Polysynthetically-twinned TiAl crystals were deformed by compression with loading axis parallel and perpendicular to the lamellar interfaces. The deformation structures on the free surfaces were scanned using a dimension AFM with scan directions parallel and perpendicular to the lamellar interfaces. Abnormal deformation behaviors were observed to occur in both orientations. When the compression axis is parallel to the lamellar interfaces, the gamma and alpha lamellae deform primarily by shear in planes inclined with the lamellar interface, while the shear vectors lie in the interface. However, in-plane shear, shear in slip planes parallel to the lamellar interfaces, also occurs along the lamellar interfaces. When the loading axis is perpendicular to the lamellar interface, in-plane shear was found to be dominant at the beginning stage of plastic deformation and contributes more to the macroscopic strain. These behaviors are controversial to the Schmid's Law since the applied resolved shear stress for these deformation systems is zero. The abnormal phenomenon was explained by the large coherency stresses along the lamellar interfaces.

Formation and morphology of D022 compound Ni3V in γ-fcc alloys were investigated as a model case in order to understand fundamentals for microstructure control of new class of austenitic steels strengthened by Kurnakov-type GCP intermetallic compound. The formation process of the D022 phase in γ matrix varies, depending on the composition and heat treatment temperature, and precipitation of D022 takes place at temperature above T0 in the γ+D022 two phase region. The morphology of coherent precipitates of the D022 compound is sensitive to misfit strains against matrix and can be controlled by alloying addition. The habit planes between the two phases become irrational, parallel to both directions of the invariant line and an a-axis of D022, since the lattice misfit becomes negative along a-axis (δa) and positive along c-axis (δc) of the D022. The calculation based on the lattice invariant theory as well as experimental results clearly demonstrate that the misfit strain ratio δc/δa is a dominant factor to determine the habit plane. In addition, the shape of D022 phase, either prism or plate, depends strongly on the magnitude of |δa|. These findings will extend to Ni-Fe-Nb-V quaternary system, by partial replacement of Ni with Fe and that of V with Nb.

Structure and mechanical properties of binary Ti-TM (TM-other transition metals) and ternary Ti-Fe-(TM, B or Si) alloys produced in the shape of the arc-melted ingots of about 25 mm diameter and 10 mm height are studied. The formation of high-strength and ductile hypereutectic alloys was achieved in the Ti-Fe, Ti-Fe-Cu and Ti-Fe-B systems. The structures of the high-strength and ductile hypereutectic alloys studied by X-ray diffractometry and scanning electron microscopy were found to consist of the primary cubic Pm3 m intermetallic compound (TiFe-phase or a solid solution on its base) and a dispersed eutectic consisting of this Pm3m intermetallic compound + BCC Im 3 m β-Ti supersaturated solid solution phase. The hypereutectic Ti-Fe alloy showed excellent compressive mechanical properties. The addition of Cu improves its ductility. B addition increased mechanical strength. Ni, Cr and Mn additions caused embrittlement owing to the formation of alternative intermetallic compounds. The deformation behaviour and the fractography of the Ti-based alloys were studied in details. The reasons for the high strength and good ductility of the hypereutectic alloys are discussed.

Sub-nano and nano-structures of intermetallics such as LaNi5 and its related alloys were studied by in-situ X-ray and neutron diffraction methods. From the profile shape analysis, changes in lattice strain and crystalline size during hydrogenation/dehydrogenation were estimated, while the crystal (sub-nano) structures were refined by the Rietveld method using diffraction patterns. The crystallite size of the alloys studied did not change during hydrogenation and dehydrogenation. It was found formation of remarkably dense dislocations and vacancies in the lattice of hydrides of LaNi5 and related intermetallics.

In Ni-Ti-Nb ternary system, there are some geometrically close-packed (GCP) phases with long-period stacking sequences of a close-packed plane (CPP). Among them, our focus is on the Ni3(Ti0.90Nb0.10) crystals with Pb3Ba-type rhombohedral structure with nine-fold stacking sequence. Compression tests were conducted using the single crystals and the temperature and orientation dependences of plastic deformation behavior were investigated in comparison with those of D024-Ni3Ti crystals with the four-fold stacking sequence. The K-W locking of screw dislocation was found to occur not only in the compounds such as Ni3Al and Ni3Ti with a relatively small unit cell, but also even in complex compounds with longer-period stacking structures by slip on the common CPP in the GCP structures.

