Study on the formation of core–rim structure in Ti(CN)-based cermets

Ti(CN)-based cermets were synthesized from Ti(CN)WCMo₂CTaCNiCo composite powders by vacuum-low pressure sintering. The phase evolution and the formation of core–rim structure in Ti(CN)-based cermets were systemically investigated during difference reaction stages at 950–1450 °C. The results show that the secondary carbides such as Mo₂C and TaC are begun to dissolve at 950 °C, finished at 1150 °C, and the solution temperature of WC phase is range from 1150 to 1300 °C, which are result in increase of the cermets lattice constant. At the same time, the inner rim is also formed, and Ti(CN)-based cermets are composed of (Ti, W, Mo, Ta)(CN) and Ni/Co solid solution phase. While at 1350 °C, it was found that the outer rim began to precipitate from the liquid phase with the metal binder. With increase of sintering temperature, mechanical properties of cermets improved obviously were related intimately to the increase of outer rim thickness.     

Effects of deep cryogenic treatment on the microstructure and properties of WCFeNi cemented carbides

The effects of deep cryogenic treatment on microstructure and properties of WCFeNi cemented carbides were investigated in this paper. The WCFeNi cemented carbides were deep cryogenically treated at about − 196 °C for 2, 12 and 24 h. In order to study the phase composition and quantitative analysis of the deep cryogenically treated specimens, a selective electrolytic corrosion was used. The internal friction, mechanical properties, wear properties and corrosion behavior of the deep cryogenically treated WCFeNi cemented carbides were measured. The results show that with an increase in deep cryogenic treatment time, martensitic phase transformation of binder phase from γ → α has taken place, the α-(Fe,Ni) phase content in the binder phase gradually increases from 12.7% to 86.8% (wt.%) and W particles precipitate from the binder phase. Compared with the as-sintered specimens, the maximum hardness and transverse rupture strength of the specimens treated by cryogenic environment increase by almost 20% and 7.7%, respectively. The fracture toughness decreases from 25.7 MPam^½ for as-sintered specimens to 19.6 MPam^½ for the alloy after deep cryogenic treatment. The wear rate and friction coefficient decrease by almost 56% and 17.2%, while the corrosion resistance slightly decreases compared with the alloys without deep cryogenic treatment. The change of the properties can be primarily attributed to the fact that the martensite phase transformation from γ-(Fe,Ni) to α-(Fe,Ni) and precipitation of W particles in the binder phase improve the hardness and strengthen the binder phase during the deep cryogenic treatment.     

Effect of boron on the thermodynamic stability of amorphous polymer-derived Si(B)CN ceramics

The reason for the higher thermal persistence of amorphous polymer-derived SiBCN ceramics (T ～ 1700–2000 °C) compared to SiCN ones (T ～ 1500 °C) has been a matter of debate for more than a decade. Despite recent experimental results which indicate a major kinetic effect of boron on the thermal persistence of the ceramics, no experimental investigation of the thermodynamic stability of the materials has been reported. In this work, we present measured energetics of a series of the amorphous ceramics with various boron contents (0–8.3 at.%) using high-temperature oxidative drop-solution calorimetry. Through measurement of the drop-solution enthalpies in molten sodium molybdate at 811 °C, the formation enthalpies of the amorphous ceramics from crystalline components (SiC, BN, Si₃N₄, C) at 25 °C were obtained and found to be between ?1.4 and ?26.6 kJ g-atom^?1. The determined enthalpy data plus the estimated positive entropy of formation values point to the thermodynamic stability of the amorphous ceramics relative to the crystalline phases, but such stabilization diminishes with increasing boron content. In contrast, the higher boron content increases the temperature of Si₃N₄ crystallization despite less favorable energetics for the amorphous phase, implying more favorable energetics for crystallization. Thus the so-called “stability” of SiBCN ceramics in terms of persistence against Si₃N₄ crystallization appears to be controlled by kinetics rather than by thermodynamic stability.     

