Defect and Diffusion Forum Vol. 404

Abstract: Amorphous carbon coatings have the potential to effectively reduce friction and wear in tribotechnical systems. The appropriate application of amorphous carbon layers requires both, a very good understanding of the tribological system and knowledge of the relationships between the fabrication of the coatings and their properties. In technical practice, however, the coatings’ development and their selection on the one hand and the design of the tribological system and its environment on the other hand are usually very strongly separated. The present work therefore aims to motivate the integrated development of tribotechnical systems with early consideration of the potential of amorphous carbon coatings. An efficient integrated development process is presented, which makes it possible to determine the boundary conditions and the load collective of the tribological system based upon an overall system and to derive the requirements for a tailored coating. In line with the nature of tribology, this approach must cover several scales. In this respect, the development process follows a V-model. The left branch of the V-model is mainly based upon a simulation chain including multibody and contact simulations. The right branch defines an experimental test chain comprising coating characterization to refine the contact simulation iteratively and tribological testing on different levels to validate the function fulfillment. Within this contribution, the outlined approach is illustrated by two use cases, namely the cam/tappet-pairing and the total knee replacement.

Abstract: Aluminium alloys are among the metals that can be easily passivated, demonstrating notable anticorrosion properties. Under aggressive environments, like in seawater, corrosion may appear though due to presence of chloride ions (pH>8.5) leading to pitting failures. The objectives of the presented research were to examine the possibility of functionalizing the surface of an aluminium alloy through a polydopamine (PDA) layer with homogeneously dispersed silver nanoparticles (AgNPs) and examine the corrosion behaviour of the nanostructured coating. The development of a PDA coating provides a promising approach for immobilization of silver nanoparticles onto AA6061 substrate. Exposure to salt spray for 60 h and assessment of the corrosion status through various methods were applied. Depending on the process parameters for the fabrication of the PDA-AgNPs layer, an enhanced corrosion protection was achieved compared to the undoped with AgNPs film and the uncoated Aluminium alloy.

Abstract: Cold extrusion is an established technology for the production of dimensionally accurate components in large series. Due to the high material and energy efficiency, a resource-saving manufacturing of high-performance parts is possible. Forming at room temperature leads to an advantageous grain structure and work hardening of the material, resulting in components with favorable operating characteristics. Nevertheless, a challenge is the generation of residual stresses during forming, which are influencing the fatigue behavior. The modification of the tribological conditions is one method for influencing the parts’ residual stress state. However, the high strength and work hardening of the materials formed at room temperature leads to high tribological loads between billet and die. These challenges are intensified by the increasing use of stainless steels due to growing demands for corrosion resistant components. The aim followed within this paper is therefore to investigate the applicability of typical lubricant coatings in the forward rod extrusion of stainless steels. For this purpose, the ferritic stainless steel X6Cr17 (DIN 1.4016) and the ferritic-austenitic stainless steel X2CrNiMoN22-5-3 (DIN 1.4462) are extruded with an equivalent plastic strain of ε̅ ≈ 1. The research is performed with a molybdenum disulfide (MoS₂), a soap and a polymer-based lubricant coating. For reproducing different contact conditions, the die geometry is varied with die opening angles of 60°, 90° and 120°. The suitability of the lubricants is evaluated using the integrity of the lubricant coating after forming. From the correlations between process forces, temperatures and surface integrity, recommendations for the application of the researched lubricants are derived.

Abstract: TiCN coatings of the same chemical compositions were deposited on HW/K05-K20 cemented carbide inserts via physical (PVD) and medium temperature chemical vapor deposition (MTCVD) techniques. Nano-indentations coupled with appropriate FEM simulations were used for characterizing the film and substrate mechanical properties. Furthermore, uncoated cemented carbide substrates were annealed in vacuum at temperatures and durations corresponding to the related ones during the PVD and MTCVD process for recording the effect of the deposition temperature and duration on the substrate strength properties. Perpendicular and inclined impact tests at various loads were performed for checking the coating fatigue endurance and adhesion respectively. These material data were considered in FEM supported calculations for predicting the developed stress fields in the cutting edge during turning cast iron GG30 using the PVD and MTCVD TiCN coated inserts. According to the obtained result, both coatings possess the same stress-strain properties. Hereupon, the MTCVD coatings are characterized comparably to PVD ones by improved fatigue properties and adhesion strength. Although these properties contribute to an increased tool life in finishing turning, the significant reduction of the substrate strength properties, due to the elevated temperature during the MTCVD process, results in a premature coating failure and a consequent intensive wear evolution in roughing.

