We have examined segregation behavior of various alloying elements at lamellar interfaces of C40-NbSi2/C11b-MoSi2 duplex silicide by a phase-field simulation, which takes into account not only bulk chemical free energy but also segregation energy evaluated by the first principles calculation to reflect interaction between solutes and interface. The simulation suggests that segregation behaviors greatly depend on additive elements. In the case of Cr-addition, the C40-phase becomes enriched with Nb and Cr, while the C11b-phase becomes enriched with Mo, which agrees with the equilibrium phase diagram. Slight segregation of Cr atoms is observed at the interface, whereas Nb and Mo concentrations monotonically change across the diffuse interface between C11b and C40 phases. Significant segregations of Zr and Hf are formed at static interfaces, which are attributed to the chemical interaction between solute atoms and the static interface.

Deformation behavior of an 18R-type long period stacking ordered (LPSO) phase in the Mg-Zn-Y system was studied by micro-pillar compressions of single crystalline specimens prepared by focused ion beam (FIB) technique as a function of loading axis orientation and specimen dimensions. When the loading axis is inclined to the basal plane of the LPSO phase by 42°, basal slip of (0001)<11$\bar 2$0>-type is activated irrespective of the specimen dimensions. When the loading axis is parallel to the basal plane, the formation of thick deformation bands are observed for all specimens tested. Strong size-dependence of yield stress values is observed for both types of micro-pillar specimens with different loading axis orientations.

The deformation behaviour of the ζ (zeta) phase in the Fe-Zn system has been investigated via room-temperature compression tests of single-crystal micropillar specimens prepared by the focused ion beam method. Trace analysis of slip lines indicates that {110} slip occurs for the specimens investigated in the present study. Although the slip direction has not been uniquely determined, comparison of Schmid factors and yield stress values suggests that the slip direction might be <1$\overline 1 $2>, which is inconsistent with the easiest slip system {110}[001] predicted on the basis of the primitive Peierls-Nabarro model.

The development of a new high temperature structural material is recently required in various fields. As one of the potential materials, Nb-Si alloys have attracted attention due to their high melting point and low density. A microstructure composed of ductile Nb matrix containing finely dispersed spherical Nb5Si3 phase is obtained by the addition of ternary elements such as Au and it is found that such microstructure is effective in improving room temperature toughness. The main purpose of the present study is evaluating fracture toughness of Nb-Si-Au alloys using small specimens and investigating the effects of the microstructure and other minor elements on the fracture toughness. Alloy ingots of Nb-15at.%Si-3at.%Au and Nb-3at.%Au are prepared by arc-melting under Ar atmosphere, followed by heat-treatments at up to 1500oC for 100 hours. Chevron notched specimens with a size of 1.0x2.0x10mm are subjected to four-point bending tests under a laser confocal microscope for in-situ observation of crack propagation, and the effect of the microstructure and minor elements such as oxygen on the evaluated fracture toughness is investigated on both the Nb/Nb5Si3 alloys and the Nb solid solution (Nbss) alloys.

Temperature dependence of the lattice parameter and elastic moduli in Fe-40 and -43Al (at.%) was investigated by high temperature X-ray diffractometry (XRD) and the Electro-Magnetic Acoustic Resonance (EMAR) method. The thermal vacancy concentration was estimated from the activation enthalpy and entropy data of vacancy formation previously reported for FeAl. It was found that both the lattice parameter and the elastic moduli of FeAl have a linear relationship with temperature even in the temperature range where thermal vacancy concentration rapidly increases (above 400 °C), thus suggesting that newly generated thermal vacancies at elevated temperature do not make significant influence on the lattice parameter and the elastic properties of B2-type FeAl.

