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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Influence of alloy composition and thermal history on carbide precipitation in γ-based TiAl alloys

Carbide precipitation in TiAl alloys with different alloying element additions and thermal history was investigated by transmission electron microscopy and high energy X-ray diffraction. The results reveal that Nb addition in TiAl alloys does not increase the carbon solubility in the γ matrix significantly. With increasing carbon concentration in the alloys, a splitting of the P-type carbides takes place earlier in the course of ageing at 800 °C and the formation of H-type carbides is promoted. For a nearly single γ phase alloy Ti51Al5Nb0.5C, H-type carbides are the thermodynamically stable phase. However, with decreasing Al concentration, P-type carbides become thermodynamically stable at low carbon concentration (below 1%) in Ti45Al and Ti45Al5Nb alloys. It is feasible to achieve high thermodynamical stability of the P-type carbides in TiAl alloys through controlling alloying elements.     

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.     

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.     

Superhard and tougher SiC/diamond-like-carbon composite films produced by electron beam physical vapour deposition

SiC/diamond-like carbon (DLC) composite films have been produced on metal substrates via electron beam physical vapour deposition process with various substrate temperatures. The films deposited at 700 °C contain a DLC matrix and nanocrystalline 3CSiC. However, the films deposited at 900 °C contain a 3CSiC matrix and DLC plus nanocrystalline diamond. Both nanoindentation and Hysitron testing have shown that the Young’s moduli and hardnesses of the films increased with the substrate temperature. The hardness could reach ～60 GPa in some parts of the films produced at 900 °C. Meanwhile, the fracture toughness, measured using a micro-beam bending technique, reached 9.2 ± 2 MPa^1/2 for such a composite film. Both high hardness and toughness could be explained by the unique microstructure of the composite film.     

Atom site preference and γ′/γ mismatch strain in NiAlCoTi superalloys

The structure and chemistry of NiCoAlTi quaternary superalloys are investigated at the microstructural and atomic scale. Atom probe tomograghy (APT) is used to quantify phase compositions and elemental partitioning behavior. Using aberration corrected electron microscopy, the site occupancy of the atoms within the A₃ B structure (L1₂–type) γ′ phase is determined via atomic resolution energy dispersive X-ray spectroscopy (EDX). Ni is observed to preferentially occupy the A sub-lattice positions for all alloys, while Al and Ti occupy the B sub-lattice. In contrast, Co's site preference changes from a random distribution to the A sub-lattice as the alloy composition changes, in agreement with theoretical predictions from literature. Finally, the lattice strain across the γ′/γ interfaces is measured as a function of alloy composition.     

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.     

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.     

Thermomechanical modeling and simulation of aluminum alloy behavior during extrusion and cooling

The purpose of this work is the modeling and simulation of aluminum alloys during extrusion processes. In particular, attention is focused here on aluminum alloys of the 6000 series (AlMg Si) and 7000 series (Al Zn Mg). In the current paper, a number of aspects of the structural simulation as well as that of extrusion as a thermomechanical process are considered. These aspects include contact and adaptive mesh refinement, heat transfer inside the billet, heat transfer between the workpiece and the container, frictional dissipation, mechanical energy and surface radiation. The friction is considered to model the so called “dead material zone”. The radiation constant has been estimated so that the results are close to the experimental results.     

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.     

First-principles investigation of magnetic properties and metamagnetic transition of NiCoMnZ(Z = In,Sn, Sb) Heusler alloys

We employed the density functional theory to investigate the structural, magnetic properties and metamagnetic transition on Mn and Co doped-Ni₂MnZ (Z = In, Sn, Sb) Heusler alloys. The calculated formation energy indicates that excess Mn and Co prefer to occupy Z and Ni sites, respectively. The energy difference between austenite and martensite phases exhibits a monotonic increase with Mn doping, and a decrease with Co doping, which are consistent with the trend of experimental martensitic transformation temperature. The evaluated magnetic exchange parameters show a strong dependence on Z element, which can be explained by the super-exchange interaction mediated by Z sp states near the Fermi level. Bond analysis of martensite phase reveals that the strength of MnSb bond is stronger than that of MnIn and MnSn bond and it explains the larger driving magnetic field in NiMnSb than NiMnZ(Z = In, Sn) is need for metamagnetic phase transformation. In addition, we predict NiCoMnZ (Z = Sn, Sb) alloys require a smaller compressive epitaxial strain for metamagnetic transition than NiCoMnIn alloys.     

Thermophysical properties of TiB2SiC ceramics from 300 °C to 1700 °C

In the present work, high-frequency induction heating is used to fabricate TiB₂SiC ceramics and the relative density was more than 97%, and then the thermophysical properties of TiB₂SiC ceramics were investigated in detail. The specific heat showed the weak dependence on the test temperature due to the presence of the interface gap because the relative density was not 100%. As the sintering temperature increased, the thermal diffusivity of TiB₂SiC ceramics increased, which was due to the increase of relative density and grain growth. The thermal conductivity of TiB₂SiC ceramics showed a marked increase with increasing grain size and relative density. This could be attributed to a reduction in the number of grain boundaries that interrupt the heat flow path, resulting in an increase in the mean free path of the phonons. Larger grains led to an increase of mean free path of the phonons and thus contributed to a further increase in thermal conductivity.     

Crystal structure and magnetic properties of an ionic multi-component complex of fullerene (OMTTF·I3)·C60: Comparison with OMTTF·I3 salts

A new ionic multi-component complex (OMTTF·I₃)·C₆₀ comprising neutral C₆₀ molecules and OMTTF⁺ and I₃⁻ ions has been obtained by the diffusion method. The complex has a layered structure with the alternation of closely packed hexagonal C₆₀ layers and the layers composed of OMTTF⁺ and I₃⁻ ions arranged in a chequer-like manner. The polycrystalline complex shows a strongly asymmetric EPR signal consisting of four components in the 4–293 K range attributable to OMTTF⁺. Temperature dependent magnetic susceptibility indicates an antiferromagnetic interaction of spins localized on OMTTF⁺ with an antiferromagnetic hump near 4.5 K. According to the one-dimensional Heisenberg antiferromagnet model the exchange interaction was estimated to be J/k_B = −3.3 K. Two possible pathways contribute to this interaction: through the diamagnetic I₃⁻ anions and the direct interaction between adjacent OMTTF⁺. The crystal structures of three phases of the OMTTF·I₃ salt are also presented.