The coarsening behaviour of coherent precipitates and particularly of gamma-prime (γ′) precipitates in Ni-base alloys is reviewed. In such elastically constrained systems, strange coarsening phenomena sometimes appear, e.g. the deceleration of coarsening, the split of a single particle into a doublet or an octet, etc. Such unbelievable phenomena can clearly be explained by introducing new coarsening theories like the Bifurcation theory in which the elasticity effect and particularly the effect of elastic interaction energy between particles are incorporated into the driving force for coarsening. Not only the surface energy but also the elastic interaction energy really plays an essential role in the formation and the stability of various precipitate morphology including coarsening.

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We present in this work a simple phenomenological model of the hysteresis loop in thermoelastic martensitic transformations. The model is based on the equilibrium condition arising from the minimization of the Gibbs free energy at every transformation step. For simplicity, the simplest form of the different terms of the balance equation has been taken. From this choice some considerations are made on the contributions to the non-chemical energy that should be taken into account. Application of the model allows one to identify the role and physical meaning of the different energy contributions to the transformation behaviour, but also to predict the subloop behaviour in the validity domain of the model. The main results obtained from the model are: (i) the equilibrium condition applied to the reversible Gibbs free energies at any transformed fraction leads to the reversible path of the transformation which would be followed in absence of any irreversible contribution; (ii) the slope of the forward/reverse transformation paths is not only due to the stored elastic strain energy, but to an increasing dissipative energy as well; (iii) the knowledge of the dependence of the starting temperatures of the forward and reverse transformations on the minimum and maximum transformed fractions in a subloop is essential in order to characterize completely the global hysteresis loop and the subloop behaviour. The model is supported by experimental examples both in global and partial hysteresis cycles.

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The 6061 aluminum alloy matrix composite reinforced with 13 vol% β-phase silicon nitride whisker was fabricated by squeeze casting and its high temperature strength and interface microstructure between whiskers and matrix were examined with TEM. As compared with the 6061 alloy, the strength of the composite increased about 20% and the elongation reached about 4% at room temperature. The strength beyond 300°C was quite excellent.
The whisker has the [001] axis as the growing axis and a hexagonal cross-section surrounded by six {100} planes. The whisker has a few nm thick amorphous layers on the surface. The layer binds whiskers tightly in the preform. No trace of a severe reaction after casting was observed but a few nm thick crystalline layers were found on the (100) face of the whisker, which was determined to be aluminum nitride. The orientation relationship between the whisker and the aluminum nitride layer is expressed as follows:
{100}_{β-silicon nitride}//{001}_{Aluminum nitride}
[100]_{β-silicon nitride}//[100]_{Aluminum nitride}
The bottom faces and the (110) side faces, which did not have any clear crystalline layer, showed a severer reaction than the (100) side faces. Those two faces of the whisker seem not to have a suitable crystallographic orientation for growing aluminum nitride as the (100) plane. The α-silicon nitride particles 1 μm in diameter were also observed in the matrix.

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An Al₈₈Ni₉Ce₂Fe₁ alloy with ultrahigh tensile fracture strength exceeding 950 MPa in the temperature range from room temperature to 573 K was found to be obtained by rapid solidification in the structural state where the nanoscale fcc-Al particles without internal defects disperse homogeneously in the amorphous matrix. The ultimate tensile strength is as high as 1560 MPa at room temperature and 970 MPa at 573 K. The high strength values were obtained in the mixed structure where the volume fraction of Al phase was about 25%. It is notable that the strength values at room temperature and 573 K are about 3 and 15 times, respectively, as high as those for conventional age-hardening type aluminum alloys. The extremely high strengths are presumably due to the dispersion strengthening resulting from the homogeneous dispersion of the nanoscale Al particles without internal defects. Furthermore, the excellent elevated-temperature strength is also presumed to originate from the high resistance of the defect-free Al particles against the softening as well as the particle growth.

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Ellipsometry has been widely used for measuring Si oxide thickness in semiconductor industry. However, as the gate oxide (SiO₂) thickness for MOS (Metal-Oxide-Semiconductor) ULSI’s (Ultra-large-scale Integrations) decreases with the increasing integration density, the error in measuring the thickness has become a problem. In this study, it is shown on the basis of the ESCA studies of the oxide concentration, chemical state and SiO₂/Si interface structure that the oxide thickness can be defined and obtained from Si2p (oxidized) intensity as measured by ESCA (Electron Spectroscopy for Chemical Analysis). This thickness is that of SiO₂, and unlike that of ellipsometry, the conventional method, it contains no effects of an adsorption layer. This thickness is defined from the results on thermal oxide films less than several nm thick formed in O₂/N₂ atmosphere at several hundred °C. However, it is considered that the same definition can also be used for the evaluation of the thickness of “natural” oxide films formed at room temperature.