The plastic deformation behaviour of single crystals of Pt3Al with a chemical composition of Pt-27 at.%Al was investigated in compression from 77K to 1,273K. The L12 structure is not stable below around 220 K, transforming into either D0c, D0c’ or Pt3Ga structures. {001} slip system was operative for most loading axis orientations while {111} slip system was operative for a narrow orientation region close to [001]. The CRSS for {111} slip gradually decreases in the temperature range where the L12 structure is stable, followed by a sharp decrease above 1,073 K, without showing positive temperature dependence. On the other hand, the CRSS for {001} slip gradually decreases below 673 K and moderately increases above 673 K. Dislocations on {111} tend to align along their screw orientation, suggesting high Peierls stress for their motion, while those on {001} are edge-oriented and fairly curved on a local scale, suggesting relatively low Peierls stress. Dislocations on both {111} and {001} with a Burgers vector b = [$\bar 1$01] dissociate into two collinear superpartials with b = 1/2[$\bar 1$01] separated by an anti-phase boundary.

Atomic scale characterization of the La2Ni7 hydrides by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) revealed that not only the anisotropic expansion of the La2Ni4 unit layer previously reported but also the shearing on the basal plane of the La2Ni4 unit layers occur during one-cycle of hydrogen absorption/desorption process. Two different types of orthorhombic La2Ni7 hydrides with the same atomic arrangement of La and different atomic arrangement of Ni were observed depending on the maximum hydrogen concentration achieved during one hydrogen absorption/desorption cycle.

Microstructural variations of directionally-solidified (DS) MoSi2/Mo5Si3 eutectic composites caused by ternary additions of V, Cr, Nb, Ta and W were investigated. Ternary addition of relatively large amount of V resulted in the apparent modification of the morphology as well as the macroscopic inclination angle of one type of the interfaces extending nearly along the growth direction in the DS ingots. Ternary addition of Cr was found to change the microstructures of the DS ingots from a cellular-type with coarse boundary regions to a plate-like cellular-type with increasing the amount of the ternary addition. No significant change of scriptlamellar morphology was observed for the DS ingots containing Nb, Ta and W irrespective of the amount of the ternary addition.

Deformation behavior of the directionally-solidified MoSi2/Mo5Si3 eutectic composites has been investigated as a function of the average thickness of MoSi2 phase over a temperature range from 900 to 1500°C. The average thickness of both MoSi2 and Mo5Si3 phases in the directionally-solidified ingots with script-lamellar morphologies grown by optical floating zone method decreases with increasing the growth rate. Plastic deformation was observed above 1000°C for all the DS ingots grown at different growth rates when the loading axis is parallel to [1¯10]MoSi2 close to the growth direction. Yield stress decreases monotonically with increasing temperature. Yield stress at 1400°C increases drastically with decreasing the average thickness of MoSi2 phase.

Fe-50 wt% Co alloy powders with average particle size of 10 μm were compacted by spark plasma sintering (SPS) at 700, 800, 900 and 950oC by applying 40, 80, 100 MPa uniaxial pressures for 2, 5, 10 minutes. The densities of the samples were found to increase with temperature from 700 to 900oC for constant sintering pressure and time and to decrease for the material sintered at 950oC. The effects of sintering time on density were more significant in samples sintered at 700oC and 800oC than those densified at 900oC. The consequences of small increases in mechanical pressure during sintering on density values were significant for samples sintered at 700oC. The coercivity (Hc) of the compacts decreased significantly with increasing sintering temperature, and with increasing dwell time at sintering temperatures lower than 700oC. The sample sintered at 950oC, which contains the largest grains among the prepared samples and porous microstructure, exhibited the minimum coercivity. Unlike Hc, the remanence (Br) and saturation induction (Bsat) values were more strongly affected by the specimen density than by grain size. Br and Bsat values were found to vary linearly with sintering temperature and pressure owing to increasing density. An increase in soaking time at 800 and 900 oC, although enabling higher density, exhibited contradicting effects on Bsat values. The SPS parameters to obtain maximum density and optimum magnetic properties for Fe-50% Co alloy were found to be 900oC, 80 MPa and 2-5 minutes.

