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In this study, nanostructured titania (TiO2; n-TO) and nanostructured alumina-titania (Al2O3-13 wt.%TiO2; n-ATO) coatings were successfully deposited on the 6061 aluminum alloy by applying the high-velocity oxy-fuel process. The n-TO coating showed limited pores or microcracks accompanied by both partially and fully melted areas within splats. The n-TO coating exhibited about 25% higher microhardness compared with the n-ATO coating. The agglomerated non-molten nanostructured TiO2 particles that are randomly dispersed and embedded within the n-TO coating microstructure act as arresters of cracks through either branching or blunting crack tips, resulting in about 17% higher bonding strength, as compared to the n-ATO coating with a looser microstructure. The n-TO coating demonstrated superior hardness, higher wear resistance, and smoother wear scar than the n-ATO and uncoated Al substrate. The electrochemical test indicated that the n-ATO coating had about a 50% higher corrosion rate than the n-TO coating because of its looser structure. The immersion test revealed that the n-ATO coating had been severely attacked by blistering and deep cracks corrosions, whereas limited attacks could be distinguished using the n-TO coating in the substrate interface. Based on the results, the n-TO coating can effectively protect the Al alloy substrate against 3.5 wt.% NaCl solution.

One of the high potential material, lanthanum zirconate (LZ) is deposited on superalloy 625 due to its excellent phase stability, low thermal conductivity as well as the high melting point. However, microstructural defects were detected due to lamellar structure behaviour exhibited from the plasma-sprayed coating techniques. This paper investigated the effect of surface modification on LZ thermal barrier coating (TBC) by using laser glazing method. The double ceramic layer (DCL) TBCs are composed of NiCoCrAlYTa bond coating formed via the HVOF process while 8YSZ ceramic top coat and La2Zr2O7 as the third layer were produced by utilizing the APS technique. Nd:YAG pulsed laser has been used to modify the surface layer of plasma-sprayed LZ coatings. The microstructural morphologies of both as-sprayed and laser glazed samples were investigated using Scanning Electron Microscopy (SEM). The phases of the coatings were analysed with X-ray Diffractometry (XRD). The results showed that the laser glazing process reduced surface roughness attributed to the sealing of porosities and other structural defects of the coating. Finally, the impacts of laser energy input and laser distance on the characterization of the glazed layer are discussed.

In this paper, two coating techniques, the high velocity oxy-fuel (HVOF) and air plasma spray (APS) techniques, were used to deposit a bond coat of NiCoCrAlYTa on the Inconel 625 substrate, followed by applying a topcoat of yttria-stabilized zirconia (YSZ). The samples were preoxidized in an argon-controlled furnace at a temperature of 1000 °C for 12 and 24 h to characterize the microstructure of a thermally grown oxide (TGO) using the two coating techniques. The most suitable preoxidized samples were further tested for isothermal oxidation at 1000 °C for up to 120 h, and a hot corrosion test was performed at 1000 °C for up to 52 h or until spalling occurred. As-sprayed and oxidized samples prepared with different coating techniques were evaluated in terms of their microstructure using different characterization methods, such as field emission scanning electron microscopy (FESEM), variable pressure scanning electron microscopy (VPSEM), energy dispersive X-ray spectroscopy (EDS) equipped with energy dispersive X-ray and X-ray diffraction (XRD) analyses. In addition, the mechanical properties of these samples were evaluated using adhesion tests. The results show that the YSZ/NiCoCrAlYTa coating applied with the HVOF technique forms a more thin and continuous layer of TGO than that obtained when applying a YSZ/NiCoCrAlYTa coating using the APS technique, indicating that a severe brittle oxidation interface exists between the two layers. The results also indicate that the mechanical strength obtained from the adhesion test of the coated samples is observably affected by the oxidation behaviors obtained with the different deposition techniques chosen.

