Combining thermal spraying and magnetron sputtering for the development of Ni/Ni-20Cr thin film thermocouples for plastic flat film extrusion processes

In the digitalization of production, temperature determination is playing an increasingly important role. Thermal spraying and magnetron sputtering were combined for the development of Ni/Ni-20Cr thin film thermocouples for plastic flat film extrusion processes. On the thermally sprayed insulation layer, AlN and BCN thin films were deposited and analyzed regarding their structural properties and the interaction between the plastic melt and the surfaces using Ball-on-Disc experiments and High-Pressure Capillary Rheometer. A modular tool, containing the deposited Ni/Ni-20Cr thin film thermocouple, was developed and analyzed in a real flat film extrusion process. When calibrating the thin film thermocouple, an accurate temperature determination of the flowing melt was achieved. Industrial type K sensors were used as reference. In addition, PP foils were produced without affecting the surface quality by using thin film thermocouples

Reduction of ejection forces in injection molding by applying mechanically post-treated CrN and CrAlN PVD films

In injection molding, the reduction of ejection forces is a process relevant aspect to improve the production rates. For this purpose, CrN and CrAlN films were sputtered on cylindrical and quadratic AISI H11 cores of an injection mold in order to investigate their influence on the resulting ejection forces to demold polypropylene test components. Within this context, the ejection forces of the PVD coated cores were compared to those of uncoated cores made of AISI H11. For both the cylindrical and quadratic cores, the as-deposited CrN and CrAlN films exhibit higher ejection forces than the uncoated cores due to the increase of the roughness profile after sputtering. It is known that the ejection forces are directly related to the surface roughness. In order to ensure comparable surface conditions to the uncoated surfaces, and to demonstrate the potential of PVD coated mold surfaces when reducing the ejection forces, the coated surfaces were mechanically post-treated to obtain a similar roughness profile as the uncoated cores. The combination of a PVD deposition and post-treatment ensures a significant reduction of the ejection forces by 22.6% and 23.7% for both core geometries

Improved in vitro test procedure for full assessment of the cytocompatibility of degradable magnesium based on ISO 10993-5/-12

Magnesium (Mg)-based biomaterials are promising candidates for bone and tissue regeneration. Alloying and surface modifications provide effective strategies for optimizing and tailoring their degradation kinetics. Nevertheless, biocompatibility analyses of Mg-based materials are challenging due to its special degradation mechanism with continuous hydrogen release. In this context, the hydrogen release and the related (micro-) milieu conditions pretend to strictly follow in vitro standards based on ISO 10993-5/-12. Thus, special adaptions for the testing of Mg materials are necessary, which have been described in a previous study from our group. Based on these adaptions, further developments of a test procedure allowing rapid and effective in vitro cytocompatibility analyses of Mg-based materials based on ISO 10993-5/-12 are necessary. The following study introduces a new two-step test scheme for rapid and effective testing of Mg. Specimens with different surface characteristics were produced by means of plasma electrolytic oxidation (PEO) using silicate-based and phosphate-based electrolytes. The test samples were evaluated for corrosion behavior, cytocompatibility and their mechanical and osteogenic properties. Thereby, two PEO ceramics could be identified for further in vivo evaluations

Impact of structure on mechanical properties and oxidation behavior of magnetron sputtered cubic and hexagonal MoNx thin films

Molybdenum nitride films exhibit superior tribological properties, due to the possibility to form Magnéli phases when exposed to elevated temperatures. MoNx thin films were deposited by means of DC magnetron sputtering, while varying the bias-voltage and substrate temperature in regard to control the crystalline structure of the thin films. XRD experiments reveal a two-phase structure consisting of over stoichiometric cubic B1-NaCl and hexagonal MoNx phases for a high bias-voltage, whereas for lower bias-voltages the metastable cubic MoN phase was observed. Enhanced mechanical properties, obtained by means of nanoindentation, were analyzed for the thin films exhibiting the two-phase composite structure. The influence of the phase composition on the oxidation behavior, like oxidation state and formed oxide phases, was studied by means of in-situ XRD and XAS experiments using synchrotron radiation up to 700 °C. The oxidation processes start at 400 °C, forming oxides in amorphous state. Thin films composed of hexagonal MoN reveal a higher oxidation state up to 400 °C compared to cubic structured thin films, which changes above 400 °C. MoO2 and MoO3 were formed as primary oxides, independent from the crystalline structure of the deposited film. With an increase of temperature to 550 °C and 700 °C, the Magnéli-phases Mo9O26/Mo8O23 and Mo4O11 were formed

Impact of Tungsten Incorporation on the Tribomechanical Behavior of AlCrWxSiN Films at Room and Elevated Temperature

