The phase relationship of Re-alloyed Ru2Si3 and the variations of the crystal structures and thermoelectric properties of the Ru1-xRexSiy chimney-ladder phases have been studied as a function of the Re concentration. The Ru1-xRexSiy chimney-ladder phases are formed in a wide compositional range. Compositional formula of the chimney-ladder phases are determined to be Ru1-xRexSi1.5386+0.1783x (0.14 ≤ x ≤ 0.76), which are systematically deviated from the idealized composition conforming the valence electron counting rule: VEC=14. Measurements of thermoelectric properties of single crystals with different compositions reveals that the chimney-ladder phases exhibit n-type semiconducting behavior at low Re concentrations and p-type semiconducting behavior at high Re concentrations. These results suggests that the VEC=14 rule can be used for predicting the semiconducting behavior of the chimney-ladder phases through the adjustment of VEC values by substituting elements, producing p-type semiconductors for VEC<14 and n-type for VEC>14, with the carrier concentration related to the deviation from VEC=14.

The high temperature strength of new Co-Al-W based alloys consisting of a ?-Co (fcc) matrix phase and a high volume fraction of ?'-Co3(Al, W) ternary L12 intermetallic compound has been examined in order to understand the strengthening mechanisms and to explore the possibility for high temperature applications. The flow stress exhibits a strong, positive dependence on temperature above 873 K. Additions of Ta improve the high temperature strength, and the strength of a Ta containing alloy is comparable to Ni-base superalloys at 1173 K. Transmission microscopy on the deformed Ta containing alloy revealed that the active slip modes within the ?' precipitates are <110>{111} and <112>{111} below and above the peak temperature, respectively. At the peak flow temperature, multiple slip modes including <110>{111}, <110>{001} and <112>{111} were observed.

Multi phase alloys at the Mo-rich end of the Mo-Si-B system have drawn recent attention because of their high temperature performance capabilities. Previous studies on two- and three-phase alloys have confirmed the central role of the Mo-rich solid solution phase in affecting creep resistance and low-temperature toughness in these multiphase alloys. Thus, it is important to understand the intrinsic mechanical response of the matrix solid solution. In this study, compression and tensile tests were conducted over a nominal strain rate regime spanning 10-4 s-1 to 10-7 s-1 and temperature ranging from 1000°C to 1300°C in vacuum on a Mo-Si-B solid solution alloy (Mo-3Si-1.3B in at.%) that contained a low fraction (~5 %) of the T2 phase. The microstructure of the deformed specimens was examined to elucidate the underlying deformation mechanisms.

Ab-initio calculations using the Vienna ab-initio simulation package (VASP) were performed for a high Nb bearing γ TiAl based alloy with a composition of Ti-46at.%Al-9at.%Nb in order to evaluate the effect of Nb on the crystal structure. The calculations revealed that upon doping with Nb the resulting structure can have Ti and Nb atoms on Al-sites, which leads to a reduction of the c/a ratio of the tetragonal γ TiAl cell to ~1.In contrast, the c/a ratio is increased, compared to the binary phase, if the Nb atoms occupy solely Ti sites and if Ti antisite defects (i.e. Ti on the Al sublattice) are formed. The relaxed structure models were used to perform high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image simulations. The results showed that the positions of the Nb atoms should be detectable by these high spatial resolution methods, although it might be easier by HAADF-STEM investigations due to the stronger dependence of the signal on the atomic number Z.

The relative role of thermal expansion and redistribution of alloy components in the temperature dependence of the lattice misfit in γ/γ' alloys is investigated on the basis of ab initio calculations. We show that in a wide temperature region up to approximately 0.6·Tmelt, the lattice misfit is determined by the difference in thermal expansion of γ and γ' phases and shows only a slight variation. For higher temperatures the redistribution of the major alloy components between the phases becomes a leading contribution to the lattice misfit.

