Amorphous-like Structure Research Articles

The Effect of Pressure on Magnetic Properties of Prussian Blue Analogues

We present the review of pressure effect on the crystal structure and magnetic properties of Cr(CN)6-based Prussian blue analogues (PBs). The lattice volume of the fcc crystal structure space group Fm 3 ¯ m in the Mn-Cr-CN-PBs linearly decreases for p ≤ 1.7 GPa, the change of lattice size levels off at 3.2 GPa, and above 4.2 GPa an amorphous-like structure appears. The crystal structure recovers after removal of pressure as high as 4.5 GPa. The effect of pressure on magnetic properties follows the non-monotonous pressure dependence of the crystal lattice. The amorphous like structure is accompanied with reduction of the Curie temperature (TC) to zero and a corresponding collapse of the ferrimagnetic moment at 10 GPa. The cell volume of Ni-Cr-CN-PBs decreases linearly and is isotropic in the range of 0–3.1 GPa. The Raman spectra can indicate a weak linkage isomerisation induced by pressure. The Curie temperature in Mn2+-CrIII-PBs and Cr2+-CrIII-PBs with dominant antiferromagnetic super-exchange interaction increases with pressure in comparison with decrease of TC in Ni2+-CrIII-PBs and Co2+-CrIII-PBs ferromagnets. TC increases with increasing pressure for ferrimagnetic systems due to the strengthening of magnetic interaction because pressure, which enlarges the monoelectronic overlap integral S and energy gap ∆ between the mixed molecular orbitals. The reduction of bonding angles between magnetic ions connected by the CN group leads to a small decrease of magnetic coupling. Such a reduction can be expected on both compounds with ferromagnetic and ferrimagnetic ordering. In the second case this effect is masked by the increase of coupling caused by the enlarged overlap between magnetic orbitals. In the case of mixed ferro–ferromagnetic systems, pressure affects μ(T) by a different method in Mn2+–N≡C–CrIII subsystem and CrIII–C≡N–Ni2+ subsystem, and as a consequence Tcomp decreases when the pressure is applied. The pressure changes magnetization processes in both systems, but we expect that spontaneous magnetization is not affected in Mn2+-CrIII-PBs, Ni2+-CrIII-PBs, and Co2+-CrIII-PBs. Pressure-induced magnetic hardening is attributed to a change in magneto-crystalline anisotropy induced by pressure. The applied pressure reduces saturated magnetization of Cr2+-CrIII-PBs. The applied pressure p = 0.84 GPa induces high spin–low spin transition of cca 4.5% of high spin Cr2+. The pressure effect on magnetic properties of PBs nano powders and core–shell heterostructures follows tendencies known from bulk parent PBs.

Kinetic and Electrochemical Reaction Mechanism Investigations of Rodlike CoMoO4 Anode Material for Sodium-Ion Batteries.

Sodium-ion batteries are considered the most promising power source for electrical energy storage systems because of the abundance of sodium and their significant cost advantages. However, high-performance electrode materials are required for their successful application. Herein, we report a monoclinic-type CoMoO4 material which is synthesized by a simple solution method. An optimized calcination temperature with a high crystallinity and a rodlike morphology of the material are selected after analyzing the as-synthesized powder by temperature-dependent time-resolved X-ray diffraction. The CoMoO4 rods exhibit initial discharge and charge capacities of 537 and 410 mA h g-1, respectively, when used as an anode for sodium-ion batteries. The sodium diffusion coefficient in the bimetallic CoMoO4 anode is measured using the galvanostatic intermittent titration technique and calculated in the range of 1.565 × 10-15 to 4.447 × 10-18 cm2 s-1 during the initial cycle. Further, the reaction mechanism is investigated using ex situ X-ray diffraction and X-ray absorption spectroscopy, and the obtained results suggest an amorphous-like structure and reduction/oxidation of Co and Mo during the sodium insertion/extraction process. Ex situ transmission electron microscopy and energy-dispersive spectroscopy images of the CoMoO4 anode in fully discharged and recharged state reveal the rodlike morphology with homogenous element distribution.

