The Nb-NiTi eutectic alloys were directionally solidified (DS) in an optical floating zone furnace. Columnar grains of eutectic structures containing rod-shaped Nb in the NiTi matrix is observed in the DS ingots irrespective of the alloy composition. Well-aligned rod-type eutectic microstructures can be obtained for samples with a composition of Nb-41Ni-40Ti grown at relatively slow growth rates below 2.5mm/h. The hydrogen permeability along the direction parallel to the Nb rods of Nb-41Ni-40Ti DS alloy grown at 1mm/h is 2.60×10-8mol H2 m-1 Pa-1/2 at 673K, which is over 20 times higher than that measured perpendicular to the Nb-rod direction. No hydrogen embrittlement is observed between 573 and 673K indicating that the eutectic structure itself is favorable in suppressing the hydrogen embrittlement of Nb.

In order to attain a better oxidation resistance of Ni-based superalloys for high performance engines, a ReCr-based sigma-phase diffusion barrier coating between the MCrAlY bond coat (Al reservoir) layer and a Ni-based superalloy substrate has been proposed to suppress the diffusion of Al and other elements. The deformation behavior of TMS82+ superalloy specimens with coating layers composed of an Al-rich surface layer (corresponding to a bond coat) and a ReCr sigma-phase inner layer is investigated. In-situ observation of the bending tests using a Laser scanning confocal microscopy revealed that the crack formation in the Al-rich surface layer(s) on the tension side of the bend specimen occurs at an early stage of bending. On the other hand, small cracks in the sigma-phase layer under the Al-rich surface layer(s) are formed at the slip traces in the Ni-based superalloy single crystal substrate. This suggests a good adhesion between the sigma-phase and the Ni-based superalloy. At the compression side, in both the Al-rich surface layer(s) and the sigma-phase layer no cracking was observed until the Al-rich surface layer(s) shows buckling.

New type pseudoelasticity in Fe3Al with the D03 structure was examined using the single crystals. The pseudoelasticity occurred due to a reversible motion of 1/4<111> superpartials dragging the nearest-neighbor anti-phase boundaries. The chemical composition and microstructure of Fe3Al alloys strongly influenced the shape recovery ratio and Fe-23.0at%Al alloy with fine domain structure was the most favorable for the appearance of the pseudoelasticity. The recovery ratio of Fe-23.0at%Al exceeded 80 % in the wide temperature range from -50 to 200 oC.

FePd belongs to a group of L10 - intermetallics with attractive uniaxial hard-ferromagnetic properties. In this study thin films of different composition FeXPd1-X, X= 50, 60, were deposited by pulsed laser deposition (PLD) on amorphous SiO2 and Si3N4. We characterized the microstructural evolution during the different order/disorder phase-transformations during post-deposition annealing relative to the as-deposited state in terms of morphology, grain size, texture and presence of short-range order using SEM, XRD and TEM. VSM measurements were used to monitor magnetic properties. Differences in these microstructural parameters are due to different ordering reactions FCC to L10 ordering and concomitant phase separation of ?-Fe vs. FCC to L10 ordering upon heat treatment. The relationships of the different phase transformation products to properties are discussed. Support from NSF-DMR-Metals is gratefully acknowledged.

Effect of Ti3Si particles on recrystallization texture of Ti-Nb based superelastic alloys has been investigated using X-ray pole figure measurement and electron backscatter diffraction (EBSD) technique. The alloys used were Ti-24mol%Nb-3mol%Al-Xmol%Si (X=0~0.9, termed XSi) and Ti-24mol%Nb-3mol%Si alloy (termed 3Si). The apparent phase at room temperature was β-phase (bcc). Besides, (Ti, Nb)3Si particles with PTi3 type crystal structure were formed in the alloys with Si content higher than 0.7mol%. After the cold rolling of 99% reduction in thickness, a rolling texture of the β-phase was formed to be mainly {001}β<110>β regardless of the presence of the (Ti, Nb)3Si particles. After the solution treatment at 1273K, a recrystallization texture formed to be {112}β<110>β in all the alloys except for 3Si. The average grain size of the recrystallized alloys was 20~40μm. On the other hand, the solution treated 3Si exhibited the {001}β<110>βn texture and the average grain size of 3μm. It is concluded that the {001}β<110>β texture with fine grains of the solution treated 3Si is obtained by the suppression of grain boundary migration due to the existence of the (Ti, Nb)3Si particles.

