Browsing by Author "Rao, Jeff"
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Item Open Access Bioinspired metal–polymer thin films with varying hydrophobic properties(Springer, 2017-08-14) Rao, Jeff; Anjum, Sadaf Saad; Craig, M.; Nicholls, John R.Nanocomposites involve the inclusion of one material into the layers of another material at a nanoscale level. Inspired by nature, nanocomposites material systems offer functionalities over their bulk forms which in some cases have evolved over millions of years. Here, thin film coatings have been fabricated by PVD sputtering, comprising a soft PTFE phase which is combined with a hard metallic NiTi phase. A series of coatings with PTFE ranging from 10 to 75 vol% have been prepared, and their surface energies and microstructures investigated. The surface energy of the nanocomposite films changes with the PTFE content, falling in the range between PTFE and NiTi with water contact angles between 80° and 102° for a thin film with 25 and 75 vol% of PTFE, respectively. Here, both TEM and EDX reveal PTFE forming along NiTi column boundaries. Coatings with PTFE content greater than 50 vol% failed due to a build-up of intrinsic stress. The degree of hybridization between NiTi and PTFE was found to be dependent on the PTFE layer thickness. SEM analysis of this coating reveals PTFE at the surface embedded within the NiTi matrix.Item Open Access Carbon and titanium diboride (TiB2) multilayer coatings.(2004-11-01T00:00:00Z) Rao, Jeff; Cruz, R.; Lawson, K. J.; Nicholls, John R.Titanium Diboride, (TiB2) is a metal-based refractory ceramic material that has been investigated in industrial applications ranging from, cutting tools to wear parts and for use in the aerospace industry. The unique properties which make this material so fascinating are, its high hardness, high melting point and its corrosion resistance. TiB2 is prevented from wider mainstream use because of its inherent brittle nature. With a view to overcome this in coating form and with the aim of providing in addition inherent lubricity, in this study 50 layer TiB2/C multilayer stacks have been fabricated, with varying volume fractions of ceramic, whereby the interfaces of the layers limit crack propagation in the TiB2 ceramic. TiB2 has been multilayered with carbon, to make use of the unique and hybrid nature of the bonding in carbon coatings. DC magnetron sputtering with substrate bias was the preferred route for the fabrication of these coatings. AISI tool steel has been used as the substrate material. By varying the amount of TiB2 ceramic from 50% to 95%, the Hardness of the coating is seen to increase from 5 GPa to 17GPa. The Hardness is observed to decrease as a function of increasing carbon content, agreeing with other studies that the carbon layers are not load-bearing. The graphitic nature of the sp2 bond, however, acts as a lubricant layer.Item Open Access Data relating to "Combinatorial Sputtering of Photoluminescent Europium Titanium Oxide Thin Films"(Cranfield University, 2024-11-08) Chen, Junfeng; Indrat Aria, Adrianus; Rao, JeffItem Open Access Development of low friction coatings for alsi milling(2019-04) Brzezinka, Tomaz; Endrino, José L.; Rao, JeffAluminium silicon (AlSi) alloys play an essential role in many industries because of their good machinability characteristics. However, their low degree of plasticity promotes adhesion at the tool edge during machine cutting, leading to a built-up edge (BUE) which reduces tool lifetimes, and the silicon content leads to tool abrasion. Currently, cemented carbide mill inserts coated with titanium diboride (TiB₂)offer the prospects of machining an array of structural metallic alloys including AlSi. However, the brittle nature of TiB₂ leaves it prone to extensive surface damage, particularly during the running-in stage of machining when tool adaptation takes place. An additional coating addressing abrasive wear and preventing BUE could limit TiB₂damage. Fabricating coatings of TiB₂ using arc evaporation remains challenging as an extensive cathode fracture occurs. Thus, the present work aims to address the drawbacks associated with TiB₂ by the deposition of a thin lubricious coating on top of the TiB₂.Secondly, the development of a new cathode, which would allow the deposition of TiB₂ by arc evaporation is investigated. A hybrid Physical Vapor Deposition system combining Filtered Cathodic Vacuum Arc (FCVA) and Magnetron Sputtering was developed forth is study. Three lubricious coating systems of Ti-MoS₂, single layer DLC and DLC-WS₂ were investigated as a top layer. Ti-MoS₂ was optimised for dry machining applications, and a Ti:MoS₂ ratio around 0.39 was found to prevent Al from sticking to the tool edges. The DLC and DLC-WS₂ coatings were designed for machining with coolant. In comparison to the performance of a TiB₂ benchmark, the monolayer DLC coating improved the machining length by ~60% and a two-layer DLC-WS₂ coating decreased wear rate by ~75%, having a measured coefficient of friction of 0.05. The development of TiB₂ cathodes for FCVA required a modification of the chemical composition to improve it’s sinterability and prevent cathode fracture during arc operation. A TiB₂-TiSi₂ (5 wt%)cathode ensured the best balance between arc stability and cathode utilisation while TiB₂-C(1 wt%)has provided exceptional arc stability, although the cathode utilisation was less due to the constant generation of cathode flakes.