Characterization of laser‐treated Rene 41 surface due to B4C and SiC particles at surface prior to laser treatment

Laser surface treatment of Rene 41 high‐performance alloy is carried out with the presence of hard particles at the surface. B₄C and SiC particles are uniformly distributed within 40 µm carbon film at the workpiece surface prior to laser treatment process. The effect of hard particles on residual stress and microhardness variations is investigated at the treated surface. Morphological and metallurgical changes in the treated layer are examined by using electron microscopy, energy dispersive spectroscopy, and X‐ray diffraction. Residual stress formed at the surface is determined from the X‐ray data. It is found that the treated surface is free from asperities such as large size voids and cracks. A dense layer is formed in the surface region, which causes volume shrinkage while contributing to microhardness and residual stress enhancement at the surface. B₄C hard particles result in the highest residual stress and microhardness at the surface, which is attributed to its high thermal expansion coefficient. Copyright © 2013 John Wiley & Sons, Ltd.     

Laser surface treatment of high‐speed steel: presence of TiC particles at the surface

Laser treatment of a high‐speed steel surface is carried out and metallurgical and morphological changes in the laser‐treated layer are examined using SEM, EDS and XRD. A carbon film of 50 µm thickness and containing 5% TiC particles is formed at the workpiece surface prior to the laser treatment process. The carbon film formed at the surface enhances the absorption of laser irradiation and retains TiC particles at the workpiece surface. The residual stress formed at the laser‐treated surface is determined using the XRD technique while the indentation tests are carried out to measure microhardness and fracture toughness of the resulting surface. It is found that ε‐Fe₃N, and ε‐Fe₃ (N,C) compounds are formed at the laser‐treated surface, which are attributed to the presence of carbon film and high‐pressure nitrogen‐assisting gas. The fracture toughness of the laser‐treated surface reduces because of the increased hardness and dense layer formed at the surface vicinity. Copyright © 2011 John Wiley & Sons, Ltd.     

Functionalized boron carbide for enhancement of anticorrosion performance of epoxy resin

In this study, epoxy coatings were modified by adding various compositions of B₄C particles. In order to achieve proper dispersion of particles in the epoxy coating and increasing chemical interactions between particles and polymeric coating, the surface of the B₄C particles was treated with γ‐(2,3‐epoxypropoxy) propytrimethoxysilane (KH560). The surface modification and microstructure of B₄C were characterized by Fourier transform infrared, X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical impedance spectroscopy was also used to evaluate the impedance of coatings. The results revealed that the KH560 not only enhanced the interaction between B₄C particles and epoxy resin but also exhibited a remarkable ability to improve the anticorrosion performance of epoxy resin. The epoxy coating with the 3 wt% B₄C‐KH560 particles exhibited the best anticorrosion performance, which can be attributed to the best uniform dispersion of the B₄C‐KH560 particles, and the particles effectively block the aggressive species (Cl⁻, O₂, and H₂O) from the coating.     

Preparation and properties of Ni–Co–P/nano‐sized Si3N4 electroless composite coatings

Ni–Co–P/nano‐sized Si₃N₄ composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross‐sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high‐speed reciprocating friction, respectively. It was found that a Ni–Co–P/nano‐sized Si₃N₄ composite coating on aluminum alloy substrate is uniform and compact. The existence of nano‐sized Si₃N₄ particles in the Ni–Co–P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 °C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni–Co–P coatings and Ni–Co–P/Si₃N₄ composite coatings increase with the increase of heating temperature in the range of 200–400 °C, but show different behavior for the two coatings after annealing at 500 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

Laser embedding of TiC particles into the surface of phosphor bronze‐bearing material

A carbon film containing 5% TiC particles is formed on a pre‐prepared bronze surface prior to laser treatment. The carbon film provides increased absorption of the incident laser beam and hosts TiC particles with a uniform distribution at the workpiece surface. Optical and scanning electron microscopy are used to examine the metallurgical and morphological changes in the laser treated layer. Micro‐hardness of the laser‐treated surface is measured, and the residual stress formed in the surface vicinity is measured using the X‐ray diffraction technique. It was found that a dense layer with fine grains was formed in the laser‐treated layer. The micro‐hardness of the laser‐treated surface increases almost three times compared with the base material hardness. The presence of a dense layer and the formation of Cu₃N in the surface region contribute to the hardness enhancement at the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface modification and wear test of carbon steel by plasma electrolytic nitrocarburizing