Upon annealing an as-cast Mo-10Si-20B alloy at high temperatures, a Mo solid solution phase precipitates within a supersaturated Mo5SiB2 phase. The precipitation behavior of the Mo solid solution was investigated by means of transmission electron microscopy and X-ray diffractometry. It is found that the Mo5SiB2 phase in a Mo-10Si-20B alloy contains a significant amount of structural vacancies in the as-cast state. The excess vacancies are removed to form dislocations during annealing, which provides the heterogeneous nucleation sites for the (Mo) precipitates.

Thermal stability of fully lamellar microstructures in Ti-47Al-2Cr-2Nb (at.%) alloys with and without B additions has been evaluated in the temperature range of 800 to 1200°C. The alloy with 0.15B exhibits an α2 + γ fully lamellar microstructure containing ribbon-like structures (TiB2+β) inside the lamellar colonies. During aging at 800 and 1000°C, β particles surrounded by γ grains form adjacent to the ribbon-like structures. The formation of these grains is attributed to the precipitation of thin plate-like β phase along {1100} within the TiB2 ribbon particles, resulting in the loss of α2 plates around the ribbon-like structure by scavenging Ti. This allows coarsening γ lamellar plates to form new γ grains, and then the ribbon-like structure completely dissolves to leave only β particles. At 1200°C, discontinuous coarsening (DC) of the lamellae becomes the dominant mode of microstructural change for all the alloys. However, the ribbon-like structures in the alloy with B additions play a role in pinning the DC cells, which leads to higher thermal stability of the lamellar microstructure in that alloy.

In an attempt to produce a two-phase alloy consisting of a L21–structured (Fe, Ni)2MnAl-based phase in either a B2 or b.c.c. matrix, seven Fe-Ni-Mn-Al alloys were cast. Transmission electron microscopy (TEM) of the as-cast alloys revealed a range of microstructures including single phase L21, a f.c.c./B2 eutectic, and alternating, coherent 10–60 nm wide ordered and disordered b.c.c. rods aligned along <100>. A description of the phases, including chemical compositions and hardnesses is presented.

Targeting to develop E21 Co3AlC based heat resistant alloys, phase stability of E21 Co3AlC and (Co, Ni)3AlC has been investigated together with the magnetic properties of E21’ Co3AlC0.5 which is formed by the extra ordering of carbon atoms accompanying anti-phase boundary (APB). The correlation of ferromagnetism with APB in E21’ Co3AlC0.5 was evaluated using single crystals by high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer. Anti-phase domain (APD) size affects the ferromagnetism: for instance, the saturation magnetization becomes larger as the APD size is smaller. Local atomic configuration at APB was clearly observed by HRTEM image.

Ni-18at.%Al-4at.%Ti single crystals containing small γ precipitates in γ′ matrix were prepared by aging at 1073K after solution treatment from γ′ single phase region. The size, shape and volume fraction of the γ precipitates were examined during aging and deformation by means of changes in spontaneous magnetization and coercive force. Cyclic deformation behavior of these crystals was discussed through change in the morphology of γ precipitates using magnetic technique.

Several lamellar microstructures of a Ti-48 % Al alloy were made by changing heating rate in the α+γ dual phase field, and their creep properties were investigated at 1150 K. Average spacing and average length of α2 lamellae decrease with increasing heating rate. The decrease of α2 lamellar spacing is most effective at lower heating rate, and minimum creep rate decreases with increasing the heating rate, since a high density of γ/α2 boundaries stabilizes lamellar microstructure during creep. On the other hand creep rate increases at high heating rate, since α2 lamellar length becomes shorter with increasing heating rate. A reduction of creep rate by one order of magnitude is achieved at the optimum heating rate providing the best combination of narrow spacing and sufficiently long length of α2 lamellae.

Formation energies of antisite defects and vacancies were derived for the L12-ordered intermetallics Ni3Al, Ni3Ga, Pt3Ga, and Pt3In by a supercell ab initio approach. A thermodynamic treatment of point-like defects was then used for the calculation of temperature-dependent defect properties. Energy profiles for atom jumps in Ni3Al in systematically varied atomic neighborhoods were calculated by statically displacing the jumping atom or by using a nudged elastic band method. It is discussed how a kinetic Monte-Carlo model can be modified so that the jump barrier height reflects the strongest neighborhood influences.