A protective novel (MgO) oxide layer (with 91.92% corrosion protection efficiency) was successfully applied on Mg–0.4%Ca alloy using protective oxidation at 390°C (without any pre-treatment). Oxide layer coated Mg alloy was then coated with pure epoxy coating (as top coat). This oxide inner barrier layer protected Mg substrate from 3.5wt % NaCl solution when it passes through from epoxy top layer. Lowest anodic current density and highest charge transfer resistance (1118.124 kΩ cm2) and impedance modulus (│Z│) at low frequency substantiated that the existence of thick epoxy top layer which is integrated (via physical anchoring) with the oxide inner barrier layer could considerably reduce the corrosion rate of magnesium substrate in the chloride containing solutions. Moreover, corrosion mechanism for coated Mg–0.4%Ca alloys was then suggested.

Single NbSi2 and duplex NbSi2/Nb5Si3 coatings were successfully applied on Nb substrates using halide activated pack cementation (HAPC) method at 1100 and 1300°C, respectively. Duplex NbSi2/Nb5Si3 coating with Nb5Si3 inner barrier layer, higher thickness, and lesser micro-cracks considerably decreased the infiltration of simulated body fluid (SBF) solution. This deduction was pertained to the high corrosion potential and lowest corrosion current density for the NbSi2/Nb5Si3 coated Nb alloy in corrosive solution. The Nb5Si3 inner barrier layer can protect the Nb substrate from corrosive solution when it passes through from NbSi2 top layer. Moreover, higher charge transfer resistance (Rct), impedance modulus at a low-frequency ( $$\left| Z \right|$$ ) and phase angle were also observed for the duplex NbSi2/Nb5Si3 coated Nb alloy. On the other hand, in vitro bioactivity test indicated higher capability of apatite formation on the silicide coatings compared to uncoated Nb substrate in SBF solution. In fact, modification of chemical composition and surface morphology of Nb substrate surface can provide suitable nucleation sites for apatite formation and growth in SBF solution.

Cobalt chromium alloys constitutes the base of one important group of biometallic with excellent mechanical properties. However, due to its non-bioactive and non-antimicrobial surface, cobalt chromium alloys are vulnerable to wear corrosive attack and bacterial infection. Hence, coating cobalt chromium alloys surface with superior biomaterials is the best proven techniques. In this work, nanostructure silver adopted titanium dioxide coating was deposited on cobalt chromium alloys using air plasma spray (APS) and high velocity oxy-fuel (HVOF) techniques. Nanostructure TiO2–Ag coating demonstrated superior hardness, wear resistance and lower coefficient of friction when compared to bare CoCr alloys. Reduced plastic deformation detected by microstructural analysis indicate that the interference of nano-structure coating in metallic matrix help lower the wear rate of the sample. Meanwhile, low porosity of the coating produced by HVOF technique shown a better wear resistance result than APS technique. Keywords: Cobalt–chromium alloy, Nanostructure TiO2–Ag coating, Thermal spray coating method, Surface properties, Wear performance

Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formation, which tends to endanger the efficiency of electronic circuits, and even worse, may cause short circuits to the electronic components. This research aims to investigate the effects of stress on tin whiskers’ formation and growth and the mitigation method for the immersion of the tin surface’s finish deposited on a copper substrate. The coated surface was subjected to external stress by micro-hardness indenters with a 2N load in order to simulate external stress applied to the coating layer, prior to storage in the humidity chamber with environmental conditions of 30 °C/60% RH up to 52 weeks. A nickel underlayer was deposited between the tin surface finish and copper substrate to mitigate the formation and growth of tin whiskers. FESEM was used to observe the whiskers and EDX was used for measuring the chemical composition of the surface finish, tin whiskers, and oxides formed after a certain period of storage. An image analyzer was used to measure the whiskers’ length using the JEDEC Standard (JESD22-A121A). The results showed that the tin whiskers increased directly proportional to the storage time, and they formed and grew longer on the thicker tin coating (2.3 μm) than the thin coating (1.5 μm). This is due to greater internal stress being generated by the thicker intermetallic compounds identified as the Cu5Sn6 phase, formed on a thicker tin coating. In addition, the formation and growth of CuO flowers on the 1.5 μm-thick tin coating suppressed the growth of tin whiskers. However, the addition of external stress by an indentation on the tin coating surface showed that the tin whiskers’ growth discontinued after week 4 in the indented area. Instead, the whiskers that formed were greater and longer at a distance farther from the indented area due to Sn atom migration from a high stress concentration to a lower stress concentration. Nonetheless, the length of the whisker for the indented surface was shorter than the non-indented surface because the whiskers’ growth was suppressed by the formation of CuO flowers. On the other hand, a nickel underlayer successfully mitigated the formation of tin whiskers upon the immersion of a tin surface finish.

