Toru Imura

Melting temperature of In particles embedded in an Al matrix

Abstract The melting and freezing temperatures of small In particles with a radius r of less than 20 nm embedded in an Al matrix have been measured as a function of particle size using in situ heating in an electron microscope. The melting temperature of In particles whose radii are smaller than 15 nm is higher than that of bulk material and increases with decreasing r. The freezing temperature is lower than the melting temperature of bulk material for all radii studied and has a minimum at around r = 13 nm. The behaviour of the melting of embedded particles contrasts sharply with that of free particles, for which the melting temperature decreases with decreasing r. The difference is discussed in terms of the interfacial energies between the Al matrix and liquid or solid In.

Structure of chromium-rich Cr-Ni, Cr-Fe, Cr-Co, and Cr-Ni-Fe alloy particles made by evaporation in argon

Structural analyses were performed on alloy particles of chromium-rich Cr-Ni, Cr-Fe, Cr-Co, and Cr-Ni-Fe systems. Fine alloy particles (100 to 1000Å in diameter) were prepared by evaporation of parent alloys in argon at 20 torr. In addition, alloy structures of bulk specimens of the Cr-Ni system were investigated using X-ray diffraction techniques to confirm the results obtained from the particulate alloys. In these binary systems, δ phase with W3O structure (A-15) and a phase withβ-uranium structure (Db8) were identified in addition to the α (bcc) and γ (fcc) terminal solid solutions. The compositional ranges for the σ phase in the Cr-Ni, Cr-Fe, and Cr-Co systems are from low chromium to 68, 63.4, and 62.1 wt pct Cr, respectively. The δ phase exists in the range from pure chromium to 68, 58, and 54 wt pct Cr in the respective Cr-Ni, Cr-Fe, and Cr-Co alloy systems. Similarly, in the Cr-Ni-Fe system, it was found that δ phase occurs in the chromium corner while σ phase exists in the region bridging the two binary σ phases of the Cr-Ni and Cr-Fe systems. Possible modification of phase diagrams of these systems is discussed in view of these results.

Direct Measurement of Mobility of Edge and Screw Dislocations in 3% Silicon-Iron by High Voltage Transmission Electron Microscopy

A new method to investigate directly the dynamical properties of dislocations was developed by means of HVEM. The motions of edge and screw dislocations were observed in thick foil specimens of Fe-Si being stretched in a HVEM operated at 500 kV. The dislocation motions were recorded continuously on a video tape recorder (VTR) with the aid of an image intensifier and the corresponding stress-strain curve was also recorded simultaneously. Edge dislocations moved well below the yield stress and the frequency of their motions increased with increasing applied stress. Luders band nucleated at upper yield point and propagated in transition from upper to lower yield points. The motions of screws were observed immediately after upper yield point, accompanying dislocation multiplication. Edge dislocations had much higher mobility than screws but both of them moved much faster in comparison with the observation by etch-pitting technique.

On the intrinsic temperature dependence of the stacking-fault energy in copper-aluminium alloys

Abstract The temperature variation of the separation of Shockley partials of single dissociated dislocations in Cu-6·44 at. % Al and Cu-13·43 at. % Al has been measured by means of in situ thermal cycling experiments in a high-voltage electron microscope; a weak-beam high-resolution imaging technique was used for the observations. The variations of the partial separation on changing the temperature was analysed by taking into account such factors as temperature dependence of shear modulus, the solute impedance effect, the Suzuki effect and short-range order which may give rise to the variation of partial separation, in addition to the intrinsic temperature dependence of the stacking-fault energy γ. The intrinsic temperature dependence of γ was determined in the range 77 K to 1020 K for Cu-13-43 at. % Al and in the range 120 K to 723 K for Cu-6·44 at. % Al. The nature of the intrinsic temperature dependence of γ is discussed.

Preparation of bulk amorphous alloys by high temperature sintering under a high pressure

Abstract Until now, there have been no reports in which bulk amorphous alloys of the same densities as those of the corresponding ribbons had been successfully prepared from the amorphous alloy powders by static pressure. Because of the fact that the crystallization temperature Tx of amorphous alloys increased under a high pressure, measurements of Tx on Fe78B13Si9 alloy under pressure were carried out, and it was confirmed that Tx for the alloy rose at a rate of about 10 K GPa−1. Using this phenomenon, amorphous alloy powder of Fe78B13Si9 was compacted at temperatures just below Txh (Tx under a high static pressure) at 5.4 GPa. As a result, we could prepare bulk amorphous alloys with the same densities as those of the corresponding ribbons; it was not possible to prepare these alloys by high pressure compaction below Txo (Tx under ordinary pressure). Most of the physical properties of the compacts were similar to those of the ribbons.

