Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 101, No. 1, 2023)

Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 100, No. 6, 2022)

Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 100, No. 5, 2022)

ABSTRACTThe present study investigates the microstructure of monolayer TiAlSiN and bilayer AlTiN/TiAlSiN coatings deposited on WC-Co inserts through magnetron sputtering. Further, a comparative study on the tool life and wear characteristics of uncoated, monolayer and bilayer coated inserts was performed through dry turning of tempered EN-8 steel under extreme cutting conditions. The TiAlSiN coating showed a dense fine morphology whereas the AlTiN/TiAlSiN coating showed a mixed morphology with a columnar structure for the intermediate layer of AlTiN followed by a dense nanocrystalline structure for the top layer of TiAlSiN. The dry turning experiments show that the major form of wear mechanism observed during machining was crater wear. Both monolayer and bilayer coated inserts showed promising cutting performance and the bilayer coated inserts showed better tool life than the monolayer coated inserts under most of the cutting conditions.

Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 101, No. 2, 2023)

ABSTRACTElectroless metallisation is a modern method for obtaining thin layers of metals and their alloys on various dielectric materials, which are increasingly used in various industries. One of the important stages in the pretreatment of the polymers for the chemical processes is the etching operation. It ensures surface roughening of the dielectric materials in order to improve the adhesion strength between the electroless deposited metal coating and the acrylonitrile–butadiene-styrene (ABS) substrate. Most often, this operation in practice is carried out in a chromic-sulphuric acid solution. In this work, investigations are carried out aiming to replace the harmful high chromium solution with an environmentally friendly one. A suitable environmentally friendly etching solution is proposed, with an optimal composition of the solution and working conditions. It can be used in the pretreatment of the ABS substrate for the subsequent deposition of copper or nickel coatings from the corresponding solutions with and without a reducer.

ABSTRACTHard anodic coatings were formed on 6061-T6 aluminium alloy samples using direct current. Surface morphology and cross-section of coatings, as well as their hardness and corrosion behaviour, were studied. It was found that decreasing the applied current density from 55 to 35 mA cm−2 resulted in more uniform coatings with fewer surface defects, lower porosity, and higher hardness values. The optimum electrolyte concentration and hard-anodising time, where less defective coatings were achieved, were found to be 180 g L−1 and 50 min, respectively. The hardness of the optimum film was around 500 HV, and its corrosion current density was 3.2 × 10−9A cm−2. All other samples that were produced at different current densities (30-55 mA cm−2), times (40-100 min), and electrolyte concentrations (25-220 g L−1) had lower hardness and corrosion resistance than the optimum coating. The polarisation resistance of the optimum coating was about 1100 times higher than the bare substrate.

Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 101, No. 3, 2023)

ABSTRACTNew applications of porous anodic aluminium oxide (alumina) structures for the fabrication of photonic devices, etching masks, and periodic pore templates with prospective magnetic, photoluminescent, anti-reflecting properties recently are of high interest. In this respect, new anodising processes for controllable formation of periodic structures in unconventional solutions at low voltages might be challenging. In this study, the anodic behaviour of aluminium in aqueous formate solutions was studied within a wide range of concentrations, pH, electrolyte temperatures, anodising times, and voltages. It was established that the thickness of porous anodic films depended on the concentration of solution applied (c), pH, bath temperature (T), and voltage (Ua) increasing with increase in c, Ua, and T. The thickest films were formed in the solution containing 0.2 mol L−1 formic acid at a pH of 2.5. These films contained up to 5.8 at% of entrapped carbon. The transition of porous anodising to the ‘burning’ type occurred at 22–25 V. Under appropriate anodising conditions ordered hexagonal cell arrays can be formed.

ABSTRACTAl2O3, TiO2, and Al2O3-TiO2 coatings were deposited on AISI 304 stainless steel plates by the sol–gel dipping technique, and the effects of the coating composition on microstructure, wear, and corrosion characteristics were examined. Tribological features were determined by ball-on-disc sliding tests against an Al2O3 ball under a 10 N load, while corrosion properties were evaluated by potentiodynamic polarisation tests performed in 3.5% wt. NaCl solution. γ-Al2O3, α-Al2O3, and rutile phases were detected in the hybrid coatings. The highest coating thickness was obtained in single Al2O3 film and decreased with an increasing amount of TiO2 nanoparticles. The single Al2O3 layer had both the highest wear resistance and the lowest corrosion resistance. Although TiO2 addition caused an increase in the wear rate, it improved the corrosion resistance of the coating by filling the voids in the Al2O3 film. The Al2O3-TiO2 hybrid film with a relative ratio of 6:1 as a candidate for the wear- and corrosion-resistant coating decreased wear and corrosion losses of the 304 substrates by 83% and 97%, respectively.

