Thermodynamic analysis of alloys Ti–Al, Ti–V, Al–V and Ti–Al–V

Thermodynamic analysis of three binary Ti-based alloys: Ti–Al, Ti–V, and Al–V, as well as ternary alloy Ti–Al–V, is shown in this paper. Thermodynamic analysis involved thermodynamic determination of activities, coefficient of activities, partial and integral values for enthalpies and Gibbs energies of mixing and excess energies at four different temperatures: 2000, 2073, 2200 and 2273 K, as well as calculated phase diagrams for the investigated binary and ternary systems. The FactSage is used for all thermodynamic calculations.     

The Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system

Following up on recent studies of the isothermal section of the Zn–Fe–Ni, Zn–Fe–Bi and Zn–Bi–Ni ternary systems at 450 °C, the Zn-rich corner of the 450 °C isothermal section of the Zn–Bi–Fe–Ni quaternary system with the Zn being fixed at 93 at.% was determined experimentally using the equilibrated alloys approach. The specimens were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). It was found there exist 4 two-phase regions, 5 three-phase regions and 2 four-phase regions. Two liquid L (Zn) and L (Bi) can coexist with T, ζ and δ-Ni in this isothermal section, no new phase was found in this study.     

A contribution to the Al–Pd–Mn phase diagram

A part of the Al–Pd–Mn phase diagram in the vicinity of the icosahedral phase was refined. Partial isothermal sections of 710, 850, 870 and 880°C are presented. The overall compositional range of the icosahedral phase was found to be between 5.8 and 10.5 at.% Mn and between 69.5 and 71.5 at.% Al at these temperatures. It shifts to lower Mn concentration at lower temperatures. It was confirmed that the phase usually designated Al₃Pd has a lower Al concentration in the binary alloys than that according to the formula. It extends to the ternary compositions up to about 5 at.% Mn. The increase of the Mn content results in an increase of the Al concentration of this phase.     

Identification of machine–tool–workpiece system dynamics

The aim of this paper is to present a method to identify the dynamics of a structure composed of a milling machine, a tool and a workpiece. The excitation is obtained as a result of the interrupted cutting of a narrow workpiece width and single tooth milling operations. This provides a pulse-like cutting force. The three components of the cutting force and the relative motion between the tool and the workpiece are measured simultaneously. A method was developed to determine the nine terms of the structural transfer matrix under a single cutting operation and without any assumption on the excitation direction. The proposed method is experimentally validated.     

Corrosion behavior of wrought Mg–6%Zn–1%Mn–XSi–YCa alloy

Different quantities of silicon and calcium were added to Mg–6%Zn–1%Mn alloy and its effect on corrosion behavior investigated. AC and DC polarization were carried out on the extruded rods, which contain different quantities of silicon and calcium. The phases present in the alloys have been identified by optical microscopy and TEM. Four different phases were found, i.e., intermetallics containing Si–Mn, Mg–Si, Mg–Zn, and Mg–Si–Ca phase. The corrosion behavior of the studied alloys were influenced by the amount and distribution of the second phases.     

Research on intercrystalline corrosion,exfoliation corrosion,and stress corrosion cracking of Al–Zn–Mg–Sc–Zr alloy

The intercrystalline corrosion, exfoliation corrosion (EXCO), and stress corrosion cracking (SCC) of Al–Zn–Mg–Sc–Zr alloy were investigated by means of constant temperature immersion corrosion method, optical microscopy, transmission electron microscopy (TEM), and electrochemical impedance spectroscopy (EIS). The results show that intercrystalline corrosion, and EXCO susceptibility of Al–Zn–Mg–Sc–Zr alloy decrease gradually with increasing of aging time. Corrosion susceptibility order from low to high is as follows: OA > PA > UA > NA. The SCC susceptibility index of PA temper is more than OA temper at the same strain rate. According to TEM observation, with aging time prolonging, a part of η′ phases transform to η equilibrium phases, which become coarse gradually. The distribution discontinuity of the grain boundary precipitates increases. In addition, for Al–Zn–Mg–Sc–Zr alloy without EXCO, the EIS is comprised by a capacitive impedance arc at high frequency and an inductive impedance arc at low frequency. Once EXCO occurs, the EIS is composed of two capacitive impedance arcs at high frequency and at low frequency, respectively.     

Exfoliation corrosion of Al–Zn–Mg–Cu–Zr alloy containing Sc examined by electrochemical impedance spectroscopy

The exfoliation corrosion behavior of an Al–Zn–Mg–Cu–Zr alloy containing Sc artificially aged at 120 °C for 24 h is studied by macroscopic observation techniques and electrochemical impedance spectroscopy (EIS) measurements. After 48 h immersion, the blisters start bursting and delamination initiates, along with the appearance of two time constants in the impedance diagrams. According to the simulation by equivalent circuit, the corrosion rate decreases sharply and then reaches a steady state, which is due to the change of the solution pH and oxide layer thickness, as well as the accumulation of corrosion products.     

