Numerical analysis for sequential phase growth behavior in a multi-phase diffusion couple has been proposed on the basis of the finite difference method. An initial concentration-distance curve has been obtained by inserting a new phase thin layer of the linear concentration-distance curve having 5∼10 gridpoints, between existing phase layers. In spite of simple approximations for the initial concentration-distance curve, it was found that the present method is useful for the analysis of the phase growth behavior of the new and existing phases. This method will make it possible to estimate the widths of diffusion layers formed during galvanizing and galvannealing.

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The behaviour of interdiffusion and layer growth of β and β′ phases in the Cu-Zn system was investigated in the temperature range of 325 to 651°C, and the effect of the order-disorder transformation upon the diffusion behaviour in this alloy was also studied.
The rate of the layer growth and the interdiffusion coefficient of this alloy were influenced by the order-disorder transformation and both values were remarkably reduced at the temperature of transformation.
The interdiffusion coefficient increased monotonically with the increase of Zn concentration in both phases of β and β′. The activation energy for interdiffusion increased in the β′ phase while the value decreased in β phase with the increase of Zn concentration. The activation energy for interdiffusion in the ordered β′ phase was about 1.5 times higher than that in the disordered β phase.
The intrinsic diffusion coefficient of Zn atom showed the value of about 2 times higher than that of Cu atom in the disordered phase, while these two factors were nearly coincided with each other in the ordered phase.
It was shown from the measurement of the Kirkendall effect that the diffusion was controlled by a vacancy mechanism in the disordered phase and by the six atoms-vacancy jump mechanism in the ordered phase.

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The reaction between the silicon-nitride ceramics and nickel was studied in vacuum from 1373 to 1473K for up to 176.4ks. The reaction product was composed of two layers, one formed by the diffusion of silicon into nickel, and the other composed of additive oxides particles and nickel-silicon alloy. The growth of the product layer followed the parabolic law with the following rate constants (K_p): 1.2×10^-13m²⋅s^-1 at 1373K, 3.6×10^-13m²⋅s^-1 at 1423K, and 1.7×10^-12m²⋅s^-1 at 1473K. The interdiffusion coefficents (D) obtained were of the orders of 10^-15 to 10^-14m²⋅s^-1 in the temperatures range studied. These values were found to be one half to one fifth of the interdiffusion coefficients determined with a vapour-solid diffusion couple of a nickel-plate and nickel-silicon alloy powder as diffusion source of silicon vapour. The activation energy for interdiffusion (Q) was about 330kJ⋅mol^-1, independent of the Si concentration.

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Two types of binary diffusion couples, γFe-βTi and αFe-βTi, were prepared and the layer growth of intermediate phases formed in these couples was examined at 1000°C. The layer growth rate constants of intermediate phases in diffusion couples of the Fe-Ti and Cu-Zn systems were numerically calculated by the previous method from data where one of the principal limiting factors, i.e., the diffusion coefficient, the concentration range of the solibility area and the adjoining two-phase area of a given phase, was changed into an arbitrarily assumed value.
The results obtained experimentally and numerically have made it clear that the layer width of any intermediate phase formed in a couple is greater as the compositions of the two alloys, the constituents of the couple, are brought closer to that of the intermediate phase.
The effect of the above limiting factors in an intermediate phase on the layer growth rate constants of its phase and the other phases formed in a couple have been disclosed by the numerical calculation. A simple approximate expression for the layer growth rate of any intermediate phase formed in a couple has been given by the interdiffusion coefficients and the solubility ranges of all the phases in the couple. The distinctive features have been discussed for the exceptional phase in a couple where its layer growth rate shows an abnormal deviation from this expression.