Abstract: PVD (physical vapor deposition) hard coatings are widely used and common in manufacturing technologies, for the use as wear and oxidation protection of tools and components. Therefore, many specialized hard coatings systems have been developed until now. Nevertheless, there is a demand to improve the functionality of PVD hard coatings, i.e. due to a self-lubricating effect through tribological activation. According to the current state of research, solid lubricants with lattice layer structure and oxidic solid lubricants are particularly suitable for this purpose. This work gives an overview on the functional mechanisms as well as required environmental conditions and activation mechanisms of transition metal dichalcogenides (TMD) and Magnéli-phases.

Abstract: Within the scope of this work, a new approach named laser implantation process has been investigated, in order to improve the tribological performance of hot stamping tools. This surface engineering technology enables the generation of dome-shaped, elevated and highly wear resistant microfeatures on tool surfaces in consequence of a localized dispersing of hard ceramic particles via pulsed laser radiation. As a result, the topography and material properties of the tool and thus the tribological interactions at the blank-die interface are locally influenced. However, a suitable selection of hard ceramic particles is imperative for generating defect-free surface features with a high share of homogenously disturbed particles. For this purpose, different niobium (NbB₂ and NbC) as well as titanium-based (TiB₂ and TiC) materials were embedded on hot working tool specimens and subsequently analyzed with regard to their resulting shape and mechanical properties. Afterwards, modified pin-on-disk tests were carried out by using conventional and laser-implanted tool surfaces, in order to evaluate the wear and friction behavior of both tooling systems.

Abstract: The surface treatment of tools plays an important role for the operational behaviour of forming processes. Up to now, industrial standard is the manual finishing of tool surfaces, which can lead to a varying quality of the surface finish and therefore influence the tool service life and the forming results. One method to perform the polishing operation automatically is to remelt the top layer of materials by laser polishing. This is accompanied by a considerable change in the material properties in this zone. Therefore, the effect of laser polishing with respect to the local modification of the tool surface is investigated in this study. The results of the investigations reveal that a precise adjustment of the laser parameters is required in order to reduce the roughness of the surface. The heat input also leads to a significant influence on the microstructure of the material. In this study laser polishing remelts the material up to a depth of approximately 20 µm. Furthermore, it can be observed that the heat input during the process results in a heat affected zone of up to a depth of 30 µm. As a contrast to laser polishing, abrasive blasting is investigated as a roughness increasing surface modification.

Abstract: Due to continuously increasing requirements on lightweight sheet metal constructions, new processes and technologies are necessary to face current and future challenges. A trend in lightweight construction is the multi-material mix with sheets of different geometric and mechanical properties. To manufacture these so-called composite structures, new joining technologies and methods are required. One possibility is the further development of the self-pierce riveting joining process. For the simulation and evaluation of new and adapted processes of self-pierce riveting, numerical models are used to investigate process parameters and constraints. Besides precise material models for the numerical simulation of this joining process, the identification of friction parameters between the individual sheets and rivet elements is necessary to achieve exact results. Thus, a method is necessary to identify the friction coefficients between rivet elements and sheets. Such a method is presented and evaluated in this work. Different process parameters like the relative speed are varied for the experimental investigations and an analysis of the respective influence on the resulting friction coefficients is conducted. For the use of the test set-up, coefficients of friction are determined for rivet elements “RIVSET^® C 5.3x5.5” (Böllhoff GmbH) coated with Almac^® in combination with two different sheet materials HCT590X+Z and EN‑AW 6014.

Abstract: In manufacturing technology, sensors are important elements for monitoring process parameters and for recording data in the Industrie 4.0. Thin sensors manufactured by means of physical vapor deposition (PVD) offer a way to combine wear and corrosion protection on the one hand and the integration of a temperature sensor function on the other hand. For the analysis of the performance of PVD sensor coatings based on the thermoelectric effect, no standardized methods and procedures are state of the art. In this paper a measuring setup is presented, which allows reference measurements using a calibrated thermocouple and a thermographic camera besides the potential difference measurement of the sensor coating. Two measuring modes, which allow a continuous and a discontinuous measurement, are presented. The measuring methodology was evaluated using the PVD sensor coating Al₂O₃+Ni+NiCr+Al₂O₃. This multilayer sensor coating was deposited using an industrial coating unit and was tested with regard to the sensor properties. The deposition technology used for the sensor coating results in an interface without defects between the two sensor layers with a smooth transition. This provides a suitable electrical contact and a promising compound adhesion. The results show a suitable and detailed measurement of temperature and potential differences by means of calibrated measurement methods and the sensor coating. The measured results are reproducible and show a linear relationship between the potential difference and the surface temperature.