An unsaturated polyester resin was modified with plain and core-shell SiO2 aerogels having mean particles diameter of 2.5±0.5 mm. The core-shell structured particle consists of nanoporous SiO2 aerogel core and polyvinyl alcohol shell fabricated using fluidized bed coating process. Two types of polymer composites were prepared at a 30% (by volume) of plain and core-shell aerogels and the thermal conductivities and viscoelastic behaviors of the composites were compared using hot-disk thermal analyzer and dynamic mechanical analysis. The results in this work reveal better thermal insulation and dynamic mechanical properties of the composite containing core-shell aerogels due to preserved aerogel pores and better filler-matrix interaction.

Plasma electrolytic oxidation (PEO) was developed as a bond coat for air plasma sprayed (APS) nanostructure ZrO2 as top coat to enhance the corrosion resistance and antibacterial activity of Mg alloy. Corrosion behavior and antibacterial activities of coated and uncoated samples were assessed by electrochemical tests and agar diffusion method toward Escherichia coli (E. coli) bacterial pathogens, respectively. The lowest corrosion current density and the highest charge transfer resistance, phase angle and impedance modulus were observed for PEO/nano-ZrO2 coated sample compared with those of PEO coated and bare Mg alloys. Nano-ZrO2 top coat which has completely sealed PEO bond coat is able to considerably delay aggressive ions transportation towards Mg alloy surface and significantly enhances corrosion resistance of Mg alloy in simulated body fluid (SBF) solution. Moreover, higher antibacterial activity was also observed in PEO/nano-ZrO2 coating against bacterial strains than that of the PEO coated and bare Mg alloys. This observation was attributed to the presence of ZrO2 nanoparticles which decelerate E. coli growth as a result of E. coli membranes.

This work proposes a process for the fabrication of a silica aerogel (SA)–polyvinyl alcohol (PVA) core–shell structure using the fluidized bed method. First, nearly spherical hydrophobic SA particles with a diameter between 0.5 mm and 3.0 mm were prepared from rice husk ash via a sodium silicate route and ambient-pressure drying. Subsequently, a specific batch size of the SA particles was suspended in a heated air stream and sprayed with aqueous PVA using a bottom nozzle via the fluidized bed process. Coating of an individual SA particle is possible for large particle sizes and hydrophobization of the SA surface prevents penetration of PVA into its pores. The core–shell structured material showed a combination of high thermal insulation and good mechanical stability, rendering it suitable for use as filler in polymer resin, paints, and coatings. The core–shell structured material had an average density of 0.09 g cm−3 with well-preserved SA pores. The average shell volume fraction was 2.5%; the shell thickness varied below 50 μm, and was mostly approximately 20 ± 5 μm. Thermal analysis using transient plane hot-disk method and thermogravimetric analysis showed that the SA–PVA/core–shell structure exhibited lower thermal conductivity (0.035 W/mK) and higher thermal stability than uncoated SA.

Plasma electrolytic oxidation (PEO) coatings in the aluminate-silicate-based mixture electrolyte solution with different duty cycles were successfully applied on Mg alloy. The corrosion behavior of the samples was evaluated by water contact angle test, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion tests. Hydrophobic PEO coating could be obtained by adjusting the duty cycle of the applied electric signal. This coating considerably diminished the Mg dissolution and could enhance the impedance values of Mg alloy in 3.5 wt % NaCl solution. However, the surface of other PEO coated samples showed more hydrophilic properties compared to that of the uncoated sample. Dense structure of the modified PEO multiphase (including Mg2SiO4, MgO and MgAl2O4 phases) coating and also its appropriate thickness provided an effective barrier to remarkably delay corrosive solution penetration into the PEO coating. This phenomenon led to major decrease in anodic current density of alloy in chloride solution.

