Diffusion behavior of composition variation peaks in supersaturated solid solutions has been discussed using Fourier transform of Cahn-Hilliard’s diffusion equation. For the cases where the peak of positive compositional deviation at the location x=0 is a maximum of composition variation, it is shown that the condition for a rise of the peak is given by ψ−\ ildeD_x=0>0. Here, \ ildeD_x=0 is the interdiffusion coefficient of the peak composition and ψ=−2Kβ²[∑_h=−∞^∞h⁴Q(h)⁄∑_h=−∞^∞h²Q(h)]. hβ and Q(h) are the wavenumber of a Fourier wave and its component, respectively, and K is (gradient energy coefficient)×(mobility of atoms). In high solute alloys, the peak rises even in the range where −\ ildeD_x=0<0 by formation of the Fourier spectra for which ψ>0, and ψ becomes equal to \ ildeD_x=0 when the composition peak reaches the equilibrium composition. In very low solute alloys the peak sinks even in the range where −\ ildeD_x=0>0 by generation of the spectra for which ψ<0.

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The structural change and the shape memory behavior in quenched Mn-(5–20) at%Cu alloys have been studied at both normal and elevated temperatures using X-ray and electron diffraction methods and electron microscopy supplemented by metallographic observations. Quenched alloys are tetragonal and show a banded surface relief due to transformation twinning parallel to {101} planes. These tetragonal alloys are transformed to a cubic structure by heating to moderate temperatures, and the transformation temperatures increase linearly with manganese content. The banded surface relief becomes attenuated with increasing temperature and disappears at the fct→fcc reverse transformation temperature. On subsequent cooling to room temperature a similar banded structure appears and the angle between the surfaces in neighbouring light and dark bands increases as the temperature decreases. Similar structural changes are observed by an electron microscope. The fcc\ ightleftharpoonsfct transformation is of diffusionless (martensitic) type and takes place over a small temperature range which is less than 1 K . All quenched alloys show an ordinary shape memory effect and also a reversible shape memory effect. The behavior of shape recovery both on heating and cooling is discussed on the basis of metallographic and electron microscopic observations, and it is suggested that the residual magnetic ordering is responsible for a reversible shape memory effect.

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The property of the ion-softnitriding layer formed on S15C steel and the wear resistance of the ion-softnitrided S15C steel under a dry sliding condition were investigated. S15C steel was ion-softnitrided in N₂–H₂–CH₄ gas mixtures of various compositions at 823 K for 14.4 ks under a pressure of 6.67×10² Pa. With increasing CH₄ gas content in the atmosphere, the compound layer becomes thinner and the diffusion layer also becomes shallower or does not form. The thick compound layer is formed in the gas compositions of [CH₄%]<1/12[N₂%]+1/3. The phase composition of the compound layer is affected by the CH₄ gas content in the atmosphere and ε-Fe₂₋₃(CN) phase is easily formed by the addition of CH₄ gas. The increase in CH₄ gas content brings about the formation of Fe₃C and finally results in sooting. The ion-softnitriding markedly improves the wear resistance of steel and is more effective for the wear resistance at high speeds under high loads than the ion-nitriding.

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The initiation and propagation of cracks during both quenching and deformation in polycrystalline Cu–Al–Ni alloys have been investigated under various conditions. The results obtained are summarized as follows; (1) Quenching-cracks may be avoided by choosing the temperature of quenching media close to or below the M_s temperature of the alloys, so that many deformation modes are available under given thermal stresses. (2) In the superelastic temperature region, cracks which are formed either by quenching stress or by external stress were found to be initiated and propagate along grain boundaries. This was ascribed to the stresses which accumulated at grain boundaries due to large elastic anisotropy of the present alloys. (3) In specimens in a martensitic state, the propagation paths of cracks were found to easily deviate from grain boundaries, although they are initiated at three-fold nodes of grain boundaries at the very beginning. This is because the stress concentrations at crack tips become more essential in this case, since stresses at grain boundaries are easily accommodated by many deformation modes in a martensitic state.
As a whole, it was concluded that the brittleness of the present alloy and other β phase alloys are due to the large elastic anisotropy and grain sizes, and that the large ductility in Ti–Ni alloys are due to the small elastic anisotropy and grain size of the latter.

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Using a derivatograph, the temperatures and heats of decomposition of MnO₂ and Mn₂O₃ as well as the temperature and heat of transformation of Mn₃O₄ have been studied. Using CaCO₃ as standard, the heat of decomposition of MnO₂ to Mn₂O₃ has been determined to be 25.56±1.67 kJ/mol of MnO₂, and that of decomposition of Mn₂O₃ to Mn₃O₄ to be 15.94±2.09 kJ/mol of Mn₂O₃. The temperatures of decomposition of MnO₂ and Mn₂O₃ to lower oxides, namely, Mn₂O₃ and Mn₃O₄ respectively, have been found to be 843±5 K and 1263±5 K respectively under atmospheric conditions. It has been confirmed that Mn₃O₄ undergoes a crystalline transformation during cooling at 1453±5 K with 4.35±0.04 kJ/mol of Mn₃O₄ as the heat of transformation.

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The superplastic behavior and changes in microstructural parameters were studied in the Pb–Sn eutectic alloy with initially banded structures and grains elongated in one or two directions. These microstructures were obtained by an appropriate thermomechanical processing of the cast alloy. The flow stress was observed to depend on the direction of loading relative to the bands or elongated grains. Furthermore, there was strain dependency of flow stress at a given strain rate unlike the usual steady state flow behavior of superplastic deformation. This was accompanied by the break up of the non-equiaxed microstructure leading to the evolution of equiaxed structure with increasing strain.

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Single crystals with the [100] and [110] axes have been tested up to different numbers of cycles under a constant plastic strain amplitude of 0.2% with a cyclic strain rate of 10⁻³ s⁻¹ at 423 K, and the formation of substructures has been examined by electron microscopy. Screw dislocations were predominant after the initial stage of cycles. Cells with loose tangles of dislocations appeared in the final stage of the initial rapid cyclic hardening process. In the case of the [100] crystal, the dislocations were aligned to form sheet-like cell walls parallel to a {100} plane. Surface rumpling and crystal misorientation did not appear until this stage. In the final stage, the substructures of both crystals transformed to sub-boundary structures with the development of the surface rumpling. Development of surface rumpling during the cycles has been considered to have a bearing on the increase in the misorientation in view of the fact that neither misorientation nor surface rumpling appeared at low temperature.

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