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 Fabrication of Smart Intercalated Polymer - SMA Nanocomposite(Cranfield University, 2015-03-16) Anjum, Sadaf Saad; Nicholls, J. R.; Rao, JeffMimicking nature gives rise to many important facets of biomaterials. This study is inspired by nature and reports on the fabrication of an intercalated polymer-NiTi nanocomposite that mimics the structural order of urethral tissue performing micturition. PTFE is chosen due to its hydrophobicity, low surface energy, and thermal and chemical stability. NiTi has been selected as a prime candidate for this research due to its excellent mechanical stability, corrosion resistance, energy absorbance, shape memory and biocompatibility. Nanoscale engineering of intercalated nanocomposites is done by PVD sputtering PTFE and NiTi. FTIR spectroscopy confirms that PTFE reforms as polymer chains after sputtering. Suitable PVD sputtering parameters were selected by investigating their influence on deposition rates, microstructure and properties of PTFE and NiTi thin films. PTFE forms stable nanocomposite coatings with NiTi and displays favourable surface interactions, known as ‘intercalation’. Intercalated PTFE-NiTi films were fabricated as layered and co-sputtered thin films. Co-sputtered nanocomposites contained nearly one-third vacant sites within its internal microstructure because of intercalation while intercalation introduced minute pits in fibrous NiTi columns of layered nanocomposites. These pits allow PTFE to extend their chains and crosslinks, resulting in microstructural and functional changes in the thin films. Intercalated PTFE-NiTi nanocomposites offer a close match to the natural tissue in terms of responding to the fluid contact (wetting angle modifications), and allow the soft and hard matter to incorporate in one framework without any chemical reactions (intercalation). An intercalated microstructure in co-sputtered and layered nanocomposites was verified by EDS-SEM and EDS-TEM techniques. The functional responses were witnessed by changes in water contact angle (WCA) and coefficient of friction (CoF) values measured on the film surface. The WCA (99°) and CoF (0.1 – 0.2) of the intercalated nanocomposite (sample PNT12) were different to the NiTi (top layer). WCA and CoF indicate the internal microstructural interactions because of intercalation.Although the pseudoelastic behaviour of NiTi can provide additional fluid response but the difficulty is an absence of crystallinity in as-deposited NiTi, and the heat treatment that melts PTFE. However, DSC and XRD techniques were employed to find the optimum NiTi composition and transition temperatures for phase transformation related to pseudoelasticity. This study provides the basis to incorporate the shape memory (pseudoelasticity or thermal shape memory effect (shape memory effect)) features of NiTi into the intercalated nanocomposite in future. The intercalated PTFE-NiTi nanocomposite reveals a fascinating research precinct, having the response generating characteristics similar to that of natural tissue.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.Item Open Access Low temperature ITO thin film deposition for solar cells(Cranfield University, 2008-09) Seraffon, Maud; Impey, Susan A.; Lawson, K. J.; Rao, JeffThe electrical and optical properties as well as the microstructure of indium tin oxide thin films deposited on glass and flexible substrates is demonstrated in this project report. This project is a part of an MSc in Advanced Materials at Cranfield University. The understanding and improvement of indium tin oxide coatings deposited by magnetron sputtering on both glass and polymer substrates has been an area of extensive research in the last decade. This technology appears to be very interesting in terms of money saving and efficiency in the solar cell domains where the coatings are used in thin film solar cells. Research into the thin film solar cells mechanism, the sputtering process and ITO coatings is reported, along with detailed consideration of the best results obtained in the past in terms of ITO films’ electrical and optical properties. ITO