Atmospheric plasma spraying was carried out to deposit a bilayered NiCrAlY/nTiO2-CNT composite coating. Initially, NiCrAlY, as an under-layer with a thickness of around 100 µm, was deposited. Afterwards, nanostructured TiO2 (nTiO2), as an over-layer with a thickness of 135 μm, was deposited with and without the incorporation of carbon nanotubes (CNTs) on the Mg alloy surface. In contrast to NiCrAlY and NiCrAlY/nTiO2, the NiCrAlY/nTiO2-CNT nanocomposite coating displayed a higher bonding strength. The wear behaviour of the coatings was examined by the pin-on-disc test and the results revealed that the incorporation of CNTs into the nTiO2 coating considerably enhanced the tribological behaviour of Mg alloy due to the CNT’s bridging mechanism.

Titania nanoparticles were utilized as suspension in alkaline aluminate electrolyte to form nanocomposite coatings on magnesium alloy containing 1 wt% calcium by plasma electrolytic oxidation process. Microhardness, wettability, potentiodynamic polarization, wettability, electrochemical impedance spectroscopy (EIS), and immersion tests were performed in 3.5% NaCl solution to study corrosion behavior of the coated samples in reference to the uncoated Mg alloy. The coating with 4 g/L concentration of nanoparticles showed the highest microhardness, lowest hydrophilic properties and highest corrosion resistance. This coating substantially diminishes the Mg dissolution in the in 3.5% NaCl solution and increases the charge transfer resistance of the Mg alloy. Although higher concentrations of nanoparticles enhanced the defect density in the coating, they resulted in lower corrosion resistance. © 2016 Elsevier B.V.

Thermally grown oxide (TGO) plays important roles in thermal barrier coating system (TBC) for high temperature application such as in aircraft gas turbine engine blades (GTE). The TGO formed between the bond coat and topcoat interface can increase oxidation resistance to creep of GTE blades by minimizing oxygen diffusion into the metal substrate. In this research a NiCoCrAlYTa metallic bond coat was deposited on Inconel 625 substrate using two methods of deposition namely; high velocity oxy-fuel (HVOF) and atmospheric plasma spray (APS). After coating process, both types of samples underwent pre-oxidation in argon furnace for 12-24 hours at 1000 °C. Results showed that the TGO formation for samples in which the bond coat deposited via HVOF method produced much thinner and continuous TGO formation compared to APS deposition. This TGO characteristic is very useful to lengthen the lifetime of the metals substrate.

Nanostructured composite ceramic coatings consisting of Al2O3–13%TiO2 and Al2O3–13%TiO2/TiO2 on NiCoCrAlYTa-coated Mg alloys were sprayed using the atmospheric plasma spraying method. The composition and microstructure of the coated samples were investigated by XRD and FESEM equipped with EDS. Corrosion and wear behaviours of the coated samples were also evaluated. The results showed that Al2O3–13%TiO2/TiO2 coating is able to reduce the anodic dissolution of the Mg alloy in chloride solutions compared to other samples. The surface of the Al2O3–13%TiO2/TiO2 coating with the lowest wear rate exhibited a typical mild wear mode with narrow wear tracks along with very few small transferred particles. This observation was mainly related to the dense structure of the TiO2 coating, which could reduce severe spalling within the splats during the wear test.

Micro arc oxidation (MAO) layer (as bond coat) was successfully deposited on Mg–1%Ca alloy in KF + NaAlO 2 electrolyte. In order to improve the corrosion resistance of the conventional MAO coated Mg–1%Ca alloy, air plasma sprayed (APS) nanostructure TiO 2 coating (as top coat with bimodal structure) was successfully applied on the aforementioned bond coat. The results indicated that the porous MAO layer was effectively sealed by the (APS) nanostructure TiO 2 top coat which showed compact and dense structure along with nano regions. In fact, MAO coating acted as interlayer to provide inert rough surface and necessary hardness for the Mg alloy to bond with air plasma sprayed TiO 2 top layer. The positive effect of the air plasma sprayed nanostructure TiO 2 coating was attributed to its mechanical isolation against aggressive medium to the MAO coating and Mg matrix. So, novel duplex ceramic composite coating (MAO/nanoAPSTiO 2 ) could significantly improve the corrosion resistance of the Mg–1%Ca alloy in the chloride solutions.