Micro-compression behavior of single crystalline Ni-base superalloy CMSX-4 has been studied especially focusing on a specimen size range comparable to the size of Ni3Al (γ’) precipitates of about 500 nm using square cross-section micro-pillar specimens. The variation in stress levels exhibited a considerable increase for smaller micro-pillar specimens with edge lengths below 2 μm. Shearing of both the Ni (γ) channels and the γ’ precipitates was observed indicating that stress levels were significant enough to cause the dislocations to cut into the γ’ precipitates at room temperatures.

Diffusion brazing is a potential method to repair parts made from TiAl-alloys. Two different brazing materials with varying contents of titanium, iron and nickel were investigated. The phases present in the brazed zone were identified by high energy X-ray diffraction (HEXRD) at the material science beamline HEMS at the PETRA III synchrotron facility at DESY in Hamburg, Germany, and the microstructure was characterised by scanning electron microscopy (SEM). The braze zone itself is composed of one to two transitional layers from the substrate material to the middle of the joint. Near the substrate material the phase constitution reassembles a TiAl-alloy while the middle of the joint is similar to α/β-titanium alloys. Besides phases commonly encountered in TiAl-alloys such as γ, α2 and β, additional phases, which are related to the presence of nickel or iron as melting point depressing elements are present. The microstructure of the brazed zone changes significantly during a subsequent heat treatment.

Creep tests of monocrystalline Co–Al–W-based alloys with a tensile stress of 137 MPa at 1000 °C were carried out. The microstructures of the crept specimens were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM). The γ′ phase in the specimens was not only elongated along the stress direction as expected by the sign of the lattice misfit but also elongated in one of the <100> directions perpendicular to the stress direction. As a result, the shape of the γ′ phase is not a rod but a plate. In the TEM images, it was observed that many SISFs are induced in the γ′ phase by creep. A similar microstructure is also observed in Ni-based superalloys, but the microstructure was formed under relatively lower temperatures and higher applied stresses. The observation of numerous stacking faults in the γ′ phase is a clear indication that the γ′ phase precipitated in the present alloy is weaker than that in many modern Ni-based superalloys.

In this work, we report the effect of high energy ball milling (HEBM) on Nb doped R2Fe16Nb1 (R= Gd, Er) compounds. The focus of the work is to bring enhancement in magnetic properties of R2Fe17 (2:17) compounds with the ball milling. Specifically, we find that the ball milling increases saturation magnetization, coercivity, and Curie temperature. The increase in the magnetization and Curie temperature upon ball milling is related to the lattice expansion and microstrains while the increase in coercivity is related to the grain refinement.

Nowadays, aeronautic and aerospace are the more demanding sectors for shape memory alloys (SMA) after the bio-medical one. In particular the interest has been recently focused on very high temperature SMA, which would be able of working as sensors and actuators in the hot areas of the engines and exaust devices.

In the present work we undertook a study of the Ru-Nb SMA Intermetallics, which undergo two succesive martensitic transformations around 1050 K and 1180 K respectively, depending on composition. This study has been focused on measurements of internal friction spectra and dynamic modulus variation up to 1700 K, which have been carried out in a sub-resonant torsion mechanical spectrometer.

The internal friction and dynamic modulus have been studied as a function of the heating-cooling rate and the frequency in order to compare experimental behaviour with theoretical models for martensitic transformations. In addition to the internal friction peaks linked to both martensitic transformations we have also observed a complex relaxation process around 950 K, which seems to be linked to the interaction of the martensite interfaces with structural defects. An analysis and discusion of the potential microscopic mechanisms are also presented.

Single crystals of E21 (L12) Ni3AlC1-x were prepared by the unidirectional solidification using the optical floating zone melting method to determine their mechanical properties. Particularly the effects of interstitial carbon atoms on mechanical properties were evaluated by compression tests at room temperature. Operative slip system of E21 Ni3AlC is {111}<011> type which is the same as that of L12 Ni3Al. Strength of Ni3AlC single crystals increases with carbon concentration due to the solid solution effect, though the stress relief of yielding behavior is enhanced at the intermediate carbon content at around 3at%. A large gap appears in the carbon concentration dependence of critical resolved shear stress (as well as yield stress) at almost the same carbon content. This discontinuity in strengthening is attributed to the interaction between multiple solute carbon atoms and mobile dislocations.

