Papers by Keyword: Surface Coating

Abstract: This paper conducted extensive review of extant literature on fusion-based technique for surface modification of austenitic stainless steel AISI 304 grade (304SS) for high temperature self-lubricating application using refractory carbides. Careful systematic review of available literature indicates that among the families of refractory carbides, only silicon carbide (SiC) and titanium carbide (TiC) were successfully adsorbed on the surface of 304SS via fusion melting techniques with TiC having more documentation. Yet, this information was limited to ambient temperature properties of the TiC coatings as such high temperature properties as creep-fatigue, thermal stability, hot corrosion and oxidation were not reported. Additionally, information on the incorporation of hexagonal boron nitride (hBN) into TiC coatings to address the high temperature self-lubricating challenges associated with the alloy was not available. Further, literature is scarce on multi-layer longitudinal and transverse coatings to address the challenges inherent with single layer coating. The review established that there is a wide gap in both knowledge and practice in the deposition of self-lubricating high temperature properties in 304SS substrate material using fusion-based technique which offers a window for research exploration.

Abstract: Mg-Li system alloys also has excellent cold-workability compared to commercial hcp-structured Mg alloys. However, Mg-Li alloys have poor corrosion resistance because not only that is Mg-based alloy but Li as a major alloying element is a less noble metal. For example, Mg-Li alloy sheet indicates high corrosion rate and exfoliation corrosion as a result of long-term corrosion test. The authors reported Mg-14 mass%Li-3 mass%Al alloy has the highest corrosion resistance in β-type solid solution alloy. Even though the optimized alloy composition, the alloy does not have enough corrosion resistance for practical use. In this study, anodized coating on Mg-Li alloy using phosphate solution was investigated. Anodizing of Mg-Li alloy facilitates the dissolution of substrate because of high Li concentration in this alloy. Therefore, the anodizing conditions were widely examined. As a result, the coating with approximately 15-20 μm of the surface layer was successfully formed. The surface layer was composed of MgAl₂O₄ and some phosphorus compounds. The thickness of anodized layer varied with the anodizing conditions. The dense surface layer was formed at a certain anodizing voltage and the corrosion resistance of anodized Mg-Li alloys was improved. However, the surface has some cracks and large flaky compounds. The formation mechanism of dense layer during anodizing were discussed.

Abstract: This study deals with the hardening of titanium surface by carburising of CP Ti Gr 2 substrate by using laser sintering process. The objective of this project is to harden the surface to improve surface wear resistance of titanium. In this study graphite powder is used as source of Carbon. Carbon from graphite reacts with titanium and TiC layer of 109 micron was measured on the titanium surface. The microstructure and phase analysis results show that presence of only TiC phase on the surface of the titanium substrate. TiC grains are nearly 5 times finer than titanium substrate grains. Grain refinement of TiC phase all over the surface of the substrate resulted in increase in hardness and development of significant wear resistance surface in titanium substrate. Hardness of TiC layer was found to be 2191Hv which is nearly ten times higher than the substrate titanium. Wear test results of pin and disc type shows negligible wear rate as compared to CP Ti substrate. TiC grains are nearly 5 times finer than titanium substrate grains.

Abstract: Lithium-rich manganese-based oxides (Li_1.2Mn_0.54Ni_0.13Co_0.13O₂, LMNCO) as cathode materials were prepared by the sol-gel method. Then, LMNCO was coated with γ-basic manganese oxide (γ-MnOOH) to form the composite cathodes. Through the structural characterization and performance test, it is found that the composite cathode with 10% γ-MnOOH coating exhibits the best electrochemical performance. After 50 cycles at 0.1 C (1 C = 200 mA g^-1), the specific discharge capacity is 264.4 mAh g^-1 with capacity retention of 96.1%. Even at a high current density of 1C, its discharge capacity reaches up to 200.5 mAh g^-1 after 30 cycles, which suggests that surface coating of γ-MnOOH is an effective strategy for further enhancing the electrochemical performance of LMNCO.

Abstract: Biodegradable stents (BDS) are projected to be degraded while supporting the blood vessel lumen. Equipping BDS with coated drugs will enhance its biological properties. In this study, everolimus drug was coated on poly (L-lactic acid) (PLLA)/poly (D-lactic acid) (PDLA) scaffolds by utilising polydopamine (PDA) as an intermediate layer. The immobilisation time for the coating process was tailored at 12 and 24 hours. The effects of different immobilisation time of everolimus (12 and 24 hours) were characterised through an ATR-FTIR, SEM and water contact angle analyses to investigate the chemical functionalities, surface morphology and hydrophilicity properties, respectively. The ATR-FTIR results indicated the presence of chemical functionalities of the coating and the scaffolds. The scaffold surfaces were having a transition from smooth to irregular surfaces after the PDA grafting and the coating of everolimus. More homogeneous surface formation was observed and greater hydrophilicity was recorded on the PLLA/PDLA scaffolds coated with everolimus at 24 hours immobilisation compared to the 12 hours immobilisation. These findings are beneficial for the fabrication of BDS with the implementation of everolimus and PDA as coating materials.