AlCrWxSiN thin films (0 ≤ x ≤ 17.1 at.%) were synthesized by means of a hybrid magnetron sputtering process, merging direct current (DC) as well as tungsten high power impulse magnetron sputtering (HiPIMS) supplies. The influences of increasing the tungsten contents on the structural as well as the friction and wear behavior at room and high temperatures (500 °C) were elaborated. As a reference, a W61.4N38.6 system served to analyze synergetic effects on the oxidation behavior. Increased tungsten contents in AlCrWxSiN resulted in more distinctive (200)-, (202)-, and (311)- crystal orientations. A W/Cr ratio of ~1 could be correlated with a denser film growth, the highest hardness (24.3 ± 0.7 GPa), and a significantly decreased wear coefficient (<0.3 × 10−5 mm3/Nm). Tribological tests performed at room temperature revealed that the coefficient of friction decreased with higher tungsten contents to µ~0.35. In contrast, at elevated temperatures, the coefficient of friction increased with higher W concentrations due to spotty oxidations in the wear track, which resulted in a locally increased surface roughness. Finally, a phase transformation of the WN film to m-WO3 did not contribute to a friction reduction at 500 °C

Tribomechanical Behaviour of TiAlN and CrAlN Coatings Deposited onto AISI H11 with Different Pre-Treatments

In the metalworking industry, different processes and applications require the utilisation of custom designed tools. The selection of the appropriated substrate material and its pre-treatment as well as the protective coating are of great importance in the performance and life time of forming tools, dies, punches and coated parts in general. TiAlN and CrAlN coatings have been deposited onto the hot work tool steel AISI H11 by means of Direct Current Magnetron Sputtering. Prior to the deposition, the steel substrate was modified by the implementation of three different pre-treatments: nitriding of the annealed substrate [Nitr.], heat treatment of the steel (quenching and double tempering) [HT] and nitridation subsequent to a heat treatment of the substrate [HT + Nitr.]. The purpose of this research is to obtain valuable information on the microstructural properties and tribomechanical behaviour of two of the most promising ternary transition metal nitride coatings, TiAlN and CrAlN, when deposited on the AISI H11 steel with different initial properties. The different pre-treatments performed to the steel prior to the deposition favour the tailoring during the design and construction of tools for specific applications. The microstructure, the adhesion and the wear resistance of TiAlN coatings were highly influenced by the substrate preparation. Contrarily, CrAlN results were more independent of the substrate preparation and no high influences were found. For instance, the adhesion of the TiAlN coating varied from 17 to 43 N for the coating deposited onto the HT + Nitr. substrate and the HT substrate respectively, while the lowest and highest adhesion of the CrAlN coating varied between 42 and 53 N for the HT and the HT + Nitr. respectively. Likewise, the wear coefficient of the CrAlN were ten times smaller than those found for the TiAlN coatings, presumably due to the presence of hex-AlN phases and the small differences on the Young´s Modulus of the substrate and the CrAlN coatings

Influences of substrate pretreatments and Ti/Cr interlayers on the adhesion and hardness of CrAlSiN and TiAlSiN films deposited on Al2O3 and ZrO2-8Y2O3 thermal barrier coatings

Using atmospheric plasma spraying (APS), ceramic Al2O3 and ZrO2-8Y2O3 thermal barrier coatings (TBC) were applied on AISI H11 (1.2343) and subsequently polished to serve as a substrate to magnetron sputter CrAlSi7.5N and TiAlSi7.9N films. The influences of polishing as well as plasma etching processes on the surface roughness and residual stresses of the TBCs were correlated with the adhesion of the metal nitride films. As metallic interlayers are typically used to metallize insulating substrates to increase the film adhesion, the effect of different Cr and Ti interlayer thicknesses (50–150 nm) on the CrAlSi7.5N and TiAlSi7.9N adhesion was examined. Despite tensile stresses in the TBCs, a duplex coating structure, consisting of Al2O3 + Ti100 nm/TiAlSi7.9N, generated a high adhesion (Lc3 = 61.04 ± 2.36 N). In contrast to Cr, titanium interlayers are assumed to lead to a stress relaxation in the interface between the TBC and the PVD film. In general, using ZrO2-8Y2O3 as a substrate resulted in a minor adhesion of all PVD film combinations, which is traced back to lattice mismatches between the substrate and the films. Moreover, the number of pores on the TBC surface is crucial for the adhesion and hardness of CrAlSi7.5N and TiAlSi7.9N. Keywords: Duplex coating, Thermal barrier coating, CrAlSiN, TiAlSiN, Coating adhesion, Microhardnes

