Intermediate Coatings Research Articles

Corrosion Properties of Thermally Sprayed Bond Coatings Under Plasma-Sprayed Chromia Coating in Sulfuric Acid Solutions

Plasma-sprayed chromia coatings are known to have excellent corrosion and wear properties in highly acidic conditions at ambient and elevated temperatures, but are not watertight due to their intrinsic porosity. Therefore, in applications involving aggressive environments, the whole component is usually made of a corrosion-resistant alloy, to which the Cr2O3 coating imparts the necessary wear resistance. However, in such aggressive environments, the survival of thermal spray metallic bond layers becomes an issue. The present study deals with the performance in sulfuric acid solutions of coated systems consisting of a Hastelloy C-276 substrate and a plasma-sprayed Cr2O3 top coating with four different intermediate bond coatings. The bond coatings were HVOF-sprayed Ni-20Cr, Hastelloy C-276 and Ultimet alloys and plasma-sprayed tantalum. Open-circuit measurement, electrochemical polarization and electrochemical impedance spectroscopy tests were carried out at room temperature (RT) in solutions with various concentrations. Also, static immersion tests were performed at RT and 60 °C. The results revealed that the HVOF-sprayed Ni-20Cr and Ultimet alloy coatings were significantly attacked by the sulfuric acid electrolyte, especially at 60 °C, whereas the HVOF-sprayed Hastelloy C-276 and plasma-sprayed Ta coatings performed significantly better.

Anticorrosive effectiveness of coatings with reduced content of Zn pigments in comparison with zinc-rich primers

ABSTRACTTypically, an anticorrosive coating system for long-term protection consists of a primer, one or several intermediate coats, and a topcoat. In such systems, zinc-rich primers are often used as they ensure good adhesion to the substrate and protect it from corrosion. Such coatings are very highly pigmented, which sometimes leads to losses in cohesive strength and deterioration of mechanical properties. Furthermore, Zn is known to be harmful to the environment. In this work we present Zn primers with reduced Zn content and better protective properties than traditional zinc-rich primers. The formulations of different Zn pigments in the epoxy matrix were developed with the concentration of zinc particles reduced to about 50% in the dry coating. To evaluate the distribution of pigments scanning electron microscopy has been employed. The anticorrosive properties were tested using the salt spray test and electrochemical impedance spectroscopy. The mechanical properties of the coatings were also tested.

Micro-structural study and wear resistance of thermal barrier coating reinforced by alumina whisker

The present study describes the experimental results regarding the effect of the addition of ceramic whisker, on the microstructural and friction property of plasma sprayed yttria-stabilized zirconia coating sprayed on an Inconel substrate with optimized process parameters. To deposit a bond layer between the ceramic top coat and substrate surface, all samples have coated with the metallic intermediate NiCrAlY bond coat. For the microstructural study, the powders/coatings morphology and wear marks on YSZ coated were investigated by a Field Emission Scanning Electron Microscopy and Energy Dispersive X-ray analysis (FE-SEM/EDS). The mass loss, wear resistance and coefficient of friction of the YSZ top coat against Alumina Ball were tested with a ball-on-disc wear testing at loads of 7,10 and 13 N. The results showed that reinforced coating gives a higher wear resistance compared to the conventional coating without changing the friction coefficient. The improvement in wear resistance of the ceramic whisker reinforced coatings could be mainly due to the interlocking interface between splats and decrease of intralamellar cracks in the top coat. The wear mechanisms of reinforced and unreinforced TBC were discussed in terms of exfoliation and degradation wear mechanisms.

Preparation and Properties of an Anti-Friction and Anti-Corrosive Radar Absorbing Material with Periodic Intermediate Coating

In this paper, an anti-friction and anti-corrosive radar absorbing material with periodic structure intermediate coating is studied. The preparation process is introduced and its electrical and mechanical properties are studied. The radar reflection loss of the material is less than -10 dB in the X-band and a tensile strength of 16 MPa, and the material has the characteristics of abrasion resistance and anticorrosion. The radar absorbing materials solve the problem of the existence of extended damage in the middle layer due to the continuity of the fiber cloth in the existing coating technology.

Applications of polydopamine modifications in capillary electrophoretic analysis.

