Effects of Ni content on microstructure,mechanical properties and Inconel 718 cutting performance of AlTiN-Ni nanocomposite coatings

AlTiN-Ni coatings with various Ni contents (0–3?at%) were deposited using cathodic arc evaporation. X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, a nanohardness tester, scratch-adhesion tester, and cutting tester were used to examine the microstructure, mechanical properties, and cutting performance of the coatings. The AlTiN coatings exhibited a columnar structure, while the AlTiN-Ni coatings exhibited a nanocrystal structure due to the formation of nc-AlTiN/Ni nanocomposite coatings. The nanohardness of the AlTiN-Ni coatings decreased from 26.2?GPa to 20.9?GPa as the Ni content increased from 0 to 3?at%. At an Ni content of 1.5?at%, the coating possessed a high toughness and sufficient adhesion strength; however, these dropped drastically for the AlTiN-Ni coating with 3?at% Ni owing to the presence of amorphous Ni. The results for the Inconel 718 turning indicated that the wear mode is adhesion at the rake face, abrasion and adhesion (built-up edge) at the flank face, and chipping at the cutting edge. Compared to AlTiN-Ni₃ and AlTiN-coated tools, the lifetime of the AlTiN-Ni_1.5 coated tool increased to 160% at a cutting speed of 40?m/min. This was attributed to less adhesion at the rake face and chipping at the cutting edge, due to the nanocrystal structure and higher toughness of the AlTiN-Ni_1.5 coating.     

Evaluation of plasma sprayed alumina–40 wt% titania and partially stabilized zirconia coatings on high density graphite for uranium melting application

Ceramic coatings have been proposed on high density graphite crucibles for the application of uranium consolidation and distillation of molten salt in pyrochemical reprocessing of metallic fuels. Towards this, uranium melting experiments were carried out on plasma sprayed partially stabilized zirconia (PSZ) and Al₂O₃–40 wt% TiO₂ (A40T) coated high density graphite samples at 1350 °C using induction heating system for evaluating the compatibility of these coatings with molten uranium. The coated high density graphite samples were characterized before and after uranium melting test by scanning electron microscopy attached with energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy. Microstructural observations revealed that no significant reaction layer or product was formed between uranium and PSZ coating, while uranium significantly adhered to A40T coating. PSZ coating offers better stability and protection to high density graphite crucibles from the chemical attack by molten uranium.     

Syntheses of nano-multilayered TiN/TiSiN and CrN/CrSiN hard coatings

Nano-structured superhard coatings represent the state-of-the-art in the rapidly increasing worldwide market for protective coatings. In this study, the combination of nano-composite and nano-multilayered structures into the same coating was attempted. Nano-multilayered coatings of TiN/TiSiN and CrN/CrSiN were deposited on tool steel substrates by closed-magnetic-field unbalanced DC magnetron sputter ion plating. The coating structures were characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. Mechanical characterizations were performed including nano-hardness measurement, progressively-increasing-load scratch test, and wear test. TiN/TiSiN coatings have a nano-hardness of 40.2 GPa, whereas CrN/CrSiN coatings have a hardness of 30.9 GPa. TiN/TiSiN coatings also showed a higher critical failure force and scratch fracture toughness as well as better wear resistance and lower acoustic emission signal, indicating less total damage to the coatings.     

Characterisation of in-situ reactive plasma-sprayed nano-(Ti,V)N composite ceramic coatings with various V concentrations

The effect of V concentration on the microstructure and phase composition of nano-(Ti, V)N composite ceramic coatings prepared by in-situ reactive plasma spraying of mechanically mixed Ti–V powders were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray energy dispersive spectroscopy, and transmission electron microscopy. The microhardness, toughness, wear resistance, and strengthening mechanism of the prepared nano-(Ti, V)N coatings were measured and analysed. The results showed that the nano-(Ti, V)N coating comprised a large proportion of nano-(Ti, V)N grains, which was the solid solution of TiN and VN. All the V atoms completely entered the TiN lattice and the solubility limit of V in TiN is approximately 25 wt%. The grains of the (Ti, V)N (25 wt% V) coating had a face-centred cubic structure and a large quantity of twins; they were primarily equiaxed grains morphology with a few columnar grains. From comparing the experimental statistics, the (Ti, V)N (25 wt% V) coating displayed the highest microhardness (1952 ± 78.5 Hv) and the most even dispersion but a slightly lower toughness compared with the (Ti, V)N (35 wt% V) coating. The (Ti, V)N (25 wt% V) coating with a dense microstructure obtained a high microhardness due to dislocation strengthening, fine grain strengthening, and solid solution strengthening (from the solid solution of VN in TiN). Furthermore, a lower friction coefficient and wear volume loss indicated that the (Ti, V)N (25 wt% V) coating had superior tribological properties and great potential as a wear resistant coating.     

