Formation of Silicides and their Influence on the Structure and Properties of Cast Alloys of the Ti–18Nb–xSi System for Biomedical Purposes

Materials Science - We study new biomedical alloys of the Ti–18Nb– x Si system with 0.6–1.2 wt.% Si both in the as-cast state and quenched in water after holding at temperatures...     

Prediction of the Inversion Curve and the Maximum Value of μJ–T for Some Refrigerants

In the present work, the thermodynamic states of the inversion curve have been obtained using only p–v–T data. We have also shown a linear relationship between compressibility factor and pressure for each branch of the inversion curve. These lines can be used to find the maximum inversion pressure, P _in ^M . Finally, we have predicted the temperature at which the Joule–Thomson coefficient, _J–T, has its maximum value for each isobar, by using the specific heat capacity, isobaric expansivity, or compressibility factor.     

Electrochemical Properties of Nitride Phases in the Si3N4–Ca3N2and Si3N4–AlN–Ca3N2Systems

The electrical conductivity of silicon nitride and its solid solutions with calcium nitride and aluminum nitride was measured in the ranges 400–900 and 1000–1300°C. The conduction mechanisms were found to be substantially different in these temperature ranges. The Si₃N₄–Ca₃N₂solid solutions exhibited high ionic conductivity between 400 and 900°C. The densest and most oxidation-resistant materials were obtained in the Si₃N₄–AlN–Ca₃N₂system (Al introduced as fine powder and then nitrided).     

Effect of carbon content on the microstructure and properties of W–Si–C–N coatings fabricated by magnetron sputtering

A series of W–Si–C (4–5 at.%)–N nanocomposite coatings with different C contents have been deposited on Si wafer substrates by reactive magnetron sputtering of W–Si–C composite target in Ar + N₂ mixed atmosphere. Microstructure characteristics and mechanical properties of W–Si–C–N coatings were investigated in this paper. Results exhibited that W–Si–C–N coatings possess nanocomposite microstructure where nano-crystallites W₂(C, N) embedded in amorphous matrix of Si₃N₄/CNx/C. As the C content increased, the hardness and Youngs’ modulus of the W–Si–C–N coatings first increased and then decreased, reaching the maximum value of approximate 36 GPa and 382 GPa, respectively, for coatings containing 11.1 at.% C. All the coatings are in compressive stress state, ranging from 0.8 to 2.0 GPa. In addition, friction coefficient of the W–Si–C–N coatings considerably decreased with the increase of C content.     

p–T–x Phase Diagram of the Sb–O System

Vaporization processes in the Sb–O system are studied by Knudsen cell mass spectrometric measurements. The results indicate that Sb₂O₄ sublimes congruently and is the most stable oxide in the system. Experimental data are used to evaluate the enthalpies of formation of Sb₂O₃, Sb₂O₄, and Sb₆O₁₃ and to construct the p–T–x phase diagram of the Sb–O system.     

Influence of ion energies on the structure,composition, and properties of multilayer Ti–Al–Si–N ion-plasma-deposited coatings

It is established that the energy of deposited particles influences the structure, composition, and properties of multilayer nitride coatings consisting of alternating layers of nanocrystalline TiN and amorphous Si₃N₄ phases with inclusions of nanocrystalline hexagonal AlN formed at energies of titanium, aluminum, and silicon ions exceeding ~317 × 10^–19, 267 × 10^–19, and 230 × 10^–19 J, respectively. As the energy of titanium ions bombarding the substrate increases above ~512 × 10^–19 J, the phase transition from disordered TiN _x to Ti₃N₂ and the appearance of 2- to 3-nm-thick sublayers in 15-nm-thick nanocrystalline TiN _x layers take place in the coating. The maximum hardness of such coatings reaches a level of ~54 GPa.

     

Optimization of PVD Parameters for the Deposition of Ultrahard Ti–Si–B–N Coatings

Multicomponent Ti–Si–B–N coatings were deposited on high-speed steel (HSS) substrates by reactive magnetron sputtering using a SHS TiB + 20 wt% Si target. The influences of the substrate temperature, bias voltage, and nitrogen partial pressure on the structure and the elemental compositions of the films were studied. The films were characterized by high-resolution transmission electron microscopy (HRTEM), Auger spectroscopy (AES), and X-ray diffraction (XRD). The results of HRTEM analysis indicated the formation of an ordered–disordered structure with fine crystalline grains of hexagonal Ti(B,N) _x phase and amorphous integrain layers. The stoichiometry of the Ti(B,N) _x phase was strongly affected by PVD process parameters. The films were characterized in terms of their microhardness and wear resistance. The reasons for the high value of microhardness appear to be the result of stoichiometric phase composition, compressive residual stress, and dense and fine microstructure of the Ti–Si–B–N coatings. The tribological wear test results indicated the superior wear-resistant properties of Ti–Si–B–N coatings compared to TiN and Ti(C,N) coatings.     