Plasma electrolytic nitrocarburizing (PEN/C) was applied to the surface of carbon steel under the boiling condition of saturated urea electrolyte. In addition to the general effect of the bath temperature, different applied voltages and processing times were also considered in this new process. Optical and scanning electron microscopy, X‐ray diffraction, microhardness and pin‐on‐disc wear tests were used to characterize the PEN/C‐treated surfaces. A mixture of θ‐(Fe₃C) and ε‐(Fe_2–3N) was found in the compound layers. At certain conditions, dense surface layers with minimum porosity were observed at the top of the samples. The boiling condition resulted in special character of the compound layers on the surface. The layers consisted of some irregularities grown inward the samples andaffected the characteristics of the surface layers. The microhardness of the PEN/C‐treated layers increased up to 1280 HV0.1, which was 3 to 4 times higher than that for untreated material and higher than that obtained by other investigators (750 HV0.1). PEN/C decreased the wear loss of carbon steel significantly due to the change of the adhesive wear of untreated material to the abrasive mode of treated surfaces. The major advantage of this technique was a higher growth rate of the nitrocarburized layers and a more significant improvement in the tribological performance of the treated samples if compared to similarly oriented surface treatments. Copyright © 2011 John Wiley & Sons, Ltd.     

Synergetic effect of sol–gel silica coating and physical/chemical pre-treatment on the oxidation behavior of Ti-6Al-4V alloy

The Ti-6Al-4V alloy was treated in concentrated phosphoric acid solution and by powder blasting, respectively, subsequently coated by silica using sol–gel dip-coating technique. A barrier layer of titanium pyrophosphate (TiP₂O₇) was synthesized at the Ti-6Al-4V substrate surface after the heat treatment. XRD and SEM/EDS analysis revealed that an amorphous silica coating was formed on the alloy. The isothermal and cyclic oxidation behavior of the treated alloy with silica coating and the corresponding bare alloy was investigated at 600 °C in static air to investigate the synergetic effect of the SiO₂ coating and surface treatment on the oxidation resistance of the alloy by thermogravimetry. The average parabolic rate constants of the treated specimens with silica coating were greatly reduced. The stratified oxide layer formed on the bare alloy, while thinner oxide layer formed on the treated alloys with silica coating. The oxidation resistance of the present alloy was improved. The effect of silica coating on the microhardness of the substrate was investigated.     

Special features of preparation of nanosized zirconium diboride powders of various dispersity

Products of the zirconium powder reaction with amorphous boron in a Na₂B₄O₇ ionic melt at 650–850°C and those of the ZrCl₄ reaction with NaBH₄ at 300–725°C have been studied by means of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, and elemental analysis. At temperature ≥750°C, single-phase ZrB₂ with the particle size of 60–80 nm is formed in a Na₂B₄O₇ ionic melt, whereas the ZrB₂ powder obtained via the reaction of ZrCl₄ with NaBH₄ at temperature ≥575°C consists of particles differing in the shape, some of which are close to spherical with diameter of 10–35 nm.     

Post‐oxidizing effects on surface characteristics of salt bath nitrocarburized AISI 02 tool steel type

The effect of post‐oxidizing treatment on the characteristics of modified surface layers produced by salt bath nitrocarburizing on the industrial American Iron and Steel Institute (AISI) 02 tool steel types is investigated. Nitrocarburizing treatment is performed for 6 h and 8 h at 570 °C and post‐oxidizing treatment for 30, 60 and 90 min at 520 °C, using argon–steam mixture. Formed layers are characterized by their basic properties such as thickness layer, depth, surface hardness and wear resistance. Detailed estimation of the modified metal surface quality, in terms of chemical composition, formed phases, microstructures and diffusion mechanisms are performed by metallographic techniques, EDX, X‐ray diffraction, scanning electron microscopy (SEM) and glow discharge optical electron spectroscopy (GDOES). The corrosion resistance was investigated in 0.4 M H₂SO₄ solutions, using steady‐state electrochemical polarization methods. The obtained results revealed the existence of a superficial oxide layer which consists of magnetite (Fe₃O₄) and hematite (Fe₂O₃) and the presence of an ε‐phase associated with a small amount of γ′‐phase. Important improvements in wear, microhardness and corrosion resistance occur after these treatments and it is specifically concluded that the sole application of a nitrocarburizing treatment does not significantly ameliorate the corrosion resistance of the as‐received steel. In fact, post‐oxidation treatment contributes to increase corrosion resistance by forming a dense magnetite layer and at the same time, it partially covers the compound layer pores. Copyright © 2009 John Wiley & Sons, Ltd.     