thin films were deposited on glass and different sputtering parameters were changed in order to investigate their influence on the coatings properties: film thickness, chamber pressure, rotation, oxygen amount and sputtering power. A decision was made to establish the best sputtering parameters. These parameters were set to deposit ITO on polyethylene terephthalate (flexible substrate). The samples were also annealed at 150°C and 370°C. An ITO thin film with a resistivity of 1x10-4 Ωcm and a 90% transmissivity was obtained. An Energy Dispersive Spectrometry analysis was finally made on samples showing a substoichiometric composition of the ITO films.Item Open Access Nickel titanium and nickel titanium hafnium shape memory alloy thin films(Elsevier Science B.V., Amsterdam., 2010-04-01T00:00:00Z) Rao, Jeff; Roberts, T,; Lawson, K. J.; Nicholls, John R.Shape memory alloy (SMA) coatings of NiTi and NiTiHf have been deposited onto Si substrates using pulse DC sputtering. Coatings of NiTi with compositions containing 45 to 65 at.% Ti have been fabricated by co-sputtering NiTi with Ti. NiTiHf coatings with Hf compositions ranging from 2 to 30 at.% Hf have been fabricated by co-sputtering NiTi with Hf. XRD results reveal the as-deposited coatings as amorphous. A high temperature, 1100 à °C anneal followed by a low temperature, 550 à °C anneal was employed to crystallise the coatings. The XRD then shows the coatings to be martensitic at room temperature. Two sets of samples were produced for characterisation; one set was used for indentation studies and the other set used to prepare freestanding films required for differential scanning calorimetry (DSC) studies. Using the DSC, a NiTi coating containing 52 at.% Ti shows an endothermic austenite peak phase transformation, (Ap) at around 105 à °C and an exothermic peak martensite phase transformation, (Mp) at 65 à °C, resulting in a hysteresis of 40 à °C. For a NiTi coating containing 65 at.% Ti the hysteresis remained unchanged at 40 à °C, but there was a decrease in the phase transformation enthalpies when compared with the coatings containing 52 at.% Ti. Calculated phase transformation enthalpies in the NiTi coatings ranged from 6 to 13 J/g for the austenite phase and â  8 to â  11 J/g for the martensite phase. The NiTiHf coating shows SMA behaviour for a film containing 30 at.% Hf. DSC reveals an â  Râ  phase transition in this film. It is understood that this phase is present in films that have high internal stresses and is understood to nucleate near Ti3Ni4 precipitates. Phase transformation temperatures occur at 98 à °C and 149 à °C during heating and occur at 99 à °C during cooling. Phase transformation enthalpies range between 2 and 3 J/g for the austenite phase and â  7 J/g for the martensite phase. A scratch tester equipped with a 5 mm spherical tip has been utilised with loads ranging from 1 to 5 N to determine the recovery properties of the films. The results in this study conclude that NiTi films containing 65 at.% Ti deform 3 times more than films containing 52 at.% Ti. For NiTiHf thin films, increasing the Hf composition from 2 at.% to 30 at.%, doubled the deformation measurItem Open Access The potential of reverse innovation to improve urban toilets(2017-12) Tierney, Ross; Williams, Leon; Rao, JeffThe lack of desirable, waterless toilet options in urban environments around the world leads to major issues that will continue to get worse as population density increases. At the bottom of the economic pyramid, 2.3 billion people lack access to adequate sanitation accelerating the spread of disease through contaminated water and leading to the deaths of over a million children per year. At the top of the economic pyramid, the ubiquitous flushing toilet uses nine litres of water per flush, equating to the average person using 15,000 litres of water per year. As clean water becomes a scarcer resource, wasting and polluting water has to be avoided. Developing new water-saving, desirable toilets to provide a pleasant user experience will increase the likelihood of adoption of more sustainable options. Defecation is a basic human function but also a universal cause for embarrassment and disgust. As the repulsion is visceral and ‘hard-wired’ human behaviour, many of the same issues arise whether the user is in the poorest slum or a modern apartment building. Designing new products for low income countries that find a secondary market in a high income country is an approach called reverse innovation and has a proven record of producing disruptive innovations by working to strict requirements. This research discusses how reverse innovation has potential to address the challenges and issues associated with low-water sanitation to increase adoption of more sustainable technology. To achieve this, an