMoV12 and a nitriding steel 15CrMoV5-9 to investigate the infuence of the microstructure on the nitriding layer development. In addition, the developed model is intended to serve as a prediction tool for the resulting layer thicknesses and nitrogen distributions depending on process temperature and time. The intended nitriding model was developed using the commercial FE-program DEFORM (R) and validated based on the results of plasma-nitrided samples at three different nitriding temperatures (480, 520, 560 ?) and processing times (2, 4, 16 h). DEFORM (R) enables the implementation of a real microstructure using a script-based approach. Up to now, only a few simulation concepts exist for nitriding processes on materials with a defined microstructure. With the developed model, a prediction of the resulting nitriding zone and nitrogen distribution within the validated range is possible for a carbide-free and carbide-rich microstructure. As expected the resulting nitriding zone increases with rising temperature and time. In addition, the nitriding steel (15CrMoV5-9) reaches significantly higher layer thicknesses than the high-alloy steel (X153CrMoV12). Furthermore, it is observed that areas with many carbides show lower layer thicknesses compared to carbide-free areas.

Plasma nitriding offers great potenzial for improving the wear properties of austenitic steels. Here, the austenitic standard grades 1.4307 and 1.4404, as well as the titanium-stabilized grades 1.4541 and 1.4571 were investigated regarding the influence of the material condition on the nitriding result and corrosion behavior. Special focus was put on the influence of the Ti-stabilisation. In addition, it was investigated to what extent corrosion properties are influenced by cold-forming induced defect structures. In comparison to 1.4307 and 1.4404, less nitrogen is incorporated in areas with forming martensite in titanium-stabilized austenitic steels and lower nitriding temperatures, while an increased diffusion of nitrogen is observed, when only slip bands are present. The corrosion resistance is generally improved by the plasma nitriding parameters used for this study. In general, a higher thickness of the S-phase, which forms during the plasma nitriding, results in better corrosion resistance and higher surface hardness. The titanium stabilization inhibits nitrogen diffusion in the presence of deformation induced martensite at lower nitriding temperatures and promotes diffusion in the presence of deformation induced slip bands.

Plasma nitriding is a state-of-the-art thermochemical treatment, which is used by the processing industry for hardening of the surface-near material volumes of tools and components. An artificial neural network, particularly backpropagation neural network, has been developed to investigate the hardness behavior of different steel types according to various process parameters. Therefor eleven steels with different chemical compositions were plasma nitrated with different concentrations of nitrogen at various temperatures. The hardness profiles were studied with indentation measurement. The experimental data were used to train the neural network with the Levenberg-Marquardt algorithm. For an optimal training, weight distribution, hidden neurons and gradients of neuron activation functions were varied, to allow simulations of hardness profiles for the different types of steel with deviant nitriding parameters.

Niobium-containing diamond-like carbon (Nb-DLC) films were deposited in a reactive high power impulse magnetron sputtering (HIPIMS) process, using a niobium target in an argon/acetylene atmosphere. Investigations of the electrical properties revealed their good suitability to serve as sensor material in strain gauges, with an elevated gauge factor of 35.5 and the possibility to adapt the temperature coefficient of the electrical resistance (TCR) to values near zero. Structure analysis of the crystallinity, chemical composition, and morphology of this material give insights of the correlations between structure and piezoresistive properties. A structure zone model in relation to the Nb content was developed, combining the results of the different measurements.

Porous thermal barrier coatings (TBC) reduce the thermal load of gas turbine components. State-of-the-art TBCs consist of partially yttria-stabilized zirconia (PSZ) and are deposited by means of thermal spray techniques or electron beam physical vapor deposition. In this paper, an alternative, innovative deposition technique (reactive gas flow sputtering - GFS) is investigated and the influence of process parameters on the microstructure and the suitability of GFS coatings as TBCs is discussed. PSZ coatings were deposited on polished FeCrAlY-alloy substrates, with varying substrate temperature and oxygen flow rate, and characterized by means of SEM, and XRD. The substrate temperature is the crucial parameter. Between 500 and 800 degrees C, four types of columnar microstructures are found based on XRD pattern and morphology. The growth direction of the columns changes from <111> to <100>, accompanied by a change in shape from triangular to four-sided. Varying the oxygen flow rate at a given substrate temperature alters the microstructure defined by the substrate temperature. While oxygen flow rates above a certain level do not have an effect, low oxygen flow rates lead to further densification and compressive stresses, rendering these conditions unsuitable for TBC manufacturing. In conclusion, promising microstructures are presented accompanied by guidelines for process parameters.