The influence of Cr and B additions on the mechanical properties and oxidation behaviour of L21-ordered Fe–Al–Ti-based alloys at high temperatures

Several Fe25AlTiX (X = Cr, B) L2₁-ordered (Heusler phase) alloys with 15 or 20 at.% Ti and varying Cr and B contents have been investigated with respect to their mechanical properties and their oxidation behaviour at elevated temperatures. The mechanical properties have been characterized by means of high-temperature compression tests, four-point-bending tests and creep tests at 750, 800 and 850 °C. The oxidation behaviour has been examined using thermogravimetric analysis at 800 °C in synthetic air. The results show that when Cr and B are added, the latter results in the formation of TiB₂, is beneficial for the creep resistance and has no influence on the still-excellent oxidation resistance. However, the alloys show rather high brittle-to-ductile transition temperatures, which can be lowered by the addition of TiB₂ as a result of grain refinement.     

Manufacture of a new kind diamond grinding wheel with Al-based bonding agent

A new kind diamond grinding wheel with Al-based bonding agent was prepared in this paper. The influence of sintering temperature to the relative density (R.D.), hardness and service life of diamond grinding wheels with AlSnTi, AlSnTiNiCo, AlSnTiNi and AlSnNiCo bonding agent was studied. The microstructure of different bonding agent sintered at different temperature was observed. The service life of the Al-based grinding wheels was compared with Cu-based or resin-based ones. The results showed that the AlSnTiNiCo is the best composition system in this research. The best sintering temperature is 300 °C. The sample has a high relative density after sintered at 300 °C. The retention of Al-based bonding agent to diamond grit is strong. The service life of this Al-based diamond grinding wheel is about three times as long as that of resin-bonded grinding wheel.     

Designed fabrication of hard CrCr2O3Cr7C3 nanocomposite coatings for anti-wear application

Nanocrystalline CrCr₂O₃Cr₇C₃ composite coatings were fabricated by electrodeposition followed by thermal treatment. The structures of coatings were investigated using high-resolution transmission electron microscopy and X-ray diffraction analysis. The composition, elemental chemical state, mechanical properties and wear resistance of coatings were determined using energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, nanoindentation and oscillating friction-wear testing, respectively. Wear tracks were observed by scanning electron microscopy. The results show that the as-deposited coating exhibits amorphous structure. The subsequent thermal treatment at 600 °C induces the crystallization and the generation of nanoscale Cr₂O₃ and Cr₇C₃ particles in the Cr-matrix, which results in the hardness of the coating increasing to 21 GPa with slight increase in elastic modulus. Owing to the compromise between high hardness and low elastic modulus, the obtained CrCr₂O₃Cr₇C₃ composite coating exhibits excellent wear resistance.     

Structural,mechanical and electrical-contact properties of nanocrystalline-NbC/amorphous-C coatings deposited by magnetron sputtering

Niobium-carbide nanocomposite coatings with a carbon content varying from 43 to 64 at.% were deposited by dual DC magnetron sputtering. X-ray diffraction, x-ray photoelectron spectroscopy and electron microscopy showed that all coatings consisted of nanometer sized NbC grains embedded in a matrix of amorphous carbon. Mechanical properties and electrical resistivity showed a strong dependency on the amount of amorphous carbon (a-C) and NbC grain size in the coating. The highest hardness (23 GPa), elastic modulus (295 GPa) and the lowest resistivity (260 μΩ cm) were measured for the coating with about 15% of a-C phase. Contact resistance measurements using a crossed cylinder set-up showed lowest contact resistance for the coating containing 33% a-C (140 μΩ at a contact force of 100 N), which is comparable to a Ag reference (45 μΩ at a contact force of 100 N). Comparison with TiC-based nanocomposites studied under similar conditions showed that the NbC system has less tendency to form a-C and that lowest contact resistance is obtained at comparable amounts of a-C phase in both material systems (33% for NbC compared to 35% for TiC). With these good electrical contact properties, the NbC nanocomposites can be considered as a potential material for electrical contact applications.     

Well defined carbazole-based hole-transporting amorphous molecular materials

Monodisperse carbazole-based oligomers have been synthesized via CN bonds formation by the modified Ullmann reaction. The full characterization of their structure is presented. These derivatives are highly thermally stable amorphous compounds with glass transition temperatures of 167–171 °C and thermal decomposition temperatures of ca. 400 °C. Amorphous films of the materials were fabricated and their hole-transporting properties were tested in a light emitting device with Alq₃ as an electroluminescent and electron-transporting material.     