The anomalous strength peak and the transition of slip direction in β-CuZn

Abstract The macroscopic slip directions of β-CuZn have been determined by studying the reorientation of single crystals with three different initial orientations during tensile deformation, between room temperature and 280°C, where the anomalous strength peak takes place. The macroscopic slip directions below and above T p (the temperature at which the peak in the curve of yield stress versus temperature occurs) were quite different from each other; below T p 〈111〉 slip was predominant, while above T p non- ≥ 111 ≥ slip was predominant. This result was in good agreement with TEM observation of the dislocation structures of β-CuZn deformed below and above T p. Thus, it is concluded that the anomalous strength peak and other peculiar phenomena observed in β-CuZn at high temperatures are to be attributed to a transition of the slip direction.

A newly developed warm extrusion technique for compacting amorphous alloy powders

Abstract Improvement in warm extrusion processing have been made to prepare bulk amorphous alloys from amorphous alloy powders. Flake-form amorphous alloys of Fe78B13Si9 and Co69Fe4Ni1Mo2B12Si12 were used. When a billet of powder, packed into a cylindrical container, was extruded, a completely homogeneous bulk amorphous alloy was not obtained. However, when a core of suitable material and diameter was placed along the central axis of the container, a homogeneous bulk amorphous alloy was obtained by extruding the billet under certain specific conditions. The compacts obtained, moreover, had a density equal to 99.9% that of ribbon, and the magnetic properties were the best so far reported for bulk amorphous alloys. In this paper, the effects of different process conditions on compactibility are also discussed.

Preparation of bulk amorphous alloys by explosive consolidation and properties of the prepared bulk

Abstract Preparation of bulk amorphous alloys was carried out by explosive consolidation, using iron- and cobalt-based flaky amorphous alloy powders or iron- and nickel-based spherical amorphous alloy powders. In the cylindrical compacts prepared at first, some cracks and crystallization were found in the region near the central axis. To prevent those occurring, a metallic bar with a shock impedance similar to that of the amorphous alloy powders was put at the centre of the container. As a result, bulk amorphous alloys with a density of 99.7% or more of the density of amorphous alloy ribbon were prepared successfully without inducing cracks. Other properties such as Youngs modulus, Curie temperature, electrical resistivity and Vickers hardness of the bulks were close to those of ribbon prepared by melt spinning.

Anti-phase boundary energy in β-CuZn

Abstract The ⟨111⟩ superlattice dislocations in a B2 ordered β-CuZn alloy have been studied using weak-beam electron microscopy, and the anti-phase boundary (APB) energy γ has been determined without ambiguity from the separation of two super-partials for {110} and {112} planes. Values of 50 mJ m−2 and 37 mJ m−2 are obtained for γ110 and γ112, respectively. The operative slip systems in β-CuZn at low temperatures have been discussed on the basis of the direct measurement of γ110 and γ112.

Single crystal growth of IVa-diborides from metal solutions

Abstract The conditions of growth of TiB 2 single crystals from iron, cobalt and nickel solutions and those of ZrB 2 and HfB 2 from iron solution have been investigated and the quality of the crystals grown by this method have been characterized. The diboride crystals were formed only when the mole percent of the metal diboride and solvent metal were higher than a critical value in each case. TiB 2 crystals grown from iron contained less than 0.2 wt% Fe, those from cobalt contained about 1 wt% Co and those from nickel contained more than 1.5 wt% Ni. ZrB 2 and HfB 2 crystals from iron solution included less than 0.5 wt% Fe. Etch-pit densities of the (0001) plane of TiB 2 single crystals grown from iron were lower than those from cobalt or nickel. It was possible to obtain single crystals of low etch-pit density in the case of ZrB 2 and HfB 2 . Lang X-ray topographs of TiB 2 , ZrB 2 and HfB 2 crystals grown from iron showed images representing low internal stresses. In contrast, the topographs of TiB 2 crystals grown from cobalt and nickel showed high internal stress images.