Keiichi N. Ishihara

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.

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.

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.

FeAl multilayers by sputtering: heat treatment and the phase evolution

Abstract Multilayers of Fe and Al corresponding to the composition Fe 58 A1 42 (equal layer thickness) have been deposited by sputtering. The as-deposited layers have been characterised by X-ray diffraction (XRD) techniques and transmission electron microscopy (TEM) to determine the initial phases present. The results indicate the presence of both the elements and there is no evidence for any intermetallics to be present in the as-deposited films. The evolution and transformation of these elemental multilayers to intermetallic compound on heating is studied using differential scanning calorimetry (DSC) coupled with XRD and TEM techniques. The results of solid state heat treatment are compared to that of laser mixing carried out on these samples. Attempts are made to understand the sequence of the observed phases from the knowledge of thermodynamics and kinetics.

Bulk metallic multilayers produced by repeated press-rolling and their perpendicular magnetoresistance

Bulk Fe/Ag multilayers with layer thickness of about 10 nm have been successfully fabricated by repeated press-rolling directly from a macroscopic stack of metal sheets. The press-rolled multilayers exhibited giant magnetoresistance of 13% in the current perpendicular to the plane geometry and 4% in the current in the plane geometry at 5 K.

Mechanical alloying of Fe-B alloys

Mechanical alloying (MA) of Fe-B alloy systems using a conventional ball mill has been performed. The structure change of Fe100−xBx for the composition range 10≤x≤90 has been investigated using X-ray diffractometry, thermal analysis, transmission electron microscopy, scanning electron microscopy and Mössbauer spectroscopy. According to the X-ray diffraction analysis, the sequences of transformation have been classified into three groups,x≤20, 25≤x≤35 andx≥50 for Fe100−xBx. The amorphous phase whose composition is nearlyx=30, first appeared for the whole composition range. This amorphous phase changed into a tetragonal Fe2B-like compound on further milling for 1000 h. On further milling of thex= 50 sample, the Fe2B compound phase disappeared and orthorhombic FeB compound appeared.

The formation of metastable phases by mechanical alloying in the aluminum and copper system

A wide composition range of aluminum-copper alloys has been prepared by mechanical alloying (MA). The microstructure and phase formation have been investigated by X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy. The primary grain size of the powders subjected to ball milling for the aluminum-rich compositions is less than 30 nm. The solid solubility of coppe in aluminum can reach 2.7 at. pct Cu and that of aluminum in copper can reach 18.0 at. pct Al. Over a wide composition range, formation of a nonequilibrium distorted body-centered cubic (bcc) phase which possesses some ordering has been confirmed.