Synthesis and characterization of IIa-type S-doped diamond in FeNi catalyst under high pressure and high temperature conditions

In this work, service through nitrogen getter we have successfully synthesized sulfur(S) doped IIa-type diamond single crystals at 1400 °C and 5.5 GPa in FeNi-C system. We found that the synthetic diamond are mainly composited of the {111} faces because of the addition of S in the synthesis system. In addition, the color of our produced diamond changed from white to light brown and the shape of diamond changed from Cub-Octahedron to Octahedron with increase of S addition in the FeNi-C system. Furthermore, we notice that many kinds of defects, such as stratiform defects, craters and inverted pyramid defects appeared on the surfaces of diamonds induced by the additive of S. The FTIR results show that the obtained diamond crystals are IIa-type diamonds, containing less than 1 ppm nitrogen. XPS measurement indicates that S was successfully incorporated into our produced diamond lattice in the SC and CSO forms. Raman spectra reveal that the as-growth S-doped IIa-type diamond single crystals possess a high-quality sp³ structure. Photoluminescence (PL) spectra demonstrate that nitrogen-vacancy is formed during diamond growth. Our work also helpful for understanding the formation of nature diamond.     

New 1,3,4-oxadiazole containing materials with the effective leading substituents: The electrochemical properties,optical absorptions,and the electronic structures

The electrochemical and optical absorption properties as well as the thermal stabilities of a series of 1,3,4-oxadiazole dimers 1,3-bis[2-(4-methylphenyl)-1,3,4-oxadiazol-5-yl]benzene (OXD-X) and its derivatives with the different alkoxy substituents on the central benzene ring such as O(CH₂)_n−1CH₃ (OXD-An, n = 3, 7, 10, 16), O(CH₂)_nOC₆H₅CH₃ (OXD-Bn, n = 6), and O(CH₂)_nOC₆H₄NNC₆H₄OCH₃ (OXD-Cn, n = 3, 6, 10) are studied. The DSC measurements exhibit dramatically elevated glass transition temperatures for OXD-X and OXD-An (120–245 °C) in contrast to the well-known PBD (∼60 °C), indicating the better thermal stabilities. From OXD-X to OXD-An, OXD-Bn or OXD-Cn, the cyclic voltammograms and UV–vis absorption spectroscopy display significant variation, in which the later three species show additional lower energy absorptions at λ > 330 nm compared with OXD-X and particularly, both of OXD-Bn and OXD-Cn display an oxidation peak at ∼+1.0 V and two successive redox reactions occur for OXD-Cn. Theoretically, the B3LYP/6-31g calculations explore that these extraordinary properties are due to the influence of the substituents on the benzene ring to the frontier molecular orbital distribution, especially the O(CH₂)_nOC₆H₄NNC₆H₄OCH₃ groups in OXD-Cn deduce the new pictures of the frontier molecular orbitals, causing the electron-transporting behavior originally happening on the molecular skeleton transferred to the side chain.     

Nitridation of Ti6Al4V alloy under ultrasonic impact treatment in liquid nitrogen

X-ray photoelectron spectroscopy and scanning electron microscopy with energy dispersive X-ray microanalysis were employed to study the effect of mechanical treatment on the surface chemical state, composition and morphology of commercial Ti6Al4V alloy. It has been demonstrated that ultrasonic impact treatment of Ti6Al4V in a liquid nitrogen (LN2) environment results in substantial grain refinement and formation of nitrides and oxynitrides of all the alloy components. The mechanochemical synthesis of the nitrides and oxynitrides from LN2 was found to efficiently occur not only within the impacted area but outside it as well. The layer with a high content of incorporated nitrogen and average atomic ratio N/Ti = 0.94 was estimated to be at least ～2 μm thick. As a result of the combined effect of cryogenic deformation, nanoscale grain refinement and nitriding, a 3-fold increase in the microhardness of Ti6Al4V alloy is obtained. The impact treatment in LN2 was observed to be accompanied by material transfer from the hardened steel pin to the alloy followed by incorporation of the pin components into Ti6Al4V and formation of the FeN, FeC and TiC bonds.     

