Browsing by Author "Fox-Rabinovich, German S."
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Item Open Access Benchmarking of several material constitutive models for tribology, wear, and other mechanical deformation simulations of Ti6Al4V(Elsevier, 2019-05-12) Liu, Cen; Goel, Saurav; Llavori, Iñigo; Stolf, Pietro; Giusca, Claudiu L.; Zabala, Alaitz; Kohlscheen, Joern; Paiva, Jose Mario; Endrino, José L.; Veldhuis, Stephen C.; Fox-Rabinovich, German S.Use of an alpha-beta (multiphase HCP-BCC) titanium alloy, Ti6Al4V, is ubiquitous in a wide range of engineering applications. The previous decade of finite element analysis research on various titanium alloys for numerous biomedical applications especially in the field of orthopedics has led to the development of more than half a dozen material constitutive models, with no comparison available between them. Part of this problem stems from the complexity of developing a vectorised user-defined material subroutine (VUMAT) and the different conditions (strain rate, temperature and composition of material) in which these models are experimentally informed. This paper examines the extant literature to review these models and provides quantitative benchmarking against the tabulated material model and a power law model of Ti6Al4V taking the test case of a uniaxial tensile and cutting simulation.Item Open Access DLC and DLC-WS2 coatings for machining of aluminium alloys(MDPI, 2019-03-15) Brzezinka, Tomasz L.; Rao, Jeff; Paiva, Jose M.; Kohlscheen, Joern; Fox-Rabinovich, German S.; Veldhuis, Stephen C.; Endrino, José L.Machine-tool life is one limiting factor affecting productivity. The requirement for wear-resistant materials for cutting tools to increase their longevity is therefore critical. Titanium diboride (TiB2) coated cutting tools have been successfully employed for machining of AlSi alloys widely used in the automotive industry. This paper presents a methodological approach to improving the self-lubricating properties within the cutting zone of a tungsten carbide milling insert precoated with TiB2, thereby increasing the operational life of the tool. A unique hybrid Physical Vapor Deposition (PVD) system was used in this study, allowing diamond-like carbon (DLC) to be deposited by filtered cathodic vacuum arc (FCVA) while PVD magnetron sputtering was employed to deposit WS2. A series of ~100-nm monolayer DLC coatings were prepared at a negative bias voltage ranging between −50 and −200 V, along with multilayered DLC-WS2 coatings (total thickness ~500 nm) with varying number of layers (two to 24 in total). The wear rate of the coated milling inserts was investigated by measuring the flank wear during face milling of an Al-10Si. It was ascertained that employing monolayer DLC coating reduced the coated tool wear rate by ~85% compared to a TiB2 benchmark. Combining DLC with WS2 as a multilayered coating further improved tool life. The best tribological properties were found for a two-layer DLC-WS2 coating which decreased wear rate by ~75% compared to TiB2, with a measured coefficient of friction of 0.05.Item Open Access Elevated temperature repetitive micro-scratch testing of AlCrN, TiAlN and AlTiN PVD coatings(Elsevier, 2017-08-24) Beake, Ben D.; Endrino, José L.; Kimpton, Christine; Fox-Rabinovich, German S.; Veldhuis, Stephen C.In developing advanced wear-resistant coatings for tribologically extreme highly loaded applications such as high speed metal cutting a critical requirement is to investigate their behaviour at elevated temperature since the cutting process generates frictional heat which can raise the temperature in the cutting zone to 700–900 °C or more. High temperature micro-tribological tests provide severe tests for coatings that can simulate high contact pressure sliding/abrasive contacts at elevated temperature. In this study ramped load micro-scratch tests and repetitive micro-scratch tests were performed at 25 and 500 °C on commercial monolayer coatings (AlCrN, TiAlN and AlTiN) deposited on cemented carbide cutting tool inserts. AlCrN exhibited the highest critical load for film failure in front of the moving scratch probe at both temperatures but it was prone to an unloading failure behind the moving probe. Scanning electron microscopy showed significant chipping outside the scratch track which was more extensive for AlCrN at both room and elevated temperature. Chipping was more localised on TiAlN although this coating showed the lowest critical loads at both test temperatures. EDX analysis of scratch tracks after coating failure showed tribo-oxidation of the cemented carbide substrate. AlTiN showed improved scratch resistance at higher temperature. The von Mises, tensile and shear stresses acting on the coating and substrate sides of the interface were evaluated analytically to determine the main stresses acting on the interface. At 1 N there are high stresses near the coating-substrate interface. Repetitive scratch tests at this load can be considered as a sub-critical load micro-scale wear test which is more sensitive to adhesion differences than the ramped load scratch test. The analytical modelling showed that a dramatic improvement