Reduced curing kinetic energy and enhanced thermal resistance of phthalonitrile resins modified with inorganic particles

The effects of inorganic particles such as Al₂O₃ and B₄C on the solidification kinetics and heat resistance of phthalonitrile resin were investigated. The properties of the blends and the cured products were tested by rheometer, differential scanning calorimetry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The results revealed that B₄C and Al₂O₃ inorganic particles could prolong the gel time of phthalonitrile resin and broaden the processing window. The curing kinetic analysis showed that the presence of the particles could significantly reduce the curing activation energy of phthalonitrile resins by 72.38 kJ/mol down to 43.03 kJ/mol. Meanwhile, the heat resistance of the phthalonitrile resin was improved. Among them, the blend system combined with 30% B₄C showed prominent thermoresistance. And while the T_d5% weight loss temperature was 600°C, char yield at 1000°C was higher than 86% under nitrogen atmosphere; while the T_d5% weight loss temperature was 581°C, char yield at 1000°C was higher than 80% under air atmosphere. Hence, the resulting resins were good candidate matrix of high‐temperature structural composites.     

Preparation of poly(p‐oxybenzoyl) crystals using direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides

Poly(p‐oxybenzoyl) (POB) crystals were prepared by reaction‐induced crystallization during direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides. Polymerizations were carried out at 300 °C in dibenzyltoluene at a concentration of 1% with three kinds of anhydrides of boronic acid such as 3,4,5‐trifluorophenylboronic acid (TFB), 4‐methoxyphenylboronic acid (MPB) and 4‐biphenylboronic acid (BPB). The POB crystals were formed as precipitates in the solution and the morphology was considerably influenced by both the structure of the boronic anhydride and its concentration (c_B). Needle‐like crystals were firmed in the presence of TFB anhydride (TFBA) at c_Bs of 5 and 10 mol % by the spiral growth of lamellae. Spherical aggregates of slab‐like crystals were formed at c_Bs from 50 to 100 mol %. The polymerization with MPB anhydride and BPB anhydride (BPBA) also yielded the needle‐like crystals at c_Bs of 50 and 5 mol %, respectively. The polymerization with TFBA at lower c_B was favorable to prepare the needle‐like crystal. Molecular weight was also influenced by the structure of the boronic anhydride and c_B. M_n increased generally with c_B and BPBA gave the highest M_n of 14.7 × 10³ at c_B of 100 mol %. The loose packing of the molecules in the crystal caused by the bulkiness of the end‐groups made the polymerization in the crystals more efficiently. Morphology and molecular weight of the POB crystals could be controlled by the chemical structure and the content of boronic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Controlled synthesis,characterization and thermal properties of Mg<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>

Optimum conditions for synthesizing monoclinic and triclinic Mg₂B₂O₅ compounds by high-temperature solid-state reactions were investigated. Mixtures composed of boric acid and magnesium oxide at MgO:B₂O₃ mole ratios of 1:0.25, 1:0.5 and 1:1.5 were heated for 1 hour at temperatures between 600–1050°C and the formed phases were identified by XRD analysis. Monoclinic Mg₂B₂O₅ was formed by heating at 850°C for 4 hours together with minimum amounts of triclinic Mg₂B₂O₅, while triclinic Mg₂B₂O₅ was formed as a single phase at 1050°C for the same reaction time. The products obtained at optimum conditions were subjected to a series of tests to determine their chemical compositions, particle size distributions, surface area values, IR spectra and TG/DTA patterns.      

Microscopic structures of the B7 phase: AFM and electron microscopy studies

A wide variety of morphologies, such as screw‐like filaments, ribbons, etc., have been observed in polarizing microscopy studies of the B₇ phase in a melt or with free surface. In this paper, we present the results of AFM and scanning electron microscopy measurements of structures formed by a columnar‐type B₇ phase. These measurements are aimed at elucidating the three‐dimensional structure of the observed patterns.     

