Browsing by Author "Brzezinka, Tomasz L."
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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 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.