The melt spinning of Pb–Bi system alloy with Pyrex glass was investigated as a means of producing a superconducting long filament with high T_c.
A Pb₈₀Bi₂₀ filament with maximum T_c of 11.0 K was obtained from the molten state at 1500 K with a spinning speed of 0.95 m·s⁻¹. The filament was 43×10⁻⁶ m in diameter and a ductile material with tensile strength of 50 MPa and elongation of 2.9%. The filament consisted of fine crystal grains with grain size of 1000×10⁻¹⁰ m, and its structure was metastable and a mixture of fcc with ⟨111⟩ fiber texture and hcp.

View full abstract

The martensite to martensite transformation, β₁′→α₁′, stress-induced secondly in single crystals of Cu–Zn–Al alloys is crystallographically studied in detail. The transformation proceeds by a simple shear on the basal plane of β₁′ martensite with the 9R long period stacking structure to form the 3R stacking structure of fct. The crystallographic orientation relations are obtained to be (001)_β1′⁄⁄(111)_α1′ and [100]_β1′⁄⁄[11\bar2]_α1′. Two types of stress-strain curve, “two-stage type” and “stress-drop type”, are observed in the tensile test depending upon the tensile direction and testing temperature. In the former case, the α₁′ martensites are transformed after completing the first transformation β₁→β₁′, while in the latter, two variant crystals of β₁′ cross each other to produce the α₁′ martensite inside. The drop in stress level is well understood by considering the smaller critical resolved shear stress for the second transformation, τ_α, as compared with that for the first one, τ_β.

View full abstract

A large number of stress-strain (S-S) curves obtained for Cu–Zn–Al alloy single crystals with the electron atom ratio of 1.40 are quantitatively analysed, and values of the critical resolved shear stress (CRSS) for the two successive transformations, β₁\ ightleftarrowsβ₁′\ ightleftarrowsα₁′, are evaluated. As reported previously, two types of S-S curves, two-stage type and stress-drop type, are recorded depending upon the tensile direction and testing temperature. These curves are analysed by a systematic procedure of calculating the shape deformation of the transformation, referring to the morphological change due to the interaction of β₁′ variant crystals as well as the formation of α₁′ martensite. The obtained value of CRSS in the first transformation, β₁→β₁′, i.e., τ_β, shows a linear positive temperature dependence, whereas, the CRSS, τ_α, in the second transformation, β₁′→α₁′, indicates a slightly negative temperature dependence. It is reported that the obtained values of τ_β or τ_α are on a linear line with respect to the temperature independent of the type of S-S curves. The difference in the temperature dependence between τ_β and τ_α is attributed to the difference in the mechanism of the successive transformations. Very small values of τ_α, 25–40 MPa, and negative values of τ_α′, (−10)–(−20)MPa, are obtained for the forward and reverse transformations, respectively. Brief discussion has been made on the inducibility and stability of α₁′ martensite which are associated with the character of fatigue fracture and the appearance of reversible shape memory in this alloy system.

View full abstract

Recrystallization in Cu and Cu–Al alloys has been investigated by the aid of in situ experiments with a 3 MV electron microscope. The results are summarized as follows: (a) Recrystallization generally becomes difficult to occur in crystals with low stacking fault energies (LSFE-crystals) because of small crystal-rotation in local regions. (b) The heterogeneous deformation markedly results from the twin-deformation in LSFE crystals, and the nucleation sites of recrystallization are limited to such heavily deformed regions. (c) The easiness of recrystallization increases again with decreasing stacking fault energy in heavily deformed specimens, because the occurrence of twin-deformation is inversely proportional to the stacking fault energy. (d) Growth rate of recrystallized grains decreases with decreasing stacking fault energy because of high formation rate of annealing-twins.
Based on the results, the effect of stacking fault energy recrystallization is discussed.

View full abstract

The brittleness of Sendust with the nominal composition of 9.6 mass% silicon, 5.4 mass% aluminum and the balance of iron has been studied experimentally. By high thermal stress due to temperature gradient in the crystal, cleavage cracks along {001} plane or grain boundary cracks are easily introduced during either solidification after casting or subsequent heat treatments. The {001} cleavage cracks are also formed under applied external stress. Fracture stress of hot rolled Sendust examined by bending tests is higher than that of cast one, indicating the removal of internal defects by hot rolling. The single crystal which was prepared by zone-melting, and therefore, less-stressed thermally can be bent plastically even at room temperature, showing a lack of internal defects acting as the origin of cracking.

View full abstract

The form of the compounds of Mn and Fe–Mn carbides produced by the carbon thermic reduction of their oxides is determined by the effluent gas analysis (EGA) method using He-O₂ gas mixture. The obtained results are as follows:
(1) The oxidation of Mn carbide to Mn₂O₃ starts at 789 K and that of Fe–Mn carbide occures from 730 K, resulting in a mixture of Mn₂O₃ and Fe₂O₃.
(2) By the isothermal EGA method at 953 and 903 K, Mn and Fe–Mn carbides are identified to be Mn₇C₃ and (Fe, Mn)₇C₃ phases, respectively.
These observations are supported by the results of EPMA and X-ray diffraction examinations. Thus, it is concluded that the EGA method is useful tool for a state analysis of carbides.

View full abstract

Rapid scan, slow scan, potentiostatic and scratch techniques have been applied to determine the pitting potentials of Ni in 0.1, 1 and 7%NaCl solutions at 294, 323, 353 and 373 K. The lowest and most accurate pitting potentials are given by the potentiostatic techniques. The corrosion potentials obtained from these various electrochemical techniques are compared with the values of the pitting potential determined by the long term immersion tests. It is shown that the corrosion potentials attained prior to the onset of pitting in immersion tests are close to the values determined by the potentiostatic method. A critical pitting temperature (CPT) and critical crevice temperature (CCT) diagrams have been constructed on the basis of the exposure tests. The CPT diagram shows that there is both an upper and lower temperature limit for pitting corrosion on the basis of the existence of a reversal temperature observed during the determination of pitting potentials.

View full abstract

Measurements of thermodynamic quantities for the molten Ag₂S–Sb₂S₃ and Cu₂S–Ni₃S₂ binary mixtures were carried out by using a quantitative thermodynamic analysis method. A double adiabatic wall calorimeter was used as an experimental apparatus to accurately determine heat contents of the sulfide mixtures.
The activities, a_Ag2S and a_Sb2S3, for the Ag₂S–Sb₂S₃ system at 1123 K presented considerably large, negative deviations from Raoultian behaviour, and the excess stability showed a large maximum in the vicinity of the Sb₂S₃ mole fraction of 0.25, suggesting the influence of a compound of Ag₃SbS₃. On the other hand, the activities, a_Cu2S and a_Ni3S2, for the Cu₂S–Ni₃S₂ system at 1423 K presented small deviations from ideal mixing.

View full abstract