Phase decomposition and ordering reactions in beta-phase containing TiAl alloys were utilized to establish a novel, previously unreported, type of laminate microstructure. The characteristic constituent of this microstructure are laths with a nanometer-scale substructure that are comprised of several stable and metastable phases. The constitution and microstructure of this novel type of alloy has been assessed by high-resolution transmission electron microscopy. Finally brief mention is made of the mechanical properties of the material.

We studied antiphase domain (APD) growth and lamellar structure formation during isothermal annealing of Ti-39at%Al single crystals at α2+γ dual phase temperature after quenching from α single phase state, intending to obtain a APD/lamellae mixed microstructure and to examine whether such a microstructure provides a strength higher than that obtained only by refining lamellar structure. The effect of plastic deformation prior to the annealing was also examined expecting a acceleration of γ lamellae formation through a preferential nucleation of γ-plates at dislocations. The lower was the annealing temperature, the smaller both the APD size and the lamellar spacing at the moment of a homogeneous lamellar structure formation tended to be, although naturally both the APD growth and the γ lamellae formation were slower. However, the APD size in the homogeneous lamellar structure was no smaller than 400 nm. A structure with finer APDs and finer lamellar structure was obtained by deforming the crystal before annealing since the lamellar structure formation was accelerated and the time for APD growth before the lamellar structure formation was shortened. For instance, a structure with an average lamellar spacing of 88 nm and an average APD size of 214 nm was obtained by deforming the crystals to 10 % plastic strain and subsequently annealing at 1073 K for 1×104 s, while no γ plate was obtained only by such an annealing without deformation.

The thermal stability of multiphase intermetallics at temperatures to 1400°C was investigated by studying two model eutectic systems: Cr-Cr3Si having a lamellar microstructure and NiAl-Mo having a fibrous microstructure. In drop cast Cr-Cr3Si, coarsening was found to be interface controlled. The coarsening rate could be reduced by microalloying with Ce and Re, two elements which were chosen because they were expected to segregate to the Cr-Cr3Si interfaces and decrease their energies. Similarly, directional solidification, which is also expected to lower the Cr-Cr3Si interfacial energy, was found to dramatically decrease the coarsening rate. In the case of NiAl-Mo, coarsening was found to occur by fault migration and annihilation. Microalloying with B was found to significantly decrease the coarsening rate. The fiber density in the B-doped alloy was smaller than in the undoped alloy, suggesting that B affects the coarsening rate by lowering the fault density.

The microstructure, defect structure and thermoelectric properties of two different semiconducting transition-metal silicides, ReSi1.75 and Ru2Si3 upon alloying with a substitutional element with a valence electron number different from that of the constituent metal have been investigated in order to see if the crystal and defect structures of these silicides and thereby their physical properties can be controlled through defect engineering according to the valence electron counting rule. The Si vacancy concentration and its arrangement can be successfully controlled in ReSi1.75 while the relative magnitude of the metal and silicon subcell dimensions in the chimney-ladder structures can be successfully controlled in Ru2Si3. As a result, the improvement in the thermoelectric properties and the p- to n-type conduction transition are successfully achieved respectively for these semiconducting transition-metal silicides.

All shape memory binary alloys (SMBA) that exhibit not only perfect shape recovery but also partial shape recovery were reviewed and classified into three groups, B2, A2 and A1 type, according to the parent phases. There are the thirteen, six and eleven alloys belonging to B2, A2 and A1 type, respectively. In the group of B2 type SMBA the alloys are divided into two categories due to the combination of the elements. Over A1 and A2 type SMBA the atomic composition of one element is larger than the other so the larger one is called a major element. The major elements, Ti, U, Fe, and Cu, of A2 type SMBA do not belong to the group 5 and 6 in which the elements have a typical BCC (A2) crystal structure. In the A1 type SMBA there are four major elements, Mn, Fe, Co, and In and the SMBA except for In-based SMBA have ferromagnetic or antiferromagnetic natures. The shape memory effect (SME) for A1 (FCC) type SMBA might need the magnetic properties.

In this paper we provide a summary review of our research regarding the effect of composition on the A1 to L10 transformation in binary FePt with compositions in the range of 39.3 to 55.3 at.% Pt and ternary FeCuPt alloys with Cu additions in the range of 1.0 to 19.4 at.%. These binary and ternary alloy films have been studied using non-isothermal differential scanning calorimetry (DSC) combined with the calculation of TTT diagrams generated via experimentally validated Johnson-Mehl-Avrami-Kolmogorov (JMAK) analysis. Composition is found to play a significant role in the transformation kinetics in both FePt and FeCuPt. However, when comparing equivalent FePt and FeCuPt alloys, the addition of Cu has no significant effect. TTT diagrams show that as little as a 90 °C increase in peak temperature from the DSC measurements can result in a >300× increase in the time required for full transformation using isothermal anneals. Our results on the effect of Cu additions are compared with those reported in the literature.