Oxidation of a quaternary two-phase Cu–40Ni–17.5Cr–2.5Al alloy at 973–1073 K in 101 kPa O2

Oxidation of a quaternary two-phase Cu–40Ni–17.5Cr–2.5Al (at.%) alloy was investigated at 973–1073 K in 101 kPa O₂. The alloy is composed of two phases. One light phase with lower Cr content forms the matrix of the alloy, and the other medium gray phase richer in Cr is presented in the form of continuous islands. At 973 and 1073 K, the kinetic curves for the present alloy deviate evidently from the parabolic rate law. They show a large mass gain in initial stage, and then their oxidation rates decrease evidently with time until they become very small up to 24 h. Cross sectional morphologies show the present alloy is able to form continuous external scales of chromia over the alloy surface with a gradual decrease in the oxidation rate. However, the previous studies showed that a ternary two-phase Cu–40Ni–20Cr alloy is unable to form protective external scales of chromia over the alloy surface, but is able to form a thin and very irregularly continuous layer of chromia at the top of the mixed internal oxidation region. Therefore, substituting Cr in Cu–40Ni–20Cr alloy with 2.5 at.% Al is able to decrease the critical content required to form Cr oxide and help to form continuous external scales of chromia under lower Cr content in two-phase alloys.     

The microstructures and mechanical properties of cast Mg–Zn–Al–RE alloys

The microstructures and mechanical properties of cast Mg–Zn–Al–RE alloys with 4 wt.% RE and variable Zn and Al contents were investigated. The results show that the alloys mainly consist of α-Mg, Al₂REZn₂, Al₄RE and τ-Mg₃₂(Al,Zn)₄₉ phases, and a little amount of the β-Mg₁₇Al₁₂ phase will also be formed with certain Zn and Al contents. When increasing the Zn or Al content, the distribution of the Al₂REZn₂ and Al₄RE phases will be changed from cluster to dispersed, and the content of τ-Mg₃₂(Al,Zn)₄₉ phase increased gradually. The distribution of the Al₂REZn₂ and Al₄RE phases, and the content of β- or τ-phase are critical to the mechanical properties of Mg–Zn–Al–RE alloys. The Mg–6Zn–5Al–4RE alloy with cluster Al₂REZn₂ phase and low content of β-phase, exhibits the optimal mechanical properties, and the ultimate tensile strength, yield strength and elongation are 242 MPa, 140 MPa and 6.4% at room temperature, respectively.     

Microstructure and grain refining performance of a new Al–Ti–C–B master alloy

A kind of Al–Ti–C–B master alloy with a uniform microstructure is prepared using a melt reaction method. It is found that the average grain size of α-Al can be reduced from 3500 to 170 μm by the addition of 0.2 wt.% of the prepared Al–5Ti–0.3C–0.2B and the refining efficiency does not fade obviously within 60 min. It is considered that the TiC_xB_y and TiB_2−mC_n particles found at the grain center are the effective and stable nucleating substrates for α-Al during solidification, which accounts for the good grain refining performance.     

Microstructure and martensitic transformation of Ni–Fe–Ga–Si ferromagnetic shape memory alloys

The effects of the fourth element Si on the martensitic transformation and magnetic properties of Ni–Fe–Ga magnetic shape memory alloys were investigated. A complete thermoelastic martensitic transformation in Ni–Fe–Ga–Si alloys was observed in the temperature range of 218–285 K. The martensitic transformation temperatures of Ni–Fe–Ga alloys are obviously decreased by the substitution of Si for Ga element, that is, the substitution of 1 at.% Si for Ga leads to a decrease of martensitic transformation temperature of about 39.6 K. Moreover, the substitution of Si for Ga leads to a decrease of the saturation magnetic field and the magnetic anisotropy constant K₁ obviously.     

Influence of annealing on magnetic field-induced structural transformation and magnetocaloric effect in Ni–Mn–In–Co ribbons

A study of the magnetic field-induced martensitic transformation and magnetocaloric effect in Ni₄₅Mn₃₇In₁₃Co₅ and Ni₄₆Mn₃₅In₁₄Co₅ ribbons prepared by melt-spinning was carried out. Annealing significantly increases the degree of ordering in the austenite phase, reduces the critical field and hysteresis of the magnetically induced martensitic transformation and increases the magnetically induced shift of martensitic transformation temperatures. For the most In-rich sample, Ni₄₆Mn₃₅In₁₄Co₅, annealing at 900 °C for 2 h leads to the formation of Co-rich face-centered cubic γ precipitates. The Curie temperature of the γ phase is about 370 K. The formation of the second phase has little impact on the hysteresis, but broadens the transformation interval and reduces the magnetic entropy change.     