Influences of substrate pretreatments and Ti/Cr interlayers on the adhesion and hardness of CrAlSiN and TiAlSiN films deposited on Al2O3 and ZrO2-8Y2O3 thermal barrier coatings

Using atmospheric plasma spraying (APS), ceramic Al2O3 and ZrO2-8Y2O3 thermal barrier coatings (TBC) were applied on AISI H11 (1.2343) and subsequently polished to serve as a substrate to magnetron sputter CrAlSi7.5N and TiAlSi7.9N films. The influences of polishing as well as plasma etching processes on the surface roughness and residual stresses of the TBCs were correlated with the adhesion of the metal nitride films. As metallic interlayers are typically used to metallize insulating substrates to increase the film adhesion, the effect of different Cr and Ti interlayer thicknesses (50–150 nm) on the CrAlSi7.5N and TiAlSi7.9N adhesion was examined. Despite tensile stresses in the TBCs, a duplex coating structure, consisting of Al2O3 + Ti100 nm/TiAlSi7.9N, generated a high adhesion (Lc3 = 61.04 ± 2.36 N). In contrast to Cr, titanium interlayers are assumed to lead to a stress relaxation in the interface between the TBC and the PVD film. In general, using ZrO2-8Y2O3 as a substrate resulted in a minor adhesion of all PVD film combinations, which is traced back to lattice mismatches between the substrate and the films. Moreover, the number of pores on the TBC surface is crucial for the adhesion and hardness of CrAlSi7.5N and TiAlSi7.9N

Tribomechanical behaviour of TiAlN and CrAlN coatings deposited onto AISI H11 with different pre-treatments

In the metalworking industry, different processes and applications require the utilisation of custom designed tools. The selection of the appropriated substrate material and its pre-treatment as well as the protective coating are of great importance in the performance and life time of forming tools, dies, punches and coated parts in general. TiAlN and CrAlN coatings have been deposited onto the hot work tool steel AISI H11 by means of Direct Current Magnetron Sputtering. Prior to the deposition, the steel substrate was modified by the implementation of three different pre-treatments: nitriding of the annealed substrate [Nitr.], heat treatment of the steel (quenching and double tempering) [HT] and nitridation subsequent to a heat treatment of the substrate [HT + Nitr.]. The purpose of this research is to obtain valuable information on the microstructural properties and tribomechanical behaviour of two of the most promising ternary transition metal nitride coatings, TiAlN and CrAlN, when deposited on the AISI H11 steel with different initial properties. The different pre-treatments performed to the steel prior to the deposition favour the tailoring during the design and construction of tools for specific applications. The microstructure, the adhesion and the wear resistance of TiAlN coatings were highly influenced by the substrate preparation. Contrarily, CrAlN results were more independent of the substrate preparation and no high influences were found. For instance, the adhesion of the TiAlN coating varied from 17 to 43 N for the coating deposited onto the HT + Nitr. substrate and the HT substrate respectively, while the lowest and highest adhesion of the CrAlN coating varied between 42 and 53 N for the HT and the HT + Nitr. respectively. Likewise, the wear coefficient of the CrAlN were ten times smaller than those found for the TiAlN coatings, presumably due to the presence of hex-AlN phases and the small differences on the Young´s Modulus of the substrate and the CrAlN coatings

Effects of AlN and BCN thin film multilayer design on the reaction time of Ni/Ni-20Cr thin film thermocouples on thermally sprayed Al2O3

Thin film thermocouples are widely used for local temperature determinations of surfaces. However, depending on the environment in which they are used, thin film thermocouples need to be covered by a wear or oxidation resistant top layer. With regard to the utilization in wide-slit nozzles for plastic extrusion, Ni/Ni-20Cr thin film thermocouples were manufactured using direct-current (DC) magnetron sputtering combined with Aluminiumnitride (AlN) and Boron-Carbonitride (BCN) thin films. On the one hand, the deposition parameters of the nitride layers were varied to affect the chemical composition and morphology of the AlN and BCN thin films. On the other hand, the position of the nitride layers (below the thermocouple, above the thermocouple, around the thermocouple) was changed. Both factors were investigated concerning the influence on the Seebeck coefficient and the reaction behaviour of the thermocouples. Therefore, the impact of the nitride thin films on the morphology, physical structure, crystallite size, electrical resistance and hardness of the Ni and Ni-20Cr thin films is analysed. The investigations reveal that the Seebeck coefficient is not affected by the different architectures of the thermocouples. Nevertheless, the reaction time of the thermocouples can be significantly improved by adding a thermal conductive top coat over the thin films, whereas the top coat should have a coarse structure and low nitrogen content