Single Γ-phase Research Articles

Hydrogen absorption properties of the γ-Mg17Al12 phase

In the present work, the Mg-Al system was studied towards hydrogen absorption properties.Several MgxAl100-x compounds from X=47.5 to 70 by incremental step of 2.5 were prepared by ball-milling with post-annealing. Different experimental measurements were performed and are in mutual agreement with properties of existing phases. They show that deviation from the ideal composition of Mg17Al12 (X=58.62) leads to a decrease of the homogeneity. The single γ-phase range is extended at room temperature for initial 55≤X≤62.5 atomic % of Mg.The hydrogenation properties have been investigated for two compounds at the nominal composition X=50 and X=58.6. The hydrogen absorption is presented at 350°C and shows a maximum hydrogen capacity of 3.5 and 3.7 wt% respectively. For these two compounds, the pressure-composition isotherm (PCT) curves show two absorption plateaux, with equilibriums around 10 bars which are higher than that of pure MgH2. The shape discontinuity corresponds to a transformation into a 2-step process as described in this work. After final desorption, the initial compounds are recovered, indicates that the reactions are reversible.

Auto-ignition route to thermoelectric oxide Na xCo 2O 4 powder with high compactibility

The ultra fine powder of thermoelectric oxide Na x Co 2O 4 has been synthesized via an auto-ignition route following with airflow shatter process, which has the flaky shape in different nominal x compositions. Single γ-phase Na x Co 2O 4 crystal structure was obtained in varying Na contents of 1.4–1.8 at the calcining temperature of 1153 K. The airflow shatter process was found to be beneficial for obtaining uniform particles with smaller the average size and larger BET surface area. The compaction module and the nonlinear exponent of powder compaction are about 4.037 MPa and 4.368 calculated form Huang Peiyun's compacting equation, respectively, which reveals that the Na x Co 2O 4 powder has high compactibility.

Limits of the Mg–Al γ-phase range by ball-milling

In the present work, the homogeneity range of the Mg–Al γ-phase was studied by ball-milling with post-annealing. In order to estimate the limit of its domain range, several Mg X Al 100− X compounds from X = 47.5 to 70 by incremental steps of 2.5 were prepared. Different experimental measurements (XRD, SEM, EDX, DSC) were performed and are in mutual agreement with the properties of the existing phases. They show that deviation from the ideal composition of the intermetallic Mg 17Al 12 structure ( X = 58.62) leads to a decrease of the homogeneity (morphological and chemical compositions). Rietveld refinements on XRD patterns show that the single γ-phase range is extended at room temperature and is identified for 55 ≤ X ≤ 62.5 at.% of nominal Mg powder.

Thermodynamic Assessment of the Al-Cr System by Combining the First Principles and CALPHAD Methods

Thermodynamic assessment of the Al-Cr system has been carried out by incorporating first-principles calculations into the CALPHAD approach. A regular solution approximation was adopted to describe the Gibbs energy of the solution phases. The several phases appearing in the composition range between about 30 and 42 at.%Cr were treated as a single homogeneous γ-phase, based on recent experimental results, and the Gibbs energy of the γ-phase was represented using the four-sublattice model with the formula (Al,Cr)8(Al,Cr)8(Cr)12(Al)24. The calculated results enable the reproduction of experimental results on both the phase equilibria and thermochemical properties. In addition, a B2 ordered bcc phase, which was suggested to form as an equilibrium phase in a previous X-ray diffraction study, is not likely to form in either the stable state or metastable state based on our first-principles calculations.

Elastic-stiffness distribution on dual-phase stainless steel studied by resonance ultrasound microscopy

Distribution of the elastic stiffness coefficient in a dual-phase stainless steel is studied using resonance ultrasound microscopy and electron backscattering patterns. Using a monocrystal langasite oscillator, the resonance frequency change due to contact with the material is measured contactlessly using a solenoid coil antenna. A theoretical calculation based on the contact between two anisotropic bodies is proposed to determine the contact stiffness from the resonance frequency. The measured stiffness distribution is compared with that predicted from the orientation distribution determined using the electron backscattering-pattern method. They generally agreed but the stiffness determined by resonance ultrasound microscopy is nonuniform even in a single γ-phase grain. The nonuniformity of the chromium concentration can be a principal cause of the stiffness distribution.

Synthesis of ternary L10 compounds of Ti–Al–Zr system and their mechanical properties

Abstract A number of ternary Ti–Al–Zr alloys with different compositions around the binary γ-TiAl (L1 0 structure) were prepared and annealed at 1273 K for 10 h followed by quenching. Almost single γ-phase is produced in a rather wide composition region of Al 50 (Ti 50− x − y Al x Zr y ) with 0 ≤ x ≤ 15 and 0 ≤ y ≤ 15. Both lattice parameters, a and c increase with increasing Zr concentration due to larger atomic radius of Zr than those of Al and Ti. The c / a ratio of Al 50 Ti 50− x Zr x decreases towards unity as x increases. The Vickers hardness value increases rapidly with increasing Zr substitution. Compression tests at high temperatures for Al 50 Ti 50− x Zr x and Al 55 Ti 45− x Zr x with x = 5, 10 or 15 showed that except for Al 50 Ti 45 Zr 5 , specimens underwent brittle fracture below 1000 K; only the Al 50 Ti 45 Zr 5 specimens exhibited a considerable plastic strain at all the test temperatures, and the temperature dependence of the yield stress showed a peak at 973 K with the peak yield stress as high as 1000 MPa, indicating a possible application of this ternary alloy.