Characteristics of Plasma-Electrolytic Oxide Coatings Formed on Aluminum and Titanium in Electrolytes with Siloxane Acrylate and Particles of Vanadium,Boron, and Aluminum Oxides

It is shown that aqueous suspension-emulsion electrolytes containing sodium silicate, siloxane-acrylate emulsion, and dispersed particles of oxides are promising for direct synthesis by the plasma-electrolytic oxidation method of coatings with multicomponent composition on titanium and aluminum. The formation processes, composition, and structure of the coatings were studied in electrolytes with 1–4-μm particles of V₂O₅, B₂O₃, or Al₂O₃. The average content of metals and nonmetals of dispersed particles in the surface part of the coatings is ~1–2 at %. The coatings have a developed surface morphology and contain in the surface part up to 50–73 at % carbon.     

Dramatic Fluorescence Enhancement of Bare Carbon Dots through Facile Reduction Chemistry

Reduction of bare carbon dots (CDs) in aqueous NaBH₄ solution is a facile and effective approach to enhance their fluorescence without any surface coverage. CDs are treated with dilute aqueous NaBH₄ solutions, enhancing their quantum yields (QYs) successfully from 1.6 % to 16 % which is comparable to semiconductive QDs in aqueous environments. If pristine CDs are treated hydrothermally prior to reduction by NaBH₄, QYs reach 40.5 %. This value is among the highest QYs reported for bare CDs in the literature. The approach to enhance fluorescence through chemical reduction is generally applicable to other kinds of CDs synthesized by various methods. Alteration of the chemical structure of the CDs by NaBH₄‐reduction is analyzed by ¹³C NMR, X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy, which demonstrate that the carbonyl group content is decreased after NaBH₄‐reduction, whereas the number of sp³‐type carbon defects is increased. The valence‐band maxima (VBM) near the surface related to the surface energy bands of the CDs are estimated by XPS. VBM data show a semiconducting layer on the surface of the CDs, and the VBM of the CDs decrease with increasing NaBH₄‐reduction time. The layered graphite structures in the cores of the CDs are clearly observed by transmission electron microscopy (TEM). CDs could perhaps be regarded as semiconductive surface defect layers formed by chemical erosion over conductive graphite cores. Chemical reduction by NaBH₄ changes the surface‐energy bands of the CDs, thus, enhances their fluorescence. The fluorescence properties of aqueous NaBH₄‐reduced CDs are also studied for possible biological applications.     

Oxygen‐Controlled Catalysis by Vitamin B12‐TiO2: Formation of Esters and Amides from Trichlorinated Organic Compounds by Photoirradiation

An oxygen switch in catalysis of the cobalamin derivative (B₁₂)‐TiO₂ hybrid catalyst for the dechlorination of trichlorinated organic compounds has been developed. The covalently bound B₁₂ on the TiO₂ surface transformed trichlorinated organic compounds into an ester and amide by UV light irradiation under mild conditions (in air at room temperature), while dichlorostilbenes (E and Z forms) were formed in nitrogen from benzotrichloride. A benzoyl chloride was formed as an intermediate of the ester and amide, which was detected by GC‐MS. The substrate scope of the synthetic strategy is demonstrated with a range of various trichlorinated organic compounds. A photo‐duet reaction utilizing the hole and conduction band electron of TiO₂ in B₁₂‐TiO₂ for the amide formation was also developed.     

Preparation and Properties of Nickel and Iron Oxides obtained by Calcination of Layered Double Hydroxides

A constant pH precipitation method has been applied to obtain solids with Ni/Fe molar ratios of 2/1, 3/2, 1/1, 2/3, and 1/2. In all cases, a phase with the hydrotalcite‐like structure is obtained, containing Ni^II and Fe^III in the brucite‐like layers and carbonate in the interlayer, and, for samples with a Ni/Fe molar ratio lower than 2/1, amorphous hydrated iron oxides, undetected by X‐ray diffraction, are also formed. The solids have been characterized by element chemical analysis, powder X‐ray diffraction, differential thermal analysis, thermogravimetric and differential thermogravimetric analysis, FT‐IR spectroscopy, temperature‐programmed reduction and assessment of specific surface area by nitrogen adsorption at ?196 °C. In all cases reduction leads to zero‐valent state for the metals, reduced nickel particles probably favouring reduction of Fe^III species; the specific surface area increases with the iron content, probably due to the amorphous nature of the hydrated iron oxides formed. Calcination at 1200 °C in air leads to well crystallized solids, formed by NiFe₂O₄ spinel and, additionally, rocksalt‐type NiO for Ni/Fe ratios larger than 1/2. In this way, solids with tailored compositions of these two phases can be prepared.     