We present a theoretical study of the electronic structure, surface energies and work functions of orthorhombic Pt monosilicide and germanides of Pt, Ni, Y and Hf within the framework of density functional theory (DFT). Our calculated bulk structures are within 1-2% of reported experimental values. Calculated work functsions for the (001) surfaces of PtSi, NiGe and PtGe are 5.12, 4.57 and 4.83 eV, respectively, suggesting that these metals and their alloys can be used as self-aligned contacts to p-type silicon and germanium. Work functions for Y and Hf germanides range from 2.4 to 4.3 eV making them a possible n-type contact material. In addition, we also report an ab-initio calculation of the Schottky-barrier height at the Si(001)/PtSi(001) interface. The p-type Schottky barrier height of 0.28 eV is found in good agreement with predictions of a simple metal induced gap states (MIGS) theory and available experiment. This low barrier suggests PtSi as a low contact resistance junction metal for silicon CMOS technology. We identify the growth conditions necessary to stabilize this orientation.

Phase-separations of coherent precipitates of ordered phases were investigated by means of transmission electron microscopy (TEM) and the theoretical analysis from a thermodynamic point of view. When the two-phase microstructures of A1+L12 in elastically constrained Ni-Al-Ti and Ni-Si-Fe alloys are isothermally heated inside the two-phase region of A1+L12 , coherent L12 precipitate particles sometimes exhibit a phase-separation and A1 phase newly appears and grows in L12 particles. Phase-separations of the same type as the above are also observed in coherent two-phase microstructures of A2+D03 and A2+B2 in elastically constrained Fe-Si-V and Fe-Al-Ni alloys respectively: coherent D03 or B2 precipitates exhibit a phase-separation and A2 phase newly appears and grows in both precipitates. Such phase-separation is realized under the influence of chemical free energy and elastic energies.

γ(TiAl) alloys containing Ti3AlC perovskite precipitates show overlapping planar faults, which can apparently rearrange into embryonic twins and subsequently grow into large twins. An electron-microscopical study is introduced and followed by a micromechanical modelling of the fault and twin development process. The thickness and length of the embryonic twins can be predicted with the developed model.

First-principles theory of alloys is based on electronic structure calculation at the ground state and statistical mechanics calculation at finite temperatures. The former clarifies the stability of an ordered compound against competing phases and the latter is employed mainly to derive a phase diagram. The author performed a series of first-principles investigations on binary alloy systems including noble metal alloys, semiconductor alloys and Fe-based alloy systems by combining FLAPW electronic structure total energy calculations with Cluster Variation Method. Recently, the theoretical framework is extended even to calculate microstructural evolution process. By exemplifying Fe-based alloy systems, the progress of the first-principles calculation is reviewed and future prospect is discussed.

To design and to develop Half-Heusler based high-temperature thermoelectric materials, thermoelectric properties of n-type MNiSn and p-type MPtSn (M = Hf, Zr) were investigated based on two respective strategies. For the n-type (Hf, Zr)NiSn, a combined process of optical floating zone melting and hot-pressing was applied aiming to reduce thermal conduction through the lattice contribution. For the p-type HfPtSn, power factor and hence figure of merit ZT were dramatically improved by the p-type doping of Ir and Co targeting for Pt-site, which effectively lower electrical resistivity. The additions of Ir and Co are expected not only to increase carrier concentration but also to suppress the lattice thermal conduction by substituting for Pt.

The crystal structures and thermoelectric properties of Ba-Ge based type-III clathrate compounds in Ba-Al-Ge and Ba-In-Ge systems have been investigated as a function of Al and In content. The absolute values of electrical resistivity and Seebeck coefficient increase, while that of lattice thermal conductivity decreases with increasing Al and In content. The increase in electrical resistivity and Seebeck coefficient is discussed in terms of the number of the excess electrons deduced from the Zintl concept, on the other hand, the decrease in lattice thermal conductivity is discussed in terms of an anisotropic deformation of the open-dodecahedron cage encapsulating Ba atom. High ZT values of 0.74 and 0.87 are obtained at 780 and 580 °C for Ba24Al12Ge88 and Ba24In16Ge84, respectively.