NiCo-DH nanodots anchored on amorphous NiCo-Sulfide sheets as efficient electrocatalysts for oxygen evolution reaction

A lamellar reverse micelle directed assembly strategy was proposed to integrate NiCo layered hydroxides (NiCoDH) nanodots and NiCo sulfide (NiCoS) nanosheets (NiCoDH/NiCoS) by one-step solvothermal method. The NiCoDH/NiCoS features with an interconnected 3D architecture composed of ultrathin amorphous NiCoS nanosheets (∼1.5 nm), decorated by ultra-small NiCoDH nanodots (2–3 nm). The optimal NiCoDH/NiCoS exhibits a low overpotential of 303 mV at current density of 20 mA cm−2, together with a small Tafel slope of 77.6 mV dec−1, the high Faraday efficiency of about 95% as well as good stability. The excellent OER performance and enhanced stability should be ascribed to the strong interface-coupling of NiCoDH nanodots/NiCoS nanosheets, highly synergistic effect of bimetal Co and Ni, amorphous-like structure to expose more active sites, and interconnected 3D architecture for effective mass transport and structural stability. This work provides a significant insight regarding the strong interface-coupling effect on OER electrocatalysis, and offers a new strategy to design highly efficient OER catalysts.

Electronic states realized by the interplay between Li diffusion and Co3+/Co4+ charge ordering in LixCoO2

Measurements of dc magnetization $(M)$ and electrical resistivity $(\ensuremath{\rho})$ have been carried out as a function of temperature $(T)$ for layered oxide ${\mathrm{Li}}_{x}{\mathrm{CoO}}_{2} (0.51\ensuremath{\le}x\ensuremath{\le}1.0)$ using single-crystal specimens. After slow cooling of the specimens down to 10 K, both of the $M(T)$ and $\ensuremath{\rho}(T)$ curves are found to exhibit a clear anomaly due to the occurrence of ${\mathrm{Co}}^{3+}/{\mathrm{Co}}^{4+}$ charge ordering (CO) at ${T}_{\mathrm{S}}\ensuremath{\sim}155\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ for $0.6\ensuremath{\le}x\ensuremath{\le}0.98$ (at ${T}_{\mathrm{S}}\ensuremath{\sim}180--190\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ for $0.5\ensuremath{\le}x\ensuremath{\le}0.55)$. After rapid cooling of the specimens, additional anomalies are observed related to the onset of Li diffusion at ${T}_{\mathrm{F}1}\ensuremath{\sim}370\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ and/or ${T}_{\mathrm{F}2}=120--130\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Due to phase mixing with compositions of nearly ${\mathrm{LiCoO}}_{2}$ and ${\mathrm{Li}}_{2/3}{\mathrm{CoO}}_{2}$, the specimens with $0.7\ensuremath{\lesssim}x\ensuremath{\lesssim}0.9$ show anomalies both at ${T}_{\mathrm{F}1}$ and ${T}_{\mathrm{F}2}$. For $0.6\ensuremath{\lesssim}x\ensuremath{\lesssim}0.9$, the resistivity measured after rapid cooling is found to be fairly larger than that measured after slow cooling below ${T}_{\mathrm{S}}$. The enhanced resistivity can be explained by the scenario that disordered ${\mathrm{Co}}^{3+}/{\mathrm{Co}}^{4+}$ arrangements, which have been observed and revealed to have an insulating electronic structure contrasting to the regular CO state in the previous scanning tunneling microscopy measurements [K. Iwaya et al., Phys. Rev. Lett. 111, 126104 (2013)], are realized due to the formation of an amorphouslike structure of Li ions after rapid cooling via interlayer Coulomb coupling. An electronic phase diagram for $0.5\ensuremath{\le}x\ensuremath{\le}1.0$ is proposed.