Mussel-inspired polydopamine has been widely used in capillary electrophoresis as a facile and universal tool for the surface modification of capillary, mainly due to its versatility, stability, strong adhesiveness, and biocompatibility properties. In this review, the recent development of mussel-inspired surface chemistry with rapid deposition of polydopamine was introduced, and the recent applications of polydopamine in capillary electrophoresis (2011-July 2018) were summarized into four main aspects, namely, sample pretreatments, functional coatings, codeposition coatings, and intermediate coatings. Further study may be focused on clarifying the mechanisms of polydopamine formation and polydopamine-assisted codeposition, and expanding coatings methods to plant polyphenols.

Control of cytokine-driven eosinophil migratory behavior by TGF-beta-induced protein (TGFBI) and periostin.

Periostin, which is induced by interleukin (IL)-13, is an extracellular matrix (ECM) protein that supports αMβ2 integrin-mediated adhesion and migration of IL-5-stimulated eosinophils. Transforming growth factor (TGF)-β-induced protein (TGFBI) is a widely expressed periostin paralog known to support monocyte adhesion. Our objective was to compare eosinophil adhesion and migration on TGFBI and periostin in the presence of IL-5-family cytokines. Eosinophil adhesion after 1 h and random motility over 20 h in the presence of various concentrations of IL-5, IL-3, or granulocyte macrophage-colony stimulating factor (GM-CSF) were quantified in wells coated with various concentrations of TGFBI or periostin. Results were compared to video microscopy of eosinophils. Cytokine-stimulated eosinophils adhered equivalently well to TGFBI or periostin in a coating concentration-dependent manner. Adhesion was blocked by anti-αMβ2 and stimulated at the lowest concentration by GM-CSF. In the motility assay, periostin was more potent than TGFBI, the coating-concentration effect was bimodal, and IL-3 was the most potent cytokine. Video microscopy revealed that under the optimal coating condition of 5 μg/ml periostin, most eosinophils migrated persistently and were polarized and acorn-shaped with a ruffling forward edge and granules gathered together, in front of the nucleus. On 10 μg/ml periostin or TGFBI, more eosinophils adopted a flattened pancake morphology with dispersed granules and nuclear lobes, and slower migration. Conversion between acorn and pancake morphologies were observed. We conclude that TGFBI or periostin supports two modes of migration by IL-5 family cytokine-activated eosinophils. The rapid mode is favored by intermediate protein coatings and the slower by higher coating concentrations. We speculate that eosinophils move by haptotaxis up a gradient of adhesive ECM protein and then slow down to surveil the tissue.

Influence of Ageing with UV Radiation on Physicochemical Properties of Acrylic-Polyurethane Coatings

Investigated systems of acrylic-polyurethane coatings consisted of three kinds of coatings: base coat (acrylic), intermediate (polyurethane) and top coat (acrylic); each made up of two layers. Mean thickness of the coating system was equal (145 ± 1) μm. In time of accelerated UV ageing, electromagnetic radiation was emitted of wave length in the range (300 - 400) nm which was progressively inducing a destruction of coatings chemical structure, especially photooxidation and photolysis of coating material. Carried out X-ray investigations revealed increased contents of oxygen in aged coatings due to their photooxidation which resulted in increased tendency of coating microfragments to chip off from surface layer with the ageing time flow. The hardness increase of UV aged coatings was also observed which intensified their surface layer brittleness. This contributed to their thickness decrease by more than 10% after 2016 h of ageing. Photodestruction of UV aged coatings was documented as well by characteristics obtained during investigations carried out with DMA method use. A noticeable physical destruction of the coatings was observed in the form of silver cracks, etchings and grooves in surface layer as well as craters extending also into interlayer. Processes of physical and chemical destruction undergoing in aged coatings influenced roughness profile change and coatings surface topography shaping. After 2016 h of UV ageing, the roughness parameters (Ra, Rz, Rt) increased several times. Long-lasting UV radiation influence on the surface of investigated acrylic-polyurethane coating systems contributed to their decorativeness loss. Microscopic examinations revealed colour change (yellowing) of blue pigment contained in polyurethane interlayer. Decline in coating gloss was also observed as the result of surface roughness increase.