Mo-rich Mo-Si-B multiphase alloys are currently being explored for their potential as high-temperature structural materials for components in hot sections in aircraft engines. In this paper, we present crack growth behavior in one such two-phase alloy consisting of a Mo solid solution matrix in which is dispersed approximately 40 volume percent of the Mo5SiB2 (T2) phase. Crack growth under monotonic and cyclic loading is considered over a temperature range spanning 20°C to 1400°C. The effects of loading rate (in monotonic loading) and dwell times at maximum stress (in cyclic loading) at high temperatures on crack growth were examined to understand the contribution from creep. Results confirm a gradual increase in fracture toughness upto 1000°C, beyond which the increase is more substantial with temperature; fatigue susceptibility was also observed in excess of 900°C and crack-tip-stresses-driven microstructural instability is evident at 1400°C. At this temperature, slow loading rates or dwell times at maximum stress lead to crack-tip recrystallization and creep cavitation that together degrade the material's properties.

Magnetic behavior in Co-based Heusler alloys Co2MnZ (Z=Si, Ge, Sn) is investigated as a function of quenching temperature. The mean magnetic moment decreases with increase in quenching temperature in Co2MnSi and Co2MnGe while it remains almost constant in Co2MnSn. Relation between the magnetic behavior and the atomic disorder is discussed.

The results of the lattice constant and the electrical resistance measurements are also reported.

In order to overcome the brittleness of Nb-Si intermetallic compounds, a novel microstructure control through a eutectic solidification and a eutectoid decomposition reactions has been proposed for obtaining Nb matrix alloys with Nb-silicide dispersion by the present authors. As the additions of Zr and Mg accelerate the eutectoid decomposition rate and spheroidization of Nb-silicide during heat treatment, the effects of these additives on the eutectic microstructure are investigated. The effect of the growth rate during the uni-directional solidification on the microstructure of a selected alloy was examined and it was found that the following eutectoid reaction rate is strongly affected by the growth rate.

Polycrystalline ingots of the lanthanide based ternary intermetallics: LaNiSb, GdNiSb, ErNiSb and ErPdSb were prepared and characterized. The thermoelectric properties of ErNiSb and ErPdSb were measured at high temperatures. We succeeded in preparing the single phase ingots of ErNiSb and ErPdSb, while the ingots of LaNiSb and GdNiSb contain appreciable quantities of the impurity phases. ErNiSb and ErPdSb crystallize the MgAgAs-type structure (half-Heusler structure). ErNiSb and ErPdSb indicate positive values of the Seebeck coefficient. The values at room temperature are 36 and 240 micro VK-1 for ErNiSb and ErPdSb, respectively. The electrical resistivity of ErNiSb and ErPdSb decreases with temperature, indicating semiconductor-like behavior. ErPdSb exhibits a relatively large power factor 1.5x10-3 Wm-1K-2 at around 700 K, which is approximately two times larger than that of ErNiSb.

Texture formation was studied in high Nb bearing g-TiAl based alloys with compositions of Ti-45Al-(5,7.5,10)Nb-(0,0.5)C (compositions are in atomic percent). In order to start with texture-free material hot-isostatically pressed powder compounds were used. The deformation was performed either in uniaxial compression or by hot rolling. After compression at 700 °C and 800 °C fiber textures with <110> and <302> components occur. These deformation textures can be verified by computer simulations using a yield surface model of g-TiAl. With higher deformation temperatures the <110> fiber vanishes and new accumulations of orientations are formed, which are due to dynamic recrystallization.

Hot rolling was performed at temperatures in the upper part of the (a+g) phase field and, therefore, with more than 50% a-phase existing. The co-deformation of a- and g-phase during rolling leads to correlated components in the independently measured textures of both phases. The texture of the g-phase shows a maximum of orientation around the Goss2 component and the texture of the a-phase exhibits an orientation maximum around the transversal component. The correlation is the Blackburn orientation relation, although the textures are not caused by phase transformations, but by co-deformation. Hot rolling with many passes and reheating between the passes lead to the formation of a cube component with an alignment of the c-axes in transverse direction. In general, this is a typical recrystallization-induced component in hot rolled TiAl.