In this study, plasma sprayed multilayered coatings were successfully applied on the Mg alloys. On the other hand, corrosion behaviors of the coated magnesium alloy substrates with three different plasma sprayed coatings consisting of NiCrAlY, NiCrAlY/nano Al 2 O 3 ·13%TiO 2 and NiCrAlY/nano Al 2 O 3 ·13%TiO 2 /nano TiO 2 coatings were elaborated in 3.5 wt% NaCl solution. Electrochemical studies depicted that the novel coating (NiCrAlY/nano Al 2 O 3 ·13%TiO 2 /nano TiO 2 ) is able to reduce the corrosion rate of the Mg alloy and increase impedance values compared to the other samples. In fact, TiO 2 sealing layer could fill some micro-pores in the Al 2 O 3 –13 wt%TiO 2 coating and could prevent the concentration of the electrolyte in the Al 2 O 3 –13 wt%TiO 2 coating.

Al-AlCr was coated on Mg-Ca and Mg-Zn-Ce-La alloys using physical vapor deposition method. The surface morphology of the specimens was characterized by x-ray diffraction, scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy, and atomic force microscopy (AFM). The AFM results indicated that the average surface roughness of Al-AlCr coating on the Mg-Ca alloy is much lower than that of Al-AlCr coating on the Mg-Zn-Ce-La alloy. However, Al-AlCr coating on the Mg-Ca alloy presented a more compact structure with fewer pores, pinholes, and cracks than Al-AlCr coating on the Mg-Zn-Ce-La alloy. Electrochemical studies revealed that the novel coating (Al-AlCr) can remarkably reduce the corrosion rate of the Mg-Ca alloy in 3.5 wt.% NaCl solution. It was seen that the anodic current density of the Al-AlCr-coated Mg-Ca alloy was very small when compared to the Al-AlCr-coated Mg-Zn-Ce-La and uncoated alloys. Impedance modulus (Z) of the Al-AlCr-coated samples was higher than that of the bare Mg alloys. Z of Al-AlCr-coated Mg-Ca alloy was higher than that of the Al-AlCr-coated Mg-Zn-Ce-La alloy at low frequency.

Al and Al/AlCr were coated on Mg–Zn–Ce–La alloy by physical vapour deposition (PVD). Microstructural characterization depicted that the average surface roughness of the nano-Al/AlCr coating is higher than that of the mono-layered Al coating, which was mainly related to the surface morphology of the Mg–Zn–RE alloy. Nano Al coating (1 1 1) presented a more compact structure with fewer pinholes and cracks than the Al/AlCr coating (1 1 0). Electrochemical studies reveal that Al coated Mg alloy has better corrosion resistance than the other samples. The lowest anodic current density and the highest charge transfer resistance were observed in the Al coated Mg alloy.

In this study, nano-silicon (Si) thin films were deposited on biodegradable Mg–6Zn–0.8Mn–3Ca substrates by physical vapor deposition (PVD) method. Subsequently, nano-hydroxyapatite (HA) was coated as a second layer on the nano-Si film using electrochemical deposition (ED). The surface morphology and the corrosion behavior of the composite coatings were evaluated using scanning electron microscope, X-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, potentiodynamic polarization tests and immersion tests. The Si/HA nano-composite coating, with an average particle size of 72 nm, represented a uniform and dense film consisting of HA as the outer layer (8–10 μm) and Si as the inner layer (1.5–2 μm). However, some micropores and microflaws were observed in the Si thin film. The polarization test indicated that Si/HA coating could efficiently reduce the corrosion rate of Mg alloy in simulated body fluid from 2.57 to 0.12 mm/year. However, only moderate reduction in corrosion rate was observed in the case of single layer nano-Si coating. Hydrogen evolution studies showed greater reduction in degradation rate of Si/HA and Si coated samples, compared to uncoated alloy. Immersion test showed the formation of apatite layer on the surface of Si/HA film after immersion in SBF that resulted in noticeable improvement of bioactivity.

