The material of the substrate prior to the deposition of PVD coatings as well as its surface roughness and microstructure, hardness, and Young's modulus both on the surface as well as in the material ...matrix, and their residual stresses on the surface and in depth, have a high influence on the adhesion of the coating to the substrate. During metal forming processes, tools are exposed to high loads, which promote plastic deformation in the material of the tool and thus reduce its lifespan. In this regard, different substrate pre-treatments, allow modifying the hardness and toughness of the substrate, positively affecting the adhesion of the coating/substrate compound as well as the overall performance of the PVD coated tool.
In this investigation, four different pre-treatments were performed on the hot work tool steel AISI HI I (X37CrMoV5-1). Plasma nitriding, two different heat treatments, and polishing sequences (austenitizing, quenching and double tempering) as well as a combination of these two processes (heat treatment prior plasma nitriding). Subsequently, TiAlN coatings with a 3 μm thickness were deposited onto the four differently treated substrates by means of Direct Current Magnetron Sputtering. Residual stresses of the substrate surface, before and after coating deposition were determined by means of X-ray diffraction. Additionally, residual stresses depth profiles of the steel after each pre-treatment prior to the deposition of the coatings were measured utilizing selective electropolishing of the substrate surface. To evaluate the adhesion of the TiAlN monolayers to the coatings, scratch tests and Rockwell C adhesion tests were performed on the coating/substrate compounds. The adhesion of the coatings, deposited on steel with lower residual stresses prior to the deposition and flatter residual stress gradients, was improved.
•Flatter gradients before coating leads to and increment in compressive stresses.•Low compressive stresses and flatter gradients induce high critical loads.•Scratch and Rockwell C tests presented comparable results, high adhesion in HT2.•Surface integrity of steel is critical to predict adhesion of PVD coatings.
Residual stresses in the substrate and in the PVD coating have a significant influence on the coating adhesion and lifespan of machining as well as forming tools. Therefore, the understanding and ...control of the system's residual stresses will lead to a better performance of the coated components. Moreover, although investigations were conducted in the field of stress analysis of PVD coatings, they do not focus on interdependencies of residual stresses in the substrate and in the coating.
In this investigation, three different metallographically prepared substrates were used. SiC grinding, diamond grinding, and SiC grinding and plasma nitriding preparations were selected, due to the substantial differences in their final residual stress states. Additionally, a Ti/TiAlN multilayer coating and a reference TiAlN monolayer were deposited on each pre-treated substrate.
Their initial and final residual stress states were measured by means of X-ray diffraction. In addition to the residual stress analyses, tribo-mechanical tests, such as nano-indentation, ball-on-disc, and scratch tests were performed in order to correlate the results with these residual stress states.
•Low residual stresses lead to high elastic and plastic deformation of the substrate.•Residual stresses in the substrate influence residual stresses in the coating.•Multilayer systems present higher residual stresses than TiAlN monolayer systems.•The adhesion of the coatings is improved by increasing hardness of the substrate.
The deposition of ternary nitrides with the incorporation of carbon atoms into its structure has demonstrated to be a promising approach in the pursuit of wear-resistant and self-lubricating ...coatings. Firstly, both TiAlN and TiAlCN monolayers were deposited using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) onto quenched and tempered AISI H11 tool steel to be used as references. Acetylene was used as a carbon precursor, producing DCMS and HiPIMS TiAlCN coatings with 9.0 and 21.7 at.% C, respectively.
Subsequently, TiAlN/TiAlCN multilayers of various designs were also developed as follows: 5×10/500, 5×50/500 and 5×100/500 nm. Residual stresses of the coating systems were determined by X-ray radiation utilising an ETA-diffractometer with a Cu-Kα radiation source applying the sin2ψ method. Additionally, residual stresses depth gradients of the substrate before and after the deposition of the coatings were determined in a LEDDI 8-circle diffractometer equipped with a W-X-ray tube and operated in the energy-dispersive mode of diffraction. Great reduction of the compressive residual stresses in the coatings was observed after the introduction of carbon into the TiAlN coating structure, shifting from −1047 ± 149 to −307 ± 211 MPa for the DCMS and from −7035 ± 1361 to +989 ± 187 MPa for the HiPIMS coatings. In the multilayer coatings, compressive residual stresses increase along with the increment of the TiAlN interlayer. Additionally, residual stresses of the substrate in the near-surface are dragged from low compressive stresses (−218 ± 61) to tensile stresses in the range of 1000 to 2000 MPa for all the DCMS/substrate systems, a behaviour only presented in HiPIMS by the TiAlN monolayer. Wear coefficients of all the evaluated HiPIMS systems are notoriously lower than their DCMS counterparts. Compared to TiAlN, TiAlCN HiPIMS presented a lower coefficient of friction but a higher wear coefficient, which in turn was not reduced by the introduction of the multilayer systems. Finally, Scratch test and Rockwell C adhesion tests have shown higher adhesion of DCMS coatings than HiPIMS coatings, and a detriment of the monolayers adhesion by the implementation of TiAlN/TiAlCN multilayer systems. The understanding of the residual stresses, both in the coating and in the substrate, and the way they affect the tribomechanical performance of the system coating/substrate continues to be of great importance, especially for coatings deposited by new technologies such as HiPIMS and self-lubricating coatings.