Hot forging is an effective production method producing safety relevant parts with excellent mechanical properties. The economic efficiency directly depends on the occurring wear of the tools, which limits service lifetime. Several approaches of the presenting research group aim at minimizing the wear caused by interacting mechanical and thermal loads by using enhanced nitriding technology. Thus, by modifying the surface zone layer it is possible to create a resistance against thermal softening provoking plastic deformation and pronounced abrasive wear. As a disadvantage, intensely nitrided surfaces may possibly include the risk of increased crack sensitivity and therefore feature the chipping of material at the treated surface. Recent projects (evaluated in several industrial applications) show the high technological potential of adapted treatments: A first approach evaluated localized treatments by preventing areas from nitrogen diffusion with applied pastes or other coverages. Now, further ideas arc to use this principle to structure the surface with differently designed patterns generating smaller ductile zones beneath nitrided ones. The selection of suitable designs is subject to certain geometrical requirements though. The intention of this approach is to prevent the formation and propagation of cracks under thermal shock conditions. Analytical characterization methods for crack sensitivity of surface zone layers and an accurate system of testing rigs for thermal shock conditions verified the treatment concepts. Additionally, serial forging tests using adapted testing geometries and finally, tests in the industrial production field were performed. Besides stabilizing the service lifetime and decreasing specific wear mechanisms caused by thermal influences, the crack behavior was influenced positively. This leads to a higher efficiency of the industrial production process and enables higher output in forging campaigns of industrial partners.

Sputter deposition of magnetic material provides some challenges. In the case of soft magnetic materials, usually thin targets and strong magnetic arrays of the sputtering cathode are used for an effective magnetron sputtering. In the case of hard magnetic material, the situation is different. The magnetic field lines are closed in the target and the magnetron is effectively acting as a diode sputtering system. Hollow cathode processes in contrast require no magnets at all to enhance the ionization. Therefore, high rate deposition of hard magnetic films becomes possible.In this paper results of gas flow sputtering (GFS), a modification of hollow cathode processes, for deposition of hard magnetic CoSm films are presented. Especially for the deposition of thick films (10 pm and more) gas flow sputtering is an economic process. Using GFS high dynamic deposition rates of several 10 pm per hour are achievable. The influence of the deposition parameters on the magnetic properties coercivity and magnetic remanence are discussed. (C) 2017 Elsevier B.V. All rights reserved.

This publication describes a new quick and economical method for the simulation of tool wear in the deep drawing and stretch forming of steel sheets in the area of the drawn edge. This method also allows a comparative evaluation of the properties of different tool materials versus reference materials. In order to reduce the amount of required test cycles, a controlled amount of wear inducing particles is added to the contact zone between tool and sheet metal.Initially, investigations with a high load tribometer were carried out for the selection of suitable wear inducing particles. In order to cause a degree of wear similar to normal circumstances within a shorter amount of time, wear inducing particles were added. Signs of wear were analysed by scanning microscopy and EDX analysis. The wear particles were also used for wear initiation for a strip drawing test.Subsequently, a wear testing stand was modified for the new concept allowing for a controlled amount of wear particles to be applied. After optimization of the test parameters, it was found that after 50 strokes with a test time of 2.5 min a result similar to 94,000 strokes without wear particles was obtained. (C) 2017 Elsevier B.V. All rights reserved.

The aim of this work is to gain an understanding of the influence of substrate temperature during deposition on the resulting microstructure and crystallographic properties of gas flow sputtered (GFS) partially yttria stabilized zirconia coatings (PSZ).PSZ coatings were deposited on a FeCrAl-Alloy substrate, varying the substrate temperature between 500 degrees C and 800 degrees C. Regardless of the substrate temperature, all coatings were columnar, but varied in their morphology. Four different groups of sub-microstructures, each defined by a substrate temperature range, were identified based on morphology and X-ray diffraction (XRD) pattern.The two low-temperature groups exhibit a novel microstructure characterized by three dense ridges at intervals of 120 converging at the column center. Supported by these ridges small stacked plates lead to a featherlike porosity. The XRD pattern revealed a monoclinic fraction, besides the tetragonal and/or cubic one, and a (111) growth direction. Higher temperatures diminish the monoclinic fraction until it vanishes at 800 degrees C accompanied by a change in growth direction to (100).Thermal cycling experiments were conducted between 1050 degrees C and 100 degrees C. Macroscopic spallation occurred for one group while the other samples were intact after the end of the experiment at 1300 cycles. Microscopic de laminations were found between a pure alumina scale and a mixed oxide zone, consisting of zirconia particles embedded into an alumina matrix. A hypothesis was proposed explaining the observed failure mode. (C) 2017 Elsevier B.V. All rights reserved.