Toughening effect of ZrO2-particles on MoSi2-based materials is one of the important toughening mechanism. In this work, the influence of particle size and volume percentage of unstabilized ZrO2-addition on toughening in MoSi2-matrix composites was studied. The measured data revealed that the fine particle size, < 1 ìm, with certain volume percentages around 20% have given more effective toughening results. The tested materials were prepared by two different sintering processes: pressure-less sintering (PLS) and PLS + Hipping sintering. The results on sintered density, RT-hardness and RT-toughness indicated that the PLS process could be a practical and economical method for producing MOSi2-ZrO2 composites in industry. Oxidation behavior of MoSi2-ZrO2 composites was also studied in the work. Clearly, the ZrO2-addition made the composites having a worse oxidation resistance than the monolithic MoSi2, which means that a low ZrO2-addition should be used in the composites, as far as an acceptable toughening effect was reached.

The formation process of Rhenium-based diffusion barrier coating on Nickel-based superalloy has been investigated in present paper. The diffusion barrier can be formed by two steps, electroplating and Cr cementation. A tri-layer film structure consisting of Ni / Re~63Ni~37 / Ni was prepared by electrolytic plating onto the substrate of a Ni-based single-crystal superalloy, it was found that the Re-Ni plating film composed of amorphous alloy which is characterized by X-ray diffraction (XRD) analysis. The changes of the barrier films which formed by followed Cr-Pack cementations at 1573 K for 20 min, 50 min, 240 min, 360 min and 600 min, respectively, were investigated by Scan Electron Microscope (SEM) and Electron Probe Micro Analyzer (EPMA). Changing in the thickness of barrier film exhibited two stages, and the composition of barrier film changed along the curve of solubility limit of Ni in Re-Ni-Cr sigma phase.

High-energy synchrotron X-ray diffraction is a powerful tool for bulk studies of materials. In this investigation, it is applied to the investigation of an intermetallic γ-TiAl based alloy with a composition of Ti-46Al-9Nb. The morphology of the reflections on the Debye-Scherrer rings is evaluated in order to approach grain sizes as well as crystallographic correlations. An in-situ heating cycle from room temperature to a temperature above the α-transus temperature has been conducted starting from a massively transformed sample. With increasing temperature the occurrence of strain relaxation, chemical and phase separation, domain orientations, phase transitions, recrystallization processes, and subsequent grain growth can be observed. During cooling to room temperature, crystallographic correlations between the re-appearing γ-phase and the host α-phase, known as the Blackburn correlation, are observed in the reciprocal lattice, which splits into different twinning and domain orientation relationships present in the fully lamellar microstructure.

The concentration and arrangement of Si vacancy in aluminum or phosphorus containing ReSi1.75 based silicides have been investigated. Both aluminum and phosphorus are substituted with silicon. In addition to the (001)C11b twins usually observed in binary ReSi1.75, planar defects are heterogeneously formed in both of the silicon substituted ternary alloys with small amount. By using the high resolution electron micrograph (HREM) technique, the planar defects are assigned as crystallographic shear (CS) planes lying on (109) C11b and (107) C11b in aluminum and phosphorus containing ReSi1.75, respectively. The CS vector in both ternary alloys is [100]C11b. Since the concentration of vacancies in the ReSi1.75 structure is changed by the introduction of these crystallographic shear, ternary alloys with silicon substituted by aluminum and phosphorus contain more or less amount of vacancies than the binary alloy, respectively. This implies us that concentration of Si vacancies changes so as to retain the average number of valence electron. We can control the concentration of Si vacancy in the ReSi1.75 based alloys.

Magnetic field has been known to be effective in solidification processes. Recently, however, it has been revealed that the magnetic field is also effective for controlling the arrangement of variants, which are formed in association with a solid-solid transformation, in some ferromagnetic intermetallic-based alloys with a large magnetocrystalline anisotropy. In this presentation, we will show two of such cases: one is the rearrangement of martensite variants by magnetic field in intermetallic-based ferromagnetic shape memory alloys (Ni2MnGa and Fe3Pt), and the other is formation of mono-variant state by ordering heat-treatment under magnetic field in a L10-type CoPt. The former process is diffusionless and proceeds by the movement of twinning plane under a magnetic field. The latter is a diffusion controlled process. For both the cases, a large magnetocrystalline anisotropy is essentially important for controlling the arrangement of variants, although kinetics of the two processes is quite different each other.