Abstract: Titanium (Ti) has been used in metallic implants since the 1950s due to various biocompatible and mechanical properties. However, due to its high Young’s modulus, it has been modified over the years in order to produce a better biomaterial. Tantalum (Ta) has recently emerged as a new potential biomaterial for bone and dental implants. It has been reported to have better corrosion resistance and osteo-regenerative properties as compared to Ti alloys which are most widely used in the bone-implant industry. Currently, Tantalum cannot be widely used yet due to its limited availability, high melting point, and high-cost production. This review paper discusses various manufacturing methods of Tantalum alloys, including conventional and additive manufacturing and also discusses their drawbacks and shortcomings. Recent research includes surface modification of various metals using Tantalum coatings in order to combine bulk material properties of different materials and the porous surface properties of Tantalum. Design modification also plays a crucial role in controlling bulk properties. The porous design does provide a lower density, wider surface area, and more immense specific strength. In addition to improved mechanical properties, a porous design could also escalate the material's biological and permeability properties. With current advancement in additive manufacturing technology, difficulties in processing Tantalum could be resolved. Therefore, Tantalum should be considered as a serious candidate material for future bone and dental implants.

Abstract: This work deals with the deposited cadmium sulfide (CdS) quantum dots thin films on transparent conductive fluorine-doped tin oxide (FTO) substrates prepared by successive ionic layer adsorption and reaction technique (SILAR). QD deposition based on SILAR is easy, cheap and effective method which improves the surface quality and performance of QD-based devices. The effect of the number of cycles of SILAR on the morphology and size of the quantum dots has been investigated. SILAR technique was adopted for the deposition of CdS on anatase TiO₂ and the three main factors contributing to the performance of QDs processed by SILAR, namely the number of cycles used, the concentration of the precursor solution, and the reaction dipping time, are discussed. The structural, morphological and optical properties were studied using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), Raman spectra analysis and UV-Vis NIR analysis, respectively. The particle size of CdS was calculated from XRD pattern using Debye Scherrer’s equation and the calculated particle size was 4.5-9.5 nm. Using CdSQDs, quantum dot sensitized solar cells (QDSSC) were fabricated on FTO substrates as being a transparent conductive oxide. Optical absorption property proved that the band gap energy value was about 2.44 eV. The result delivered from J-V curve revealed that the overall energy conversion efficiency increased with increasing the deposition cycles giving the best efficiency of 2.73 % at 7 cycles.

Abstract: Properties of parts after a shot-blasting of a surface are investigated. Change of size of compression stresses in a surface layer of the cemented tempered parts processed by different compositions of materials in shot blasting units is shown. After shot jetting peening of parts increase in a limit of endurance for 40 – 60% is reached. The maximum effect at a shot jetting peening of toothed parts is reached when using for a shot blasting of the mix consisting of steel chopped fraction and glass balls.

Abstract: Laser deposition is an advanced manufacturing technology capable of enhancing service life of engineering components by hard-facing their functional surfaces. There are quite a number of parameters involved in the process and also desirable output characteristics. These output characteristics are often independently optimised and which may lead to poor outcome for other characteristics, hence the need for multi-objective optimisation of all the output characteristics. In this study, a laser deposition of Ti-6Al-4V wire and tungsten carbide powder was made on a Ti-6Al-4V substrate with a view to achieve a metallurgical bonded metal matrix composite on the substrate. Single clads were deposited with a desire to optimise the composite clad characteristics (height, width and reinforcement fraction) for the purpose of surface coating. Processing parameters (laser power, traverse speed, wire feed rate, powder feed rate) were varied, the experiment was planned using Taguchi method and output characteristics were analysed using principal component analysis approach. The results indicated that the parameters required for optimised clad height, width, and reinforcement fraction necessary for surface coating is laser power of 1800 W, traverse speed of 200 mm/min, wire feed rate 700 mm/min and powder feed rate of 30 g/min. The powder feed rate was found to most significantly contribute 43.99%, followed by traverse speed 39.77%, laser power 15.87% with wire feed rate having the least contribution towards the multi-objective optimisation. Confirmation results showed that clad width and reinforcement fraction were significantly improved by the optimised parameters. The multi-objective optimisation procedure is a useful tool necessary to identify the process factors required to enhance output characteristics in laser processing.

Abstract: A latex cup is used to collect latex from a rubber tree which is an economic plant in Thailand. The fresh latex or crude rubber consists of organic compound and water which can wet and adhere to surface of the collecting cup. In this research, surface of the latex cup was treated with polymethylhydrogen siloxane-functionalized silica compound to improve hydrophobicity so that it could repel the dirt and latex, resulting in an anti-adhesion between the latex and the cup. Surface of the latex cup was etched with 10 % v/v hydrofluoric acid for 30 min before application of the siloxane coating which was performed by immersion in the solution, painting and spraying, respectively. The result revealed that the immersion method exhibited optimum property justified by high value of water contact angle, low surface free energy, surface roughness and the field test. At the optimum polymethylhydrogen siloxane : fumed silica ratio of 3 : 1 wt%, the treated sample had water contact angle of 139.24 ± 0.78 degrees and possessed surface energy of 1.07 mJ/m². The field test conducted in the rubber field in Trang province revealed good durability of the coating. The water contact angles were 132.15 ± 2.05 and 129.20 ± 2.34 degrees after 2 weeks and 1 month, respectively, of the field service.