Thermal shock behavior of a 8YSZ/CoCrAlYTaSi thermal sprayed barrier coating on GH202 superalloy

The thermal shock behavior of a thermal barrier coating (TBC) prepared by plasma spraying at 1100 °C was investigated. The TBC consisted of a double layer structure of 8YSZ/CoCrAlYTaSi. The morphology, microstructure, phases and the elemental distribution of the TBCs were characterized using scanning electron microscopy (SEM), transmission electron microscope (TEM), scanning transmission electron microscope (STEM), X-ray diffraction (XRD) and electron probe micro-analysis (EPMA). The characterization results showed that the film consisted primarily of metastable tetragonal phases (t′), and a large number of micro-cracks were present in the 8YSZ crystals. Following eighty-six thermal shock cycles of the specimens a large areal spallation was observed on the 8YSZ coating. The decreased concentration of yttrium at the coating interfaces weakened the inhibition of crystal growth and the phase transition of the Al₂O₃. The growth of TGO (Thermal growth oxide) and the diffusion into the 8YSZ coating produced deformation and stress in the ceramic coating. Tantalum appeared to absorb the oxygen that diffused into the coatings and delayed the growth of TGO in the interface between the CoCrAlYTaSi and substrate, which was beneficial to prolonging the life of the TBC.     

In situ TiBX/TiXNiY/TiC reinforced Ni60 composites by laser cladding and its effect on the tribological properties

Ni-based composite coatings reinforced by TiB_X/Ti_XNi_Y/TiC with different Ti6Al4V contents were precipitated on a 35CrMoV substrate via laser cladding. The phase composition, elemental distribution, and precipitated phases of the coatings were characterised using X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. The mechanical and tribological properties of the cladding layer were also characterised. The results showed that the coating contained TiB₂, TiC, TiB, Ni₃Ti, and NiTi₂ phases with uniform elemental distribution and grain refinement. A schematic of the growth model and precipitation sequence of the reinforced phases was generated. The microstructure, elemental segregation, hardness, and friction behaviour of the cladding layer were significantly influenced by the addition of Ti6Al4V. The optimal microstructure and best mechanical properties were obtained by the addition of 4 wt% Ti6Al4V, with that coating possessing a hardness, average friction coefficient, and wear volume of 770.8 HV₁, 0.180 and 6132 um³, respectively.     

Alumina-silica composite coatings on graphite by CVD at 550°C

Alumina-silica composite coatings were prepared on the surface of graphite paper by chemical vapor deposition using AlCl₃/SiCl₄/H₂/CO₂ as precursor in the temperature range of 300 to 550°C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the phase composition and the microstructure of the coating, respectively. The results indicated that a dense, uniform, and adherent alumina-silica composite coating can be prepared on graphite paper substrate by chemical vapor deposition at 550°C. Alumina-silica composite coating is composed of particles or nodules of varying size. Each particle is often composed of a number of finer particles. The phases of the 550°C composite coating include γ-alumina and amorphous silica. The elemental chlorine content in the composite coating decreases with increasing deposition temperature. The surfaces of the alumina-silica composite coatings are affected by deposition temperature. There are some obvious micro-cracks in the 300°C composite coating, which are attributed to a mismatch of the coefficient of thermal expansion between composite coating and graphite paper. The 550°C alumina-silica composite coating can be completely turned into mullite after heat-treatment at 1350°C for 0.5 hr in argon atmosphere.     