Pseudoelasticity in Fe3Al single crystals doped with a small amount of Ga, Ge and Si was investigated focusing on the antiphase boundary (APB) energy and the ordered domain structure. Single crystals of Fe-23at%Al and Fe-21at%Al-2at%X (X=Ga, Ge, Si) were grown by a floating zone method. In Fe-23at%Al single crystals, superpartial dislocations with Burgers vector (b) of 1/4<111> moved dragging APB during loading, while APB pulled back the superpartials during unloading. This resulted in giant pseudoelasticity regardless of martensitic transformation and the recoverable strain was about 5%. Ga addition was found to be effective in increasing the recovery strain compared with Fe-23at%Al crystals. In contrast, both Ge and Si additions decreased the amount of shape recovery. Stress at which the shape recovery started, was increased by Ga, Ge and Si additions. This means the APB energy increased by the additions, since the surface tension of APB pulling back the superpartials increases with increasing the energy. On the other hand, the frictional stress of the superpartials with b=1/4<111> increased significantly by Ge or Si doping due to solid solution hardening, though the stress of Ga-doped crystals was almost the same as that of the binary crystals. Higher frictional stress of Ge- and Si-doped crystals made the reversible motion of the superpartials difficult, resulting in the small recovery ratio. Ordered domains with displacement vector (R) of 1/4<111> in Fe-23at%Al and Fe-Al-Ga alloys were observed to be small, less than 100nm. In contrast, Ge and Si additions increased the domain size to more than 500nm. Since the domain boundaries with R=1/4<111> played an important role in the individual motion of the superpartials with b=1/4<111>, the fine domain structure was found to be favorable for giant pseudoelasticity in Fe3Al single crystals. Ga addition increased the APB energy following the superpartials and kept the domain size small, resulting in the increase in recovery strain.

High strength γ-TiAl based alloys, such as Ti-46Al-5Nb-1W (Alloy 7), which were originally developed for gas turbine and automotive applications are now being considered for application in Micro Electro Mechanical Systems (MEMS). This requires the evaluation of these materials upon the microscale. As international standards do not currently exist for the evaluation of the mechanical properties of samples with dimensions equivalent to those required by MEMS devices, the development of new methods was required. The method developed here is intended for the fatigue testing of samples measuring ≈ 10μm (B) × 20μm (W) × 40μm (L). This is completed using a machine recently developed at Tokyo Institute of Technology to load samples of lamellar γ-TiAl based material to failure in compressive bending. This method is intended to work alongside methods previously developed for the fracture toughness testing of similar microsized cantilever bend specimens.

In this work sample cantilevers of Alloy 7 are Focussed Ion Beam (FIB) machined from foil ≈ 20μm thick and their stress - life (S-N) fatigue behaviour evaluated. The dependence of fatigue life upon lamellar orientation for a given peak stress / stress range is considered. The effect of the reduced scale of these samples upon the mean and scatter of these sample lifetimes is also considered through comparison with previous data obtained from the S-N testing of macrosized samples of the same material.

Two Ti2AlNb intermetallic orthorhombic (O) alloys, Ti-15Al-33Nb and Ti-21Al-29Nb(at.%), were subtransus processed into sheets, using pancake forging and hot-pack rolling, and evaluated in tension (25 and 650°C) and creep (650–710°C) and the properties and deformation behavior were related to microstructure. Some of the microstructural features evaluated were grain boundary character, grain size, phase volume fraction, and morphology. The alloy Al content was important to strength and elongation-to-failure (εf), where higher Al contents lead to greater tensile strengths and lower εf values and a corresponding brittle fracture response. However, the room temperature (RT) strengths of Ti-15Al-33Nb, which exhibited greater BCC phase volume fractions than Ti-21Al-29Nb and ductile failure (εf >2%), were always greater than 775 MPa. The creep stress exponents (n) and activation energies (Qapp) suggested that a transition in the dominant creep deformation mechanism exists and is dependent on stress and microstructure. Supertransus heat treatment, which increased the prior-BCC grain size and resulted in a lath-type O+BCC microstructure, resulted in reduced creep strains and strain rates. In fact, the supertransus heat-treated Ti-15Al-33Nb microstructures exhibited greater creep resistance than subtransus heat-treated Ti-21Al-29Nb microstructures. Combining the creep observations with the tensile response, the supertransus heat treated Ti-15Al-33Nb lath O+BCC microstructures exhibited the most attractive combination of tensile strength, εf values, and creep resistance.