•Great reduction of compressive residual stresses with the carbon inclusion in TiAlN.•High superficial residual stresses on the substrate after DCMS deposition.•Adhesion of DCMS coatings systems to AISI H11 is always higher than HiPIMS.•Ceramic/ceramic multilayer designs did not improved adhesion or wear.
Ensuring a good adhesion of the coatings to the substrate is one of the key points during the manufacturing of machining and forming tools. The nature of the substrate material and the way it is ...pre-treated and cleaned before the deposition plays an important role in the adhesion of the coatings. The in-situ cleaning processes as plasma etching and metal ion etching have demonstrated to have an influence on the adhesion of different coating/substrate systems. The introduction of HiPIMS technologies for the in-situ cleaning and the deposition of PVD coatings throughout this technique has opened varied opportunities to improve the performance of the coated parts. Systematic and comparative analysis of the influence of plasma etching itself (PE), plasma etching and metal ion etching (PE + MIE), and plasma etching and HiPIMS etching (PE + HiPE) etching processes on the adhesion of the TiAlN to the hot work tool steel AISI H11 has been performed. Additionally, subsequent to the etching processes, TiAlN coatings have been deposited using DCMS, HiPIMS and hybrid (DCMS/HiPIMS) technologies. Residual stresses of the heat treated AISI H11 were evaluated before and after the different etching process as well as after coating's deposition. It has been shown that the etching process affects the growth direction and microstructure of the TiAlN coatings, especially of those deposited by DCMS and hybrid. For instance, DCMS and hybrid TiAlN coatings deposited after PE have the presence of the TiAlN (200) reflection, not evidenced on the coatings deposited after PE + MIE and PE + HiPE. Moreover, hybrid coatings on PE + HiPE have a preferential (220) growth orientation and a (111) orientation when deposited on PE and PE + MIE cleaned substrate. Finally, in order to evaluate the adhesion of the coatings to the substrate, both scratch test and Rockwell C indentation test were used. The coatings deposited on the mere plasma etched (PE) substrate turn out to be the coatings with the highest critical load Lc3 and the lowest HF standards (HF1–HF3). This behaviour is attributed to the conservation of the substrate's surface integrity and the no promotion of surface tensions that can act in detriment of the adhesion of the coating.
•Plasma, metal ion and HiPIMS etching were proposed to improve TiAlN adhesion.•Etching processes influence the crystal growth of TiAlN coatings.•Plasma etching favours the adhesion of the TiAlN coatings to heat-treated AISI H11.•Highly stress TiAlN HiPIMS presented similar critical loads to TiAlN DCMS.
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.
Emotion recognition in text, the task of identifying emotions such as joy or anger, is a challenging problem in NLP with many applications. One of the challenges is the shortage of available datasets ...that have been annotated with emotions. Certain existing datasets are small, follow different emotion taxonomies and display imbalance in their emotion distribution. In this work, we studied the impact of data augmentation techniques precisely when applied to small imbalanced datasets, for which current state-of-the-art models (such as RoBERTa) under-perform. Specifically, we utilized four data augmentation methods (Easy Data Augmentation EDA, static and contextual Embedding-based, and ProtAugment) on three datasets that come from different sources and vary in size, emotion categories and distributions. Our experimental results show that using the augmented data when training the classifier model leads to significant improvements. Finally, we conducted two case studies: a) directly using the popular chat-GPT API to paraphrase text using different prompts, and b) using external data to augment the training set. Results show the promising potential of these methods.