Phase transformation of tetragonal ZrO2 to monoclinic phase and also increment of bond coat oxidation kinetic (TGO thickening) can substantially restrict the life time of thermal barrier coating systems (TBCs). So, nanostructured and conventional Y2O3 stabilized ZrO2 coatings were evaluated in fused V2O5-Na2SO4 salts during thermal exposure in air. Microstructural characterization showed lower hot corrosion products (monoclinic zirconia, YVO4 crystals) formation and reduction of TGO thickness in thermal barrier coating system consisting of nanostructured Y2O3 stabilized ZrO2 (YSZ) top coat. It was found that inhomogeneities, pores and micro-cracks played a principal role in the molten salts infiltration into the YSZ coating during three steps of hot corrosion process. In the nanostructured YSZ coating with tri-model structure, nano zones which surrounded by fully molten parts could fill the aforementioned defects and could act as barrier for the oxygen and corrosive molten salts penetration into the TBC.

Si/TiO2 nano-composite and Si were coated on Mg–Ca alloy by physical vapour deposition (PVD). The surface morphology of specimens was characterised by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) and atomic-force microscopy (AFM). The AFM results indicated that the average surface roughness of the nano-Si/TiO2 coating is lower than that of the mono-layered Si coating. However, the nanocomposite coating presented a more compact structure with fewer pores, pinholes and cracks than the Si coating. Nano-Si/TiO2 composite coating consisted of TiO2 (110) as the outer layer and Si (111) as the inner layer, producing a greater thickness (1.765 μm) than the Si coating (1.139 μm). Electrochemical studies reveal that there is a less significant reduction in the corrosion rate for the nano-Si/TiO2 and Si coatings. However, the nano-Si/TiO2 coating considerably enhanced the corrosion resistance of bare Mg alloy in NaCl solution.

Fluorine-doped hydroxyapatite (FHA) and calcium deficient hydroxyapatite (CDHA) were coated on the surface of biodegradable magnesium alloy using electrochemical deposition (ED) technique. Coating characterization was investigated by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The result shows that nano-FHA coated sample presents nano needle-like structure, which is oriented perpendicular to the surface of the substrate with denser and more uniform layers compared to the nano-CDHA coated sample. The nano-FHA coating shows smaller crystallite size (65 nm) compared to the nano-CDHA coating (95 nm); however, CDHA presents thicker layer (19 μm in thickness) compared to the nano-FHA (15 μm in thickness). The corrosion behaviour determined by polarization, immersion and hydrogen evolution tests indicates that the nano-FHA and nano-CDHA coatings significantly decrease corrosion rate and induce passivation. The nano-FHA and nano-CDHA coatings can accelerate the formation of bone-like apatite layer and significantly decrease the dissolution rate as compared to the uncoated Mg alloy. The nano-FHA coating provides effective protection to Mg alloy and presents the highest corrosion resistance. Therefore, the nano-FHA coating on Mg alloy is suggested as a great candidate for orthopaedic applications.

The microstructure and bio-corrosion behavior of binary Mg-xZn (x = 1.25, 2.5, 4) and ternary Mg-Ca-xZn (x = 1.25, 2.5, 4) alloys have been studied using scanning electron microscopy (SEM), electrochemical, and immersion tests. Microstructure analysis indicated that the binary Mg-Zn alloys are composed of primary α-Mg matrix and Mg12Zn13 phases, while, ternary Mg-Ca-Zn alloys are composed of α-Mg, Mg2Ca, and IM1 (Ca3MgxZn15-x) (4.6 & le; x & le; 12) phases or α-Mg, IM1 and IM3 (Ca2Mg5Zn13) phases. Electrochemical results showed that Mg-4Zn alloy has lowest corrosion rate among binary alloys. At constant Ca content of 0.8 wt.%, the addition of Zn up to 1.25 wt.% decreased the corrosion rate, while further addition of Zn increased the corrosion rate of ternary alloys. Immersion tests results demonstrated that the formation of Zn oxide layer in binary Mg-Zn alloy and evolution of eutectic phase (α-Mg+IM1+Mg2Ca) significantly retard the bio-degradation rate of the ternary alloys.