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A numerical method has been developed for exactly solving the equations describing binary multi-phase interdiffusion. The layer growth rate constants of the intermediate phases, formed in Cu-Zn and Fe-Ti couples for example, were numerically calculated from the interdiffusion coefficients, phase boundary compositions and partial molal volumes given in the literature. The resulting rate constants are in good agreement with literature values, in spite of some uncertainty of the numerical values for the calculation.
No numerical solution satisfying the diffusion equations and the requirement that the growth rates of all the intermediate phases are positive, could be found in the case of an Fe-Ti couple. This result is essentially consistent with the experimental results by other investigators that all of the three intermediate phases predicted from the equilibrium diagram do not appear in the diffusion zone of Fe-Ti couples.

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The tensile behavior has been observed on the metallic composites arranged in a chequered flag pattern with two elements of metals which are soluble and insoluble in each other. The composites were prepared by hot pressing; the condition for the Al-Cu composite was 2 hr at 550°C and that for the Cu-Fe composite was 24 hr at 950°C under a total pressure of 2 tons.
The Al-Cu composite of the soluble type, formed an intermetallic compound at the interface when the composite was fabricated and its tensile behavior was greatly influenced by this intermetallic compound. The tensile behavior of Cu-Fe composite of the insoluble type, was influenced by the Cu elements having a low elasticity compared with Fe.

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Monofilament composites were prepared by Ni electrodeposition on the commercial SiC fibers. Having been subjected to thermal cycle between 473 K and up to 1273 K, the composites were investigated by SEM observations.
Cavities were formed at SiC/Ni interface and developed as the thermal cycle proceeded. The rate of reaction between SiC and Ni decreased with increasing the number of cycle irrespective of the amount of cavities.
The results obtained are discussed in terms of thermal stress which arises from the difference in thermal expansion between SiC fiber and Ni. A mechanism of grain boundary sliding in Ni phase at high temperatures is proposed to the cavity formation and interfacial debonding.

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The strength of Al-Al₃Ni functionally graded material (FGM) has been studied through 3-point bending experiments for two different manufacturing conditions. Specimens with rectangular cross-section of 8 mm thickness×9 mm width are machined from thick-walled tube, which are manufactured in laboratory and vacuum atmosphere. They have graded compositions of Al₃Ni phase in aluminum matrix in the radial direction. The nominal volume fractions of Al₃Ni phase at the crack initiation site are V_f=41 and 15 vol.% under air, and V_f=35 and 0 vol.% under vacuum casting. Fracture of specimens occur more abruptly in the case of specimens manufactured in air than those made under vacuum condition. The fracture strengths are calculated from maximum bending load considering the graded Young's modulus and are plotted on the Weibull probability sheet. Each data set obeys a good linear relationship and the reliability of strength data is better in case of vacuum specimens. The average value of fracture stress improved with increase of volume fraction of Al₃Ni for both the manufacturing conditions. However, in the case of vacuum manufactured specimens, coefficient of variation is small. The bending strength of Al-Al₃Ni FGM is controlled by size, shape and distribution profile of Al₃Ni particles, because the cleavage fracture of Al₃Ni phase dominates the fracture process.

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Laser alloy experiments using TiO₂ particles coated with Ni by electroless plating were conducted to form a hard, structurally uniform alloyed layer on an Al substrate. The alloyed layer formed using this TiO₂-Ni composite powder had a smoother surface and a more uniform structure than layers formed using TiO₂ or Ni powder independently because composite powder featured high absorption for a CO₂ laser beam and good reaction on melted Al. Increasing Ni content in the alloy powder, increased alloyed layer hardness due to the crystallization of intermetallic compounds. The optimum alloyed layer was obtained when the weight ratio of TiO₂ to Ni was about 1:1. The alloyed layer was 0.6-0.7mm thick and surface roughness about Rz 70 microns. The micro-Vickers hardness of the alloy was Hv 200±50. TiO₂-Ni composite powder is thus useful in laser alloy.