Facile synthesis of hierarchical porous carbon from crude biomass for high-performance solid-phase microextraction

Porous materials have great prospective applications for solid-phase microextraction (SPME) technology because of their large specific surface area and pore volume. In this study, a hierarchical porous carbon (HPC) was synthesized by simple hydrothermal reaction and potassium hydroxide (KOH) activation of crude biomass and found to be an efficient adsorbent for SPME of organic pollutants. Results show that the as-prepared HPC has a partly graphitic amorphous-like structure with ultrahigh specific surface area (2551 m2/g), high pore volume (1.53 cm3/g), good pore size distribution (PSD) (mesopore/micropore ratio of 68%), and great thermal stability (>450 °C). When we utilized it as SPME fiber coating, the extraction capacities for chlorobenzenes (CBs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and phthalates (PAEs) were, respectively, 1.13–39.46, 2.40–7.78, 1.34–36.02, and 1.50–1.83 times higher than those of a commercial polydimethylsiloxane (PDMS) fiber. Under the optimized extraction conditions, an analytical method for CBs with low detection limits (0.01–0.24 ng/L), good repeatability (1.00%–4.93% for intra-day, 1.11%–6.94% for inter-day), and great reproducibility (1.48%–8.91%, n = 3) was developed. Moreover, we evaluated the practicality of the developed method for environmental water sample and obtained satisfactory recoveries (86.21%–104.34%). The findings provide a novel and promising HPC from crude biomass using a low-cost and facile synthetic route for SPME applications.

Structural behavior of supercritical fluids under confinement.

The existence of the Frenkel line in the supercritical regime of a Lennard-Jones (LJ) fluid shown through molecular dynamics (MD) simulations initially and later corroborated by experiments on argon opens up possibilities of understanding the structure and dynamics of supercritical fluids in general and of the Frenkel line in particular. The location of the Frenkel line, which demarcates two distinct physical states, liquidlike and gaslike within the supercritical regime, has been established through MD simulations of the velocity autocorrelation (VACF) and radial distribution function (RDF). We, in this article, explore the changes in the structural features of supercritical LJ fluid under partial confinement using atomistic walls. The study is carried out across the Frenkel line through a series of MD simulations considering a set of thermodynamics states in the supercritical regime (P=5000 bar, 240K≤T≤1500K) of argon well above the critical point. Confinement is partial, with atomistic walls located normal to z and extending to "infinity" along the x and y directions. In the "liquidlike" regime of the supercritical phase, particles are found to be distributed in distinct layers along the z axis with layer spacing less than one atomic diameter and the lateral RDF showing amorphous-like structure for specific spacings (packing frustration) and non-amorphous-like structure for other spacings. Increasing the rigidity of the atomistic walls is found to lead to stronger layering and increased structural order. For confinement with reflective walls, layers are found to form with one atomic diameter spacing and the lateral RDF showing close-packed structure for the smaller confinements. Translational order parameter and excess entropy assessment confirms the ordering taking place for atomistic wall and reflective wall confinements. In the "gaslike" regime of the supercritical phase, particle distribution along the spacing and the lateral RDF exhibit features not significantly different from that due to normal gas regime. The heterogeneity across the Frenkel line, found to be present both in bulk and confined systems, might cause the breakdown of the universal scaling between structure and dynamics of fluids necessitating the determination of a unique relationship between them.

Phase transformation in white etching area in rolling contact fatigue

Rolling contact fatigue (RCF) involves microstructural change in the subsurface of contact. The changed microstructure is generally termed as white etching area (WEA) as it appears white under optical microscope when etching in nital solution. WEA has been acknowledged as one of the primary failure modes in RCF since it causes severe local inhomogeneity of microstructure. It was reported that WEA consists of nano ferrites as martensite grains and carbides are significantly refined in the WEA. Some carbides are dissolved. In some cases, an amorphous-like structure was occasionally observed in the WEA, indicating that phase transformation may possibly occur. The WEAs were studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Electron back scattered diffraction (EBSD). The result showed that WEA is dominated with an amorphous phase with martensite, austenite and carbides embedded interior. A distinct interface between the matrix and the WEA was present. In addition to grain refinement down to nanometers, phase transformation including amorphization and austenitization happened in WEAs. The content of austenite was increased from 2% in the matrix to 20% in the WEA. The analysis showed that phase transformation is controlled by plastic deformation mechanism.