in the performance of AlTiN in the 1 N test at 500 °C could be explained by the stress distribution in contact resulting in a change in yield location due to the high temperature mechanical properties. The increase in critical load with temperature on AlTiN and AlCrN is primarily a result of the changing stress distribution in the highly loaded sliding contact rather than an improvement in adhesion strength.Item Open Access Facilitating TiB2 for filtered vacuum cathodic arc evaporation(MDPI, 2020-03-06) Brzezinka, Tomasz L.; Rao, Jeff; Paiva, Jose M.; Azkona, Ibon; Kohlscheen, Joern; Fox-Rabinovich, German S.; Veldhuis, Stephen C.; Endrino, José L.TiB2 is well established as a superhard coating with a high melting point and a low coefficient of friction. The brittle nature of borides means they cannot be utilised with arc evaporation, which is commonly used for the synthesis of hard coatings as it provides a high deposition rate, fully ionised plasma and good adhesion. In this work, TiB2 conical cathodes with non-standard sintering additives (carbon and TiSi2) were produced, and the properties of the base material, such as grain structure, hardness, electrical resistivity and composition, were compared to those of monolithic TiB2. The dependence of the produced cathodes’ electrical resistivity on temperature was evaluated in a furnace with an argon atmosphere. Their arc–evaporation suitability was assessed in terms of arc mobility and stability by visual inspection and by measurements of plasma electrical potential. In addition, shaping the cathode into a cone allowed investigation of the influence of an axial magnetic field on the arc spot. The produced cathodes have a bulk hardness of 23–24 GPa. It has been found that adding 1 wt% of C ensured exceptional arc-spot stability and mobility, and requires lower arc current compared to monolithic TiB2. However, poor cathode utilization has been achieved due to the steady generation of cathode flakes. The TiB2 cathode containing 5 wt% of TiSi2 provided the best balance between arc-spot behaviour and cathode utilisation. Preventing cathode overheating has been identified as a main factor to allow high deposition rate (±1.2 µm/h) from TiB2-C and TiB2-TiSi2 cathodes.Item Open Access Features of electronic and lattice mechanisms of transboundary heat transfer in multilayer nanolaminate TiA1N/Ag coatings(Nature Publishing Group, 2017-12-06) Kovalev, Anatoly I.; Wainstein, D. L.; Vakhrushev, V. O.; Gago, R.; Soldera, F.; Endrino, José L.; Fox-Rabinovich, German S.; Veldhuis, Stephen C.Plasmon resonance heterogeneities were identified and studied along Ag and TiAlN layers within a multilayer stack in nanolaminate TiAlN/Ag coatings. For this purpose, a high-resolution plasmon microscopy was used. The plasmons intensity, energy, and depth of interface plasmon-polariton penetration were studied by scanning reflected electron energy loss spectroscopy. The heat conductivity of such metal-insulator-metal (MIM) nanolaminate coatings was measured by laser reflectometry. Dependencies of thermal conductivity coefficient of coatings, MIM interfaces, and resistivity of Ag layers as a function of the Ag-TiAlN bilayer thickness were calculated on the basis of experimental data. The contribution of plasmon resonance confinement to the abnormal lower thermal conductivity in the MIM metamaterial with Ag layer thickness below 25 nm is discussed. In particular, the results highlight the relevant role of different heat transfer mechanisms between MI and IM interfaces: asymmetry of plasmon-polariton interactions on upper and lower boundaries of Ag layer and asymmetry of LA and TA phonons propagation through interfaces.Item Open Access Hybrid Ti-MoS2 coatings for dry machining of aluminium alloys(MDPI, 2017-09-16) Brzezinka, Tomasz L.; Rao, Jeff; Chowdhury, Mohamad; Kohlscheen, Joern; Fox-Rabinovich, German S.; Veldhuis, Stephen C.; Endrino, José L.Combinatorial deposition, comprising filtered cathodic vacuum arc (FCVA) and physical vapor deposition (PVD) magnetron sputtering is employed to deposit molybdenum disulphide (MoS2) and titanium (Ti) thin films onto TiB2-coated tool inserts specifically designed for the dry machining of aluminium alloys. Titanium is deposited by FCVA while MoS2 is magnetron sputtered. The deposition set up allows several compositions of Ti-MoS2 to be deposited simultaneously, with Ti content ranging between 5 and 96 at. %, and their machining performances to be evaluated. Milling took place using a CNC Vertical Machining Center at a 877 mm/min feed rate. The effect of different coating compositional ratios on the degree of aluminium sticking when a milling insert is used to face mill an Al alloy (SAE 6061) was investigated using a combination of energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. XPS studies suggest that the greater degree of Al sticking on the rake face of the inserts is due to the formation of greater amounts of non-protective Ti-O phases. EDX mapping of the milling inserts after machining reveal that a Ti:MoS2 ratio of around 0.39 prevents Al from sticking to the tool edges. Since we prevent Al from sticking to the tool surface, the