Characterisation of Ceramic-Coated 316LN Stainless Steel Exposed to High-Temperature Thermite Melt and Molten Sodium

Currently, stainless steel grade 316LN is the material of construction widely used for core catcher of sodium-cooled fast reactors. Design philosophy for core catcher demands its capability to withstand corium loading from whole core melt accidents. Towards this, two ceramic coatings were investigated for its application as a layer of sacrificial material on the top of core catcher to enhance its capability. Plasma-sprayed thermal barrier layer of alumina and partially stabilised zirconia (PSZ) with an intermediate bond coat of NiCrAlY are selected as candidate material and deposited over 316LN SS substrates and were tested for their suitability as thermal barrier layer for core catcher. Coated specimens were exposed to high-temperature thermite melt to simulate impingement of molten corium. Sodium compatibility of alumina and PSZ coatings were also investigated by exposing samples to molten sodium at 400 °C for 500 h. The surface morphology of high-temperature thermite melt-exposed samples and sodium-exposed samples was examined using scanning electron microscope. Phase identification of the exposed samples was carried out by x-ray diffraction technique. Observation from sodium exposure tests indicated that alumina coating offers better protection compared to PSZ coating. However, PSZ coating provided better protection against high-temperature melt exposure, as confirmed during thermite melt exposure test.

Effect of coating thickness on the stress profile at the epoxy/silicone interface subjected to pull-off loading: A finite element analysis

Previous experimental studies of silicone coatings have shown three distinct types of release behavior in the tensile flat punch test, depending on coating thickness. The mechanical response in the punch test is highly dependent upon the Poisson's ratio of the coating and its confinement ratio (punch radius divided by coating thickness). This study developed a high accuracy finite-element model of the punch test using the adaptive p-method with extensive mesh refinement to produce smooth stress profiles up to the punch edge. Stress distributions were found for a wide range of confinement parameters and Poisson's ratios. At a typical Poisson's ratio of 0.49, the highest center stress occurred for the intermediate thickness coatings—not thin or thick. Also, the thickest coatings demonstrated steadily increasing high stress towards the edge, while other thicknesses showed the steep singularity at the edge with a protective stress depression bordering inside it. The results further help explain why the critical pull-off force continues to increase as the thickness decreases, even with different release mechanisms. The stress profiles for thick coatings have almost no sensitivity to Poisson's ratio, unlike other thicknesses which show high sensitivity. Edge peeling is most likely to occur for all thick coatings, while other debonding modes are most likely for thin and intermediate thickness coatings. Together, results show the stress mechanics of the flat punch test follow three distinct types of confinement.

Preparation and Characterization of a Novel Hydrogel-Based Fouling Release Coating

With the rapid development of marine transportation industry, biological fouling not only affects the speed of navigation but also highly increases fuel consumption. In the paper, a novel hydrogel-based fouling release coating is developed to address the issue by a combination of non-stick property with a low surface tension of the coating. A hydrogel-based silicone fouling release coating was synthesized and two kinds of different intermediate coatings were studied to give a proper match as the tie layer between the substrate coated with primer and the hydrogel silicone on the surface. The adhesion strength, surface tension as well as surface topography of the fouling release coating were studied. The corrosion resistance and anti-fouling performance of the substrates sprayed with the coating were characterized by salt spray test and immersion test in a simulated marine system. The results show that the adhesion between the substrate and the fouling release coating is grade two measured by grid test. The water contact angle of the coating is 104.8o and Rz of the coating is 10.71μm. The specimen is intact after 1000 hours under salt spray test. No diatom was found settled on the specimens in a simulated static marine system while a little diatom was observed on the specimens in a simulated dynamic marine system. It has been found that the intermediate coating comprising of epoxy resin gives proper match between the primer and the fouling release coating consisting of PDMS resin. The coating exhibits superior anti-fouling performance under stationary state.

Microstructure Effect of Intermediate Coat Layer on Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings

The inherent pores and carbides of Cr3C2-NiCr coatings significantly reduce the corrosion resistance, the former by providing preferential paths for ion diffusion and the latter by forming cathodic sites in galvanic couples (between NiCr and Cr3C2). Adding a dense intermediate layer (intermediate coat layer) between the Cr3C2-NiCr coating (top coat) and substrate increases the corrosion protection of the coating if the layer acts as cathode in connection to the top coat. In the present work, NiCr, NiAl, and NiCoCrAlY layers were deposited by high-velocity air-fuel process as intermediate coat layers for the Cr3C2-NiCr top coat. Effects of coating microstructure on corrosion behavior of single- and bi-layer coatings were studied by open-circuit potential and polarization tests in 3.5 wt.% NaCl at room temperature. A zero resistance ammeter technique was used to study the galvanic corrosion of the coupled top and intermediate coat layers. Methods such as SEM and XRD were employed to characterize the as-sprayed and corroded coatings and to investigate the corrosion mechanisms. The results showed that the NiCoCrAlY coating not only presented a more positive corrosion potential (Ecorr) than the Cr3C2-NiCr coating, but also provided a better passive layer than the single-phase NiCr and NiAl coatings.