Two types of as-cast microstructures have been observed in a series of near-equiatomic FeNiMnAl alloys: 1) an ultrafine microstructure in Fe30Ni20Mn20Al30 [1] and Fe25Ni25Mn20Al30, which consists of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler) phases aligned along <100>; and 2) a fine two-phase microstructure in Fe30Ni20Mn30Al20 and Fe25Ni25Mn30Al20, which consists of alternating (Fe, Mn)-rich f.c.c. and (Ni, Al)-rich B2-ordered platelets with an orientation relationship close to f.c.c (002) // B2 (002); f.c.c. [011] // B2 [001] [2]. The phases in Fe25Ni25Mn20Al30 coarsened upon annealing with no significant change in the chemical partitioning. The hardness behavior was studied as a function of the annealing time at 823 K. AnL21-to-B2 transition, which occurred at 573-623K, was observed using in-situ heating in a TEM. After annealing at 973 K for 100 h, needle-shaped clusters of (Fe, Mn)-rich precipitates were observed along the grain boundaries and in the matrix. The temperature dependence of the yield strength of as-cast Fe25Ni25Mn20Al30 was also studied.

Mo fiber reinforced NiAl in-situ composites with a nominal composition Ni-43.8Al-9.5Mo (at.%) were produced by specially controlled directional solidification (DS) using a laboratory-scale Bridgman furnace equipped with a liquid metal cooling (LMC) device. In these composites, single crystalline Mo fibers were precipitated out through eutectic reaction and aligned parallel to the growth direction of the ingot. Mechanical properties, i.e. the creep resistance at high temperatures (HT, between 900 °C and 1200 °C) and the fracture toughness at room temperature (RT) of in-situ NiAl-Mo composites, were characterized by tensile creep (along the growth direction) and flexure (four-point bending, vertical to the growth direction) tests, respectively. In the current study, a steady creep rate of 10-6s-1 at 1100 °C under an initial applied tensile stress of 150MPa was measured. The flexure tests sustained a fracture toughness of 14.5 MPa·m1/2at room temperature. Compared to binary NiAl and other NiAl alloys, these properties showed a remarkably improvement in creep resistance at HT and fracture toughness at RT that makes this composite a potential candidate material for structural application at the temperatures above 1000 °C. The mechanisms responsible for the improvement of the mechanical properties in NiAl-Mo in-situ composites were discussed based on the investigation results.

A couple of FeAl alloys containing up to 1.4 at.% Li have been produced by vacuum induction melting. Though previous reports indicated a significant effect of Li on the properties of FeAl, no marked changes with respect to binary FeAl are observed. Specifically, no decrease of the lattice constant and no significant increase in ductility are found by alloying with Li. If at all, there is a slight increase of the lattice constant.

We have examined the compression response of a ternary Fe2Nb Laves phase by deforming micropillars with a diameter of ~2 μm produced by focused ion beam milling from a two-phase Fe-15Nb-40Ni (at.%) ternary alloy consisting of the Laves phase and γ-Fe. The Laves phase micropillars exhibit high strength of about 6 GPa (of the order of the theoretical shear strength of the material), followed by a burst of plastic strain and shear failure on the basal plane. If dislocation sources are introduced on a non-basal plane in the micropillars by nanoindentation prior to compression, yielding occurs at a significantly lower stress level of about 3 GPa and plastic deformation by slip proceeds on a pyramidal plane close to (-1-122). Furthermore, if regenerative dislocation sources for basal slip are present in the micropillar, the Laves phase can be continuously plastically deformed in a stable manner to at least 5% strain at a significantly lower stress of 800 MPa. We thus demonstrate the plastic deformation of this ternary Laves phase at the micron-scale at room temperature when sufficient dislocation sources are present.