Composition,Structure, and Mechanical Properties of (Ti–Hf)N Coatings on Titanium Alloy

Technical Physics - Variations of the composition, structure, and mechanical properties (hardness, elastic modulus) of (Ti–Hf)N coatings with increasing Hf content (Ti : Hf ratio) are...     

Thermal Stability of Structure and Properties of Gradient and Gradient-Layered Coatings of the Ti–Al–Si–Cu–N System

Russian Physics Journal - Using the methods of dark-field electron microscopy analysis, energy-dispersive X-ray microanalysis, hardness measurements and scratch testing, the variations of elemental...     

Study of the Microstructure,Crystallographic Structure and Thermal Stability of Al–Ti–Nb Alloys Produced by Selective Electron Beam Alloying

This paper aims an investigation of the microstructure and crystallographic structure as well as the thermal stability of Al–Ti–Nb formed by selective electron beam surface alloying. The fabrication of the samples has been carried out using circular sweep mode, as two velocities of the sample movement have been chosen: V₁ = 1 cm/s and V₂ = 0.5 cm/s. The studied microstructure and crystallographic structure have been investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) respectively. The thermal behavior of the obtained surface alloys are evaluated by the coefficient of thermal expansion (CTE) which has been evaluated by neutron diffraction measurements at high temperature. The results show that in the earlier stages of formation, the microstructure of the intermetallic phase is mainly in the form of coarse fractions, but at the following moments they dissolve, forming separated alloyed zone and base Al substrate as the alloyed zone consists of fine (Ti,Nb)Al₃ particles dispersed in the Al matrix with small amount of undissolved intermetallic fractions. Formation of preferred crystallographic orientation as a function of the speed of specimen motion has not been observed. The performed neutron diffraction measurements show that the lattice parameters of the obtained intermetallic (Ti,Nb)Al₃ are less upshifted in comparison to pure Al. It has been found that the aluminium lattice is much more unstable at high temperatures than that of the intermetallic phase. The CTE for the intermetallic phase is 8.70 ppm/K for a axis and 7.75 ppm/K for c axis respectively while considering Al it is 12.95 ppm/K.     

Thermal Stability of Microstructure and Mechanical Properties of V–Me(Cr,W)–Zr Alloys as a Function of Heat Treatment Modes

Russian Physics Journal - Using the methods of scanning and transmission electron microscopy, a study is performed of the influence of high-temperature annealing on the parameters of...     

First-principles studies of the structural and electronic properties of the C14 Laves phase XCr2 (X = Ti,Zr, Nb,Hf and Ta)

The optimized structures, electronic properties and bonding characteristics of the hexagonal C14 Laves phase XCr₂ (X?=?Ti, Zr, Nb, Hf and Ta) have been investigated using first-principles calculations. Our results reveal that the equilibrium formation enthalpies are not depends entirely on the atomic numbers. The total and the partial density of states and valence charge densities of Laves phases are also calculated and applied to reveal the nature of the bonding character in consideration of the different atomic numbers.     

Thermal and structural characterization of Cu–Al–Mn–X (Ti,Ni) shape memory alloys

In this study, the Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys at the range of 10–12 at.% of aluminum and 4–5 at.% manganese were produced by arc melting. We have investigated the effects of the alloying elements on the transformation temperatures, and the structural and the magnetic properties of the quaternary Cu–Al–Mn–X (X = Ni, Ti) shape memory alloys. The evolution of the transformation temperatures was studied by differential scanning calorimetry with different heating and cooling rates. The characteristic transformation temperatures and the thermodynamic parameters were highly sensitive to variations in the aluminum and manganese content, and it was observed that the nickel addition into the Cu–Al–Mn system decreased the transformation temperature although Ti addition caused an increase in the transformation temperatures. The effect of the nickel and the titanium on the thermodynamic parameters such as enthalpy and entropy values was investigated. The structural changes of the samples were studied by X-ray diffraction measurements and by optical microscope observations at room temperature. It is evaluated that the element Ni has been completely soluble in the matrix, and the main phase of the Cu–Al–Mn–Ni sample is martensite, and due to the low solubility of the Ti, the Cu–Al–Mn–Ti sample has precipitates, and a martensite phase at room temperature. The magnetic properties of the Cu–Al–Mn, Cu–Al–Mn–Ni and Cu–Al–Mn–Ti samples were investigated, and the effect of the nickel and the titanium on the magnetic properties was studied.     