In vitro and in vivo evaluation of an oral multiple-unit formulation for colonic delivery of insulin

A multiple-unit formulation for time-dependent colonic release of insulin was obtained by coating insulin and sodium glycocholate immediate-release minitablets with: (i) Methocel® E50, a low-viscosity hydroxypropyl methylcellulose (inner coating), (ii) 5:1 w/w Eudragit® NE/Explotab® V17, a mixture of a neutral polymethacrylate with a pore-forming superdisintegrant (intermediate coating), and (iii) Aqoat® AS, enteric-soluble hydroxypropyl methylcellulose acetate succinate (outer coating). Sodium glycocholate was added as a permeation enhancer while the inner, intermediate and outer coatings were aimed, respectively, at delaying the onset of release through swelling/erosion processes, extending the duration of the lag phase by slowing down water penetration into the underlying functional layer, and overcoming variable gastric residence time. In vitro studies showed that neither insulin nor sodium glycocholate were released from the three-layer system during 2h of testing in 0.1N HCl, while complete release of the protein and of the enhancer occurred in phosphate buffer, pH 6.8, after consistent lag phases. No significant changes were noticed in the release profiles following twelve-month storage at 4°C. Oral administration of the novel formulation to diabetic rats elicited a peak in the plasma insulin concentration after 6h, which was associated with a sharp decrease in the glycemic levels. The relative bioavailability and pharmacological availability of such a formulation, as determined vs. the uncoated tablets, were 2.2 and 10.3, respectively. Based on these results, the three-layer system presented was considered a potentially interesting tool for oral colonic delivery of insulin and adjuvant compounds.

Metal Oxide Assisted Preparation of Core-Shell Beads with Dense Metal-Organic Framework Coatings for the Enhanced Extraction of Organic Pollutants.

Dense and homogeneous metal-organic framework (MOF) coatings on functional bead surfaces are easily prepared by using intermediate sacrificial metal oxide coatings containing the metal precursor of the MOF. Polystyrene (PS) beads are coated with a ZnO layer to give ZnO@PS core-shell beads. The ZnO@PS beads are reactive in the presence of 2-methylimidazole to transform part of the ZnO coating into a porous zeolitic imidazolate framework-8 (ZIF-8) external shell positioned above the internal ZnO precursor shell. The obtained ZIF-8@ZnO@PS beads can be easily packed in column format for flow-through applications, such as the solid-phase extraction of trace priority-listed environmental pollutants. The prepared material shows an excellent permeance to flow when packed as a column to give high enrichment factors, facile regeneration, and excellent reusability for the extraction of the pollutant bisphenol A. It also shows an outstanding performance for the simultaneous enrichment of mixtures of endocrine disrupting chemicals (bisphenol A, 4-tert-octylphenol and 4-n-nonylphenol), facilitating their analysis when present at very low levels (<1 μg L(-1) ) in drinking waters. For the extraction of the pollutant bisphenol A, the prepared ZIF-8@ZnO@PS beads also show a superior extraction and preconcentration capacity to that of the PS beads used as precursors and the composite materials obtained by the direct growth of ZIF-8 on the surface of the PS beads in the absence of metal oxide intermediate coatings.

High-temperature stability of yttria-stabilized zirconia thermal barrier coating on niobium alloy—C-103

Thermal barrier coatings (TBCs) of yttria-stabilized zirconia (YSZ) of different thicknesses with an intermediate bond coat were deposited on C-103 Nb alloy using the air plasma spraying technique. The coatings were subjected to rapid infra-red (IR) heating (∼25°C s−1) up to ∼1250°C and exposed up to 100 s at this temperature with heat flux varying from 55 to 61 W cm−2. The TBCs were found to be stable and intact after the heat treatment. In contrast, at the same conditions, the uncoated C-103 alloy specimen showed extensive oxidation followed by weight loss due to spallation. A maximum temperature drop of ∼200°C was observed on the opposite side of the coated alloy with 600 μm YSZ coat; as against negligible temperature drop in case of bare alloy specimen. The temperature drop was found to increase with the coating thickness of YSZ. The coatings before and after IR heating were investigated by scanning electron microscopy, X-ray diffraction, electron probe microanalysis, microhardness and residual stress measurements in order to understand the effect of thermal shock on the properties of the TBC. On account of these high-temperature properties, YSZ coating along with the bond coat is expected to find potential thermal barrier coating system on niobium alloys for supersonic vehicles.