Block and star block copolymers by mechanism transformation. VI. Synthesis and characterization of A4B4 miktoarm star copolymers consisting of polystyrene and polytetrahydrofuran prepared by cationic ring‐opening polymerization and atom transfer radical polymerization

The synthesis of A₄B₄ miktoarm star copolymers, where A is polytetrahydrofuran (PTHF) and B is polystyrene (PSt), was accomplished with orthogonal initiators and consecutive cationic ring‐opening polymerization (CROP) and atom transfer radical polymerization (ATRP). The compound formed in situ from the reaction of 3‐{2,2‐bis[2‐bromo‐2‐(chlorocarbonyl) ethoxy] methyl‐3‐(2‐chlorocarbonyl) ethoxy} propoxyl‐2‐bromopropanoyl chloride [C(CH₂OCH₂CHBrCOCl)₄] with silver perchlorate was used to initiate the CROP of tetrahydrofuran. The obtained polymer contained four secondary bromine groups at the α position to the original initiator sites and was used to initiate the ATRP of styrene with a CuBr/2,2′‐bipyridine catalyst to form a C(PTHF)₄(PSt)₄ miktoarm star copolymer. The miktoarm copolymer was characterized by gel permeation chromatography and ¹H NMR. The macroinitiator C(PTHF)₄Br₄ was hydrolyzed to afford PTHF arms. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2134–2142, 2001     

Nanostructured ZrO2 and Zr‐C‐N Coatings from Chemical Vapor Deposition of Metal‐Organic Precursors

Nanocrystalline zirconium carbonitride (Zr‐C‐N) and zirconium oxide (ZrO₂) films were deposited by chemical vapor deposition (CVD) of zirconium‐tetrakis‐diethylamide (Zr(NEt₂)₄) and ‐tert‐butyloxide (Zr(OBu^t)₄), respectively. The films were deposited on iron substrates and characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). The Zr‐C‐N films show blue, golden brown or bronze colours, with colour stability depending upon the precursor composition (pure metal amide or mixed with Et₂NH). The deposition temperature showed no pronounced effect on the granular morphology of the Zr‐C‐N films. The XRD data of the films correspond to the formation of carbonitride phase whereas the XPS analyses revealed a strong surface oxidation and incorporation of oxygen in the film. The films deposited using a mixture of Zr(NEt₂)₄ and Et₂NH showed higher N content, better adhesion and scratch resistance when compared to films obtained from the CVD of pure Zr(NEt₂)₄. Subject to the precursor composition and deposition temperature (550‐750 °C), the microhardness values of Zr‐C‐N films were found to be in the range 2.11‐5.65 GPa. For ZrO₂ films, morphology and phase composition strongly depend on the deposition temperature. The CVD deposits obtained at 350 °C show tetragonal ZrO₂ to be the only crystalline phase. Upon increasing the deposition temperature to 450 °C, a mixture of tetragonal and monoclinic modifications was formed with morphology made up of interwoven elongated grains. At higher temperatures (550 and 650 °C), pure monoclinic phase was obtained with facetted grains and developed texture.     

Synthesis of Highly Dispersed Zirconium Diboride for Fabrication of Special-Purpose Ceramic

Reduction of zirconium dioxide with boron carbide and nanofibrous carbon in argon yielded a highly dispersed powder of zirconium diboride. Characteristics of zirconium diboride powders were examined by various analytical methods. The material obtained is represented by a single phase, zirconium diboride. Powder particles are for the most part aggregated. The average size of particles and aggregates is 10.9–12.9 μm with a wide size distribution. The specific surface area of the samples is 1.8–3.6 m² g^–1. The oxidation of zirconium diboride begins at a temperature of 640°C The optimal synthesis parameters were determined: ZrO₂: B₄C: C molar ratio of 2: 1: 3 (in accordance with stoichiometry), process temperature 1600–1700°C, synthesis duration 20 min.