Development,characterization and erosion wear response of plasma sprayed fly ash–aluminum coatings

This paper describes the processing, characterization and the erosion wear response of a new class of metal–ceramic composite coatings deposited on metal substrates by plasma spraying. Coatings are developed on aluminum substrates using fly ash pre-mixed with aluminum powder in different weight proportions at various plasma torch power levels ranging from 9 to 18 kW DC. The coatings are characterized in terms of thickness, interface adhesion strength and deposition efficiency. Maximum adhesion strength of about 35 MPa is recorded with coatings deposited at 12 kW power level. It is noticed that the adhesion strength of fly ash coating is improved with pre-mixing of aluminum up to 15 wt.% in the feed material. To study the erosion wear behavior of the coatings, a plan of experiments based on the Taguchi technique is used to acquire the erosion test data in a controlled way. An orthogonal array and signal-to-noise ratio are employed to investigate the influence of the impingement angle, impact velocity, erodent size, stand-off-distance and the aluminum content in the feed stock on the erosion rate. The study reveals that the impact velocity is the most significant factor influencing the erosion wear rate of these coatings.     

Microstructural evolution and tribological behavior of Mo–Cu–N coatings as a function of Cu content

Ternary Mo–Cu–N coatings with various Cu contents were deposited on Si wafers and AISI 304 substrates by magnetron co-sputtering from two elemental targets of Mo and Cu in Ar–N₂ gas mixtures. The influence of copper content was investigated with regard to the microstructure, morphology, and tribological properties of these coatings. The results indicated that the Mo–Cu–N coatings exhibited face-centered-cubic B1-MoN phase structure. No diffraction peaks of Cu phase appeared in the coatings with Cu content below 11 at.%. The copper segregated in the amorphous inter-granular phase in the coatings. Incorporation of Cu into the growing Mo–N coating led to grain refinement. The average friction coefficient of the Mo–Cu–N coatings decreased from 0.40 to 0.21 with increasing Cu content up to 11 at.% due to formation of lubricious oxides of CuMoO₄.     

Microstructural characterization and quantification of Zn–Al–Mg surface coatings

The microstructure of Zn–Al–Mg coatings on steel sheets is characterized with the energy dispersive X-ray technique. Optimum parameters on the scanning electron microscope with a field emission gun have been found in order to laterally resolve the fine structure of the individual phases. A quantification of the microstructure is done with a mean shift algorithm that is usually applied for image segmentation in pattern analysis. This nonparametric technique is here based on the chemical composition and the spatial domain. The measured area is partitioned by a quantitative feature space analysis into phases with similar chemistry. A backscattered electron image is compared with the results of the X-ray point map of the same area. As an application the influence of the chemical composition of the melt on the resulting microstructure is compared for two different alloys.     

Formation of composite Cu–graphite and Cu–PTFE coatings and their tribological characterization

The Dynamic Chemical Plating (DCP) technique allows production of 2-μm copper films containing particles of graphite or PTFE in 18 and 15 min, respectively, at ambient temperature. DCP yields composites with particle-incorporation fractions of 12% for graphite micro-particles and 22% for PTFE nano-particles. The composite films show excellent tribological properties, acting as self-lubricating coatings with friction coefficients as low as 0.18.     

Study of the microstructure of plasma sprayed coatings obtained from Al2O3–13TiO2 nanostructured and conventional powders

The microstructure of coatings obtained from nanostructured or conventional Al₂O₃–13TiO₂ powders and deposited by plasma spraying technique on low-carbon steel was examined by transmission electron microscopy techniques. The dominating phase in both coatings was γ-Al₂O₃ phase. It has been observed that the grains of γ-Al₂O₃ grew in various shapes and sizes, that are particularly visible in the case of coating sprayed from nanostructured powder. The coatings obtained from the fully melted conventional powders exhibited a typical lamellar microstructure, into which the strips of TiO₂ phase were extended. The microstructure of coatings produced from agglomerates of nanostructured particles also revealed the regions consisting of partially melted α-Al₂O₃ powders surrounded by the net-like structure formed from fully melted oxides that improved the coating properties. Along with the observed morphology diversity some changes in the chemical composition on the cross sections of obtained coatings have been also noticed.     

Structural and oxidation behavior of atmospheric heat treated plasma sprayed WC–Co coatings

In this study, structural and oxidation behavior of WC–Co coatings was analyzed during atmospheric heat treatment process between 150 °C and 1100 °C. Two types of WC–12%Co coatings with different particle size and morphology were deposited on steel substrates using Air Plasma Spraying. The coated samples were heat treated in atmosphere in different temperatures between 500 and 1100 °C. Microstructural evaluation, X-ray diffraction analysis and microhardness testing were performed before and after heat treatment. In this case, the results showed that, regarding increase hardness of coating samples based on increasing applied temperature, coatings kept their properties up to 500 °C. In addition, by increasing heat treatment temperature up to 1100 °C, oxidation process in coated layer accelerated and caused coating detachment from the coating-substrate interface.     