TiSiCN and TiAlVSiCN nanocomposite coatings deposited from Ti and Ti-6Al-4V targets

TiSiCN and TiAlVSiCN coatings were deposited by pulsed dc magnetron sputtering of a pure Ti target and a commercial grade Ti-6Al-4V target, respectively, in an Ar+N2+trimethylsilane (TMS) mixture. The elemental composition of the coatings was varied by increasing the TMS flow rate (fTMS) from 0 to 4sccm. The main goal of the study is to explore the possibility of using low cost commercial grade Ti-6Al-4V material as a sputtering source of Ti for depositing Ti based nanostructure coatings. The microstructure of the coatings was characterized using X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The mechanical properties, sliding wear and erosion resistances of the coatings were analyzed using nanoindentation, dry ball-on-disc test, and solid particle erosion, respectively. Higher deposition rates (35–59% increase) were observed for the TiAlVSiCN coatings than those for the TiSiCN coatings under similar deposition conditions. As the fTMS is increased, both coating systems exhibit similar structural evolution from fine columnar grain structure to nanocomposite structure, and finally to amorphous-like structure. The incorporation of a small amount of Al and V into the TiAlVSiCN coatings directly from the Ti-6Al-4V target is beneficial for improving the mechanical properties, wear resistance, and erosion resistance of the coatings. The study demonstrates that it is practical to use commercial grade Ti-6Al-4V material as a sputtering source of Ti for depositing Ti-based nanostructure coatings to achieve higher deposition rates, improved properties and lower production cost.

Structural and optical studies of Er3+-doped alkali/alkaline oxide containing zinc boro-aluminosilicate glasses for 1.5 μm optical amplifier applications

In the present work, we report on the optical spectral properties of Er3+-doped zinc boro-aluminosilicate glasses with an addition of 10 mol % alkali/alkaline modifier regarding the fabrication of new optical materials for optical amplifiers. A total of 10 glasses were prepared using melt−quenching technique with the compositions (40-x)B2O3 − 10SiO2 − 10Al2O3 − 30ZnO − 10Li2O − xEr2O3 and (40-x)B2O3 − 10SiO2 − 10Al2O3 − 30ZnO – 10MgO − xEr2O3 (x = 0.1, 0.25, 0.5, 1.0, and 2.0 mol %). We confirm the amorphous-like structure for all the prepared glasses using X-ray diffraction (XRD). To study the functional groups of the glass composition after the melt−quenching process, Raman spectroscopy was used, and various structural units such as triangular and tetrahedral-borates (BO3 and BO4) have been identified. All the samples were characterized using optical absorption for UV, visible and NIR regions. Judd-Ofelt (JO) intensity parameters (Ωλ, λ = 2, 4 and 6) were calculated from the optical absorption spectra of two glasses LiEr 2.0 and MgEr 2.0 (doped with 2 mol % of Er3+). JO parameters for LiEr 2.0 and MgEr 2.0 glasses follow the trend as Ω6>Ω2>Ω4. Using Judd–Ofelt intensity parameters, we obtained radiative probability A (S−1), branching ratios (β), radiative decay lifetimes τrad (μs) of emissions from excited Er+3 ions in LiEr 2.0 and MgEr 2.0 to all lower levels. Quantum efficiency (η) of 4I13/2 and 4S3/2 levels for LiEr 2.0 and MgEr 2.0 with and without 4D7/2 level was calculated using the radiative decay lifetimes τrad. (μs) and measured lifetimes τexp. (μs). We measured the visible photoluminescence under 377 nm excitation for both LiEr and MgEr glass series within the region 390–580 nm. Three bands were observed in the visible region at 407 nm, 530 nm, and 554 nm, as a result of 2H9/2 → 4I15/2, 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, respectively. Decay lifetimes for emissions at 407 nm, 530 nm, and 554 nm were measured and they show single exponential behavior for all the LiEr and MgEr glass series. From the photoluminescence and radiative decay lifetimes (τrad), we calculated the full-width at half-maximum (FWHM), emission cross-section (σPE) and bandwidth gain (FWHM×σPE) parameters. Near-infrared photoluminescence under 980 nm excitation was measured for all the LiEr and MgEr glass series in the region 1420–1620 nm. NIR emissions show a broadband centered at ∼1530 nm due to the transition of Er3+: 4I13/2 → 4I15/2. Decay lifetimes for NIR emission at ∼1530 nm were measured and they show a quite exponential nature for all the LiEr and MgEr glass series. From the NIR emission spectra and decay lifetimes, we calculated the full-width at half-maximum (FWHM), the emission cross-section (σPE) and the bandwidth gain (FWHM×σPE) for the NIR emission and it shows FWHM of 50–70 nm for prepared glasses, emission cross-section of (∼3.5)× 10−20 cm2, while bandwidth gain was (∼25) × 10−26 cm3.