High-pressure infrared absorption in Cs2TCNQ3 crystals grown under magnetic field

Pressure dependence of infrared absorption has been measured in Cs₂TCNQ₃ single crystals grown under magnetic field of 5 T (5 T crystals). The behavior of the CCN as well as CH stretching modes suggest that there occurs a phase transition which resembles to the one related to the insulator to metal transition in the crystals grown without magnetic field (0 T crystals). This transition, however, takes place at 4.1 GPa, slightly higher than the case of 0 T crystals. The charge transfer degree of the neutral and radical molecules are found to be ρ = 0.30–0.37 and 0.81–0.85, respectively, which are significantly different from that of 0 T crystals. These differences are suggested to arise from the changes in the relative positions of the TCNQ molecules, as indicated from the behavior of the EMV mode.     

Electrochemical and quantum chemical studies of some azomethine compounds as corrosion inhibitors for mild steel in 1 M hydrochloric acid

The corrosion inhibition effect of new azomethine compounds: PhNNC (COCH₃)NC₆H₄Y {Y = OCH₃ (SB₁), CH₃ (SB₂), H (SB₃), Br (SB₄) and Y = Cl (SB₅)} on mild steel in 1 M HCl, was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemistry analysis. It has been found that the inhibition efficiency increased with increasing inhibitor concentration. The polarization curves showed that these Schiff bases function as mixed inhibitors. The adsorption of studied compounds on mild steel surface was found to follow the Langmuir isotherm. Molecular modeling was used to correlate corrosion inhibition properties and calculated quantum chemical parameters.     

Optical,mechanical and etch properties of amorphous carbon nitride films grown by plasma enhanced chemical vapor deposition at room temperature

Amorphous carbon nitride (a-CN) films were grown on Si(1 0 0) and SiO₂/Si(1 0 0) substrates by plasma enhanced chemical vapor deposition at room temperature using gas mixtures of CH₄ and N₂. The as-deposited films showed two bond structures of CN and CN, and with increasing the N₂ content the bond structure changed to graphite-like structure. All the samples showed low optical absorption coefficient (k < 0.15) in the wavelength range of 300–800 nm. The a-CN films exhibited a good resistance to etching (i.e. higher selectivity over SiO₂), which indicates a potential use of a-CN films as a new hard mask material.     

Strong stacking behavior and large third-order nonlinear optical susceptibility χ(3) of head-to-head-type poly(3-alkynylthiophene-2,5-diyl), HH-P3(CCR)Th

The head-to-head-type poly(3-alkynylthiophene-2,5-diyl) HH-P3(CCR)Th has been shown to exhibit a strong tendency to self-assemble. The UV–vis spectrum of HH-P3(CCDec)Th (Dec = decyl) in 1,2-dichlorobenzene at 131 °C showed a peak at λ_max = 520 nm, which shifted to λ_max = 553 nm at 25 °C, with a shoulder peak at 608 nm. However, the UV–vis spectrum of an HH-P3(CCDec)Th film showed a more pronounced shift in its UV–vis absorption peak to a longer wavelength. These phenomena are the characteristics of the self-assembly of the polymer molecule. The HH-P3(CCDec)Th film had a large third-order nonlinear optical susceptibility χ⁽³⁾ of 3.6 × 10⁻¹¹ esu.     

Enhanced third-order nonlinear optical property of poly(3-decayl)thiophene films modified by N+ ion implantation

Poly(3-decayl)thiophene (P3DT) films implanted by 30 keV nitrogen ions (N⁺) with the dose range of 10¹⁵–10¹⁷ ions/cm² were characterized by FTIR-ATR spectra, which showed that the C–H bonds of the P3DT films were largely broken and new bonds like CC, CN and CN were formed as the increasing ion fluences. The third-order nonlinear optical susceptibilities (χ⁽³⁾) were measured by degenerate four-wave mixing (DFWM) technique at 532 nm. The results demonstrated that the (χ⁽³⁾) value of P3DT films was maximized to 2.61 × 10^?9 esu at an ion dose of 5.73 × 10¹⁶ ions/cm², which was almost four times larger than that of the pristine film. The enhanced third-order nonlinear properties may attribute to the enlarged expansion coefficient of the bombarded films at proper N⁺ ions dose.     

