Fe-16%Cr-17%Ni-0.1%P alloy specimens were irradiated with 28 MeV electrons to a dose of 6.0×10²² e/m² at 77 K and the positron annihilation lifetime measurements were carried out to obtain the isochronal annealing behaviour of radiation-induced defects above room temperature. The three component analysis of lifetime spectra showed that the decrease of second component intensity I₂ occurred at about 373 K and 550 K, which are considered to be due to disappearance of mono-vacancies by two different processes, namely, recombination with migrating self-interstitial atoms (SIA’s) (373 K) and long range migration of mono-vacancies to sinks (550 K). This latter stage is about 80 K higher than the corresponding stage in Fe-13%Cr-14%Ni alloy specimen, which must be due to the vacancy-phosphorus interaction. The third component (microvoid component) intensity has a peak at about 373 K and disappeared below 500 K.

View full abstract

The reversible processes of structural relaxation in Fe₇₈B₇Si₁₅ and Fe₄₀Ni₄₀P₁₄B₆ amorphous alloys were investigated by means of electrical resistivity and Mössbauer effect measurements, and these are then compared to each other and discussed. A significant difference in the contribution of chemical short range ordering (CSRO) to the electrical resistivity is observed between the two amorphous alloys: the resistivity increases with annealing temperature in Fe₇₈B₇Si₁₅ alloy but decreases in Fe₄₀Ni₄₀P₁₄B₆ alloy. The crossover effect for the resistivity is also observed in both alloys. A kinetics of CSRO in each alloy can be described as a log-normal distribution of relaxation times. The mean activation energy of the CSRO process is 222.0 kJ/mol for Fe₇₈B₇Si₁₅ alloy and 135.1 kJ/mol for Fe₄₀Ni₄₀P₁₄B₆ alloy. As a result it is suggested that the reversible resistivity changes of Fe₇₈B₇Si₁₅ and Fe₄₀Ni₄₀P₁₄B₆ alloys are responsible for CSRO between Fe and Si atoms in the former, and that between Fe and Ni atoms in the latter.

View full abstract

The effects of hydrostatic pressure on the martensitic transformations from β₁ to β₁′ in single- and poly-crystals of a Cu-28.8Al-3.8Ni (at%) alloy, and from β₁ to γ₁′ in single crystals of a Cu-28.6Al-3.2Ni (at%) alloy have been investigated by means of electrical resistivity measurements and in-situ optical microscope observations under hydrostatic pressures up to 7 GPa. The results obtained were as follows: Transformation temperatures under hydrostatic pressure increased linearly with pressure, and the pressure dependence of thermodynamic equilibrium temperature obtained from the measured transformation temperatures was about 5 K/GPa for both alloys irrespective of the single- or poly-crystals. In-situ optical microscope observation revealed that the morphology and growth and/or shrink behavior of hydrostatic pressure-induced martensites were identical to those of the thermally induced ones. A thermodynamic analysis showed that the effects of hydrostatic pressure on martensitic transformations were successfully explained by taking account of the volume change associated with the martensitic transformation.

View full abstract

Tensile tests at room temperature were performed on a boron-doped Ni₇₆Al₁₉Ti₅ single crystal to investigate the effect of boron on the deformation and fracture behavior of single crystalline Ni₃Al-base intermetallic compounds. Both yield and fracture stresses of boron-doped Ni₇₆Al₁₉Ti₅ were larger than those of undoped Ni₇₅Al₂₀Ti₅ reported previously, whereas both elongation and work-hardening rate of the two crystals were almost the same at a given orientation.
By boron addition, the mixed modes of fracture on {111} planes and non-crystallographic planes were found to become predominant with suppressed cleavage appearance, which was explained by the increased cohesive strength between cleavage planes. As a result, the fracture of a boron-doped crystal is governed by the resolved shear stress on the fracture plane.

View full abstract

A novel integration of the Gibbs-Duhem equation has been presented for quaternary solutions containing two volatile components. The new integration formulae relate to calculation of the activities of nonvolatile third and fourth components from the measured activities of volatile first and second components. These formulae are more complex than the conventional ternary or quaternary integrations for solutions consisting of all nonvolatile (or only one volatile) components with constant concentration ratios, in that it contains an additional third term and it also involves integration of a product of two partial derivatives. The present formulae are essential to activity calculations for S-bearing slags or oxygen-containing sulfides, among others. An application of the new formulae has been demonstrated for the S–O–Fe–Cu system mattes by calculating the activities of iron and copper from the observed partial pressures of sulfur and oxygen.

View full abstract

The wettabilities of α-SiC, hot pressed SiC, and reaction bonded SiC by liquid Cu were investigated using the sessile drop method under various experimental conditions.
The main results obtained are summarized as follows:
(1) The contact angle of liquid Cu on SiC depended on SiC used.
(2) The characteristic wetting was observed in the liquid pure Cu/α-SiC system, which had a hexagonal wetted area.
(3) The appearance of hexagonal wetting depended on temperature and pressure: at lower temperatures and pressures, hexagonal wetting was observed, and at relatively higher temperatures and pressures, normal wetting was observed.
(4) The mechanism of the formation of hexagonal wetting is closely related to that of hexagonal etch pits by fused KOH solution.

View full abstract

The sessile drop method was used to study the effects of surface finish, heat treatment and cold working on the wettability of solid Cu by liquid Sn. Wettability was evaluated by measuring the angle of contact between the solid and the liquid phases. It was found that electrolytic polishing is better for obtaining good wetting than mechanical polishing. It was also indicated that annealing of solid Cu substracts could promote the wettability depending on the annealing period. Cold working was also found to have an influential effect on the wettability depending on the process and the degree of cold working. (Rolling promotes the wetting by decreasing the value of the contact angle of both mechanically and electrolytically polished Cu substrates, while pressing does not cause a significant effect on the contact angle of the mechanically polished samples but has an influential effect on the contact angle of the electrolytically polished samples). These results were discussed in relation to the crystal orientation and surface energy of the solid Cu substrates.

View full abstract

The behavior of carbon deposition on iron in 20%CO–H₂–H₂S mixtures containing small amounts of H₂S gas in the range without the formation of FeS was studied by metallography and thermogravimetry. Kinetic measurements showed that carbon deposition was retarded or accelerated depending upon the ratio of partial pressure of H₂S to H₂, P_H2S⁄P_H2. At P_H2S⁄P_H2≤2.5×10⁻⁵, the rates of carbon deposition increased with P_H2S⁄P_H2, whereas the rates decrease at P_H2S⁄P_H2=5×10⁻⁵−1×10⁻³. This carbon deposition behavior may be ascribed to the acceleration or retardation of Fe₃C formation and decomposition as well as the depression of filmy carbon deposition by the action of adsorbed sulfur on the iron surface through the dissociation reaction of H₂S gas. Small amounts of H₂ in gas were found to depress the deposition of filamentous carbon, so that a part of H₂ gas may become atomic hydrogen to stabilize Fe₃C and retard its decomposition. At P_H2S⁄P_H2≤2.5×10⁻⁵, the adsorbed sulfur may have accelerated the decomposition of Fe₃C to promote the deposition of filamentous carbon by the following reaction that removes atomic hydrogen:
2H(ad)+S(ad)→H₂S(g)
At P_H2S⁄P_H2≥5×10⁻⁵, however, the excessive adsorbed sulfur over atomic hydrogen may have stabilized Fe₃C to retard the deposition of filamentous carbon.

View full abstract