Soji Nenno

Crystal structure and morphology of the metastable X phase in shape memory Ti-Ni alloys

Abstract The crystal structure and the morphology of the metastable X phase which appears in shape memory Ti-Ni alloys have been investigated by transmission electron microscopy and X-ray diffraction. The crystal structure has been determined to be rhombohedral and to belong to the space group R 3 , where the rhombohedral unit cell contains six titanium atoms and eight nickel atoms. The atom positions and the lattice parameters have been determined. The orientation relationship between the X phase and the matrix, and the habit plane have also been determined.

Temperature and Orientation Dependence of the Yield Strength of Ni3(Al, W)

The temperature and orientation dependence of the mechanical behavior of Ni3(Al, W) was investigated by compression tests on single crystal specimens. It was found that at low temperatures {111} slips operate, whereas at elevated temperatures {100} slips operate, and also that the positive temperature dependence of the yield strength occurs only in the temperature range of the {111} slips. The peak-strength temperature (transition temperature of the slip system) changes largely depending on the orientation of the compression axis. The critical resolved shear stress of the primary (111)[10] slip is also orientation dependent in a similar way to that of Ni3Ga and Ni3Ge; it increases as the stress component of the (010)[10] cross-slip increases.

Electron microscope observation of the early stages of thermoelastic martensitic transformation in a TiNiCu alloy

Abstract In situ observations by electron microscopy were made on nucleation and growth of a thermoelastic martensite in a Ti39.5Ni10.0Cu(at.%) alloy. It has been found that a stress field near defect aggregates plays an important role in the martensite nucleation. The habit plane of the martensite plates in the early stages of formation was determined to be the (334) plane of the parent cubic lattice by trace analysis. The evperimentally determined habit plane was in good agreement with the theoretically predicted one. The atomic configuration along the habit plane was considered on the basis of the evperimentally determined lattice deformation. It has been found that the macroscopic (334) habit plane is composed of (112) steps.

Transition from short-range to long-range order in Ni4Mo

Abstract Transmission electron microscopic observation was made on the transition from short-range to long-range order in Ni4Mo. The transition was found to take place by nucleation and growth of long-range-ordered domains in the short-range-ordered matrix.

Anti-phase domains and dislocation configurations in the Fe-13 at. % Si alloy

Abstract Transmission electron microscopic observations have been made on the thermally produced anti-phase domain structures and the dislocation configurations associated with ordering in the Fe-13 at. % Si alloy. Dislocations have been found to move as pairs of ordinary dislocations bound together by an anti-phase boundary of the (¼)a 0′ 〈111〉 type on {110}, {112} and {123} planes. The anti-phase boundaries of the (1/2)a 0′ 〈100〉 type very likely left behind dislocation pairs have also been observed.

Field-Ion Microscope Study of Early Stages of Ordering in Ni4Mo Alloy

Field-ion microscope observations are made on the Ni4Mo alloy to investigate the ordering process during isothermal annealing at 800°C after quenching from high temperature α-region. Field-ion images of the Ni4Mo alloy in the early stages of annealing at 800°C indicate that long-range ordered domains are distributed sparsely in the short-range ordered matrix. Thus, it is concluded that the ordering at 800°C takes place by nucleation and growth of long-range ordered domains in the short-range ordered matrix. It has been found that the ordering process of the alloy is sensitive to heat treatment, namely heating rate to the annealing temperature, 800°C, from room temperature. Some features such as dark regions observed in field-ion images of the Ni4Mo alloy are briefly discussed.

SURFACE ENERGY AND EQUILIBRIUM SHAPE OF L12-TYPE A3B ORDERING ALLOYS

Abstract Calculation of surface energy of Dla type A4B ordering alloy was made on the basis of a broken bond model using Bragg-Williams approximation. Numerical results for Ni4 Mo alloy were presented in detail as functions of surface orientation and degree of order. Calculated surface energy anisotropy in the disordered and the ordered states was shown. Change in surface energy with increasing degree of order was investigated. It was shown that surface energy changes were quite different depending on the type of a plane parallel to the surface and on the six kinds of variants on ordering. The above calculations can explain our experimental results qualitatively: (i) preferential surface ordering and (ii) surface disordering. Applying Wulffs theorem to a calculated γ-plot of the alloy, its equilibrium external shapes for the ordered and the disordered states were predicted. The Miller indices of the facet planes in the equilibrium shape in the disordered state agreed with those found by our experiment.

Field-ion microscope observation of ordering in the near-surface of Ni4Mo alloy using in situ annealing

Abstract Field-ion microscope observations were made on Ni 4 Mo alloy to investigate surface effects on ordering during in situ annealing after quenching from high temperature α phase region. Surface ordering occurred preferentially at {200} FCC and/or {111} FCC facets (at 880–835°C). Surface layers with low degree of order ranging from ten to a few tens angstroms in thickness were formed (at 760–720°C). The degree of order in relatively large ordered domains decreased near the surface (at 825–810°C). In the interior of the specimens at a range of depths 100–300 A from the surface, ordering behavior was essentially the same as that for bulk specimens (at 825–720°C). Homogeneously nucleated ordered domains coexisted with relatively large heterogeneously nucleated ones in the interior of the specimen (at 670°C). Certain relatively low index (FCC) planes faceted (at 880-720°C). Faceting originating from β structure (ordered structure) occurred on the surface (at 670°C). In addition, in situ formed deformation twin was observed (at 810–825°C).

Detection and Determination of Equilibrium Vacancy Concentrations in Aluminum

In order to obtain a direct information concerning the equilibrium vacancy concentrations and the energy of formation of a vacancy in Al, a method of combining the bulk and lattice thermal expansion measurements was used. In the present work, only the lattice thermal expansion measurements on 99.996% pure Al were made. The data obtained were analyzed using bulk thermal expansion data on Al of the same purity available in the literature. The concentration of vacancies increases exponentially with temperature and its value at the melting point is (1.1±0.2)×10 -3 and the energy of formation of a vacancy is estimated to be (0.64±0.12) e V .

Field-Ion Microscope Studies of Ni4W Type Ordering in the Near-Surface of Ni-16.6 at%W Alloy

Field-ion microscope observations were made on Ni-16.6 at.%W alloy quenched from the high temperature α phase region to investigate Ni4W type ordering in the near-surface during in-situ annealing. Somewhat below the peritectoid temperature, disc-shaped Ni4W domains of the particular variants were formed preferentially at some of {420}FCC planes on the surface regions with their disc faces being {110}BCT superlattice planes (at 950°C for ca. 5 min). The relaxation time of occurrence of an ordered domain at one of the {420}FCC nucleation sites and the rate of its thickness-increase were evaluated to be 520±260 s and 0.10±0.08 A/s, respectively. Surface layers of a few to fifteen angstrom in thickness with lower degree of order were formed upon annealing for a few minutes at 920–860°C. The degree of order in the near-surface also decreased upon annealing partially ordered tips at the same temperatures.