ABSTRACTThe current investigation's objective was to assess the air jet erosion tester's ability to measure the erosive behaviour of plasma sprayed coatings on titanium-15 alloy. 65% NiCrAlY, 30% Cr2O3, and 5% YSZ make up the coating's chemical composition. A study of microstructure and phases was carried out. Microhardness and adhesive strength have both been measured in this work. With impact angles of 30° and 90° at 300°C, 500°C, and 700°C, Al2O3 erodent was utilised in a solid particle erosion test. An optical profilometer was used to calculate the erosion volume loss. The coating erosion resistance was found to be higher than the substrate sample for the test temperature that was employed, and this was more obvious at higher impact angles and higher temperatures The ductile character of the coating is seen in the contour of the deteriorated coating surface.

Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 101, No. 1, 2023)

ABSTRACTMetal cutting is a necessary operation in any production industry. Rapid production has become a necessity as a result of recent trends in high-speed machining and automation. The demand for more sophisticated and advanced cutting tools has significantly increased in recent years. The properties of alloy metals can be improved by applying a thin film to enhance or reduce specific properties based on product needs. The effect is being able to operate the tool at a higher cutting speed, feed rate, depth of cut, and longer tool life, with a dry machining possibility for the end-user when cutting tools are appropriately coated and performing as intended using thin films. Thin coatings improve cutting tool wear resistance, oxidation resistance, friction reduction, resistance to metal fatigue, as well as thermal shock resistance. On the other hand, thin film morphology and stability are crucial challenges in cutting tool applications as thin film morphology is heavily dependent on deposition techniques. As a result, based on the available studies, this article presents a critical review of deposition coating techniques, characterisation methods, and evaluation techniques in order to prevent excessive damage and improve the mechanical properties of cutting tools. The anticipated outcomes of this review can be used as a guide to help researchers understand various coating techniques and their effects on cutting tool properties.

Published in Transactions of the IMF: The International Journal of Surface Engineering and Coatings (Vol. 100, No. 6, 2022)

ABSTRACTIn this research, hydroxyapatite powder particles were coated on a Ti-6Al-4V alloy substrate by the plasma spraying method to create bone implants by benefitting from titanium's mechanical properties and hydroxyapatite's biological properties. Hydroxyapatite prepared by the plasma spraying method suffers from decomposition, formation of other calcium phosphate phases, weak adhesion to the substrate, and microcrack formation in the coating due to residual stresses initiated by the high temperature of the coating process. To improve the hydroxyapatite coating properties, the Ti-6Al-4V alloy was preheated, and then hydroxyapatite coating took place. The results showed that residual stress in the interface decreased, and adhesion improved by preheating the substrate. However, formation of an amorphous phase on coating was observed, resulting in a higher dissolution rate in the biological environment and weak mechanical properties compared to crystalline hydroxyapatite. Experimental results showed that heat treatment after the coating process decreased the amount of this amorphous phase and heightened the crystallinity of the coating by up to more than 60%.

ABSTRACTThe possible fabrication of porous anodic oxide films on aluminium in ionic liquids based on choline dihydrogen citrate eutectic mixtures both with oxalic acid and isopropyl alcohol and ethylene glycol, has been investigated. The anodisation has been carried out in either potentiostatic or galvanostatic regime, at temperatures of 45–80°C, for different process durations. Quite compact, uniform anodic alumina layers have been obtained. Based on AFM and SEM investigations, pore diameters between 50 and 80 nm and interpore distances in the range of 160–200 nm have been estimated, with values influenced by the electrolyte type and anodisation conditions. The highest anodisation rate of about 0.4 µm min−1 has been determined by applying operation temperatures of 60°C. The recorded EIS spectra showed a pure capacitive behaviour and high anodic oxide resistances of 106–107 Ω cm2 order.