Low temperature molten salt preparation of molybdenum nanoparticles

Pure molybdenum (Mo) nanoparticles (NPs) were synthesized by a novel molten salt technique using Na₂MoO₄ and Al as starting materials and NaCl, KCl and NaF to form a reaction medium. The effects of salt type, reaction temperature and salt to reactant ratio on the synthesis of Mo NPs were investigated in detail. Phase pure Mo NPs with a crystalline size of about 46 nm were synthesized at as low as 650 °C which was much lower than that required by other conventional reduction methods. Among the salts tested, the NaClKClNaF ternary salt showed the best accelerating effect on the low temperature Mo NPs formation, and the optimal weight ratio of salt to reactant was 1.0:1.0. The “dissolution-precipitation mechanism” played a dominant role in the molten salt synthesis of Mo NPs.     

Adsorption and corrosion inhibition of phytic acid calcium on the copper surface in 3 wt% NaCl solution

The adsorption and corrosion protection effect of phytic acid calcium (PAC) film on the copper surface in 3 wt% NaCl solution was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Raman spectroscopy. Polarization curves indicate that PAC is a mixed inhibitor, affecting both cathodic and anodic corrosion currents. The inhibition efficiency of PAC film reached 92.53% at an optimized condition. Adsorption of PAC molecules on the surface followed Langmuir adsorption isotherm and the standard Gibbs energy of −37.32 kJ mol⁻¹ indicated a chemisorptive way. Raman studies suggested that PAC molecule chemically anchored at the surface via PO groups.     

Structural studies of zinc oxide films grown by RF magnetron sputtering

The main purpose of this study consists of researching the piezoelectric characteristics of ZnO films grown by RF magnetron sputtering in reactive plasma. In this way the influence of deposition parameters, such as RF power and plasma oxygen content, on the structural and morphological properties of the films are analyzed.ZnO films are grown on SiO₂/Si(1 0 0) substrate using a zinc oxide target. Different RF powers (from 50 to 200 W) and reactive plasmas (from 5 to 15% of oxygen content) have been tested and optimized to produce good quality films suitable for fabricating surface acoustic wave (SAW) devices.Crystalline structures and morphological characteristics of the films are investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively.SAW devices are fabricated with “IDT(Al)/ZnO/SiO₂Si” configuration. The frequency response of these devices is measured for their characterization.     

Supramolecular associations of poly(ketanil)s with sulfonic acid derivatives of benzenetricarboxamide via Brönsted acid–base interactions: Preparation,spectroscopic morphological and thermal investigations

Supramolecular aggregations have been obtained via ionic self-assembly of conjugated poly(ketanil)s and sulfonic acid derivatives of benzenetricarboxamides. To achieve this goal a new protonating molecule has been synthesized which is a derivative of 1,3,5-benzenetricarboxamide with sulfonic acid group at each of its ends. 1,3,5-benzenetricarboxamides of C₃ symmetry tend to form ordered supramolecular aggregations via π-stacking and this property is retained in their sulfonic acid derivative. Because of their Brönsted acid nature the new molecules can additionally associate conjugated polymers with basic centers such as poly(ketanil)s. Depending on the processing solvent used (MC or DMA) 1,3,5- the sulfonic acid derivative of benzenetricarboxamide and its associations with poly(ketanil)s form aggregations of spherullite-like or feather-like morphologies as evidenced by polarized optical microscopy and atomic force microscopy. The similarity of this supramolecular organization is also corroborated by DSC studies which in both cases show endothermic type transitions of the same origin. The supramolecular acid–base associations are semi-crystalline in nature and exhibit good mechanical properties at room temperature because of a rather low T_g, in the vicinity of 300 K. This unusual lowering of T_g by ca. 90 K as compared to the case of poly(ketanil)s in their basic form is caused by the plasticizing effect of the protonating agent. Finally polyketanil–1,3,5-benzenetricarboxamide sulfonic acid derivatives show tunable photoluminescence which depends on the solvent and SO₃H/CN molar ratio.