Microstructure analyses and thermophysical properties of nanostructured thermal barrier coatings

Nanostructured 8 wt% yttria partially stabilized zirconia coatings were deposited by air plasma spraying. Transmission electron microscopy, scanning electron microscopy, and X-ray diffraction were carried out to analyze the as-sprayed coatings and powders. Mercury intrusion porosimetry was applied to analyze the pore size distribution. Laser flash technique and differential scanning calorimetry were used to examine the thermophysical properties of the nanostructured coatings. The results demonstrate that the as-sprayed nanostructured zirconia coatings consist of the nonequilibrium tetragonal phase. The microstructure of the nanostructured coatings includes the initial nanostructure of powder and columnar grains. Moreover, micron-sized equiaxed grains were also exhibited in the nanostructured coatings. Their evolution mechanisms are discussed. The as-sprayed nanostructured zirconia coating shows a bimodal pore size distribution, and has a lower value of thermal conductivity than the conventional coating.     

Preparation and characterization of YSZ abradable sealing coating through mixed solution precursor plasma spraying

Yttria-stabilized zirconia (YSZ) ceramic matrix abradable sealing coatings were prepared by plasma spraying of a blend of YSZ solution precursor with YSZ nano-particles. The microstructure and phase compositions of the prepared abradable sealing coatings were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). In addition, the mechanical, high-temperature oxidation, and tribological properties of the coatings were systematically investigated. The results show that addition of YSZ nano-particles increased porosity and bond strength and decreased the hardness of the coating. The optimum performance value was achieved by addition of 5?g nano-particles into the coating. The coatings maintained excellent thermal stability through a ten-cycle thermal shock test at 1150?°C. The 8YSZ-5 coating had an improved oxidation constant of 5.540?×?10^?4 and exhibited remarkable oxidation kinetics at 1150?°C. The friction coefficient of the mixed solution precursor coating was remarkably decreased compared with a traditional ceramic matrix abradable sealing coating. The results indicate that mixed solution precursor plasma spraying increased abradable sealing coating application performance.     

Investigation of the thermomechanical properties of a plasma-sprayed nanostructured zirconia coating

Yttria partially stabilized nanostructured zirconia coatings were deposited by atmospherical plasma spraying (APS). The microstructure of the as-sprayed nanostructured coating was characterized with Scanning electronic microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectrum (RS). The laser-flash diffusivity method and push-rod method were used to examine the thermomechanical properties of the nanostructured zirconia coatings. The results obtained indicated that the plasma-sprayed zirconia coating possessed nano-structure and its average grain size was about 73 nm. The average thermal expansion coefficients of the nanostructured coating at the first thermal cycle and second thermal cycle from room temperature to 1200 °C are 11.0 and 11.6×10⁻⁶ °C⁻¹, respectively. The thermal diffusivity of the nanostructured zirconia coating was 1.80–2.54×10⁻³ cm²/s between 200 and 1200 °C. The microhardness of the nanostructured zirconia coating was 8.6 GPa, which was 1.6 times as large as that of traditional zirconia coating.     

Electrochemical corrosion behaviour of plasma electrolytic oxidation coatings on AM50 magnesium alloy formed in silicate and phosphate based electrolytes

PEO coatings were produced on AM50 magnesium alloy by plasma electrolytic oxidation process in silicate and phosphate based electrolytes using a pulsed DC power source. The microstructure and composition of the PEO coatings were analyzed by scanning electron microscopy (SEM) and X-ray Diffraction (XRD). The corrosion resistance of the PEO coatings was evaluated using open circuit potential (OCP) measurements, potentiodynamic polarisation tests and electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl solution. It was found that the electrolyte composition has a significant effect on the coating evolution and on the resulting coating characteristics, such as microstructure, composition, coating thickness, roughness and thus on the corrosion behaviour. The corrosion resistance of the PEO coating formed in silicate electrolyte was found to be superior to that formed in phosphate electrolyte in both the short-term and long-term electrochemical corrosion tests.     

The influence of pulse plating parameters on microstructure and properties of Ni-W-Si3N4 nanocomposite coatings

Nanosized silicon nitride (Si₃N₄) particles reinforced Nickel-tungsten composite coatings were deposited on the surface of C45 steel sheet by pulse electrodeposition. The effect of duty cycle, frequency, current pattern and presence of Si₃N₄ nanoparticles on microstructure, phases and corrosion resistance and mechanical properties of the coatings were investigated. The Si₃N₄ phase was incorporated into Ni-W alloy matrix uniformly and the inclusion content of in the coating was analyzed by energy dispersive x-ray spectrometer (EDS). The structure, microhardness and surface roughness of the coatings was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers micro-indenter and atomic force microscopy (AFM). The corrosion protection of steel by the coatings was evaluated by weight loss and electrochemical impedance spectroscopy (EIS). Corrosion rates of the coatings were determined using the Tafel polarization test. The results indicated that the duty cycle of 60%, pulse frequency of 1000 Hz, average current density of 5 A/dm⁻², and Si₃N₄ nanoparticles concentration of 30 g/L were the optimal plating conditions. The amount of Si₃N₄ particles incorporated into the coating that were produced under the optimum plating conditions was 2.1 wt%, and the microhardness was 1031 Hv as well as the crystallite size of this coating was 27 nm.     