resultant machined surface finish is improved thus validating the machining performance of TiB2-coated tools using optimum compositions of Ti:MoS2 thin film coatings.Item Open Access Influence of probe geometry in micro-scale impact testing of nano-multilayered TiAlCrN/NbN coatings deposited on WC-Co(Elsevier, 2020-11-15) Beake, Ben D.; Bergdoll, L.; Isern, Luis; Endrino, José L.; Fox-Rabinovich, German S.; Veldhuis, Stephen C.Hard nano-multilayered TiAlCrN/NbN coatings on cemented carbide have shown promise in dry high speed machining applications involving repetitive contact, such as end milling of hardened H13 steel. In this study the fracture resistance of TiAlCrN/NbN coatings under repetitive dynamic high strain rate loading has been evaluated by the micro-scale impact test method. Although the fatigue mechanisms can vary with the ratio of coating thickness t to the indenter radius R, macro-scale tests of thin coatings using probe radii in the mm range are necessarily at low t/R. Micro-impact tests at higher t/R have been performed with a range of diamond indenter geometries (R = 8, 20, 100 μm) to investigate the role of varying t/R (0.03–0.375) on the deformation behaviour. With the largest radius probe there was no clear failure for the coatings or substrate under the test conditions. With the 8 and 20 μm radius probes the behaviour of the coatings was strongly load-dependent and they were more susceptible to impact-induced damage than the carbide substrate. As the load increased there was a change from coating to substrate dominated deformation behaviour as the stress field extended further into the substrate. At lower load the dominant fracture behaviour was coating fracture through ring cracking, radial cracking and chipping. At higher load chipping became less prevalent and break-up of the carbide substrate more extensive.Item Open Access Interface-induced plasmon nonhomogeneity in nanostructured metal-dielectric planar metamateria(Hindawi Publishing Corporation, 2015) Kovalev, Anatoly I.; Wainstein, D. L.; Rashkovskiy, A. Y.; Gago, R.; Soldera, F.; Endrino, José L.; Fox-Rabinovich, German S.Transformations of the electronic structure in thin silver layers in metal-dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metallic properties of silver in the thin films. A critical layer thickness of 23.5 nm associated with the development of quantum effects was determined by X-ray photoelectron spectroscopy. Scanning Auger electron microscopy of characteristic energy losses provided images of plasmon localization in the Ag layers. The nonuniformity of plasmon intensities distribution near the metal-nitride interfaces was assessed experimentally.Item Open Access Micro-impact testing of AlTiN and TiAlCrN coatings(Elsevier, 2018-11-23) Beake, Ben D.; Isern, Luis; Endrino, José L.; Fox-Rabinovich, German S.A novel micro-scale repetitive impact test has been developed to assess the fracture resistance of hard coatings under dynamic high strain rate loading. It is capable of significantly higher impact energies than in the nano-impact test. It retains the intrinsic depth-sensing capability of the nano-impact test enabling the progression of the damage process to be monitored throughout the test, combined with the opportunity to use indenters of less sharp geometry and still cause rapid coating failure. The micro-impact test has been used to study the resistance to impact fatigue of Al-rich PVD nitride coatings on cemented carbide. The impact fatigue mechanism has been investigated in nano- and micro-scale impact tests. Coating response was highly load-dependent. A Ti0.25Al0.65Cr0.1N coating with high H3/E2 performed best in the nano- and micro- impact tests although it was not the hardest coating studied. The role of mechanical properties, microstructure and thickness on impact behaviour and performance in cutting tests is discussed.Item Open Access Spatio-temporal behaviour of atomic-scale tribo-ceramic films in adaptive surface engineered nano-materials(Springer Research, 2015-03-05) Fox-Rabinovich, German S.; Kovalev, Anatoly I.; Veldhuis, Stephen C.; Yamamoto, K.; Endrino, José L.; Gershman, I. S.; Rashkovskiy, A. Y.; Aguirre, M. H.Atomic-scale, tribo-ceramic films associated with dissipative structures formation are discovered under extreme frictional conditions which trigger self-organization. For the first time, we present an actual image of meta-stable protective tribo-ceramics within thicknesses of a few atomic layers. A mullite and sapphire structure predominates in these phases. They act as thermal barriers with an amazing energy soaking/dissipating capacity. Less protective tribo-films cannot sustain in these severe conditions and rapidly wear out. Therefore, a functional hierarchy is established. The created tribo-films act in synergy, striving to better adapt themselves to external stimuli. Under a highly complex structure and non-equilibrium state, the upcoming generation of adaptive surface engineered nano-multilayer materials behaves like intelligent systems - capable of generating, with unprecedented efficiency, the necessary tribo-films to endure an increasingly severe environment.