Enhancement of Wear Resistance of AISI 1040 Forged Steel Roller Shaft by different Ceramic Oxide Coatings using Plasma Spray Process for Sugarcane Industries

In this investigation, ceramic oxide powders alumina, titania, chromia, alumina-titania, alumina-chromia and titania-chromia are coated on AISI 1040 forged steel substrate with a coating thickness of 200 μm by using the plasma spraying technique. Ni-Cr is used as an intermediate bond coat material to improve the coating adhesion for a thickness of 20 μm over the substrate. By using a pin-on-disc machine, dry wear test was carried out as per ASTM-G99 standards for a constant load of 10N, at different sliding distances of 1000m, 2000m, 3000m respectively. The result showed that the wear rate depends on various attributes such as microstructure, thickness of coating, porosity, surface roughness and hardness. Surface roughness measurements were performed on the specimens before and after wear tests by using talysurf instrument and the results showed that the highest value (20.42 μm) was obtained from the coating of alumina-titania. From the above investigation, the results obtained showed that a pure chromia coated specimen is having very good wear resistance property among the tested specimens. Hence it is suggested that pure chromia can be used for surface coating on top mill roll shaft used in sugar industries to enhance wear resistance.

Solar photovoltaic technology on rough low carbon steel substrates for building integrated photovoltaics: A complete fabrication sequence

The purpose of this paper is to show an innovative and complete fabrication sequence of thin film photovoltaic modules based on hydrogenated amorphous silicon on non transparent substrates (high roughness low carbon steel). This fabrication sequence is oriented to monolithically interconnected modules with two main challenges (i) the development of surface treatment technology (low cost intermediate inorganic coatings based on sol–gel technology) for the deposition of thin film solar cells on non transparent substrates and (ii) the use of novel laser scribing methods in substrate configuration. After the research carried out in this work, we demonstrate that (i) surface treatment technology has been successfully developed proving its good behavior in 1cm2 steel solar cells achieving efficiencies close to 7%, and (ii) laser scribing method has also been succeeded achieving efficiencies higher than 3% in 64cm2 modules. Electrical losses due to these processes have been evaluated. It is important to point out that, although silicon based technology has been used, these advances are not directly related to any specific thin film solar technology, being suitable for CIGS and CdTe solar cells.

Effect of intermediate ZrO2-CaO coatings deposited by cold thermal spraying on the titanium-porcelain bond in dental restorations

Metal ceramic systems are used for the majority of dental crowns and fixed dental prostheses. However, problems with porcelain bonding are encountered when titanium is used as the substrate. The purpose of this study was to evaluate the effect of intermediate calcium oxide-stabilized zirconia (ZrO2-CaO) coatings deposited by cold thermal spraying on the titanium-porcelain bonding in dental restorations. Two different types of ZrO2-CaO coatings obtained by oxyacetylene cold thermal spraying deposition were applied on commercially pure titanium bars before adding the porcelain layer. Type 1 was obtained by directly spraying the ZrO2-CaO powder on the titanium substrate. Type 2 was obtained by spraying a bond coat of nickel-aluminum-molybdenum alloy before spraying the ZrO2-CaO powder. Three-point bend tests according to International Organization of Standardization 9693-1:2012 were carried out to evaluate the debonding strength for the ZrO2-CaO-coated specimens (types 1 and 2) in comparison with a noncoated group (control), which received a traditional bonder-based adhesive technique. The results were compared with ANOVA, followed by the Student-Newman-Keuls test for pairwise comparisons. Scanning electron microscopy and energy dispersion spectroscopy were used to examine the interfacial properties and the failure mode of eachgroup. Mean (±standard deviation) debonding strength values for type 1 coating (25.97 ±2.53 MPa) and control (23.51±2.94 MPa) were near the acceptable lower limit of 25 MPa indicated by the International Organization of Standardization 9693-1:2012 and were not significantly different (Student-Newman-Keuls test, P>.05). Type 2 coating produced an improved titanium-porcelain bonding (debonding strength=39.47 ±4.12 MPa), significantly higher than both type 1 (Student-Newman-Keuls test, P<.05) and control (Student-Newman-Keuls test, P<.05). Scanning electron microscopy-energy dispersion spectroscopy analysis confirmed these findings, which revealed a predominant cohesive failure mode for type2. An intermediate coating layer of ZrO2-CaO plus a substrate of bonding nickel-aluminum-molybdenum alloyapplied by oxyacetylene cold thermal spraying deposition provided an improved titanium-porcelain bond.

