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- mechanical properties (2)
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Multi-layer constructions become more and more relevant in lightweight applications due to their high strength to
weight ratio. They offer excellent crash, damping and recycling properties. Also, the morphology of thermoplastic
carbon fibre reinforced plastics (CFRP) render them interesting for large scale manufacturing processes.
Nevertheless, a major disadvantage results in a poor resistance against wear and tear, e.g. erosion, which is
attributed to weak hardness properties. Hence, this work deals with tribological investigations on orthotropic
carbon fibre reinforced polymers (PA 6) either with protective ceramic coating or without. The chosen coating
system is a well-known protective covering of metal components, e.g. metal cutting tools, produced by physical
vapor deposition (PVD). To characterize the coating system on thermoplastic CFRP, standard analyzing methods are utilized, like optical and scanning electron microscopy (SEM). The tribological investigations are conducted by the tribological ball on disk method to generate wear tracks on the sample surfaces and hence to calculate the
wear rates. These results are compared to literature findings with respect to a certain protective coating system (TiN) and a second nano-structured gel coating system, where both systems are deposited on a thermosetting
material, i.e. carbon fibre reinforced epoxy resin, respectively. For this purpose the feasibility of depositing a protective ceramic layer on thermoplastic CFRP is demonstrated. First results on suitable surface pre-treatments have shown a significant influence on the coating quality. The improved performance regarding the wear behavior with respect to tribology compared to the poor substrate and existing technologies is shown additionally.
Effect of pulse time on structure and mechanical properties of HPPMS deposited AlTiN coatings
(2016)
The use of PVD AlTiN as a protective coating on cutting tools is well known. With the introduction of pulsed deposition techniques like High Power Pulsed Sputtering
(HPPMS), a possibility is provided to the coating developers to design their coatings by the variation in pulse parameters. To analyze the effect of pulse time HPPMS
AlTiN coatings were deposited on Si (100) as well as 100Cr6 steel plates at a temperature of 500°C in a reactive gas environment. Oscilloscope measurements depicted a change in current-voltage characteristics with variation in pulse time. This influence the coating structure, deposition rates and phase formations as well. Nanoindentation results show a variation in the mechanical properties of the coatings with the change in pulse time. This study focuses on the potential of HPPMS technology for enhancement of mechanical and structural properties of AlTiN coating.
Controlled ion bombardment is a popular method to fabricate desirable coating structures and modify their properties. Substrate biasing at high frequencies is a possible technique, which allows higher ion density at the substrate compared with DC current bias. Moreover, high ion energy along with controlled adatom mobility would lead to improved coating growth. This paper focuses on a similar type of study, where effects of coating growth and properties of DC magnetron-sputtered chromium nitride (CrxN) coatings at various substrate bias frequencies are discussed. CrxN coatings were deposited by pulsed DC magnetron sputtering on Inconel 718 and (100) silicon substrates at 110, 160 and 280 kHz frequency at low duty cycle. Coating microstructure and morphology were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), scratch adhesion testing and nanoindentation. Results indicate a transformation of columnar into glassy structure of CrxN coatings with the substrate bias frequency increase. This transformation is attributed to preferential formation of the Cr2N phase at high frequencies compared with CrN at low frequencies. Increase in frequency leads to an increase in deposition rate, which is believed to be due to increase in plasma ion density and energy of the incident adatoms. An increase in coating hardness along with decrease in elastic modulus was observed at high frequencies. Scratch tests show a slight increase in coating adhesion, whereas no clear increase in coating roughness can be found with the substrate bias frequency.
Investigation of TiAlN HiPIMS coating deposited on the newly developed Ni-based superalloy AD730
(2016)
The development of new alloys for gas turbine engines has been focused on withstanding against increasing service temperatures. AD730™ is a recently developed nickel-based superalloy for turbine disk applications with superior
properties at 700°C, which is higher than the common service temperature for IN718. Use of coatings to enhance the properties of materials, such as wear resistance is widely known in various applications. This research presents an experimental study of TiAlN coatings, deposited onto AD730 superalloy using High Power Impulse Magnetron Sputtering (HiPIMS). Phase structure and chemical composition of the TiAlN films were characterized by X-ray diffractometry. Transmission electron microscopy as well as scanning electron microscopy were used to analyze the
microstructure of the coating. Mechanical properties, including hardness, Young's modulus, and adhesion strength were measured using nanoindentation und scratch test.