A Comparative Analysis of In-Medium Spectral Functions for N(940) and N ∗(1535) in Real-Time Thermal Field Theory

In the real-time thermal field theory, the nucleon self-energy at finite temperature and density is evaluated where an extensive set of pion-baryon (π B) loops are consider. On the other side, the in-medium self-energy of N ^?(1535) for π N and η N loops is also determined in the same framework. The detail branch cut structures for these different π B loops for nucleon N(940) and π N, η N loops for N ^?(1535) are addressed. Using the total self-energy of N(940) and N ^?(1535), which contain the contributions of their corresponding loop diagrams, the complete structures of their in-medium spectral functions have been obtained. The Landau and unitary cut contributions provide two separate peak structures in the nucleon spectral function while N ^?(1535) has a single peak structure in its unitary cuts. At high temperature, the peak structures of both at their individual poles are attenuated while at high density Landau peak structure of nucleon is completely suppressed and its unitary peak structure is tending to be shifted towards the melted peak of N ^?(1535). The non-trivial modifications of these chiral partners may indicate some association of chiral symmetry restoration.     

Stability and elastic properties of B2 CoX (X = Ti,Zr and Hf) intermetallic compounds as a function of pressure

By means of first-principles calculations within the generalised gradient approximation (GGA), phase stability, elastic properties and electronic structures of B2 CoX (X = Ti, Zr and Hf) compounds as a function of pressure have been investigated. The formation energy indicates that CoTi is the most stable phase in these three B2 phases under different pressures. The elastic properties of B2 Co (X = Ti, Zr and Hf), calculated via the Voigt–Reuss–Hill (VRH) approximation, increase with increasing pressure. The mechanical anisotropies are characterised by the universal anisotropy index (A^U) and the Zener anisotropy index (A^Z). The sound velocities, Debye temperatures and melting temperature under applied pressure are also evaluated. Electronic structure show that the changes in the charge distribution are moderate under applied pressure, resulting in the general characteristics of the bonding between X (X = Ti, Zr and Hf) and Co remain unchanged.     

Structure and Phase Composition of (TiB)–Ti Metal Matrix Composites Obtained by SHS and Vacuum Sintering

Russian Physics Journal - The structure and phase composition of (TiB)–Ti powder metal matrix composites synthesized by wave combustion with subsequent vacuum sintering are studied. The...     

The effect of thermomechanical treatment regimes on microstructure and mechanical properties of V–Me(Cr,W)–Zr–C alloys

The regularities of the formation of a heterophase structure in dispersion-strengthened vanadium V–Me(Cr, W)–Zr–C alloys are studied as a function of the regimes of their thermomechanical treatment. The regimes of treatment providing a substantial increase in the dispersity and homogeneity of spatial distribution of ZrC particles, temperature of recrystallization, and high-temperature (at T = 800°C) short-time strength are found in comparison to conventional treatment regimes.     

Computational investigations of mechanical and dynamical properties of gold-based compounds (X3Au,X = Ti,Zr and V)

The structural, elastic, electronic and phonon properties of X₃Au (X?=?Ti, Zr and V) compounds in the A15 structure were obtained in the framework of the density functional theory (DFT) within the generalized gradient approximation (GGA). The equilibrium lattice constants, bulk modulus and elastic constants were calculated. The calculation of elastic constants revealed that V₃Au has the highest hardness nature and incompressibility along the x-axis among them. The computed elastic constants also provided information about the ductility of X₃Au compounds which were predicted using Pugh's criteria. The results indicated that all three compounds have ductile nature. The density of states calculations revealed that electrons of Ti, Zr and V provide most contribution to the conductivity of the compounds and thus cause a metallic bonding. The investigation of stability via phonon spectra of compounds showed that these compounds are dynamically stable in the A15 structure.     

