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

Application of the eutectic high entropy alloy Nb0.73CoCrFeNi2.1 for high temperature joints

The eutectic high entropy alloy Nb0.73CoCrFeNi2.1 was manufactured by means of arc smelting and the obtained ingots were cut into 300-μm-thick foils, which were used as filler alloys to braze Crofer 22 APU to Hf-metallized yttria-stabilized zirconia (3YSZ). The brazing process was conducted in a vacuum furnace at 1200 °C for 5 min at a vacuum of 4.3·10–4 mbar. In order to minimize the intense diffusion and erosion of the steel substrate, a heating and cooling rate of 50 K/min was applied. Sound joints without any pores or flaws were obtained. The microstructure of the joints consisted of an HfO2 reaction layer at the ceramic interface and the same eutectic structure consisting of a Laves phase and a solid solution that was already detected in the smelted foil. The average hardness of the microstructure in the joint seam amounted to 352 ± 17 HV0.01 and the joints reached strength values up to 97 ± 7 MPa while the fracture area was always located at the ceramic interface in the HfO2 layer. Comparable joints, with AgCuTi3 as filler metal, brazed at 920 °C, only reached a shear strength of ~ 52 ± 2 MPa

TiAlN-Beschichtungen mittels hochenergetischer Kathodenzerstaeubung

Hochenergetische Plasmen stellen nach aktuellen Erkenntnissen ein vielversprechendes tribologisches Eigenschaftsprofil für nitridische Hartstoffschichten und deren Anwendungen dar. Jedoch resultiert aus der gesteigerten Ionisationsrate ein hohes Niveau an Druckeigenspannungen in TiAlN‐Dünnschichten (σTiAlN ∼ –6000 MPa), welches die Haftung zwischen Substrat und Beschichtung negativ beeinflussen und zu Delamination und Schädigung führen kann. In diesem Zusammenhang belegen die durchgeführten Untersuchungen, dass durch eine hybride Prozessführung, die aus der synchronen Verwendung von Gleichstrom (DC)‐ und Hochleistungs‐Impuls‐Kathodenzerstäubung (HiPIMS) besteht, eine Reduktion des Eigenspannungszustands in der Schicht erfolgen kann. Dies ermöglicht die Vorteile beider Technologien zu vereinen und somit TiAlN‐Dünnschichten für ein erweitertes Einsatzspektrum als tribologische Beschichtung für wärmebehandelte Werkzeugstähle zu qualifizieren

Heat treatment of binder jet printed 17–4 PH stainless steel for subsequent deposition of tribo-functional diamond-like carbon coatings

Diamond-like carbon (DLC) coatings deposited on additively manufactured steel greatly improve the tribological properties. However, a high substrate hardness is crucial to sustaining high mechanical loads in the tribological contact. Herein, the heat treatment of binder jet printed 17–4 PH enhances the hardness from 24 to 39 HRC. Binder jet printed 17–4 PH substrates are coated by DLC of the types hydrogen-free amorphous carbon (a-C) of ∼23 GPa and hydrogenated amorphous carbon (a-C:H) of ∼20 GPa. The influence of the heat treatment on the tribo-mechanical properties of the DLC coatings is investigated. 17–4 PH demonstrates high friction and wear against steel counterparts, but the wear rate is reduced from 693 ± 43 × 10–6 mm3/Nm to 492 ± 41 × 10-6 mm3/Nm by heat treating the steel. Both a–C and a–C:H are effective in reducing the friction and wear with wear rates below 0.3 × 10–6 mm3/Nm. The a–C and a–C:H coatings demonstrate lower plastic wear on heat treated 17–4 PH due to the higher substrate hardness. Consequently, the heat treatment is an essential process step to ensure maximum tribological functionality of the DLC coating on additively manufactured 17–4 PH steel

Investigation into deep hole drilling of austenitic steel with advanced tool solutions

Deep hole drilling processes for high-alloyed materials are characterised by worn guide pads and chatter vibrations. In order to increase feed rates, process stability and bore quality in STS deep hole drilling, various investigations were carried out with adjustments to the tool. First, a new process chain for the production of tribologically optimised guide pads and their effects on the guide pad shape is described in detail. The results of these studies show that the shape change in the area of the axial run-in chamfer through a micro finishing process leads to a better bore hole quality. Furthermore, the influence of guide pad coating and cooling lubricant on the deep hole drilling process was investigated. In addition, the machining of the austenitic steel AISI 304 is analysed by using a conventional steel boring bar and an innovative carbon fibre reinforced plastic (CFRP)-boring bar. While the conventional drill tube oscillates with different eigenfrequencies, the CFRP-boring bar damps chatter vibrations of the drill head and stabilises the process. Even at higher feed rates up to f = 0.3 mm, it is possible to machine austenitic, difficult-to-cut-materials with significantly reduced vibrations