Investigations on sputter-coated cotton fabric with regard to their microstructure, antibacterial, hydrophobic properties and thermal stability

TiON and TiON/Cu films were RF-sputtered on cotton surface under a mixed atmosphere of Ar/N2/O2. An amorphous-like structure with broadened peaks was formed in the TiON film when TiON/Cu films became crystalline with an increase in Cu contents. The deposited TiON/Cu films showed anatase TiO2 phase. TiON-coated cotton fabrics were about 90% efficacious in bacterial reduction. A sharp increase in bacterial cell reduction was observed when Cu was added to the TiON film. In addition, the contact angle of the coated cotton fabrics was higher than that of the uncoated samples. However, the contact angle of the TiON/Cu-coated cotton fabrics with different Cu contents ranged between 115° and 130°. TGA analysis indicated that TiON and TiON/Cu films had no negative effect on thermal stability of the cotton fabric.

Influence of titanium concentration on mechanical properties and wear resistance to Ti6Al4V of Ti-C:H on cemented carbide

Titanium doped hydrogenated amorphous carbon (Ti-C:H) was synthesized on silicon, YG8 cemented carbide by middle frequency magnetron sputtering technology. Doped Ti concentration was adjusted via allotting Ar/C2H2 flow rate to be 0–1.21 at.%. To investigate the influence of Ti concentration on mechanical properties and wear resistance to Ti6Al4V, stylus profiler, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and ball-on-disk friction test were applied. The results indicated that the incorporated Ti element existed as amorphous-like structure within the carbon network resulting in the decrease of sp3 fraction and increase of graphitization. The compressive stress of the film declined gradually along with the sacrifice of hardness and elastic modulus as the increase of Ti concentration. Compared with the none-doped and 1.21 at.% Ti-C:H, the friction coefficient of 0.32 at.% and 0.74 at.% Ti-C:H remained lower and more stable value of 0.07, which led to a lower wear rate of about 3.1 E-8 mm3/Nm as well. The worn surface of various Ti-C:H films after rubbing against Ti6Al4V exhibited three kinds of morphologies as adhesive wear, smooth and abrasive wear. The different morphologies and wear mechanism were discussed.

Characterization of corrosion scale formed on 3Cr steel in CO2-saturated formation water

The evolution of the corrosion scale formed on 3Cr steel was investigated by scanning electron microscopy (SEM) and X-Ray Diffraction (XRD). The inner layer was characterized by Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis-differential scanning calorimetry (TG-DSC). The results show the inner layer is an amorphous-like structure containing some nano-quasicrystalline and nanocrystalline grains which is more uniform and less porous than the crystalline FeCO3 layer. At the 2nd stage, the transition of cathodic reactions was found, and the growth of the FeCO3 phase in the inner layer dramatically decreased the film porosity, resulting in the passivation.

Microstructure and thermochromic properties of VOX–WOX–VOX ceramic thin films

W-doped VO2 films have been synthesized via oxygen annealing of V–W–V (vanadium–tungsten–vanadium) multilayered films. The effects of middle layer’s thickness of V–W–V multilayered film on structure and properties of VOX–WOX–VOX ceramic thin films were investigated. The as-deposited V–W–V multilayered film showed amorphous-like structure when mixed structure of VO2 (M) and VO2 (B) was formed in VOX–WOX–VOX ceramic thin films. Tungsten content of VOX–WOX–VOX ceramic thin films increased with increasing middle layer’s thickness. With increasing middle layer’s thickness, room temperature square resistance (Rsq) of VOX–WOX–VOX ceramic thin films increased from 65 to 86 kΩ/sq. The VOX–WOX–VOX ceramic thin film with the thinnest middle layer showed significant SMT (semiconductor–metal transition) when SMT became negligible on increasing middle layer’s thickness.