Analysis of slip activity and heterogeneous deformation in tension and tension-creep of Ti–5Al–2.5Sn (wt %) using in-situ SEM experiments

The deformation behavior of a Ti–5Al–2.5Sn (wt %) near-α alloy was investigated during in-situ deformation inside a scanning electron microscope. Tensile experiments were performed at 296?K and 728?K (≈0.4?T _m), while tensile-creep experiments were performed at 728?K and 763?K. Active deformation systems were identified using electron backscattered diffraction-based slip trace analysis. Both basal and prismatic slip systems were active during the tensile experiments. Basal slip was observed for grains clustered around high Schmid factor orientations, while prismatic slip exhibited less dependence on the crystallographic orientation. The tension-creep experiments revealed less slip but more development of grain boundary ledges than in the higher strain rate tensile experiments. Some of the grain boundary ledges evolved into grain boundary cracks, and grain boundaries oriented nearly perpendicular to the tensile axis formed ledges earlier in the deformation process. Grain boundaries with high misorientations also tended to form ledges earlier than those with lower misorientations. Most of the grain boundary cracks formed in association with grains displaying hard orientations, where the c-axis was nearly perpendicular to the tensile direction. For the tension-creep experiments, pronounced basal slip was observed in the lower-stress creep regime and the activity of prismatic slip increased with increasing creep stress and temperature.     

On the interface states and series resistance profiles of (Ni/Au)–Al0.22Ga0.78N/AlN/GaN heterostructures before and after 60Co (γ-ray) irradiation

The values of interface states (N _SS) and series resistance (R _S) of (Ni/Au)–Al_0.22Ga_0.78N/AlN/GaN heterostructures were obtained from admittance and current–voltage measurements before and after 250 kGy ⁶⁰Co irradiation. The analyses of these data indicate that the values of capacitance and conductance decrease, as the R _S increases with increasing dose rate due to the generation of N _SS. The increase in R _S with increasing dose rate was attributed to two main models. According to the first model, it has been attributed to a direct decrease in the donor concentration in semiconductor material as a result of the elimination of shallow donor states. According to the second model, it is a result of irradiation because of the formation of deep acceptor centers in the semiconductor bulk, and electrons from the shallow donor centers are captured by these acceptors.     

Microstructure,creep, and tensile behaviour of a Ti–15Al–33Nb (at.%) beta+orthorhombic alloy

The microstructural evolution, creep and tensile deformation behaviour of a Ti–15Al–33Nb (at.%) alloy was studied. Monolithic sheet material was produced through conventional thermomechanical processing techniques comprising non-isothermal forging and pack rolling. Electron microscopy studies showed that depending on the heat-treatment schedule, this alloy may contain three constituent phases including:?β?(disordered body-centred cubic), α₂ (ordered hexagonal close-packed based on Ti₃Al) and O (ordered orthorhombic based on Ti₂AlNb). Heat treatments at all temperatures above 990°C, followed by water quenching, resulted in fully-β microstructures. Below 990°C, Widmanstätten O-phase or α₂-phase precipitated within the?β?grains. The fine-grained as-processed microstructure, which exhibited 90?vol.% β-phase, exhibited excellent strength (UTS?=?916?MPa) and ductility (?_f>12%). After heat treatment, greater volume fractions of the orthorhombic phase precipitated and resulted in lower ? _f values with UTS values ranging between 836–920?MPa. However, RT elongations of more than 2% were recorded for microstructures containing up to 63?vol.% O-phase. Specimens subjected to 650°C tensile experiments tended to exhibit lower strength values while maintaining higher elongation-to-failure. Tensile creep tests were conducted in the temperature range 650–710°C and stress range 49–275?MPa. The measured creep exponents and activation energies suggested that grain boundary sliding operates at intermediate stress levels and dislocation climb is active at high stresses. Microstructural effects on the tensile properties and creep behaviour are discussed in comparison to a Ti–12Al–38Nb O?+?β alloy.     

Effects of Zr/Ti ratio on dielectric and ferroelectric properties of 0.8Pb(ZrxTi1−x)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics

The influences of Zr/Ti ratio on electrical properties of the 0.8Pb(Zr_xTi_1−x)O₃–0.2Pb(Co_1/3Nb_2/3)O₃ ceramics prepared by a mixed-oxide method (with x = 0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary composition in this system. With XRD analysis, the crystal structure of dense specimens appeared to change gradually from tetragonal to rhombohedral with increasing Zr content. The dielectric properties measurements showed a maximum dielectric constant at x = 0.50, while the transition temperature decreased with increasing Zr content in the system. Moreover, all ceramics showed diffused phase transition behaviors with a minimum diffusivity at x = 0.50. In addition, the Polarization–Electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with the Zr content. Interestingly, the loop squareness parameter reached maximum around x = 0.50. Other ferroelectric hysteresis parameters showed noticeable change at x = 0.50. These results clearly showed the significance of Zr/Ti ratio in controlling the electrical properties of the PZT–PCN ceramic systems.