This work investigates the influence of substrate temperature and applied bias voltage on the resulting microstructure and crystallographic properties of gas flow sputtered (GFS) partially yttria stabilized zirconia coatings (PSZ). On a FeCrAlY-alloy substrate PSZ coatings were deposited at substrate temperatures of 500 degrees C, 650 degrees C and 800 degrees C with bias voltages up to -100 V and were subsequently analyzed utilizing SEM, FIB and XRD. Without bias voltage, all coatings were columnar and composed of small stacked platelets, but they varied in their porosity and morphology. Higher substrate temperatures lead to higher adatom mobility decreasing the porosity and the deposition rate. For all microstructures a distinct growth direction of the columns is observed changing from < 111 > (500 degrees C and 650 degrees C) to (100) (800 degrees C). For the < 111 > morphology, three ridges at intervals of 120 are observed throughout the whole column. In addition to the tetragonal/cubic phase, monoclinic fractions are found at the two lower substrate temperatures. The application of a negative bias voltage enhances the surface mobility of the film-forming adatoms and can cause densification due to atom displacements, resputtering or channeling phenomena. Moderate bias voltages up to -40 V result in more regular columns and a lower porosity. For high bias voltages (-100 V), the densification effects seem to dominate leading to fully dense coatings with residual stresses up to -2.5 GPa and no preferential grain orientation, rendering this bias value unsuitable for thermal barrier coatings.

Sputter deposition of magnetic materials is challenging. In the case of soft magnetic materials, thin targets and strong magnetic arrays of sputtering cathode are usually used for effective magnetron sputtering. In the case of a hard magnetic material, the situation is different. The magnetic field lines are closed in to the target, and the magnetron effectively behaves as a diode sputtering system. In contrast, hollow cathode processes require no magnets to enhance ionization. Therefore, high rate deposition of hard magnetic films becomes possible with hollow cathodes. This paper shows the results of gas flow sputtering (GFS), a modification of hollow cathode processes, for the deposition of hard magnetic CoSm films. GFS has high dynamic deposition rates of several tens of microns per hour. The influence of the deposition parameters on the film magnetic properties of coercivity and magnetic remanence are discussed.

High power impulse magnetron sputtering (HIPIMS) allows the deposition of thin films from plasmas with high metallic ion content. For several applications, indium tin oxide (ITO) films were successfully deposited by HIPIMS from planar ceramic targets, e.g. for ice-free windshields or shaped glass tubes. These films present good conductivity as well as high wear resistance, derived from their nanocrystalline structure. With respect to industrial implementation, the use of rotatable cylindrical cathodes as a promising alternative due to their many advantages like better material utilization, longer durability, or reduced arcing is studied. In this work, ITO films were produced from a rotating cylindrical cathode by HIPIMS and DC magnetron sputtering. The influence of process parameters (average power, voltage, peak current and pressure) on the resulting film properties was investigated. All depositions were performed at room temperature, followed by annealing steps. Electrical and optical properties were analyzed and the process stability investigated. Highly transparent films were obtained with resistivity between 300 and 400 μΩ cm.

A series of different oxide and nitride antireflective coatings as well as single films on sapphire substrates have been deposited by magnetron sputtering. The layer stacks consist of 5–7 individual layers with a total thickness of around 300 nm. Both high-index materials and low-index material were analyzed. The mechanical stability was investigated by means of optical haze increase during falling sand (“sand trickling test”) and by thickness loss during oscillating abrasion in a sand bath (tightened “Bayer test”). The dependence of the abrasion tests results on mechanical film properties, i.e. the nanoindentor hardness, was analyzed. No clear correlation of the Bayer test results and the sand trickling test results was found, which indicates that the abrasion mechanisms are different. A nitride based antireflective coating with excellent properties from both tests has been produced.