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Hardness measurements, and optical and transmission electron microscopic observations were made on Al-8%Mg alloy specimens subjected to two kinds of thermomechanical treatments: either cold-worked in a large range up to 75% just after quenching and then aged (Process I), or else pre-aged for various times after quenching, cold-worked and finally aged (Process II). After Process I, the hardness increased with increasing cold reduction, although the precipitate density in the cold-worked specimens was lower than that in the specimen without cold-work: the precipitate density initially decreased markedly and then gradually increased with increasing cold reduction. This variation was attributed to the loss in the precipitation that required quenched-in excess vacancies and to the gain in the preferential precipitation on deformation bands revealed by TEM observations. The pre-aging treatment before cold-working in Process II resulted in a greater increase in hardness than in Process I owing to dislocation hardening without any loss in precipitate density.

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The plastic behaviours of a Ni₃Nb single crystal are studied by tensile and compression tests. Three shear systems are found to operate. They are (010)[001] slip, (010)[100] slip and {211}⟨‾10 7 13⟩ twin, and their critical resolved shear stresses (CRSS) are obtained as 44, 51 and 56 MPa in tension, and 55, 64 and 380 MPa in compression, respectively. In case of tensile test, a brittle fracture occurs in almost all the stress orientations, since the CRSS for {211} twin in tension is comparatively low and the twin plane is easy to cleave. Ductility can be expected under a tensile test, when the stress axis is parallel to [120], because at this stress orientation the twin system is difficult to operate. On the other hand, in a compression test the CRSS for the {211} twin is considerably high, and the single crystal is plastically deformed up to strain more than 15% by the operation of (010) slip system. For the stress orientations parallel to [010] or parallel to the axis on the [100]-[001] great circle, however, the (010) slip systems can not be operated and it breaks fragilly.

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A trial has been conducted to bond 1μm α-silicon carbide particles firmly with the Watts nickel matrix of the coating, by annealing the coating at temperatures as low as possible and at a reasonable rate. Formation of a strong bonding was found on annealing the coating at 600°C. The bonding reaction, as detected and characterized by tensile testing, X-ray diffraction, scanning and transmission electron microscopy, was found to have an incubation period of two minutes and then proceeded to form a bonding layer, which was a composite; SiC/Ni₅Si₂/Ni₃Si/graphite/Ni. On further annealing at 600°C, the dispersed particles transformed into Ni₃Si particles coated with graphite film. The bonding erased the easy crack at the particle/matrix interface, generated a ductility of the coatings, and doubled the tensile strength of a coating at 400°C. The strengthening was described in terms of the Orowan mechanism, wherein a reaction-induced particle growth was considered. Some properties of the coatings were described on the basis of the dense random packing of the dispersed particles. A reaction was found at the SiC/Ni interface even on 500°C annealing, but with the incubation period of about five hours.

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The centrifugal method is one of the functionally graded material (FGM) manufacturing methods proposed by the authors. However, there are certain difficulties in applying the centrifugal method to an alloy melt with high viscosity and low heat capacity. The centrifugal casting system under a vacuum condition is, thus, adopted and designed to improve the former system in air. A new system is satisfactorily constructed and Al–Al₃Fe FGM of a thick-walled tube is manufactured from Al–10 mass% Fe master alloy. The particles of intermetallics are confirmed to the Al₃Fe intermetallic by EDX analysis. The graded composition of Al₃Fe in aluminum matrix is examined and is varied from pure aluminum at inner surface of the tube to 40 vol% Al₃Fe at outer plane of the tube. The corresponding graded Young's modulus and thermal expansion coefficient of Al–Al₃Fe FGM vary from 71 to 99.5 GPa and from 25.5 × 10⁻⁶ to 21.3 × 10⁻⁶ K⁻¹, respectively. Tensile tests are carried out using thin plate standard specimen for which Al₃Fe grains are homogeneously distributed statistically. The averaged volume fraction of Al₃Fe in the specimens, which are tested, is about 28 vol%. Tensile strength of 94 MPa at 0.49% tensile strain and Young's modulus of 90 GPa are obtained.

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