Hydrogen degradation is a serious problem in industrial applications like power plants (boilers, turbines), marine structures, car and aircraft components, as it leads to failures as well as to deterioration of properties. Inconel 718 is one of the most commonly used materials for these applications. Different metal nitrides like TiN coatings have been deposited in past to prevent hydrogen degradation, which are also known for their high hardness and good wear resistance [1, 2]. However, reports on hydrogen degradation of CrN coatings, which shows better oxidation and corrosion resistance, higher temperature stability and lower friction coefficient than TiN [3, 4] has not been reported till now. Despite a lot of publications about CrN films, up to now the effect of hydrogenation on mechanical and tribological properties of CrN coatings is still not completely understood. In the current work CrxN coatings were deposited by Direct Current Magnetron Sputtering (dcMS) on Inconel 718 substrate at different chamber pressures and substrate voltages. Substrate voltage is one of the most important process parameters which determines the structure of the coating and the adhesion between substrate and coating. Simultaneously a study of the chamber pressure is also needed to understand the deposited structure and growth rate because at higher pressures the high number of argon atoms reduce the number of ionized ions available for the deposition leading to low deposition rates [5]. Gas-phase hydrogenation of the samples was performed at a temperature of 600° C and hydrogen pressure of 2 atm. It was found that CrxN coatings are resistant against hydrogen exposure as compared to uncoated surfaces. The results of changes in the mechanical, tribological properties and phase composition of the coatings after hydrogenation are discussed. Coating microstructure was studied by scanning electron microscopy (SEM). The mechanical properties of the coatings were characterized by means of nanoindentation and scratch test.
Coating growth and mechanical properties of nanolamellar Cr2AlC coatings at various sputtering power were investigated in the present study. Cr2AlC coating was deposited on the IN 718 superalloy and (100) Si wafers by DC magnetron sputtering at different sputtering powers.
The structure and properties were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. It was found that coatings had columnar structure with nanocrystalline substructure. Deposition rate increased with the sputtering power. XRD results showed the presence of the Cr2AlC MAX phase, intermetallic
AlCr2 and Cr7C3 carbide phases, along with the change in preferential coating growth orientation. TEM observations confirmed the occurrence of these phases, and the SAED patterns demonstrated significant texture of the coatings. Hardness values were measured in the range between 11–14 GPa, showing a slight increase with the sputtering power.
Role of alloying elements during thermocyclic oxidation of β/γ-TiAl alloys at high temperatures
(2016)
Gamma titanium aluminides are promising alloys known for their good mechanical properties and low densities, but their low oxidation resistance at high temperatures limits their
application. This work discusses the thermocyclic oxidation behavior of newly developed β/γ-TiAl alloys at temperatures between 600 °C and 900 °C. An influence of β-stabilizing alloying elements like Nb and V on the oxidation of these alloys has been investigated here.
The selected alloys are tested in an in-house developed thermocyclic furnace. The oxidation
study is supported by gravimetric measurements along with Scanning Electron Microscopy (SEM) and Electron Diffraction Spectroscopy (EDS) mapping of the oxide layers. Additionally, phase formation after oxidation has been determined using X-Ray Diffraction (XRD). Results show that the Nb containing alloys are more oxidation resistant as compared
to V containing alloys. The formation of a mixture of Al2O3 and TiO2 layers was found for all the alloys. The oxide kinetics controlled oxide growth and formation of
various phases at different testing temperatures.
This paper serves as an overview of the ongoing research in the field of multiscale and multidisciplinary analysis of deformation and damage in the case of oligocrystalline structures. The research focuses on experimental measurement and numerical calculation of ductile failure in the X2CrNiMo18-15-3 (AISI 316L) stainless steel. An embedding numerical technique is employed where crystal plasticity theory is used to represent plastic deformation in the material and element removal technique based on Rice&Tracey damage model for ductile void growth to simulate damage initiation inside the material, which is observed in the experiments. Additionally, the crystal plasticity model is supported by a hierarchical multiscale approach connecting nano-, micro- and meso-scales.