Low activation austenitic Mn-steel for in-vessel fusion materials

Several compositions of austenitic manganese steels (Mn-steels) were investigated for in-vessel component materials in D–T fueled fusion reactor with respect to radiation exposure and waste disposal management. The 24.5Mn–13.5Cr steel was developed in which undesired impurities, such as Ni, Mo, Nb and Co, were controlled and C (∼0.025wt%) and N (∼0.22wt%) contents were well adjusted for corrosion resistance and weldability. Experimental observation has shown that this steel has a single γ-phase structure and good properties for vacuum vessel almost the same grade as Type 316 stainless steel (316SS), such as low permeability, good weldability, good mechanical properties of strength and toughness and good corrosion resistance. Activation calculations were performed adopting this material for the JT-60 Super Upgrade (JT-60SU) vacuum vessel and the effectiveness of low activation was confirmed.

Aluminium segregation of TiAl during single crystal growth

γ-TiAl single crystals have been successfully prepared by an induction-heated cold crucible Czochralski technique which offers more flexibility than vertical float zoning. Compositional analysis of the Czochralski grown single crystals indicates a homogeneous composition after initial transition; and the average composition is close to the peritectic composition. However, γ-TiAl single crystals prepared by vertical float zoning show a small aluminium segregation profile along the growth direction; and the average composition of the as-grown crystals is close to that of the starting alloy. Compositional analysis further demonstrated the banded structure with alternative single γ-phase and α2 + γ lamellar regions in the vertical float zoned Ti-54 at.% Al.

Electroplating of zinc-nickel binary alloys from acetate baths

Zinc-nickel binary alloys have been successfully electrodeposited onto steel sheets from baths containing zinc acetate, nickel acetate and acetic acid (pH 4.4–4.6). The potentiodynamic cathodic polarization, cathodic current efficiency, morphology and composition of the deposits were determined for a variety of bath composition, temperature, current density and superimposed ac on dc. The baths are characterized by high cathodic current efficiency for co-deposition. The co-deposition shows an anomalous behaviour with zinc being the preferentially deposited metal. X-ray tests revealed the presence of a single γ-phase (rich-zinc alloys) with body centered cubic structure.

金型成形-普通焼結法による高密度TiAl焼結材の製造

In order to develop highly densified TiAl by die compaction-sintering method, the sintering behavior of Ti(or TiH2)+TiAl3 mixed powders, promising as a starting powder, was investigated.The mixed powders were consolidated by cold pressing and sintered in vacuum without extermal pressure. In the sintering behavior, the densification characteristics of mixed powders were examined as a function of particle size and composition, and the microstructure and oxygen content of the sintered TiAl were also examined.The results were as follows:(1) The densification behavior of the Ti+TiAl3 mixed powders was influenced by the particle size of constituent powders, especially the size of Ti powder. With refining Ti powder, a greater densification over 95% relative density took place.(2) The densification behavior of the mixed powders was also inflienced by their composition. Although Al-rich TiAl of 55 at%Al showed a small densification irrespective of a proper adjustment of particle size, TiAl containing 40∼50 at%Al showed excellent sinterability. This is mainly due to the α-Ti phase which appears during sintering.(3) The microstructure of sintered TiAl of 55 at%Al consisted of a single γ-phase, while those of 40∼50 at%Al were composed of equiaxis γ-phase and γ⁄α2-lamellar structure. In the mixed structures, the amount of the lamellar structure increased with a rise of sintering temperature and decreased with an increase of Al content.(4) The oxygen content of sintered TiAl was dependent on the oxygen content of starting powders, de-waxing conditions, the amount of interconnected pores and so forth. It was found that the oxygen content of the highly densified TiAl obtained by this die compaction-sintering method was 0.45∼0.55% and an appropriate handling of starting powders made it possible to reduce them less than 0.4%.

The γ-phase regions of the CuZn, NiZn and Pd-Zn binary systems

The γ-phase regions of the CuZn, NiZn and PdZn binary systems are discussed in the light of recently published studies of inversion anti-phase domain (IAPD) superstructures in the first two of these systems and with regard to the short-range-order phenomena observed in a number of γ-phase alloys. New X-ray and electron diffraction evidence for the existence of the IAPD structures in a Pd-75 at.% Zn alloy is presented. Finally, it is suggested that the currently accepted Ni-Zn and Pd-Zn equilibrium phase diagrams be modified to show only a single γ-phase field. This would provide a consistent representation of the phenomena occurring in the γ-phase region of both these and the CuZn binary systems.