Corrosion behavior of duplex coatings

The titanium alloys are used in defense, aerospace, automobile, chemical plants and biomedical applications due to their very high strength and lightweight properties. However, corrosion is a life-limiting factor when Ti alloys are exposed to different chemical environments at high temperatures. In the present paper, duplex NiCrAlY/WC–Co coating is coated onto Ti6Al4V substrate to investigate the corrosion behavior of both coated samples and the substrate. The duplex coating was performed with NiCrAlY as the intermediate coat of 200μm thickness deposited by HVOF process and WC–Co ceramic top coat with varying thicknesses of 250μm, 350μm and 450μm deposited by DS process. Potentiodynamic polarization tests were employed to investigate the corrosion performance of duplex coated samples and substrate in Ringer’s solution at 37°C and pH value was set to 5.7. Finally the results reveal that 350μm thick coated samples showed highest corrosion resistance compared to 250μm thick samples as well as bare substrate. However, the 450μm thick coated sample showed poor corrosion resistance compared to the substrate. The scale formed on the samples upon corrosion was characterized by using SEM analysis to understand the degree of corrosion behavior.

Targeted uptake of folic acid-functionalized iron oxide nanoparticles by ovarian cancer cells in the presence but not in the absence of serum

Targeted delivery of nanoparticles to cells or tissues of interest is arguably the “holy grail” of nanomedicine. Using primary human macrophages and ovarian cancer cells, we evaluated the biocompatibility and specific targeting of folic acid (FA)-conjugated iron oxide nanoparticles with organic [poly(ethylene glycol), PEG] or inorganic (SiO2) intermediate surface coatings. Reduction of folate receptor-α expression using specific siRNA resulted in a significant decrease in cellular uptake of the SiO2-coated nanoparticles, but did not affect uptake of PEG-coated nanoparticles. Notably, specific (i.e. FA-dependent) uptake was observed only in the presence of serum proteins. The strategy presented here for receptor-mediated uptake of nanoparticles with pre-defined surface chemistry may enable targeting of nanoparticles for therapeutic and imaging applications. From the Clinical EditorIn this study the receptor specific uptake of folic acid-functionalized iron oxide nanoparticles was determined in ovarian cancer cells. It was found that the presence of serum proteins is an absolute requirement for the uptake of these nanoparticles. The described strategy for receptor-mediated uptake of nanoparticles with pre-defined surface chemistry may enable a better targeting of nanoparticles for additional therapeutic and imaging applications.

Microstructural Evolution of the WC-Co/NiCrAlY Duplex Coating System on Ti6Al4 V and its Influence on Mechanical Properties

Titanium and its alloys are extensively used in aerospace and mechanical application because of their high specific strength and high fracture toughness. On the other hand, titanium alloys often show poor resistance to sliding wear, so that surface property improvement is in many cases recommended, often by thermal spray coating processes. In this investigation, NiCrAlY as the intermediate coat and WC-Co as the top coat, deposited onto Ti6Al4V substrate with duplex thermal barrier coatings, consisting of a 200μm thick NiCrAlY inter-layer deposited by High Velocity Oxygen Fuel (HVOF), followed by a 250μm, 350μm and 450μm WC-Co top coat deposited by detonation spray (DS). However, heat treatment is employed to obtain further improvement in microstructural development and mechanical properties. Coatings have been heat-treated at a range of temperatures between 600-1150oC. Inspections by SEM and phase analysis by XRD indicated that some brittle eta (η) phases (Co3W3C and Co2W4C) and unbrittle Co6W6C phases were produced at high temperature heat treatments corresponding to the top coat. Strong Cr23C6 phase and aluminium carbides were generated near topcoat/bond coat interface. Also the phase composition near NiCrAlY/substrate produced γ-Ni, β-NiAl and α-Cr phases and after 800oC heat treatment temperatures β-NiAl, γ’-Ni3Al Ti3Al, Ti2Ni and TiNi were produced. The generation of these phases improves the coating's mechanical properties (hardness, residual stresses and bond strength).