Microstructure and corrosion behaviour in simulated body fluid of as-cast and heat treated Mg–xZn (x = 3 and 6) alloys for different heat treatment times were studied. The results revealed that as-cast Mg–3Zn alloys consist of Mg12Zn13 phase and α-Mg matrix, while Mg–6Zn is composed of Mg51Zn20, Mg12Zn13 compounds and α-Mg matrix. After heat treatment of Mg–6Zn alloy at 340 °C, the Mg51Zn20 phase decomposed to the matrix and Mg12Zn13 while, the microstructure of Mg–3Zn remained unchanged. The results also indicated that heat treatment at 340 °C has little influence on the corrosion behaviour of Mg–3Zn. In contrast, heat treatment improved the corrosion resistance of the Mg–6Zn alloy as the decomposition of the Mg51Zn20 phase decreased micro-galvanic corrosion. The corrosion resistance of both as-cast Mg–3Zn and Mg–6Zn alloys marginally improved with increasing heat treatment times.

Bi-layered thermally grown oxide (TGO) layer plays a major role in the spallation of Y2O3 stabilized ZrO2 (YSZ) layer form the bond coat in the thermal barrier coating (TBC) systems during oxidation. On the other hand, bi-layered TGO formation and growth in the TBC systems with nanostructured YSZ have not been deeply investigated during cyclic oxidation. Hence, Inconel 738/NiCrAlY/normal YSZ and Inconel 738/NiCrAlY/nano YSZ systems were pre-oxidized at 1000 °C and then subjected to cyclic oxidation at 1150 °C. According to microstructural observations, nanostructured YSZ layer over the bond coat should have less micro-cracks and pinholes, due to the compactness of the nanostructure and the presence of nano zones that resulted in lower O infiltration into the nanothermal barrier coating system, formation of thinner and nearly continuous mono-layered thermally grown oxide on the bond coat during pre-oxidation, lower spinels formation at the Al2O3/YSZ interface and finally, reduction of bi-layered thermally grown oxide thickness during cyclic oxidation. It was found that pre-heat treatment and particularly coating microstructure could influence microstructural evolution (bi-layered TGO thickness) and durability of thermal barrier coating systems during cyclic oxidation.

A continuous and thin Al 2 O 3 layer would act as an infiltration barrier to diminish the growth of spinels in thermal barrier coating systems. Therefore, isothermal oxidation of normal NiCrAlY/YSZ, nano NiCrAlY/YSZ and nano NiCrAlY/YSZ/nano Al 2 O 3 coatings was investigated at 1000 °C. These samples were then subjected to thermal cycles at 1150 °C. The microstructural characterisation showed that the spinel growth in the nano NiCrAlY/YSZ/nano Al 2 O 3 coating was much lower than the other coatings. This observation can be related to the formation of a fully continuous Al 2 O 3 layer on the nano NiCrAlY coating during pre-oxidation at 1000 °C and also to the presence of a nano Al 2 O 3 layer over the YSZ coating.

Nanocrystalline diamonds (NCDs) were deposited on chemically prepared tungsten carbide substrates via hot filament chemical vapor deposition. The surface morphology of the NCDs was examined using field emission scanning electron microscopy. The NCDs formed a ballas morphology evenly across the tungsten carbide surface. Overetching affected the diamond deposition by causing the ballas to form aggregations. Cross-sectional fragmentation using a diamond wafering blade caused the nanocrystalline diamond to fragment at overetched boundaries, and delamination only occurred 30–50 µm off the edge and revealed that the thickness of the diamond film was 6 µm. Grazing XRD is an effective method to identify diamonds even at the nanoscale. The crystallite size was calculated to be 18.4 nm by modeling. Cross-sectional TEM analysis indicated that the diamond grain size was approximately 10–30 nm near the interface. Amorphous carbon, an embedded diamond and voids were also observed. TEM also revealed that the tungsten carbide surface undulates. The nanocrystalline diamonds nucleated and grew on the tungsten carbide (100) planes in the 〈111〉 direction, forming (111) planes, as observed from HRTEM, d-spacing measurements, SAD and FFT analyses for a FIB-prepared sample.

A thermally grown oxide (TGO) layer is formed at the interface of bond coat/top coat. The TGO growth during thermal exposure in air plays an important role in the spallation of the ceramic layer from the bond coat. High temperature oxidation resistance of four types of atmospheric plasma sprayed TBCs was investigated. These coatings were oxidized at 1000 °C for 24, 48 and 120 h in a normal electric furnace under air atmosphere. Microstructural characterization showed that the growth of the TGO layer in nano NiCrAlY/YSZ/nano Al2O3 coating is much lower than in other coatings. Moreover, EDS and XRD analyses revealed the formation of Ni(Cr,Al)2O4 mixed oxides (as spinel) and NiO onto the Al2O3 (TGO) layer. The formation of detrimental mixed oxides (spinels) on the Al2O3(TGO) layer of nano NiCrAlY/YSZ/nano Al2O3 coating is much lower compared to that of other coatings after 120 h of high temperature oxidation at 1000 °C.

