Phase transformations and the resultant microstructures of partially-stabilized zirconia (PSZ) are briefly reviewed with a special interest in the nature of phase transformations. The martensitic tetragonal-to-monoclinic transformation, which plays a principal role in toughening of PSZ, accompanies lattice defects such as twins or dislocations in the product phase m-ZrO₂. The diffusionless cubic-to-tetragonal (c-t) transformation is characterized by two different microstructures; one with the domain structure whose boundaries have curvilinear features showing the contrast of anti-phase domain boundaries in ordered alloys, and the other with thin-plates or lenticular features. It seems that the diffusionless c-t transformation is always completed by an initial development of domain structure over the entire region of samples. The thin plates or lenticular features may be subsequently formed by the strain accommodation. The nature of the diffusionless c-t transformation is the second order phase transition. The precipitation of t-ZrO₂ in the c-ZrO₂ matrix is commonly found in alloys heat-treated in the cubic/tetragonal two-phase region. Together with the usual precipitation structures, the modulated or tweed structure is also formed at an early stage of aging. The origin of these microstructures, and the nature of the diffusional reaction or precipitation is discussed in this paper.

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An elongation strain as large as 5.5% was obtained in Cu–Zn–Al shape memory alloys upon heating under stress at moderate temperature. The amount and behavior of shape change strongly depended on the heating temperature, tensile direction, and amount of applied stress. The morphological examination revealed that the shape change was attributed to the formation of particular variants of bainite crystals. The shape change is thought to be produced by the martensitic process in the bainitic transformation. On the other hand, the shape change was found to occur after an incubation period and to fit with a curve by the Austin-Ricketts equation which represents the kinetics of a diffusion-controlled transformation. The activation energy obtained from the Arrhenius plot of the shape change, 8.7×10⁴ J/mol, was almost the same as that of the diffusion of Zn atoms in the matrix crystal. Hence, the shape change is obviously controlled by a diffusion process. Nevertheless, this fact may not be contrary to the interpretation that the shape change is produced by the shear process, because the diffusion is thought to be necessary to prepare suitable surrounding conditions for the nucleation and growth of bainite crystals to be transformed by the shear process.

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Effects of B additions on the intragranular and cellular precipitations in a Cu-2 mass% Be alloy on aging at 523 and 623 K after quenching from 1093 K were investigated by means of hardness measurements, optical and electron microscopic observations, and X-ray analysis. The addition of 0.02–0.1 mass% B suppressed the formation of G.P. zones and retarded the precipitation of γ′ phase. The lattice parameter of the α solid solution of the B-added alloy increased with B addition. This result suggests that B atoms exist interstitially in the α solid solution and suppress the formation of G.P. zones and retard the precipitation of γ′ phase as a result of the strong interaction with vacancies. The formation and growth of grain boundary cells were suppressed by the addition of 0.02–0.05% B, but promoted by excess additions of B, 0.1%.

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The effect of temperature and strain rate on cavitation during tensile straining in Al–Mg alloys has been studied using precision density measurements, metallography and semi-empirical model of cavity growth. Cavitation occurs throughout the gauge length of the specimens, with most of the cavities being concentrated in regions near the fracture tip. The extent of cavitation has been found to increase with increasing temperature and decreasing strain rate. In fact, the cross-sectional area at fracture increased with increasing level of cavitation and its coalescence. However, cavitation is not found to be optimum around the superplastic temperature, i.e. 673 K and at an initial strain rate of ε=1.4×10⁻³ s⁻¹. This is the combination of temperature and strain rate at which the alloys show a maximum elongation to failure and strain rate sensitivity index. Cavity growth at high temperatures may be controlled either by vacancy diffusion or the power law growth process. These two growth mechanisms are examined with reference to Al–Mg alloys. It is found that diffusion growth is favoured at low strains and there is a transition to the power law growth process at a critical cavity radius (r_c). The value of (r_c) increases with increasing temperature and decreasing strain rate.

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The mechanical properties and wear resistance of 6061 alloy reinforced with Al₂O₃ fibers and a hybrid of Al₂O₃ fibers and SiC whiskers were investigated.
The elastic modulus of T6 tempered Al₂O₃/6061 and Al₂O₃–SiC/6061 composites can be expressed as E_c\doteqdot140 V_fAl2O3+68 and E_c\doteqdot140 V_fAl2O3+180 V_fSiC+68, respectively. The fiber arrangement coefficient α is found to be 0.7 for Al₂O₃ and 0.45 for SiC whisker.
The wear resistance of Al₂O₃/6061 composites is inferior to that of SiC/6061 composites. The addition of small volume franctions of SiC whisker to Al₂O₃/6061 composites gives rise to a remarkable improvement of the wear resistance which is, on the contrary, superior to that of SiC/6061 composistes.

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