Pulsed electrodeposition of carbon nanotubes-hydroxyapatite nanocomposites for carbon/carbon composites

Carbon nanotubes-hydroxyapatite (CNTs-HA) composite coatings, which behaved like single composites, were synthesized by a combined method composed of electrophoretic deposition and pulsed electrodeposition. The phase compositions and the microstructure of the composite coatings were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR). Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies showed that the CNTs-HA composite coatings protected the bare carbon/carbon composites from corrosion in simulated body fluid (SBF) solution. The adhesion strength of CNTs-HA composite coating prepared by the combined method is 14.57±1.06 MPa achieved at the CNTs EPD time of 10 min. Compared to the other CNTs-HA composite coatings with different content of CNTs, the CNT-HA composite coating with the electrophoretic deposition of 10 min showed the best corrosion resistance. The morphology of CNTs-HA composite coatings immersed in SBF solution rendered the formation of HA crystallites. In addition, in vitro cellular responses to the CNTs-HA composite coatings were assessed to investigate the proliferation and morphology of mouse cells 3T3 cell line.     

Carbon nanotube reinforced hydroxyapatite composite coatings produced through laser surface alloying

Carbon nanotube (CNT) reinforced hydroxyapatite composite coatings have been successfully fabricated by laser surface alloying. The phase compositions and the microstructure of the composite coatings were studied using X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). TEM observation showed that a large amount of CNTs can be found with their original tubular morphology in the composite coatings, even though some CNTs react with titanium element in the substrate during laser irradiation. Additionally, measurement on the elastic modulus, hardness of the composite coatings by nanoindentation tests indicated that the mechanical properties are affected by the amount of CNTs in the starting precursor materials. Therefore, CNT reinforced hydroxyapatite composite coating is a promising coating material for high-load-bearing metal implants.     

The effects to the structure and electrochemical behavior of zinc phosphate conversion coatings with ethanolamine on magnesium alloy AZ91D

This paper discussed a zinc phosphate conversion coating formed on magnesium alloy AZ91D from the phosphating bath with varying amounts of ethanolamine (MEA). The effects of MEA on the form, structure, phase composition and electrochemical behavior of the phosphate coatings were examined using an scanning electron microscopy (SEM), X-ray diffraction (XRD) potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Interpretations of the electrical elements of the equivalent circuit were obtained from the SEM structure of the coatings, assumed to be formed of two layers: an outer porous crystal layer and an inner flat amorphous layer. The result showed that adding MEA refined the microstructure of the crystal layer and that the phosphate coating, derived at the optimal content of 1.2 g/L, with the most uniform and compact outer crystal layer provided the best corrosion protection.     

Investigation of the tribological and biomechanical properties of CrAlTiN and CrN/NbN coatings on SST 304

This study examines the influence of thin layer coatings of CrAlTiN and CrN/NbN, deposited via physical vapor, on the biocompatibility, mechanical, tribological, and corrosion properties of stainless steel 304. The microstructure and morphology of the thin CrAlTiN and CrN/NbN layers were characterized by scanning electron microscopy (SEM), EDX, and X-ray diffraction. The pin on disc wear test was performed on bare and metal-nitride coated SST 304 under a 15 N load at 60 rpm and showed that the wear rates of the thin CrAlTiN and CrN/NbN film coatings were lower than the bare substrate wear ratio. The coefficients of friction (COFs) attained were 0.64, 0.5, and 0.55 for the bare substrate, CrN/NbN coating, and CrAlTiN coating, respectively. Nano indentation tests were also performed on CrAlTiN-coated and CrN/NbN-coated SST 304. The nanohardnesses and Young's moduli of the coated substrates were 28 GPa and 390 GPa (CrN/NbN-coated) and 33 GPa and 450 GPa (CrA1TiN-coated), respectively. For comparison, the nanohardness and Young's modulus of the uncoated substrate were 4.8 GPa and 185 GPa, respectively. Corrosion tests were conducted, and the behaviors of the bare and metal nitride-deposited substrates were studied in CaCl₂ for seven days. The corrosion Tafel test results showed that the metal-nitride coatings offer proper corrosion resistance and can protect the substrate against penetration of CaCl₂ electrolyte. The CrN/NbN-coated substrates showed better corrosion resistance compared to the CrAlTiN-coated ones. In evaluating the biocompatibility of the CrAlTiN and CrN/NbN coatings, the human cell line MDA-MB-231 was found to attach and proliferate well on the surfaces of the two coatings.     