Ionized sputtering like high power impulse magnetron sputtering HIPIMS opens new horizons for cost effective, environmental friendly plastic metallization with excellent adhesion. First reports on HIPIMS deposited films on polymer foils, textiles, and different untreated plastics showed significant adhesion improvement of the metallic or oxide coatings applied. Plexiglas (PMMA) is a very attractive substrate material due to its properties for several commercial applications. Since PMMA is very sensitive to the UV radiation of technical plasmas, direct metallization of the surface by sputtering is conventionally not possible. Using ionized sputtering it is shown that the adhesion can be enhanced to excellent level, passing a combined cross cut and tape test without any failure. The study of the interface correlated to the different peak current densities of the HIPIMS processes shows some trends for the significant adhesion improvement. With increasing peak current in the HIPIMS discharge, i.e. increasing degree of ionized species forming the film, the adhesion is significantly improved. The failure mechanism changes from adhesive failure and poor adhesion to a cohesive failure and excellent adhesion. Furthermore, the surface of the polymer was modified as a result of the increasing ionization. The PMMA surface reorganizes and roughens due to ions forming the film and additionally electrons providing local thermal annealing by recombination.

Aluminum oxide (Al2O3) thin films are used in microelectronics and sensor applications due to their good insulating properties. Usually, RF sputtering processes are used to produce insulating coatings for sensors, but this process has major drawbacks, mainly, a very low deposition rate which leads to higher production costs. AC reactive sputtering processes present higher deposition rates, but issues regarding arcing and creation of defects in the films need to be addressed. In this work, an AC power supply with a new concept for fast arc handling and limited current output was investigated. Alumina films were produced by means of a bipolar reactive sputtering process, using large area double rotatable cathodes. The process was very stable and arc counts are as low as 3–10arcs/h in the best deposition conditions. High deposition rates were also observed, reaching 2–3μm/h. The films obtained excellent insulating properties with breakdown voltages higher than 3kV for films with thicknesses between 2 and 3μm and a corresponding breakdown strength of 1.5kV/μm (15MV/cm).

Plasma diagnostics are a very useful tool for characterizing the main parameters of sputtering plasmas like electron density, electron temperature, or ion density. These parameters can be determined at the substrate position by the use of a Langmuir probe. This paper focuses on time-averaged and time-resolved planar Langmuir probe measurements. As a model system, a dual-magnetron configuration using two cylindrical aluminum cathodes was used. The planar Langmuir probe was placed in three substrate positions, one between the two rotatable targets and another directly in front of each target. The results differed significantly due to the physical position of the probe relative to the magnetrons. For the middle position each single pulse applied to one of the cathodes is detected by the Langmuir probe separately. Positioning the probe in front of one of the cathodes shows only one peak for the ion current for a full bipolar cycle. This was attributed to constructive superposition of the different distances between the probe and both targets. Moving from metallic to reactive sputtering caused the electron temperature to drop significantly. Finally, a correlation between the plasma parameters and film properties of alumina (Al2O3) coatings was presented.

Serial co-sputtering is an extension of conventional magnetron sputtering: it utilizes cylindrical primary rotating sputter sources within a metallic or reactive sputtering process. With one or more auxiliary sputter sources the surface of the primary sputter target is simultaneously coated with additional elements. In the primary sputtering process, these elements get implanted and mixed into the primary target material leading to production of multi-component films.In this paper we use an installation of this technology called "Megatron (TM)", which involves an effective gas separation between primary and auxiliary chamber volumes. With this setup, we fabricated TiO2:W and TiO2:Nb layers by using a rotating Titania target as primary source and planar W and Nb targets as auxiliary sources, respectively.In both cases the so called sputter yield amplification effect (SYA) was demonstrated: Within the TiO2 matrix the heavier element e.g. tungsten keeps the sputter cascade close to the target surface and thus significantly enhances the sputter rate. Additionally, by niobium doping in combination with a post-deposition annealing it is possible to get TiO2:Nb layers with tailored Nb composition as conductive transparent oxides (TCO).Due to the independent power control of the secondary target the tungsten and niobium concentration can easily be optimized. We present doping series for optimizing either the SYA effect for TiO2:W or the effect of a transparent conductive TCO for TiO2:Nb. With tungsten doping we achieved an enhancement of more than twice the DC sputter rate. With niobium doping and a post-deposition annealing step (350 degrees C) we reach resistivity values of about 1.2 x 10(-3) Omega cm. (C) 2014 Elsevier Ltd. All rights reserved.