ABSTRACTIn the present study, nanocrystalline nickel (Ni) and nickel-chromium (Ni-Cr) alloy coatings were developed on copper (Cu) substrate using pulse current. The pulse current parameters include a cycle time of 240 milliseconds at a duty cycle of 0.5 and 4.17 Hz frequency. The surface morphology, texture, hardness, scratch resistance and porosity were investigated for different coatings developed by pulse plating. Energy Dispersive Spectroscopy (EDS) analysis revealed good quality Ni and Ni-Cr alloy coatings developed on the copper substrate. The peak current of the pulse has been observed to have an impact on the coating weight and thickness. The micrographs of the coatings explored under Field Emission Scanning Electron Microscopy (FESEM), depict uniform coatings consisting of fine primary and coarse secondary granules of Ni and Cr. The hard primary and secondary Ni granules deposited on the surface of Cu increase its hardness, corrosion and wear resistance. Further, it was observed that the Ni-Cr alloy plated samples are harder and less porous in nature compared to Ni plated samples.

ABSTRACTThe development of the process to produce Metal Matrix Nanocomposite (MMNC) coatings can provide opportunity for the enhancement of mechanical and electrical properties. This research uses speciation-simulating software to screen formulations for producing nanocomposites by pulse-reverse plating (PRP). PRP is used as a controlled delivery mechanism to attract a high concentration of nanoparticles to the coating during the anodic pulse which are subsequently captured in the cathodic pulse. A disadvantage is that the anodic pulse generates passivating hydroxide layers leading to poor adhesion. Speciation plots assess the stabilising effect of chosen complexants (gluconate and glycine) within electrolytes with the aim of diminishing hydroxide formation. To confirm bath formulation effectiveness before nanoparticle incorporation, UV-Vis spectroscopy and electrodeposition were used. Gluconate and glycine both theoretically produce highly stable complexes and also produce uniform copper deposits supporting the stabilisation effect observed in theoretical studies. This work therefore supports the use of these complexants for future stages of this research.

ABSTRACTIn the present work, multi-walled carbon nanotube (MWCNT) nanofiller reinforced copper-nickel alloy (CuNi@MWCNTs) nanocomposites were synthesised by a modified electro-chemical co-deposition followed by compaction and sintering. During this method, CuNi@MWCNTs were co-deposited on a cathode tip at room temperature and collected from the electro-chemical bath in powdered form. Subsequently, the powdered nanocomposites were dried, compacted and sintered to prepare solid pellets. The influence of different amounts (25, 50 and 100 mg L−1) of MWCNT nanofillers in the deposition bath on microstructure, mechanical and anti-corrosion properties of CuNi@MWCNTs nanocomposites was investigated. The microhardness, compressive yield strength and friction coefficient of CuNi@MWCNTs (100 mg L−1) nanocomposites were enhanced by 45.7%, 37.2% and 55.1%, respectively, compared to that of pure CuNi alloy. In addition, the CuNi@MWCNTs nanocomposites obtained also exhibited improved anti-corrosion property in 3.5 wt.% NaCl solution at continuous agitation of 150 rpm and 27°C temperature. Based on the research outcomes, this approach for synthesising CuNi@MWCNTs nanocomposites may be proposed for scale-up industrial trials.

ABSTRACTOne of the widely used plastics for chemical metallisation is acrylonitrile butadiene styrene (ABS). It is a strong and flexible plastic, which makes it suitable for the preparation of details with a complex shape and leads to optimum design qualities. Metallised plastics combine the properties of dielectrics and metals, thanks to which they find application in many branches of industry. Before the chemical metallisation of samples, they are subjected to pretreatment, which includes a number of operations. Among them the most important are: etching (surface micro-roughening of the surface) and activation (adsorption of catalytically active metal centres on the surface). Prior to performing the etching operation, the surface of the polymer samples is relatively smooth. In order to increase the roughness of the surface and to facilitate the subsequent operations, an additional operation of “swelling” is included, preceding the etching operation. The influence of the swelling operation on the quality of the final electroless Cu and Ni-P coatings has been studied in the present work. The experimental results show that metal coatings with uniform thickness and good adhesion are obtained.