Texture evolution during grain growth was examined in the 84% cold-rolled Ni3Al with a Goss texture, {110}<001>, using the electron backscatter diffraction method. By recrystallization at 873K/0.5h, the texture was disintegrated and composed of several orientations, most of which had a 40° rotation relationship about <111> to the Goss orientation. Also, a small number of the Goss grains existed. With grain growth, the Goss grains grew faster than the 40°<111> rotated grains, leading to the texture reversion to the original, Goss texture. This phenomenon can be referred to Texture memory effect. In the early stage of the grain growth, the preferential growth occurred on the Goss grains surrounded by the 40°<111> rotated grains. It can be thus ascribed to the high mobility of 40°<111> grain boundary. In the late stage, the Goss grains were adjacent to each other and the preferential growth was accelerated. It is considered that the adjacent Goss grains survived in the grain coalescence process since the boundary between them are low angle boundary having a low energy.

Pump-probe imaging of femtosecond pulsed laser ablation was performed to investigate the mechanical shock induced on an intermetallic superalloy CMSX-4 during femtosecond laser machining. Time resolved shadowgraphic images were collected of the shock wave produced in the air above the target following laser exposure (0-10.3 nanoseconds). The dimensions of the shock wave were measured as a function of delay time and laser fluence (1.27 J/cm2 - 62.8 J/cm2). Time-resolved shadowgraphic images of the ablation event will be presented, and the corresponding damage morphology as a function of incident laser fluence will be discussed.

Using alloys whose initial microstructures are composed of Ni3Si(L12), Ni3Si(L12)+Ni3Ti(D024) and Ni3Si(L12)+Ni3Nb(D0a), aging phenomenon and the associated high-temperature tensile property were investigated. It was shown by micro hardness measurement that age hardening behavior due to the precipitation of the Ni3Ti(D024) phase occurs in all alloys at temperatures above 823K. It was however shown by tensile test that the precipitated Ni3Ti(D024) phase is not so much effective in improving the mechanical properties of alloys whose initial microstructures are composed of Ni3Si(L12)+Ni3Nb(D0a) or Ni3Si(L12)+Ni3Ti (D024). In alloys whose initial microstructures are composed of Ni3Si(L12)+Ni3Nb (D0a), a good combination of tensile strength and tensile elongation was found over a wide of test temperature whether or not they contain the precipitated Ni3Ti(D024) phase.

Dual multi-phase intermetallic alloys composed of Ni3Al (L12)+Ni3V (D022) phases were developed, based on the Ni3Al-Ni3Ti-Ni3V pseudo-ternary alloy system. High-temperature tensile deformation, fracture behavior, and compression and tension creep were investigated using polycrystalline and single crystalline materials. The alloys with such a novel microstructure show extremely high yield and tensile strength with good temperature retention, and also reasonable tensile ductility. Also, creep test conducted at high temperature showed extremely low creep rate and long creep rupture time. The obtained results are promising for the development of a new-type of high-temperature structural material exceeding conventional superalloys.

Spark plasma sintering (SPS) has been used in order to introduce nanocrystalline grains within fully dense FeAl consolidated parts. Hetero-nanostructured parts, consisting of nano, ultrafine and micrometric grains, have been successfully processed when milled - Y2O3 reinforced - FeAl powder was used. The large temperature differences that are spontaneously generated during the SPS process as well as the use of milled powder account for the formation of such interesting structures. The grain size distribution - that is suggested to be very potent to improve both strength and ductility - could be significantly modified by a proper selection of sintering temperature and holding time.

The L10 ordering equiatomic intermetallic FePd has been used as a model system for the investigation of the evolution of microstructure and properties during annealing at temperatures below the ordering temperature after deformation in the L10 state. The two different routes for the preparation of equiaxed L10 FePd polycrystals, annealing after cold deformation in the disordered FCC state or after cold deformation in the ordered state, produce similar grain size distributions, differ in the transformation kinetics and importantly in the sequence of texture evolution during the post-cold-deformation annealing. Cold deformed L10 FePd progresses through the classic stages of annealing known from studies of disordered elemental metals and alloys based on them. The reduced L10 SLRO of the ‘mechanically disordered’ FePd is recovered in the early stages of annealing and both the recrystallization and the grain growth stages are quite sluggish, presumably because of the slow diffusion processes in the L10 lattice.