Plastic deformation behavior of Ni3V with D022 structure was examined using the single crystals containing two dominant variants of three. Three deformation modes were confirmed to be operative depending on temperature and loading orientation. {111}1/6<112] twinning and/or {111}<110] slip is dominantly operative at low temperatures, but {111}1/2<112] slip is activated at high temperatures accompanied by a rapid drop of yield stress.

The sulfidation behaviour at 973 K in a 30 vol.% H2S-H2-H2O-N2 gas mixture of Fe-25 % at. Al, DO3-ordered alloys, binary or alloyed with niobium, was investigated. Binary alloys presented a quite good sulfidation resistance in comparison with 321 stainless steel, even if a large amount of iron sulfides FeS grew over the alumina layer on corroded samples. The sulfidation resistance of DO3 alloys could be significantly improved by an oxidation treatment prior to corrosion test. The Nb in iron aluminides was supposed to preferably react with S and therefore, to enhance sulfidation resistance through preventing the nucleation and growth of harmful FeS. Unfortunately, the scales of Nb-allloyed FeAl contained only a small amount of Nb3S4 which did not prevent efficiently the formation of iron aluminides FeS. Adding Nb to Fe-25Al even resulted in a severe deterioration of the microstructure during sulfidation due to intense diffusion of S inward the sample.

The crystallographic orientation distribution, and its change accompanied with tilting γ/γ boundaries in Ni-based single crystal superalloys have been investigated by a theoretical elastic-plastic calculation, X-ray diffractometry and SEM-EBSD analysis. The distribution of the crystallographic orientation has significantly broadened by creep deformations. The broadening can be explained by an unbalance of the amount of creep dislocations of each slip system, which agrees with the result of elastic-plastic calculations. Creep strain of superalloys crept at a condition forming the raft structure can be estimated by the measurement of the width of rocking curve of a diffraction peak.

It was previously found that two B2 phases (matrix and precipitates) appeared in Ti-32mol%Au-18mol%Co superelastic alloy. In this study, each B2 single phase alloy was tried to be fabricated individually, and phase constitution, crystal structures and hardness were investigated. The chemical compositions were Ti60-xAu40Cox and Ti34-xAu44Co22+x (x=0, 2 and 4), and the alloys were fabricated by Ar-arc melting followed by a hot-forging at 1423K for 43.2ks and a solution treatment at 1173K for 3.6ks. It was found by X-ray diffraction analysis that Ti60-xAu40Cox (called Co-poor alloys) were composed of B19 (Ti, Co)Au and A15 Ti3Au two phases, instead of B2 single phase expected. It was also found that Ti34-xAu44Co22+x (called Co-rich alloys) were composed of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) two phases, instead of B2 single phase expected. These unexpected phase constitutions appeared in this work may be due to the difference in cooling rate and/or phase transformation from B2 to C11b. Lattice parameters of the obtained phases were precisely determined. The hardness of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) are HV480 and HV780, respectively. The hardness change of Co-rich alloys can be understood in terms of the volume fraction change of these phases.

Polycrystalline L12-type Ni3(Si,Ti), Co3Ti and Ni3Al alloys prepared through the thermomechanical process from arc-melted ingots were successfully cold-rolled to thin foils with a thickness of below 200μm. The cold-rolling with over 90% reduction in thickness was possible without providing intermediate annealing. The cold-rolled foils showed high tensile strength (~2GPa) at room temperature due to heavily cold rolling although no plastic elongation was observed. Room temperature tensile elongation increased with increasing annealing temperature, and reached to ~30-40% by high temperature annealing at 1173K. Among three kinds of intermetallic alloys, the Ni3(Si,Ti) foil annealed around at 900K exhibited an extremely high tensile strength and yield strength (over 2GPa) with a reasonable tensile elongation. The observed tensile properties, especially tensile strength at low temperature for the present intermetallic foils were found to be superior to those for the conventional alloys such as nickel based alloys and stainless steels.