Nb-silicide based in-situ composites consist of a ductile Nb-based solid solution with high-strength silicides, and they show excellent promise for aircraft engine applications. The Nb-silicide controls the high-temperature tensile behavior of the composite, and the Nb solid solution controls the low and intermediate temperature capability. The aim of the present study was to understand the effects of substitutional elements on the room temperature tensile behavior and identify the principal microstructural features contributing to strengthening mechanisms.

Thermo mechanical processing of equiatomic FePd has been used to establish a nearly equiaxed microstructure that consists of mono-variant L10 ordered grains. The technically important hard magnetic properties, e.g. coercivity, of the uniaxial ferromagnetic L10-FePd with equiaxed microstructure depend on the grain size. Thus, here, the evolution of grain size during the later stages of annealing has been studied using SEM and computer assisted image analysis with the goal to determine the activation parameters for the relevant coarsening processes. Using a classical grain growth analysis the activation parameter for coarsening of the 5% largest grains in the populations of L10-ordered grains in FePd has been determined as approximately 30kcal/mol.

We present results of comparative studies of the dislocation properties and the mechanical behavior for a class of intermetallic alloys based on platinum group metals (PGM) which are being developed for ultra-high temperature applications: Ir3X and Rh3X (where X = Ti, Zr, Hf, V, Nb, Ta). For the analysis of dislocation structure and mobility, we employ a combined approach based on accurate first-principles calculations of the shear energetics and the modified semi-discrete 2D Peierls-Nabarro model with an ab-initio parametrization of the restoring forces. Based on our analysis of dislocation structure and mobility, we provide predictions of temperature yield stress behavior of PGM-based intermetallics, show that their dislocation properties are closely connected with features of the electronic structure and the L12 → D019 structural stability, and demonstrate the dramatic difference in dislocation structure and the mechanical behavior between PGM alloys with IVA and VA group elements.

In lamellar TiAl, concerted deformation occurs in adjacent true-twin related variants (O/OT). When deformation takes place in a given variant, O, by activation of the slip system with highest shear stress, slip proceeds in the companion variant, OT, by operation of a slip system of the same family in mirror orientation, including the slip direction. Depending on load orientation, the latter system may not necessarily exhibit the highest resolved shear stress. The correlation does not depend upon Burgers vector orientation with respect to the interface.

This property applies to ordinary dislocations and twinning. The variant that conforms the Schmid law is referred to as the pilot variant, the twin-related variant is dubbed driven.

Correlations between the changes in martensitic transformation start temperature (Ms) by addition of ternary elements X and several factors of the ternary additions were investigated for TiNi shape memory alloy. The change of Ms by addition of 1mol%X is referred to as ΔMs (in K/mol%), and ΔMs was systematically evaluated by differential scanning calorimetry experimentally using (Ti, X)50Ni50 solution-treated at 1273K for 3.6ks where the Ni content was kept constant to be 50mol%. The ternary additions X investigated are the transition metal (TM) elements selected from 4th period group (Zr, Hf) to 10th period group (Pd, Pt). The factors investigated are (1) the number of total outer d- and s-electrons (Nele), and electron hole number (NV), (2) electronegativity (EN), (3) atomic volume (VX) and (4) Mendeleev number (NM). It was found that the values of ΔMs are different even in a same period group; ΔMs of 6th period group are -133K/mol%Cr (3d-TM), -152K/mol%Mo (4d-TM) and -64K/mol%W (5d-TM) for example. The results found in the correlations between ΔMs and those factors are summarized as follows. (1) ΔMs depends on Nele and NV. However, the data are scattered because same Nele and NV are often given in a same period group. Then, other factors than Nele and NV are required for clear understanding of ΔMs. (2) ΔMs seems to become lowered slightly with increasing EN. (3) ΔMs weakly depends on atomic volume VX. Ternary addition with large VX increases ΔMs slightly, and with small VX decreases ΔMs largely. Since the stress field must be formed by substitution due to size mismatch, the type of stress field, tension/compression, may be an important role to determine the sign of ΔMs. (4) ΔMs shows a good correlation with NM as -9.4Kmol%−1/ΔNM where ΔNM is the difference in NM. This suggests that a ternary alloying element with smaller (larger) NM stabilizes the B19’ martensite (B2 parent) phase. Effect of site occupancy on Ms is also discussed only for Cr.