TiAlN‐Beschichtungen mittels hoch‐energetischer Kathodenzerstäubung Tillmann, Wolfgang; Stangier, Dominic; Grisales, Diego
Vakuum in Forschung und Praxis : Zeitschrift für Vakuumtechnologie, Oberflèachen und Dünne Schichten,
06/2020, Letnik:
32, Številka:
3
Journal Article
Zusammenfassung
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 (σ
TiAlN
∼ –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.
Summary
TiAlN‐coatings by means of high‐energy sputtering
According to current knowledge, high‐energy plasmas represent a promising tribological property profile for nitride hard material coatings and their applications. However, the increased ionization rate results in a high level of residual compressive stresses in TiAlN thin films (σ
TiAlN
∼ –6000 MPa), which can negatively influence the adhesion between substrate and coating and thus can lead to delamination and damage. In this context, the presented investigations prove that a hybrid process consisting of the synchronous use of direct current (DC) and high power pulse sputtering (HiPIMS) can be used to reduce the residual stress state in the coating. This allows to combine the advantages of both technologies and thus to qualify TiAlN thin films for an extended range of applications as tribological coatings for heat treated tool steels.
TiAlN‐Beschichtungen mittels hoch‐energetischer Kathodenzerstäubung Tillmann, Wolfgang; Stangier, Dominic; Grisales, Diego
Vakuum in Forschung und Praxis : Zeitschrift für Vakuumtechnologie, Oberflèachen und Dünne Schichten,
June/July 2020, Letnik:
32, Številka:
3
Journal Article
Zusammenfassung
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.
Summary
TiAlN‐coatings by means of high‐energy sputtering
According to current knowledge, high‐energy plasmas represent a promising tribological property profile for nitride hard material coatings and their applications. However, the increased ionization rate results in a high level of residual compressive stresses in TiAlN thin films (σTiAlN ∼ –6000 MPa), which can negatively influence the adhesion between substrate and coating and thus can lead to delamination and damage. In this context, the presented investigations prove that a hybrid process consisting of the synchronous use of direct current (DC) and high power pulse sputtering (HiPIMS) can be used to reduce the residual stress state in the coating. This allows to combine the advantages of both technologies and thus to qualify TiAlN thin films for an extended range of applications as tribological coatings for heat treated tool steels.
TiAlN monolayers and TiAlN/TiAlCN bilayers were successfully deposited by hybrid (DCMS/HiPIMS) technology. The increase in the acetylene flow has linearly augmented the percentage of carbon ...incorporated into the coating systems. The TiAlCN with the highest carbon content significantly increased roughness and reduced hardness and Young's modulus. Additionally, a great reduction of the compressive residual stress has been noticed.
Response surface methodology has been used from a full factorial design of experiments in order to create friction and wear maps varying sliding velocity and normal load for each of the coating systems. Tribological results showed that the coefficient of friction is not as dependent on the carbon content as it is on both the sliding velocity and normal load.
•TiAlN and TiAlCN were successfully deposited by hybrid (DCMS/HiPIMS).•The higher the flow of acetylene during deposition, the higher the carbon content.•Response surface methodology after full factorial design was utilised for tribology.•TiAlN/TiAlCN with higher content of carbon (7.8 at.%) presented tensile residual stresses.•Carbon contend had no significant influence on friction, but improved wear resistance.
Incorporation of silver particles in nitride coatings has been used to improve the mechanical resistance of steels, but few details are known about the effect of the incorporation of these metals on ...the electrochemical behavior. In order to evaluate the corrosion resistance and the possible formation of a galvanic couple between the ceramic matrix of TiAlN and the metallic Ag, a TiAlN composite coating doped with four different contents of silver (0.8-25 at.%) was deposited on AISI H11 hot working steel, using the hybrid DCMS/HiPIMS magnetron sputtering technique. The microstructure, topography, elemental chemical, and phase composition of the coatings were determined using SEM/EDS, AFM, XRD, and XPS characterization techniques. The electrochemical behavior was evaluated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The TiAlN matrix and TiAlN(Ag)-coated samples exhibit higher impedance modulus values than steel substrate, indicating better anticorrosion performance. The anodic current density of the Ag-doped coating increases with the Ag content, suggesting enhanced silver release to the surrounding electrolyte. The TiAlN coating doped with 0.8 at.% silver exhibited the highest corrosion resistance at long immersion times. Finally, it must be noted that all the coatings exhibited corrosion protection to the AISI H11 steel substrate.
PDF