Comparison of the cohesive and delamination fatigue properties of atomic-layer-deposited alumina and titania ultrathin protective coatings deposited at 200 °C

The fatigue properties of ultrathin protective coatings on silicon thin films were investigated. The cohesive and delamination fatigue properties of 22 nm-thick atomic-layered-deposited (ALD) titania were characterized and compared to that of 25 nm-thick alumina. Both coatings were deposited at 200 °C. The fatigue rates are comparable at 30 °C, 50% relative humidity (RH) while they are one order of magnitude larger for alumina compared to titania at 80 °C, 90% RH. The improved fatigue performance is believed to be related to the improved stability of the ALD titania coating with water compared to ALD alumina, which may in part be related to the fact that ALD titania is crystalline, while ALD alumina is amorphous. Static fatigue crack nucleation and propagation was not observed. The underlying fatigue mechanism is different from previously documented mechanisms, such as stress corrosion cracking, and appears to result from the presence of compressive stresses and a rough coating–substrate interface.     

Mechanical and tribological properties of V–C–N coatings as a function of applied bias voltage

The aim of this work is to determine the mechanical and tribological behavior of V–C–N coatings deposited on industrial steel substrates (AISI 8620) by using carbon–nitride coatings as a protective materials. The coatings were deposited on silicon (100) and steel substrates via magnetron sputtering and by varying the applied bias voltage. The V–C–N coatings were characterized by X-ray diffraction (XRD), exhibiting the crystallography orientations (111) fcc for V–C–N conjugated by VC (111) and VN (111) phases and (200) fcc for VCN conjugated by VC (200) and VN (200) phases. X-ray photoelectron spectroscopy (XPS) was used to determine the chemical composition of metallic carbon–nitride materials. Atomic force microcopy (AFM) was used for determination of the change in grain size and roughness with deposition parameters. By using nanoindentation, pin-on-disk, and scratch test curves, it was possible to estimate the hardness, friction and critical load of V–C–N surface material. Scanning electron microscopy (SEM) was performed to analyze morphological surfaces changes. Mechanical and tribological behavior in VCN/steel_[8620] system, as a function of a bias voltage deposition, showed an increase of 58% in the hardness, and reduction of 39% in the friction coefficient, indicating thus that the V–C–N coatings may be a promising material for industrial applications.     

Preparation and characterization of biomimetically and electrochemically deposited hydroxyapatite coatings on micro-arc oxidized Ti–13Nb–13Zr

Surface properties and corrosion resistance analyses of Ti–13Nb–13Zr coated by an oxide film (obtained by micro-arc oxidation at 300 V) or an oxide/hydroxyapatite (HA) film are reported. HA films were biomimetically or electrochemically deposited on the alloy/oxide surface, and their properties compared. Both the biomimetic and the electrochemical method yielded rough and globular apatite surfaces (10–20 μm globules for the former and 1–2 μm for the latter). As inferred from XRD data, the electrochemical method yielded more biologic-like HA films, while the biomimetic method yielded films containing a mixture of calcium phosphate phases. Coated Ti–13Nb–13Zr samples were immersed in an aerated PBS solution and continuously analyzed during 49 days. Considering that, after immersion, the biomimetically deposited films presented smaller variations in thickness and morphology and higher electric resistance (determined by electrochemical impedance spectroscopy), they clearly provide significantly better protection to the Ti–13Nb–13Zr alloy when in PBS solution.     

Fabrication and characterization of microcapsules with polyamide–polyurea as hybrid shell

Well-defined microcapsules with polyamide–polyurea as a hybrid shell have been described for biomedical applications. Interfacial polymerization method with surfactant and cosurfactant was developed for the preparation of the hybrid microcapsules. After reaction, centrifugation, and freeze drying processes, the polyamide–polyurea hybrid microcapsules with porous membranes were successfully fabricated. Compared with previous researches of the single polyamide or polyurea microcapsules, experimental data showed that the hybrid microcapsules have a thicker shell and excellent mechanical property. Various diameters and morphologies for the hybrid microcapsules can be obtained by changing the stirring rate, drying method, and surfactant content.     

Microstructure and indentation mechanical properties of plasma sprayed nano-bimodal and conventional ZrO2–8wt%Y2O3 thermal barrier coatings

The nanostructured agglomerated feedstock used for plasma spraying was obtained by the nanoparticle reconstituting technique. Nanostructured and conventional ZrO₂–8wt%Y₂O₃ (8YSZ) thermal barrier coatings (TBCs) have been prepared by atmospheric plasma spraying (APS) on 45# steel substrates with the NiCrAlY as the bond-layer. The microstructure and phase composition of feedstocks and corresponding coatings were characterized. The top layer of nanostructured 8YSZ TBCs is denser and has fewer defects than that of conventional TBCs. The elastic modulus, micro-hardness and Vickers hardness of nanostructured 8YSZ TBCs exhibit bimodal distribution while the conventional 8YSZ exhibit mono-modal distribution. The elastic modulus and elastic recoverability were also obtained by the nanoindentation test. The results indicate that the elastic modulus of nanostructured 8YSZ coating is lower than that of conventional 8YSZ coating, but the nanostructured 8YSZ coating has higher elastic recoverability than that of the conventional 8YSZ coating. The prediction of the average elastic modulus was established by the mixture law and weibull distribution according to the fraction of phases with different molten characteristic.     