understanding was gained of the user experience of different low-water toilets through literature review and an ethnographic study in Kumasi, Ghana. A new waterless toilet technology was then developed and tested, primarily targeting the residents of Kumasi before being tested with a secondary target market in the United Kingdom. There were a number of similarities across both target markets, confirming the importance of user experience. The technology was positively received and compatible with user behaviour in the secondary target market indicating the technology could be transferred and an example of reverse innovation. This research intends to encourage and inspire innovation in a sector that effects everyone in the world yet remains an ignored and embarrassing subject.Item Open Access The role of PVD sputtered PTFE and Al2O3 thin films in the development of damage tolerant coating systems(Elsevier, 2019-12-09) Ng, Chi-Ho; Rao, Jeff; Nicholls, John R.The surfaces of artificial joints are susceptible to premature wear which reduces their service life leading to the increased risk of revision arthroplasty. Tribological coatings having low coefficients of friction (CoF) and which are also biocompatible are therefore required to minimise such risks. Metal matrix composite (MMC) coatings exhibiting a modified toughness structure, thus reducing the potential to crack were successfully fabricated by cold spray (CS) technology. The coatings comprised of an ultra-low wear polytetrafluoroethylene (PTFE) + alumina (Al2O3) composite, firstly delineated by Burris and Sawyer in 2006, were prepared on cold sprayed substrate and the functionality of such coatings in terms of enhanced frictional properties was investigated. In this study, PTFE + Al2O3 thin film coatings were prepared by physical vapour deposition (PVD) and incorporated with cold sprayed MMC coatings to produce a damage tolerant coating system designed to extend the service life of artificial movable joint surfaces. Surface characterisation analysis indicated the formation of a PTFE–Al2O3 nanocomposite forming between the PTFE and Al2O3. This composite thin film exhibited excellent friction reducing ability up to an applied load of 7 N. Regardless of whether the Ti–6Al is manufactured by a layer-by-layer approach or co-sputtering method, the CoF is reduced to below 0.1 at the start of the test. Furthermore, the results reveal that the PVD sputtered PTFE + Al2O3 thin film functionalises the cold sprayed surface by offering a self-lubricating effect and that PVD combined with CS is reliable for devising material systems operating in high-wear applications.Item Open Access Titanium aluminium nitride and titanium boride multilayer coatings designed to combat tool wear(MDPI, 2017-12-28) Rao, Jeff; Sharma, Amit; Rose, TimThe lifetimes and the premature wear of machining tools impact on manufacturing efficiencies and productivities. A significant proportion of machining tool damage can be attributed to component wear. Here, titanium aluminium nitride (TiAlN) multi-layered with titanium diboride (TiB2) prepared by PVD (Physical Vapour Deposition) sputtering onto H-13 substrates are studied as potential wear-resistant coatings for forging die applications. The TiB2 content has been altered and two-sets of coating systems with a bilayer thickness either less than or greater than 1 μm are investigated by tribological and microstructural analysis. XRD analysis of the multilayers reveals the coatings to be predominately dominated by the TiAlN (200) peak, with additional peaks of TiN (200) and Ti (101) at a TiB2 content of 9%. Progressive loads increasing to 100 N enabled the friction coefficients and the coating failure at a critical load to be determined. Friction coefficients of around 0.2 have been measured in a coating containing 9% TiB2 at critical loads of approximately 70 N. Bi-directional wear tests reveal that bilayers with thicknesses greater than 1 μm have frictional coefficients that are approximately 50% lower than those where the bilayer is less than 1 μm. This is due to the greater ability of thicker bilayers to uniformly distribute the stress within the layers. There are two observed frictional coefficient regimes corresponding to a lower and higher rate of material loss. At the lower regime, with TiB2 contents below 20%, material loss occurs mainly via delamination between the layers, whilst at compositions above this, material loss occurs via a break-up of material into finer particles that in combination with the higher loads results in greater material loss. The measured wear scar volumes for the TiAlN/TiB2 multilayer coatings are approximately three times lower than those measured on the substrate, thus validating the increased wear resistance offered by these composite coatings.