Polymer precursor synthesis of novel ZrC–SiC ultrahigh-temperature ceramics and modulation of their molecular structure

In this study, ZrC–SiC composite ceramics were prepared with varying Zr/Si molar ratios using sol–gel method. Composites were characterized by Fourier-transform infrared spectroscopy (FT–IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS). FT–IR analysis confirmed macromolecular network structure of composites, in which the precursor is composed of polyvinyl butyral (PVB) as main chain, silane molecules are interlinked via –OH moieties in PVB side chains, and Zr atoms are crosslinked with Si in corresponding proportion. Ceramic precursor begins to decompose at a temperature exceeding 1300 °C and is completely transformed into ZrC–SiC composite ceramics with corresponding Zr/Si molar ratio at 1600 °C. Raman spectroscopy and TEM results reveal that after annealing at 1600 °C, ZrC powder uniformly covers surface of SiC ceramics, and high-crystallinity graphite carbon covers ZrC powder.     

Characterization and property of microarc oxidation coatings on open-cell aluminum foams

The ceramic coatings were prepared on open-cell aluminum foams by microarc oxidation (MAO) treatment in an alkaline-silicon electrolyte. The morphology, microstructure, elemental distribution, and phase composition of the MAO coatings were investigated by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction, respectively. The corrosion behaviors of the coated and uncoated foams were evaluated by electrochemical polarization measurement. The results show that the MAO coatings cover the surface of open-cell aluminum foams. The coatings were composed of an external porous layer and an internal dense layer. The main phase of the MAO coating phase is γ-Al₂O₃. The coated aluminum foams exhibit more positive corrosion potential and lower corrosion current density compared with the uncoated aluminum foams.     

Studying the in vitro corrosion response of nanostructured TaN coatings in Hank's physiological solution

The goal of this research is to determine the effect of N₂ pressure to argon pressure on the microstructural analysis and corrosion behavior of nanostructured TaN deposited coatings using a reactive DC-magnetron sputtering (RDCMS) technique. The samples coated microstructure was studied by the X-ray diffraction (XRD) and scanning electron microscope (SEM), and elemental distribution was studied using energy-dispersive X-ray spectroscopy (EDS). To investigate the corrosion behavior of nanostructured TaN coatings, the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests were performed in Hank's physiological solution. The results of different tests revealed that the coating with a content of 17.6% P_N2/P_Ar consisted of hexagonal and orthorhombic TaN phases and had denser microstructure and free pores. This coating showed superior corrosion behavior in comparison to the other ones. Also, the corrosion resistance of this coating raised by increasing the time of immersion from 48 to 168 h.     

Comparison of electrochemical behavior of CrN single-layer coating and Cr/CrN nanolayered coating produced by cathodic arc evaporation physical vapor deposition

The aim of the present work is to study the CrN single-layer coating and the Cr/CrN nanolayered coating by cathodic arc evaporation physical vapor deposition (CAE-PVD) on AISI 304 stainless steel and to assess the electrochemical behavior of the coatings. Field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were utilized to study the morphology and microstructure of the coatings. The mechanical behavior of the coatings was studied by the nanoindentation technique. The electrochemical behavior of the formed coatings in 3.5 wt.% NaCl solution was investigated via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) tests. Based on the microscopic images, it was realized that both CrN and Cr/CrN coatings were formed having a dense structure on the substrate. The results of EIS measurements showed gradual changes in the polarization resistance of the Cr/CrN nanolayered coating during the immersion time. However, significant changes in the polarization resistance of the CrN single-layer coating were seen by increasing immersion time comparing with the Cr/CrN coating. The higher polarization resistance of the Cr/CrN coating can be attributed to the effects of the interface between the layers in comparison to the CrN coating.