Quantitative X-ray diffraction analysis of development of Z phase in 12%Cr–Nb–V–N steel

Abstract

To study the evolution of nitrides (Nb,V)N, (V,Nb)N and Cr₂N, and in particular the formation of the Z phase Cr(V, Nb)N, a model alloy with composition similar to that of 12%Cr steels for high temperature applications, microalloyed with Nb and V but with a very low carbon content, has been designed. A quantitative determination of the volume fractions of the extracted nitrides that had formed after aging treatments at 650°C for up to 10 000 h was carried out by an X-ray diffraction procedure, based on the Rietveld approach. The investigation of the Z phase evolution by the Johnson–Mehl–Avrami–Kolmogorov kinetics at 650 and 700°C revealed that, as the kinetic exponent is very close to unity, the formation mechanism of this phase is not associated with a conventional process of nucleation but hints at a gradual diffusion controlled transformation of the pre-existing V and Nb nitrides.     

Scatter Analysis of Fatigue Life and Prediction of S–N Curve

In this study, the effects of salt solution, the presence of notch on fatigue life scatter, and sample size selection for estimation of fatigue life under different probabilities and confidence levels have been investigated. Comparison has been made with smooth specimen tested in air medium. It is seen that notches have significantly higher effect than other factors (salt solutions, smooth geometry, etc.). The minimum number of specimens required for fatigue life estimation within tolerable error, R _o, at different fatigue testing conditions has also been presented both for log normal and Weibull distribution models. It has been found that estimation of fatigue life using Weibull model needs higher sample size than log normal model. Beyond a certain sample size, fatigue life estimation is independent of sample size. The article also presents a method for minimum sample size selection procedure to estimate fatigue life or to draw S?CN curve.     

Microstructure and anodic polarization behavior of experimental Ag–18Cu–15Pd–12Au alloy in aqueous sulfide solution

The anodic corrosion behavior of an experimental Ag–15Pd–18Cu–12Au alloy in 0.1% Na₂S solution in relation to its microstructure was investigated using potentiodynamic and potentiostatic polarization techniques with analyses of corrosion products by X-ray diffractometry, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The role of Pd in improvement of the corrosion resistance was also investigated. In the potential/current density curve, three distinct current peaks, at –520 mV (peak I), –425 mV (peak II) and –175 mV (peak III), were observed. The Ag-rich ₂ matrix with coarse Cu and Pd-rich lamellae was the most corrosion-susceptible region, and this region was preferentially corroded at peak I with the formation of granular deposits of Ag₂S. A small amount of Ag–Cu mixed sulfide deposited on the Cu and Pd-rich coarse particles and dissolution of Ag as AgO^– might have occurred in parallel with Ag₂S formation at peak II. Enrichment of Pd on the alloy surface occurred at peak III due to preferential dissolution of Ag and Cu. A high level of corrosion resistance was attained with the formation of a thin Pd-rich sulfide film, which enhanced the passivity of the alloy in an alkaline sulfide solution. It was found that passivity is an important phenomenon not only for base metal alloys but also for noble metal alloys to maintain high levels of resistance to corrosion and tarnishing in sulfide environments.     

Density function theory investigation on the thermodynamic properties of the Li–N–H system

The electronic structures and formation enthalpies of compounds in the Li–N–H system have been studied by using the density functional theory. In order to evaluate the competition between each reaction in the system, the chemical potential phase diagrams of compounds in the Li–N–H system have been computed and discussed. Our calculations show that for LiNH₂, Li⁺ combines with [NH₂]^- by an ionic bond. For Li₂NH, the N–H bond displays covalent characteristics. The calculated formation enthalpy of compounds in the Li–N–H system is in agreement with previous results, the LiNH₂ is −212.27 kJ mol⁻¹, LiH is −91.66 kJ mol⁻¹, Li₂NH is −243.14 kJ mol⁻¹, Li₄NH is −309.72 kJ mol⁻¹, Li₃N is −189.11 kJ mol⁻¹, and NH₃ is −102.27 kJ mol⁻¹, respectively. Using the chemical potential phase diagrams, six reversible reactions are discussed. It is found that Li₄NH takes part in the three reversible reactions and some NH₃ formed in the system react with other compounds in the Li–N–H system. These reversible reactions are confirmed by the proposed mechanism from experiments.     