The use of fracture mechanics outside the area of mechanics, including materials science, is evidence that the concept is capable of handling failures involving almost any types of crack propagations. This paper outlines the simple method on how to use fracture mechanics concepts in coating study by using a concrete example that is easy to follow. The example presented here is the use of fracture mechanics to develop equation governing the blister propagation using the concept pioneered by Sih, the SED concept. Despite being simple, the method gives excellently good agreement with those available solutions derived by other methods.

Metallic multilayers of Cu/Al/Ti composition were studied by transmission electron microscopy (TEM) and plasmon energy-loss mapping as prototypes of nanoscale reactive multilayer systems with exothermic alloy formation in oxygen-free conditions. The selection and arrangement of alloy phases by the system during ex situ and in situ heating experiments were found to depend not only on temperature but strongly on the initial volume ratios of metals, and to a lesser degree on the dimensionality of the reactive sample. Here, a two-dimensional sample was represented by ex situ heating of the full multilayer structure, a one-dimensional sample refers to in situ heating of thin cross-sectional TEM specimens, while a zero-dimensional sample (or metallic dot-array) was obtained after cutting thin pillars using focused ion beams. Lamellar self-organized alternation between Heusler phase and Cu9Al4 was found.

A nanocrystalline diamond bilayer has been deposited via hot filament chemical vapour deposition method. The bilayer has been produced by two different deposition parameters. The first is by limiting microcrystalline diamond growth and the second layer by pulsing additional oxygen gas into the system. The two layers become indistinguishable after the deposition ends. The pretreatment of the substrate, tungsten carbide has been varied i.e. its various seeding sizes (

YVO4crystals and monoclinic ZrO2are known as hot corrosion products that can considerably reduce the lifetime of thermal barrier coatings during service. The hot corrosion resistance of two types of air plasma sprayed thermal barrier coating systems was investigated: an Inconel 738/NiCrAlY/YSZ (yttria-stabilized zirconia) and an Inconel 738/NiCrAlY/YSZ/nano-Al2O3as an outer layer. Hot corrosion test was accomplished on the outer surface of coatings in molten salts (45% Na2SO4+ 55% V2O5) at 1000°C for 52 hour. It was found that nanostructured alumina as outer layer of YSZ/nano-Al2O3coating had significantly reduced the infiltration of molten salts into the YSZ layer and resulted in lower reaction of fused corrosive salts with YSZ, as the hot corrosion products had been substantially decreased in YSZ/nano-Al2O3coating in comparison with normal YSZ coating after hot corrosion process.

Oxidation has been considered as one of the principal disruptive factors in thermal barrier coating systems during service. So, oxidation behavior of thermal barrier coating (TBC) systems with nanostructured and microstructured YSZ coatings was investigated at for 24 h, 48 h, and 120 h. Air plasma sprayed nano-YSZ coating exhibited a trimodal structure. Microstructural characterization also demonstrated an improved thermally grown oxide scale containing lower spinels in nano-TBC system after 120 h of oxidation. This phenomenon is mainly related to the unique structure of the nano-YSZ coating, which acted as a strong barrier for oxygen diffusion into the TBC system at elevated temperatures. Nearly continues but thinner Al 2O 3 layer formation at the NiCrAlY/nano-YSZ interface was seen, due to lower oxygen infiltration into the system. Under this condition, spinels formation and growth on the Al 2O 3 oxide scale were diminished in nano-TBC system compared to normal TBC system.

Metallic multilayers have been used in cross-sectional TEM specimen geometry to explore nanostructuring routes using ion and electron beams (top-down) as well as self-organised nanopatterning (bottom-up). Intermetallic alloy formation during heat treatment is studied for binary and ternary layer compositions. A choice of pillars (0D), 1D and 2D layer geometries are used to explore dimensionality effects.