Molecular dynamic simulation: Studying the effects of Brownian motion and induced micro-convection in nanofluids

ABSTRACTNanofluids are suspensions of nanoparticles into convectional heat transfer fluid to enhance the thermal conductivity of its base fluid. The roles of Brownian motion of nanoparticles and induced micro-convection in base fluid in enhancing the thermal conductivity of nanofluids were investigated using molecular dynamic (MD) simulation. The roles were determined by studying the effect of particle size on thermal conductivity and diffusion coefficient. Results show that the Brownian motion and induced micro-convection have insignificant effects on enhancing the thermal conductivity. The hydrodynamic effect is restricted by an amorphous-like interfacial fluid structure in the vicinity of the nanoparticle due to its higher specific area.

Effect of microstructure on mechanical and tribological properties of TiAlSiN nanocomposite coatings deposited by modulated pulsed power magnetron sputtering

TiAlSiN nanocomposite coatings were deposited in a closed field unbalanced magnetron sputtering system by reactive sputtering from Ti0.475Al0.475Si0.05 targets using modulated pulsed power magnetron sputtering (MPPMS) under a floating substrate bias. The ratio of the nitrogen flow rate to the total gas flow rate (fN2) was varied from 0 to 40%. The application of MPPMS as sputtering sources was aimed at generating a high ionization degree of the sputtered material and a high plasma density by using a pulsed high power approach. When fN2=0%, an amorphous-like structure Ti0.479Al0.454Si0.066 coating was deposited with a hardness of 10GPa. When nitrogen was added, an optimized nanocomposite structure of nc-TiAlN/a-Si3N4 formed in the TiAlSiN coating deposited at fN2=10%, in which 5–10nm TiAlN nanocrystallites were embedded in a 2–3nm thick amorphous Si3N4 matrix. As the fN2 was increased up to 40%, the elementary composition of the coatings remained almost the same, but the grain size of nanocrystallites approached to 10–20nm and the AlN phase gradually precipitated. A maximum hardness (H) of 33.2GPa, a hardness to the elastic modulus (E) ratio of 0.081 and an H3/E*2 ratio of 0.19GPa were found in the coating deposited at fN2=10%. The friction coefficient of the TiAlSiN coatings was around 0.8–0.9 as sliding against a Si3N4 counterpart under a normal load of 0.5N. A wear rate of 2.0×10−5mm3N−1m−1 was measured in the TiAlSiN coatings deposited at fN2=20–40%. As only a low residual stress is found in the TiAlSiN coatings, we consider the complete phase separation is responsible for the enhanced mechanical and tribological properties of the nc-TiAlN/a-Si3N4 nanocomposite coatings.

Scanning transmission electron microscopy analysis of Ge(O)/(graphitic carbon nitride) nanocomposite powder

Analytical electron microscopy has revealed the structure of particles that were synthesized by chemical reaction of GeO2 with NaBH4 in the basic solution including graphitic carbon nitride (g-C3N4) powders. The g-C3N4 was arranged by recrystallization of melamine at 600°C under N2 gas atmosphere. The samples were dried at 60°C or 180°C for 4h. The g-C3N4 was observed as lamellae of several ten nm or less in size and had an amorphous-like structure with a distorted lattice in an area as small as a few hundred pm in size. The reaction product was Ge(O) particles as fine as several nm in size and composed of Ge and O atoms. Most of the particles must be of GeO2−x with the amorphous-like structure that has also a distorted lattice in an area of a few hundred pm in size. In the sample dried at 60°C, the particles were found to be dispersed in a wide area on the g-C3N4 lamella. It is hard to recognize those particles in TEM images. The particles in the sample dried at 180°C became larger and were easily observed as isolated lumps. Hence, these powders can be regarded as GeO2/g-C3N4 or Ge/GeO2/g-C3N4 nanocomposites, and expected to be applicable to anode materials for high energy Li-ion batteries due to Ge catalysis effect, accordingly.

Structural features and physico-mechanical properties of AlN-TiB2-TiSi2 amorphous-like coatings

The coating of the AlN-TiB2-TiSi2 system has been produced by the magnetron sputtering of a target. At the high-temperature (900 and 1300°C) actions the coating crystallization to form crystallites of sizes 11–25 nm has been observed. It has been defined that the amorphous-like structure is promising for the use of these coatings as diffusion barriers both as the independent elements and a contacting layer in multilayer wear-resistant coatings. It has been shown that the use of the resultant composite as an effective protective coating for cutting tools will make it possible to increase the tools wear resistance by more than 30% at the temperature up to 1300°C in the cutting zone.