Structural and chemical stability of Ta–Si–N thin film between Si and Cu

Thermal stability and barrier performance of reactively sputter deposited Ta–Si–N thin films between Si and Cu were investigated. RF powers of Ta and Si targets were fixed and various N₂/Ar flow ratios were adopted to change the amount of nitrogen in Ta–Si–N thin films. The structure of the films are amorphous and the resistivity increases with nitrogen content. After annealing of Si/Ta–Si–N(300 Å)/Cu(1000 Å) structures in Ar–H₂ (10%) ambient, sheet resistance measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) were employed to characterize barrier performance. Cu₃Si and tantalum silicide phase are formed at the same temperature, and the interdiffusion of Si and Cu occurs through the local defect sites. In all characterization techniques, nitrogen in the film appears to play an important role in thermal stability and resistance against Cu diffusion. A 300 Å thick Ta₄₃Si₄N₅₃ barrier shows the excellent barrier property to suppress the formation of Cu₃Si phase up to 800°C.     

Thermodynamic Modeling of BC x N y Chemical Vapor Deposition in the B–C–N–H System

Thermodynamic analysis of the chemical vapor deposition of BN-based films in the B–C–N–H system was carried out for reduced pressures (133 and 1.33 Pa) and a wide temperature range (300–1300 K). The results indicate that, using mixtures of trimethylamineborane, (CH₃)₃N · BH₃, with H₂, NH₃, or N₂, one can produce films of various compositions: from BN to mixtures of BN, carbon, and boron carbide.     

Prediction of the temperature dependence of fracture toughness of 12Cr–2Ni–Mo refractory steel

We study the influence of temperature and the size of the specimens on the characteristics of static crack resistance of 12Cr–2Ni–Mo refractory steel. It is shown that, in the temperature range 20–450°C, the increase in the thickness of specimens leads to an insignificant increase in fracture toughness obtained along a 5% secant line according to the standards of evaluation of the characteristics of crack resistance. The evaluation of the characteristics of crack resistance of 12Cr–2Ni–Mo steel with regard for the scale effect according to an earlier developed numerical-experimental model reveals the existence of satisfactory agreement with the experimental data in the entire investigated temperature range. Translated from Problemy Prochnosti, No. 4, pp. 78–88, July–August, 2009.     

Fabrication and characterization of p-type In–N codoped ZnMgO films

Indium (In) and nitrogen (N) codoped ZnMgO films (ZnMgO:In–N) were fabricated on quartz substrates by radio frequency magnetron sputtering and ion-implantation technique. p-ZnMgO:In–N films were successfully achieved after post-implantation annealing at an appropriate temperature ranging from 570 to 590?°C. X-ray diffraction (XRD) indicates that severe damage in films is introduced by N ion implantation and the damaged lattice can be partially recovered after post-implantation annealing. The analysis of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) demonstrates that post-implantation annealing can promote a reduction of donor type zinc interstitials (Zn_i) and the formation of In_Zn+2N_O acceptor complex, which mainly contribute to the realization of p-type ZnMgO:In–N films.     

Spectra of the Transverse and Longitudinal Components of Electronic Transitions in As2Se3 in the Range 2–12 eV

The spectra of the transverse and longitudinal components of electronic transitions in As₂Se₃ in the range 2–12 eV for the E || a, E || b, and E || c polarizations are derived from experimental reflection spectra using Kramers–Kronig integral relations and combined Argand diagrams. The principal parameters of the components are determined: energy position E _i, half width H _i, and area S _i. The energy positions of the transverse components are shown to correlate with those of the longitudinal components.     

Maximisation of the ratio of microhardness to the Young's modulus of Ti–12Mo–13Nb alloy through microstructure changes

Alloys for orthopaedic and dentistry applications require high mechanical strength and a low Young's modulus to avoid stress shielding. Metastable β titanium alloys appear to fulfil these requirements. This study investigated the correlation of phases precipitated in a Ti–12Mo–13Nb alloy with changes in hardness and the Young's modulus. The alloy was produced by arc melting under an argon atmosphere, after which, it was heat treated and cold forged. Two different routes of heat treatment were employed. Phase transformations were studied by employing X-ray diffraction and transmission electron microscopy. Property characterisation was based on Vickers microhardness tests and Young's modulus measurements. The highest ratio of microhardness to the Young's modulus was obtained using thermomechanical treatment, which consists of heating at 1000 °C for 24 h, water quenching, cold forging to reduce 80% of the area, and ageing at 500 °C for 24 h, where the final microstructure consisted of an α phase dispersed in a β matrix. The α phase appeared in two different forms: as fine lamellas (with 240 ± 100 nm length) and massive particles of 200–500 nm size.     

Thirty years with the GÉT 43–73 standard of the unit of pressure

The main results of the use of the GÉT 43–73 State Standard of the unit of pressure over the range of reproducible pressures of 100–1500 MPa, connected with ensuring correctness of high-pressure measurements in this country, by comparing the high-pressure scales of different countries, by improving the theoretical basis of the standard, its material part, and the experimental research techniques and checking work, are presented. Basic results, which, in the opinion of the authors, may be of interest to specialists, are given.Translated from Izmeritelnaya Tekhnika, No. 1, pp. 42–45, January, 2005.