Pseudoelastic behavior of Fe3Ga single crystals regardless of a thermoelastic martensitic transformation was investigated focusing on the dislocation structure and the phase constituent. Large pseudoelasticity of 5 % recoverable strain appeared in Fe3Ga single crystals sufficiently annealed in the D03 single-phase region. In the crystals, uncoupled and paired 1/4[111] superpartial dislocations moved dragging the nearest-neighbor (NN) and next-nearest neighbor (NNN) anti-phase boundaries (APBs) during loading, respectively. During unloading, these APBs pulled back the superpartials resulting in large pseudoelasticity, which is similar to D03-ordered Fe3Al crystals. The dislocation configuration was closely related to the ordered domain structure developed in the D03 phase. Moreover, the precipitation of the thermally stable L12 phase was so slow that the metastable D03 phase developed even if the crystals were annealed in the (a+ L12) and (D03+ L12) phase fields in Fe-Ga equilibrium phase diagram. The metastable D03 phase also demonstrated large pseudoelasticity of which recovery ratio was above 80 %. On the other hand, if the L12 phase precipitated by long time annealing in the (a+ L12) region, the reversible motion of 1/4[111] superpartials was suppressed by the L12 phase resulting in a decrease in recovery ratio. In addition, the crystals aged in the (a+ D03) phase region showed small strain recovery.

Phase equilibria among the bcc Fe(α), fcc Fe(γ) and Fe2Mo(λ)_phases in Fe-Mo-Ni ternary system, particularly paying attention to the existence of the γ+λ two-phase region, have been examined at elevated temperatures below Tc (1200 K), the peritectoid reaction temperature in Fe-Mo binary system: λ?α+Fe7Mo6 (μ). At 1173 K the α+γ+μ three-phase coexisting region exists near the Fe-Mo binary edge and no λ phase region was identified. At 1073 K the λ phase in equilibrium with α and γ phases exists, although the composition homogeneity region of the ternary λ phase was limited to its binary edge toward the equi-nickel concentration direction up to about 3at % Ni. Instead, large two-phase region of γ+μ was extended along the same direction up to 20 at% Ni. The γ+λ two-phase region appears below Tc through a transition peritectoid reaction: α+μ¨γ+λ. The γ phase in equilibrium with λ phase is stable only at elevated temperatures, and it transforms martensitically to α phase during cooling. The addition of Ni stabilizes γ and μ phases against α and λ phases, thereby decreasing the relative stability of the λ phase.

Phase transformations and phase transition temperatures in several Ti-45Al and Ti-45Al-(5-10)Nb (at%) alloys were investigated experimentally and compared to thermodynamic calculation. The present study combines scanning electron microscopy, high-energy and conventional X-ray diffraction as well as differential scanning calorimetry for the characterization of the prevailing phases and phase transformations. Thermodynamic simulation based on the CALPHAD method was used to predict phase stabilities. Modifications of a commercial available database, based on the thermo-physical measurements and long-term annealing treatments, were introduced in order to achieve better agreement between calculated and experimental results.

Despite decades of intensive research iron aluminides remain characterised by relatively poor ductility at room temperature and low strength at high temperatures, especially under slow strain rate or creep conditions. A variety of strengthening particles has been tested for improving high temperature strength, but each has serious limitations: typical carbide precipitates are unable to resist dissolution or coarsening at high temperatures; as-solidified iron aluminides with sufficient amounts of transition elements such as Nb or Mo show heavy solidification segregation and are embrittled by a network of Laves phase; mechanical milling with stable oxides appears an excessively expensive processing route. A new iron-aluminium alloy has been developed with Zr and Cr additions that forms fine coherent precipitates even after extended annealing at temperatures as high as 900ºC. These precipitates have a complex Fe3Zr structure and form in a cube-on-cube orientation relationship in the bcc matrix. The low solubility and diffusivity of the solute, as well as the low energy, near-coherent interface ensures excellent stability of these intermetallic precipitates. Interesting strengthening is possible for this material under the relevant high temperature creep conditions.

Due to their high magnetic anisotropy, L10-ordered intermetallics when ferromagnetic bear a potential as high density magnetic recording materials. In their case the c-axis of the tetragonally distorted structure is the easy axis of magnetization. We present preliminary results on the details of ordering kinetics on FePd films (thickness 100 nm) epitaxially co-deposited on MgO substrates. From the observation of so called ‘order-order relaxations’ during isothermal small-step anneals monitored by residual electrical resistivity (REST) measurement we determine an ordering activation energy of about 2.4 eV, which is somewhat below the value of 2.7 eV obtained in a previous investigation on bulk material.