A 3-phase Mo-Si-B alloy consisting of Mo solid solution and the intermetallic phases Mo3Si and Mo5SiB2 (T2) was manufactured employing mechanical alloying (MA) as the crucial processing step. After consolidation via cold compaction, sintering in hydrogen atmosphere and final hot isostatic pressing (HIP) at 1500°C, one obtains an ultra-fine microstructure with a nearly continuous Mo(ss) matrix and the sizes of all phases being in the 1 micron range. Tensile tests were carried out in vacuum at initial strain rates ranging from 10-4 to 10-2 s-1 and the temperature varied between n1200 an 1400 °C. With a stress exponent of about 2 and the activation energy being close to that of Mo-self diffusion the material exhibits superplasticity at temperatures as low as 1300°C and tensile strain to failures up to 400%, thus, making sound wrought processing on industrial-scale facilities at temperatures typical for refractory metals and alloys feasible. To enhance creep resistance at high temperatures the alloys were annealed at 1700°C for 10h for a coarsening of the microstructure. While, still, the average sizes of all phases were below 10 microns, a considerable reduction in minimum creep rate was noted. This finding also demonstrates the extraordinary high thermal stability of this 3-phase Mo-silicide alloy.

The sintering of TiAl alloys by the Spar Plasma Sintering (SPS) technique is investigated in the present paper. Compactions are conducted between 1100°C and 1225°C on a Ti49Al47Cr2Nb2 powder. Single phased and lamellar microstructures are generated at low and high temperatures, respectively. The former exhibits enhanced tensile properties at room temperature but at the expense of a limited creep resistance. On the other hand, the latter suffers from a poor ductility.

The deformation systems which are activated are determined by post-mortem transmission electron microscopy. The behavior of the single phased-alloy is analyzed in terms of the Hall-Petch law.

Lack of strength, in particular creep resistance, has been considered as the principal shortcoming of Fe-Al-based alloys for long which prevented their use for structural applications at high temperatures. Only recently it has been realized that various strengthening mechanisms are available by which Fe-Al-based alloys can be sufficiently strengthened for applications at high temperatures. From the recent studies at the Max-Planck-Institut für Eisenforschung GmbH (MPIE) examples of applying different strengthening mechanisms are presented by which Fe-Al-based alloys with considerable creep resistance have been obtained.

In this study, the origin of large ductility that is seen in recently discovered rare-earth intermetallic compounds: YCu, YAg and YZn is explored by using fully anisotropic 3D dislocation dynamics simulations. The stability of the glide dislocations, the behavior of the Frank-Read sources and the strength of junctions are evaluated and compared to those seen for the common intermetallics, NiAl and Fe-25Al.

In-situ tensile-creep experiments were performed on a Ti-15Al-33Nb(at%) alloy using a specialized tensile stage placed within the vacuum chamber of a Camscan 44 FE scanning electron microscope (SEM). The creep damage evolution on the sample surface was chronicled through backscattered electron (BSE) imaging as a function of stress, time, and creep displacement at 650°C. The experiments revealed that the prior-BCC grain boundaries were the locus of damage accumulation during creep and significant grain boundary cracking was observed. The grain boundary cracking was verified to occur within the bulk of the material through post-mortem analysis.

Fe-Co-V-C quaternary alloys were drop cast and directionally solidified to obtain an in situ composite. It is found that the fully eutectic structure occurs at a composition of Fe - 40.5Co -10.4V- 8.6C (at. %) in a drop-cast alloy. Directional solidification of this composition in a high-temperature optical floating zone furnace produces a well-aligned microstructure, consisting of sub-micron VC fibers (~19% by volume) embedded in a FeCo-5V solid solution matrix containing ~ 1% C. The temperature dependencies of mechanical properties of this composite were examined by tensile tests and the composite was found to have higher yield strength and lower ductility than the matrix.

Nanoporous surfaces are formed in B2-type FeAl single crystals by quenching into iced water, followed by surface treatment and aging heat treatment. From our previous works, it was indicated that the nanoporous phenomenon is caused by the clustering of supersaturated thermal vacancies. In this study, the clustering process of supersaturated thermal vacancies was systematically investigated by transmission electron microscopy (TEM). An irreversible exothermic peak was detected for as-quenched specimens by differential scanning calorimetry (DSC). The isochronal changes of surface morphology and substructure around the exothermic peak temperature were clarified by TEM observation. The average size of the surface pores monotonously increased with increasing the temperature. Dislocations whose Burgerse vectors are parallel to <100> existed in the isochronally-heated single crystals, and its density was changed with heat treatment temperature. On the other hand, there was no dislocation zone from surface to the depth of several tens nanometers. A growth model of the surface pores is discussed

Nb-silicide based in-situ composites are promising materials for future high-temperature structural applications. Nb-silicide composites are typically alloyed with Hf, Ti, Cr, and Al to provide a balance of mechanical and environmental properties. A thermodynamic description of the Nb-Cr-Si system has been developed previously in literature based on reported isothermal sections. According to the previously calculated phase diagrams, selected alloys were directionally solidified. The as-solidified microstructures could not be interpreted using the liquidus projection calculated from the existing thermodynamic descriptions. Therefore, an improved thermodynamic description was developed by incorporating the new experimental data.