Structure and tribo-mechanical properties of MoSx:N:Mo thin films synthesized by reactive dcMS/HiPIMS

Modifying MoS2 thin films by additional elements shows great potential in order to adjust the property profile and to meet the increasing requirements regarding high wear resistance and low friction properties of industrial components. Within that context, MoSx:N:Mo thin films were deposited by a reactive hybrid dcMS/HiPIMS process. By systematically increasing the Mo target cathode power, an investigation of the structural and the mechanical properties was conducted to understand the evolution of the tribological behavior. A low Mo target cathode power of 1 kW is related to the formation of the preferential (002) MoS2 basal-plane and thus a low friction with µ = 0.2. With an increasing amount of Mo, the film loses its solid lubricant MoS2 properties and a nitride constitution of the thin film is developing due to the formation of crystalline Mo and MoN phases. Related to this transformation, the hardness and elastic modulus are increased, but the adhesion and the tribological properties are impaired. The film loses its plasticity and the generated film material is directly removed from the contact area during the sliding contact

Controlling the structural, mechanical and frictional properties of MoSx coatings by high-power impulse magnetron sputtering

Tribology, as the science and technology of interacting surfaces, typically relies on liquid lubricants which reduce friction and wear. For environmentally friendly tribological purposes and applications requiring a liquid-free performance, solid lubricants, such as MoS2 coatings, play an essential role. It is crucial to understand the interplay between the parameters of the coating synthesis and the characteristics of the coating. The impact of the deposition parameters on the structural, mechanical and frictional properties of MoSx thin films, which are synthesized by high-power impulse magnetron sputtering, are studied. The morphology, topography and stoichiometry (2.02 < x < 2.22) of the films are controlled by, in particular, the bias-voltage and heating power applied during the sputtering process. In combination with a low pulse frequency the hardness and elastic stiffness of the MoSx films are enhanced up to 2 and 90 GPa, respectively. This enhancement is assigned to a shortening of the Mo-S bonding lengths and a strengthening in the interatomic coupling as well as to a formation of small-sized crystallites at the surface. The friction coefficient reduces to µ = 0.10 for films with an initial (100) orientation and the mean roughness of the MoSx films decreases below 15 nm by shortening the cathode pulses

Tribological performance of PVD film systems against plastic counterparts for adhesion-reducing application in injection molds

The deposition of physical vapor deposition (PVD) hard films is a promising approach to enhance the tribological properties of injection molds in plastic processing. However, the adhesion is influenced by the pairing of PVD film and processed plastic. For this reason, the friction behavior of di erent PVD films against polyamide, polypropylene, and polystyrene was investigated in tribometer tests by correlating the relation between the roughness and the adhesion. It was shown that the dispersive and polar surface energy have an impact on the work of adhesion. In particular, Cr-based nitrides with a low polar component exhibit the lowest values ranging from 65.5 to 69.4 mN/m when paired with the polar polyamide. An increased roughness leads to a lower friction due to a reduction of the adhesive friction component, whereas a higher work of adhesion results in higher friction for polyamide and polypropylene. Within this context, most Cr-based nitrides exhibited coe cients of friction below 0.4. In contrast, polystyrene leads to a friction-reducing material transfer. Therefore, a customized deposition of the injection molds with an appropriated PVD film system should be carried out according to the processed plastic

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

Ultrastrong poly(2‐oxazoline)/poly(acrylic acid) double‐network hydrogels with cartilage‐like mechanical properties

The exceptional stiffness and toughness of double-network hydrogels (DNHs) offer the possibility to mimic even complex biomaterials, such as cartilage. The latter has a limited regenerative capacity and thus needs to be substituted with an artificial material. DNHs composed of cross-linked poly(2-oxazoline)s (POx) and poly(acrylic acid) (PAA) are synthesized by free radical polymerization in a two-step process. The resulting DNHs are stabilized by hydrogen bridges even at pH 7.4 (physiological PBS buffer) due to the pKa-shifting effect of POx on PAA. DNHs based on poly(2-methyl-2-oxazoline), which have a water content (WC) of around 66 wt% and are not cytotoxic, show biomechanical properties that match those of cartilage in terms of WC, stiffness, toughness, coefficient of friction, compression in body relevant stress conditions and viscoelastic behavior. This material also has high strength in PBS pH 7.4 and in egg white as synovial liquid substitute. In particular, a compression strength of up to 60 MPa makes this material superior