Paul Hideo Shingu

Fundamental absorption edge in GaN, InN and their alloys

Abstract Optical measurements were performed near the fundamental absorption edge for thin polycrystalline films with the entire region of composition in the GaNInN quasi-binary system. The direct energy gap E g for GaN and InN was found to be 3.40 and 1.95 eV, respectively. The dependence of E g on composition was found to deviate downward from linearity. The degree of bowing was expressed well by the theoretical bowing parameter (1.05 eV) calculated by the dielectric method.

Nanocrystalline metals prepared by low energy ball milling

The influence of low energy ball milling on the crystallite size, lattice strain, and storage of deformation energies of elemental metal powders is studied. The formation of nanosized grains (5–25 nm) and enhancement of lattice strain up to 0.4% is found. Excess enthalpies of up to 25% of the heat of fusion are reached.

Formation of a super-saturated solid solution in the AgCu system by mechanical alloying

Abstract Mechanical alloying in the AgCu system by the ball-milling and repeated rolling methods was performed. A super-saturated f.c.c. solid solution was formed in the entire composition range by ball milling. The lattice parameter change due to the super-saturated solid solution formation matched quite well with the reported result obtained by rapid quenching. Upon heating, the super-saturated solid solution decomposed into base silver and copper solutions, resulting in a large reduction of electrical resistivity.

Metastable phases of Al–Fe system by mechanical alloying

Abstract The preparation and characterization of metastable phases of the Al–Fe alloy system by mechanical alloying are reported. In Al-rich (up to 10 at.% Fe) alloys, the supersaturated f.c.c. solid solution of Fe in Al (up to 1 at.% Fe) is formed. Almost complete amorphization is confirmed in the composition range 17–33 at.% Fe. The metastable disordered b.c.c. solid solution of about 10 nm in grain size has also been formed by ball-milling for over 180 h in Fe-rich (above 50 at.% Fe) alloys. Examination of lattice parameter and magnetization have shown that the composition range and degree of disorder are comparable to those formed by crushing and sputter deposition.

Synthesis of near net shape high density TiB/Ti composite

TiB/Ti composite were produced by SHS (self propagating high temperature synthesis) under conditions of PHIP (pseudo-hot isostatic pressing). The synthesis conditions were optimized to produce highly dense materials conforming a high volume fraction of TiB. Self-propagating reaction of the Ti and B powders occurred above the α- to β-Ti transformation temperature (1155 K). The composites consist of Ti matrices with dispersed TiB reaction products of 2–30 μm size. Near fully dense composites with a TiB/Ti volume ratio of 33–44 vol.% were synthesized for B/Ti atomic ratios of 0.3–0.4 at pseudo isostatic pressures of 100 MPa. The Vickers hardness and fracture stress of the composites are 5.6–7.1 and 2.1–2.3 GPa, respectively, and the wear of the composite is approximately 7–9% of the Ti and Ti–6Al–4V.

Formation and crystallization of Al-Fe-Si amorphous alloys

Rapid solidification experiments of Al-based Al-Fe-Si ternary alloys have been performed both by the gun and single roller methods. Glass forming tendency is found to be largest near theβ-phase (Al9Fe2Si2) composition, where the amorphous state is obtained both by the gun and single roller methods. Crystallization behaviour of amorphous AlFe13.0Si17.4 alloy, nearβ-phase composition, followed the course of (i) the appearance of fineα-Al particles and (ii) the transformation of the matrix intoβ-phase. The ratio of crystallization temperature and the melting point,Tx/Tm, for AlFe13.0Si217.4 amorphous alloy is smaller than 0.5 indicating the difficulty of glass formation of these alloys.

Mechanical alloying of the high carbon FeC system

Abstract Mechanical alloying of iron and graphite powders was performed in composition range Fe1 − xCx (x = 0.17−0.90) by the use of a conventional ball mill. The structures of mechanically alloyed samples were examined by X-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy, 57Fe Mossbauer spectroscopy and differential scanning calorimetry. The results from X-ray, TEM and Mossbauer measurements suggested the partial formation of amorphous phase. Amorphization was notable on the sample ball milled for about 200 h. After subsequent milling, formation of metastable carbides Fe3C for the powders with x = 0.17−0.25 and Fe7C3 for x = 0.29−0.70 was detected. Formation of fine paramagnetic particles was detected by Mossbauer spectroscopy for the powders having carbon content x = 0.80−0.90.

Formation of metastable phases of Ni-C

Mechanical alloying (MA) of nickel and graphite powders was performed in the composition range Ni1-xCx (x = 0.10 to 0.90) by use of a conventional ball mill. The structure of me-chanically alloyed samples was examined by X-ray diffraction, transmission electron micros-copy (TEM), scanning electron microscopy (SEM), and differential scanning calorimetry. A remarkable supersaturation of carbon in face-centered cubic (fcc) nickel phase was observed. A metastable phase Ni3C was formed by a prolonged MA treatment. For the purpose of com-parative study, MA of cobalt and graphite powders was also performed in composition Co1-xCx(x = 0.10, 0.15, and 0.30). The supersaturation of carbon in fcc cobalt and formation of a metastable carbide Co3C were confirmed.

Mechanical alloying in the FeAl system

Abstract The mechanical alloying technique has been applied to alloy synthesis from FeAl powder mixtures containing 10, 20, 30, 40 and 50 at.% Al. An evolution of the powder morphology from flaky in the first stage to spherical in the final stage has been observed. The particle size has been estimated as 50 and 5 μm in the first and final stages of milling respectively. For all alloys studied a disordered b.c.c. solid solution has been formed by ball milling. A grain size of several nanometres and a maximum r.m.s. strain level up to 1% have been observed. The change in lattice parameter has been calculated to be up to 2.4%.

Formation of nanoscale Fe/Ag multilayer by repeated press-rolling and its layer thickness dependence of magnetoresistance

Abstract We have successfully fabricated Fe/Ag multilayers that simultaneously possess the layer thickness of 4 nm and the layer number of above 10 000 by applying the repetition of pressing and rolling directly from a macroscopic stack of metal sheets. The clear correlation between the Ag layer thickness and MR ratio is observed, indicating that the critical layer thickness exhibiting magnetoresistance is 100 nm.