Feasibility of using Y2Ti2O7 nanoparticles to fabricate high strength oxide dispersion strengthened Fe–Cr–Al steels

Abstract Addition of Al can improve the corrosion resistance of oxide dispersion strengthened (ODS) steels. However, Al reacts with Y 2 O 3 to form large Y–Al–O particles in the steels and deteriorates their mechanical properties. Herein, we successfully prepared Y 2 Ti 2 O 7 nanoparticles (NPs) by the combination of hydrogen plasma-metal reaction (HPMR) and annealing. Y 2 Ti 2 O 7 NPs with contents of 0.2 or 0.6 wt.% were then added into the Fe–14Cr–3Al–2W–0.35Ti (wt.%) steel to substitute the conventional Y 2 O 3 NPs by mechanical alloying (MA). The Y 2 Ti 2 O 7 NPs transformed into amorphous-like structure after 96 h MA. They crystallized with a fine size of 7.4 ± 3.7 nm and shared a semi-coherent interface with the matrix after hot isostatic pressing (HIP) of the ODS steel with 0.6 wt.% Y 2 Ti 2 O 7 . With the increasing Y 2 Ti 2 O 7 content from 0.2 to 0.6 wt.%, the tensile strength of the ODS steel increased from 1238 to 1296 MPa, which was much higher than that (949 MPa) of the ODS steel added with Y 2 O 3 . The remarkably improved mechanical properties of the Al-containing ODS steels were attributed to the increasing number density of Y 2 Ti 2 O 7 nanoprecipitates. Our work demonstrates a novel route to fabricate high performance ODS steels with both high mechanical strength and good corrosion resistance.

EFFECT OF ANNEALING TEMPERATURE ON HARDNESS AND WEAR RESISTANCE OF ELECTROLESSNi–B–MoCOATINGS

Formation of nickel–boron–molybdenum ( Ni – B – Mo ) coating on steel by electroless plating and evaluation of their morphology, hardness and tribological properties post heat treatment at different temperatures for 1 h is investigated. The 25 μm thick coating is uniform and adhesion between the substrate and coating is good. Ni – B – Mo coating was amorphous-like structure in their as-plated condition and by 400°C heat-treated coating, nickel fully crystallized and nickel borides and molybdenum carbide were formed. All coatings exhibited higher hardness than the substrate steel. Hardness values of all coatings up to 400°C did not change distinctively but decreased partly beyond 400°C. Friction coefficient reached lowest value post heat treatment at 300°C but later increased with increasing tempering temperature. Wear resistance was lowest in as-plated coating; however it reached the highest value at 300°C. Worn surface of the coatings showed the abrasive wear as the dominant wear mechanism. An additional adhesive wear mechanism was detected in coating tempered at 550°C. Moreover, our results confirmed that the molybdenum addition improved the thermal stability of the resulting coating. Therefore, Ni – B – Mo coating has potential for application in precision mould, optical parts mould or bipolar plates, where thermal stability is essential.

Effect of Annealing Temperature on the Corrosion Resistance of Electroless Ni-B-Mo Coatings

The Ni-B-Mo coating on steel by electroless plating and the evaluation of the morphology and corrosion performance after applying heat treatments at different temperatures for 1 h were investigated in this study. The 25-μm-thick coating was uniform and adhesion between the substrate and the coating was good. The coating consisted of an amorphous-like structure in their as-plated condition, and after annealing at 400 °C for 1 h, crystallized nickel, nickel borides, and molybdenum carbide were formed. Immersion tests in 10% HCl solution and potentiodynamic polarization measurements in 3.5% NaCl aqueous solution were applied to investigate corrosion resistance. The corrosion performance of heat-treated coatings was compared with steel and the as-plated coating. By increasing the annealing temperature, corrosion potential shifted toward a noble direction, corrosion current density decreased and the weight loss of specimens decreased, demonstrating an increase in corrosion resistance. Best corrosion performance was achieved by the coating heat treated at 550 °C .