Microstructural characterization and dry sliding wear resistance of MoO2-strengthened γ/NiMo alloys with different primary phases

Two γ/NiMo alloys strengthened by a refractory metal oxide MoO₂ phase were fabricated by a laser melting deposition process. Microstructural transformation of the alloys with different primary phases was identified and the crystal structure of the primary phases was confirmed by both X-ray diffraction and transmission electron microscopy. Meanwhile, room-temperature dry sliding wear behavior and mechanism difference of the alloys were also investigated mainly by scanning electron microscopy. Microstructures of the alloys varied from hypoeutectic to hypereutectic, as the molybdenum content increases. The hypoeutectic alloy was solidified on the basis of a Ni-base solid solution γ primary phase, whereas the hypereutectic alloy was grown based on an intermetallic compound with NiMo primary phase. The γ, NiMo primary phases and MoO₂ strengthening phase were confirmed to have face-centered cubic, orthorhombic and monoclinic structures, respectively. Compared with the hypoeutectic alloy, the hypereutectic alloy exhibited higher wear resistance under the same condition. The predominant wear mechanism of the γ/NiMo alloys transformed from micro-cutting to microcracking.     

Creep of Nextel™720/alumina–mullite ceramic composite at 1200 °C in air,argon, and steam

The tensile creep behavior of an oxide–oxide continuous fiber ceramic composite was investigated at 1200 °C in laboratory air, in steam and in argon. The composite consists of a porous alumina–mullite matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. The tensile stress–strain behavior was investigated and the tensile properties measured at 1200 °C. The elastic modulus was 74.5 GPa and the ultimate tensile strength was 153 MPa. Tensile creep behavior was examined for creep stresses in the 70–140 MPa range. Primary and secondary creep regimes were observed in all tests. Creep run-out (set to 100 h) was achieved in laboratory air for creep stress levels ?91 MPa. The presence of either steam or argon accelerated creep rates and reduced creep lifetimes. Composite microstructure, as well as damage and failure mechanisms were investigated.     

Pretreatment of nonbiodegradable landfill leachate by air stripping coupled with agitation as ammonia stripping and coagulation–flocculation processes

A combination process has developed as a pretreatment of non biodegradable leachate. The processes consist of air stripping coupled with agitation as a modified of ammonia stripping followed by coagulation–flocculation processes. The main aims of these processes are reducing a concentration of NH₃-N and organic matter as well as enhancing the biodegradability of landfill leachate. Ammonia stripped by the airflow rate of 10 L min^?1 at pH 11 for 3 h, while the agitation process applied to air stripping effluent for 2 h at the pH of 11.5 in 150 s^?1 gradient velocity. NH₃-N was removed at 96 % as removal ratio by the modified ammonia stripping in 5 h stripping time. Ferric sulfate, poly ferric sulfate and aluminum poly chloride was tested as a coagulant material in the coagulation process. Chemical oxygen demand (COD), suspended solids (SS), turbidity as well as the sludge ratios were discovered for each material operated under optimum condition of pH and dosage. The overall removal of NH₃-N, COD, biochemical oxygen demand, total organic carbon, and SS obtained by these processes were 96.5, 71.5, 56.5, 48.5, and 96.5 %, respectively, at the corresponding biodegradable ratio was modified from 0.20 to 0.31.     

Tribological properties and high-speed drilling performance of Zr–C:H:Nx% coatings with different amounts of nitrogen addition

Zr–C:H:N _x% coatings with nitrogen additions ranging from 0 to 29 at.% are deposited on AISI M2 steel substrates and micro-drills using a closed field unbalanced magnetron (CFUBM) sputtering technique. The tribological properties of the coatings are tested against AISI 52100 steel balls under loads of 10 and 100 N, respectively, using an oscillating friction and wear tester. The drilling performance of the coated micro-drills is evaluated by performing high-speed through-hole drilling tests using printed circuit boards as a test material. The wear testing results reveal that the Zr–C:H:N_8% coating has excellent tribological properties, including a low wear depth, a low friction coefficient, and an extended lifetime. Meanwhile, the drilling tests reveal that the Zr–C:H:N_8% coating increases the tool life of the micro-drill by a factor of five compared to an uncoated micro-drill when used for the high-speed through-hole drilling of PCBs and yields a considerable improvement in the machining quality of the drilled hole.