Iron silicide thin films were prepared on silicon (Si) and yittria-stabilized zirconia (YSZ) substrates using RF magnetron sputtering and evaporation methods. Epitaxial b-FeSi2 thin films were grown on (100) and (111) planes of Si and YSZ substrates, while noncrystallized films were deposited on (110) plane of both Si and YSZ substrates. The epitaxial relationships between the b-FeSi2 and YSZ were the same as those between b-FeSi2 and Si, in the case of (100) and (111) planes. It is possible that epitaxial b-FeSi2 film can be grown when substrates and b-FeSi2 surfaces consist of either a single element or only cations, while the crystalline film was not shown when either substrate or b-FeSi2 surface consists of a mixture of anions and cations or iron and silicon.

A thermomechanical process (TMP) was performed to create a fine grained and recovered structure with densely formed fine particles in Fe3Al-Cr-Mo-C alloys. The TMP consists of two parts; the first part is to obtain fine recrystallised grains using coarse particles and the second to produce deformed/recovered structure using fine particles. It was found that k-Fe3AlC (E21) carbide phase tends to precipitate coarsely, which is effective to refine grain size in the first process. In a special composition range, the k carbide phase is thermo- dynamically stable in the Fe3Al matrix only at higher temperatures and fine M(Mo,Cr,Fe)2C (B81) carbide phase precipitates at lower temperatures. This fine M2C particles stabilize recovered structure by inhibiting the migration of subboundaries in the second process. This result suggests that if the fine particle density remains high, recovered structure can be maintained at 700°C.

In this work, the material properties of AuNi5 films prepared by Pulsed Laser Deposition (PLD) to be used as contact materials in RF MEMS switches are investigated. PLD is used because it provides good wide range thickness control (few nanometers to tens of microns) while preserving ablation target stoichiometry. Films with thickness in the range 50 - 450 nm were deposited at Laser energy density (fluence) in the range 0.55 - 1.38 J.cm-2 on silicon substrates at room temperature. An aperture was placed between the plume and the substrate to filter out large particulates. The presence of the aperture reduced surface roughness from 8.5 nm to 4.3 nm as determined by optical profilometry. In addition, the presence of the aperture during deposition has been found to affect film stoichiometry. The latter was evaluated using X-ray Fluorescence and the Nickel content has been found to vary in the range 1.1 - 9.5%. Only films deposited with the aperture removed maintain target stoichiometry (5.2% Ni). Hence, it is believed that the presence of the aperture causes non-congruent transfer. The Nickel content within the range under investigation has practically no effect on film morphology or hardness. Laser fluence, however, has been found to be the dominant factor determining film properties. Finally, 100 µm wide AuNi5 strips 290 nm and 130 nm thick deposited at room temperature have been successfully formed on silicon wafers by lift-off photolithography.

Plastic deformation behavior and the dominant deformation mode in ternary (Nb1-xMox)Si2 (x=0-0.85) single crystals with the C40 structure were examined focusing on the phase stability between the C40 and C11b structures. Temperature dependence of CRSS for the (0001)<2-1-10] slip is strongly influenced by the Mo concentration accompanied by the change in the dissociation mode from the co-planar-type to the synchroshear-type. In the ternary crystals with x=0-0.30, anomalous strengthening clearly appeared, and the peak stress increased up to 1600¢ªC with an increase in the Mo content. Mo atoms may gather and form a dragging atmosphere around 1/3<2-1-10] dislocations containing a superlattice intrinsic stacking fault (SISF), resulting in anomalous strengthening. In contrast, in crystals with x=0.60-0.85, a high CRSS was obtained with fracture in a brittle manner at low temperatures, and the stress decreased remarkably with an increase in the test temperature. HRTEM observation showed that the synchroshear-type dissociation of each super-partial dislocation, 1/6<2-1-10], occurred on the neighboring slip planes, accompanied by a much wider separation distance of SF than that in the ternary crystals with a low Mo content. This change in plastic deformation behavior may be closely related to the decrease in phase stability of the C40 structure with the addition of the C11b-stabilized element, Mo. The phase stability can be represented by the ratio of (h/b), where h is the (0003) spacing and b is the amplitude of 1/3<2 0]. As the (h/b) ratio increases with the addition of Mo, the dissociation mode changes from the co-planar-type to the synchroshear-type at a ratio of 0.465.