A novel Al–Ti–B alloy for grain refining Al–Si foundry alloys

Al–Ti–B refiners with excess-Ti (Ti:B > 2.2) perform adequately for wrought aluminium alloys but they are not as efficient in the case of foundry alloys. Silicon, which is abundant in the latter, forms silicides with Ti and severely impairs the potency of TiB₂ and Al₃Ti particles. Hence, Al–Ti–B alloys with excess-B (Ti:B < 2.2) and binary Al–B alloys are favored to grain refine hypoeutectic Al–Si alloys. These grain refiners rely on the insoluble (Al,Ti)B₂ or AlB₂ particles for grain refinement, and thus do not enjoy the growth restriction provided by solute Ti. It would be very attractive to produce excess-B Al–Ti–B alloys which additionally contain Al₃Ti particles to maximize their grain refining efficiency for aluminium foundry alloys. A powder metallurgy process was employed to produce an experimental Al–3Ti–3B grain refiner which contains both the insoluble AlB₂ and the soluble Al₃Ti particles. Inoculation of a hypoeutectic Al–Si foundry alloy with this grain refiner has produced a fine equiaxed grain structure across the entire section of the test sample which was more or less retained for holding times up to 15 min.     

Synthesis of the Ni–Zn–Sm ferrites using microwaves energy

This work reports the preparation of Ni–Zn–Sm ferrite powders by combustion reaction using microwaves energy and XRD characterization. The influence of the fuel type used was investigated. The metallic nitrates and fuels (urea, glycine or 1:1 mixture) were heated in microwave oven for 5 and 10 min using the power of 450 and 630 W. Ni–Zn–Sm ferrite and traces of secondary phases were observed in the powders obtained with glycine and mixture (1:1). The powers obtained with urea presented low cristallinity, only the main peak of the Ni–Zn–Sm ferrite phase was observed.     

Electrochemical corrosion behavior of biomedical Ti–22Nb and Ti–22Nb–6Zr alloys in saline medium

The aims of this study were to investigate the effects of Zr addition and potentiodynamic polarization on the microstructure and corrosion resistance of Ti–22Nb and Ti–22Nb–6Zr alloy samples. The corrosion tests were carried out in 0.9% NaCl at 37 °C and neutral pH value, utilizing the OCP, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of XRD and optical microscopy indicated that the addition of Zr stabilized the β phase, which plays a crucial role in the corrosion resistance improvement of the Ti–22Nb–6Zr alloy. From the polarization curves, it can be seen that the alloys exhibited a wide passive region without the breakdown of the passive films and also low corrosion current densities. In addition, the values of the corrosion current densities and passive current densities decreased with the addition of 6 at% Zr into the Ti–22Nb alloy. The EIS results of these two alloy samples after 1‐h immersion in 0.9% NaCl solution, and being fitted by R_S(Q_PR_P) model, suggested that the corrosion resistance of the passive films improved with the addition of Zr and only a single passive film formed on the surfaces. However, two time constants were observed for the Ti–22Nb and Ti–22Nb–6Zr alloy samples after potentiodynamic polarization, the spectra of which can be fitted using the R_s(Q_o(R_o(Q_bR_b))) model. In addition, the corrosion resistance of the two alloy samples was reinforced significantly because of polarization when compared to the immersed samples. All these observations suggested a nobler electrochemical behavior of the titanium alloys with the addition of Zr element and after polarization.     

The electrochemical behavior of Mg–9Al–0.5Zn,Mg–9Al–0.7Zn,and Mg–9Al–1.0Zn in a NaCl solution

In this study, the electrochemical behavior of Mg–9Al–0.5Zn, Mg–9Al–0.7Zn, and Mg–9Al–1.0Zn electrodes in a 0.7 mol L^?1 NaCl solution is evaluated by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and potentiostatic oxidation. The utilization efficiencies of these materials are also determined. The results show that the Mg–9Al–1.0Zn alloy has the highest corrosion resistance and that Mg–9Al–0.5Zn displays the largest discharge current in the 0.7 mol L ^?1 NaCl solution at 25°C. In addition, the utilization efficiencies of the alloys decrease as follows: Mg–9Al–1.0Zn > Mg–9Al–0.7Zn > Mg–9Al–0.5Zn. This study illustrates that doping Zn into Mg‐Al electrodes increases the corrosion resistance and utilization efficiency but decreases the discharge activity of Mg–Al–Zn anodes when the Zn content is between 0.5% and 1.0%.     

Transition between periodic and quasiperiodic structures in Al–Ni–Co

A series of Al–Ni–Co alloys forming stable decagonal (D-ANC) quasicrystals was studied in as-cast and annealed states. It was shown that under certain conditions periodic structures with pseudodecagonal (PD) symmetry can be produced at the same compositions as stable decagonal quasicrystals. Different variants of D-ANC and PD were observed in a compositional range of 70–72.5 at.% Al and 13–18 at.% Co. As-cast D-ANC can be transformed to single-phase PD of the same local composition. Single-phase PDs can be transformed to D-ANC of the same composition by heating to a temperature higher than the formation temperature of these PDs. The transition between PD and D-ANC was studied in more detail in Al₇₁Ni_14.5Co_14.5 and Al₇₀Ni₁₅Co₁₅ by electron microscopy, powder X-ray diffractometry and differential thermal analysis. The results of this study do not confirm the thermodynamic stability of this PD structure.