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Solubilities of CO₂ and redox ratios of Sb and As (n_Sb³⁺⁄n_Sb⁵⁺, n_As³⁺⁄n_As⁵⁺, n: the number of moles) in NaO_0.5–SbO_m and NaO_0.5–AsO_m melts were studied. The equilibrium measurements were conducted over the composition range of 1>N>0.7 {=n_NaO0.5⁄(n_NaO0.5+n_MOm), M:Sb or As} under the partial pressures of CO₂ and O₂ of 0.01∼0.1 MPa and 0.005∼1000 Pa, respectively, at the temperatures of 1423 and 1523 K.
Antimony exists in NaO_0.5–CO₂–SbO_m melts not only in pentavalent (SbO₄³⁻) but also in trivalent (SbO₂⁻) state, their relative proportions depending on the experimental conditions. The CO₂ solubility in the melts is, therefore, determined by the following reactions:
3CO₃²⁻+2SbO_2.5=2SbO₄³⁻+3CO₂
CO₃²⁻=CO₂+O²⁻
and
SbO₂⁻+O²⁻+1/2O₂=SbO₄³⁻.
Arsenic exists predominantly in the form of pentavalent anion (AsO₄³⁻) in NaO_0.5–CO₂–AsO_m melts. As the pentavalent arsenic is more stable compared with antimony, the redox reaction of arsenic has almost no effect on the CO₂ solubility in the melts. Thus CO₂ solubility is determined only by the following two reactions:
3CO₃²⁻+2AsO_2.5=2AsO₄³⁻+3CO₂
and
CO₃²⁻=CO₂+O²⁻.
However, with increasing content of arsenic oxide in the melts, the evaporation reaction of trivalent arsenic oxide (As₄O₆),
AsO₄³⁻=1/4As₄O₆(g)+1/2O₂+3/2O²⁻,
becomes significant.

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The progress of nitriding follows the parabolic rate law and the apparent activation energy is calculated to be 208 kJ·mol⁻¹ at the temperature range 1073∼1473 K. By X-ray analysis, the surface product is identified to be a mixture of α-Ti and Ti₂N at 873∼973 K, and a mixture of Ti₂N and TiN at 1073∼1273 K. The corrosion resistance of the titanium nitrides increases with rise in nitriding temperature, although the nitrides formed at 873 and 973 K are easily attacked in 1 kmol·m⁻³ H₂SO₄ at 373 K. The dissolved amount of titanium for the nitrided titanium at the temperature above 1173 K is 3 orders of magnitude smaller than that for the untreated specimen, and moreover it is smaller than that for a TiN film (TiN_0.891) produced by reactive ion plating. These results indicate that a very thin layer whose nitrogen content is higher than that of the TiN film exists on the mixture of Ti₂N and TiN and hardly corrodes. When the mixture of Ti₂N and TiN is exposed, Ti₂N is selectively attacked and corrosion proceeds through small cavities extending into the base metal. On the other hand, the dissolution rate of the TiN film is lower than that of a Ti₂N film (TiN_0.578) produced by reactive ion plating, and the corrosion resistance is comparable the deposition films have high quality. In this paper, we report on the structural feature of titanium nitrides produced by both processing and the corrosion behaviour in sulfuric acid solutions.

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To know the vacancy concentration in an ordered Ni₃Al alloy, a new calculative technique based on the cluster variation method (CVM) has been developed, in which our problem is reduced to finding of a critical condition for the chemical potential of vacancy in the alloy to be vanished. With use of this method together with an appropriate interaction parameter for each nearest neighbor atomic pair, e.g. between Ni (or Al) and vacancy, we can successfully calculate the vacancy concentration, c₃, in this alloy. These calculated values have been comparable with the available experimental or theoretical data for c₃ in this alloy system. On the basis of the present results, the vacancy formation energy for each sublattice site of the alloy crystal structure has been estimated to be a reasonable value compared with the available data from experiments or different theoretical estimations. An alternative way to roughly estimate the vacancy formation energy in Ni₃Al alloys has been proposed. This method can be applied to judge with ease the relative stability of structure defect (vacancy) to anti-structure defect in the Ni₃Al alloys.

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To examine the predominant factor controlling abnormal grain growth of Ni-base oxide dispersion strengthened superalloys, microstructures were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Three kinds of particles were recognized; (1) fine, round shape of yttria particles of 10 to 80 nm in diameter, (2) large, round shape of Al and Ti oxide particles of 80 to 200 nm diameter, (3) flake shape of Cr rich phase with sizes of 0.2 to 0.4 μm in width and 0.4 to 2.5 μm in length. It was found that the major pinning obstacles of abnormal grain growth were the Cr-rich phase.

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