Diffusion is a process that is fundamental in the art and science of materials. The knowledge of diffusion behaviour, therefore, is essential for the production of materials or for their use in practical applications. In the first part of this paper, a brief review is given on the historical developments of the quantitative study of diffusion: the establishment of the diffusion law by A. Fick, the first quantitative measurement of solid-state diffusion (Au in Pb) by W. C. Roberts-Austen and the demonstration of the self-diffusion in Pb using a natural radioactive isotope by G. Hevesy. In the second part, the development and the present status of our understanding of several problems: correlation effects in diffusion, fast diffusion in metals and the mechanism of diffusion in intermetallic compounds will be reviewed.

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An AuFe ordered alloy has been synthesized artificially by depositing alternately monatomic layers of Au and Fe. The thermal stability and interdiffusion have been investigated by X-ray diffraction measurements. X-ray diffraction from the AuFe thin films shows definite superlattice lines corresponding to the L1₀-type ordered structure, although neither intermediate phase nor intermetallic compound is known for the Au–Fe binary equilibrium phase diagram. At 473 K, L1₀-type ordered structure is maintained until 10 ks and then, the structure changes to metastable disordered structure. The interdiffusivity is determined from the decay rate of the superlattice peak intensity. The interdiffusivity at 473 K is evaluated as
(1.7±0.1)×10⁻²⁵ m²s⁻¹ for L1₀-type ordered phase,
which is in good agreement with that extrapolated from the bulk-interdiffusivity at high temperatures. The diffusion is interpreted as an atomic mixing process for deteriorating the L1₀-type ordered structure.

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This study examines the erosion response of two steels in a slurry of sand plus water over a range of rotational speeds and distance traversed. Erosion tests were carried out in slurries with different concentrations of sand. The study indicates the influence of material composition on the erosion resistance of the specimens depending on the experimental condition. The specimens suffered maximum erosion rate at an intermediate speed of rotation. Similarly, a higher concentration of sand in the slurry led to reduced erosion rates. Moreover distance transversed sometimes increased and sometimes decreased the erosion rate depending on the test conditions.
The alternation in the response of the specimens (be it due to changing material composition, speed of rotation or owing to sand content in the slurry) has been explained in terms of the dominating erosion mechanisms under a given set of test conditions. The view has further been substantiated with the help of the features of the eroded surfaces and subsurface regions of the specimens.

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In an attempt to improve the wear properties of material encountering abrasion and/or erosion during operation, hardfacing layer of up to 2 mm thickness may be applied on the vulnerable parts. An attempt has been made to characterise a number of hardfacing alloys for their abrasive and erosive properties. The wear resistant properties are dependent upon both hardfacing alloy properties and operating conditions. The alloy of finer microstructure, higher hardness and high work hardening presented comparitively high wear resistance.

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Nitrogen gas atomized aluminum powder was consolidated by a powder-in sheath rolling method. Aluminum powder was filled in aluminum tube of 12 mm in outer diameter and 10 mm in inner diameter. The sealed tube containing powder was rolled to the thickness of 6 mm at ambient temperature for compaction and then consolidated by the combination of cold rolling and subsequent hot rolling at various temperatures ranging from 360 to 560°C. Rolling schedule is determined as to obtain flat bar with the thickness of 3 mm. The relative density of consolidated powder compact was more than 0.96. The mechanical property of powder compact was affected by rolling schedule and temperature. The strength of powder compact was comparable to that of bulk material. When cold reduction or hot reduction was large, the elongation of powder compact became large. However, elongation decreased with the combination of moderate cold and hot rolling. The interparticle bonding necessary for consolidation was accomplished during heating after cold rolling when large cold reduction is adopted. On the other hand, bonding is accomplished during and/or after hot rolling in large hot reduction. This method is promising for fabricating composite materials on the powder metallurgy route.

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An Al/Al₂O₃ particle reinforced metal matrix composite was fabricated by sheath rolling of powder mixture. A stainless steel tube with the inner diameter of 10 mm and outer diameter of 12 mm was used as a sheath. Mixture of aluminum powder and Al₂O₃ powder of which volume fraction was varied from 5 to 20% were filled in sheath and rolled to the reduction of thickness of 75% at ambient temperature. Rolled powder compact was sintered, and after sintering additionally rolled and annealed for improvement of mechanical properties. The powder mixture could be consolidated by sheath rolling at ambient temperature. Relative density of composite became more than 0.96. The strongest composite in the present process was obtained after additional cold rolling subsequent to sintering, while it had poor ductility. The strength and ductility of the sintered composite was improved by additional cold rolling and annealing. The strength of sintered composite and that of additionally rolled and annealed composite increased with increasing volume fraction of Al₂O₃ particles. It became about one and a half times as that of unreinforced powder compact at the volume fraction of 20%. It is proved that the sheath rolling method is promising process for fabricating metal matrix composites on powder metallurgy route.

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Rapidly solidified Al–20Si–xFe (x=3, 5 and 7 mass%) powders were prepared by gas atomization. The microstructure consisted of needle shaped δ-Al₄FeSi₂ particles and primary Si embedded in Al–Si–Fe eutectic. With increasing Fe content, the size and volume fraction of primary Si decreased. After extrusion, the microstructures of the extruded bars showed a homogeneous distribution of two different sizes β-Al₅FeSi and Si particles embedded in the α-Al matrix. By increasing the Fe content from Al–20Si to Al–20Si–7Fe, the ultimate tensile strength (UTS) increased from 215 to 404 MPa at 300 K and from 122 MPa to 240 MPa at 473 K. Of these alloys, Al–20Si–5Fe alloy showed the best wear resistance. The UTS varied significantly with the initial powder size but wear resistance was independent of powder size. The effect of the particles distributed in the Al matrix upon the UTS was considered in terms of the cooling rate and particle distribution.

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Single-Crystal TmNi samples were grown by use of a metallic crucible. The temperature dependence of specific heat was measured in the temperature range from 1.4 to 80 K by the adiabatic method and two transitions were observed at 2.7 and 3.8 K. In addition, the Schottky-type specific heat was observed and it was discussed on the basis of energy level splitting due to crystalline electronic field effect. The magnetization curves were measured in a field up to 5 T at various temperatures for principal axes. We proposed the magnetic structure in the lower temperature region. The magnetic susceptibilities were measured in the temperature range from 5.0 to 300 K for principal axes, and the average value of the effective magnetic moment for principal axes was estimated at 8.9×10⁻²⁹ Wb·m/Tm³⁺, which is in good agreement with the Tm³⁺ free ion value.

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A mass spectrometer has been used to study activities of the constituents in liquid Cu–Al alloy. According to Belton-Fruehan’s treatment, activities and heats of mixing have been able to be determined from a series of measurements of the ratio of the ion current intensities of the solution components. The activities in the Cu–Al system were found to be in excellent agreement with the values recommended by Hultgren et al. The activities exhibited negative deviation from ideality and the terms of RTlnγ_Al and RTlnγ_Cu were almost independent of the temperature within the present experimental range. Partial molar and integral heats of mixing of the liquid Cu–Al system were also estimated.

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Tensile fracture strength (σ_f) and Vickers hardness (H_v) of Zr–Al–Ni–Cu amorphous sheets with a thickness of 2.5 mm prepared by squeeze casting were found to increase by the addition of 2.5–5 at%Ti and the increase of Al content to 12.5–15 at%. The σ_f and H_v of the amorphous alloy sheets with the new compositions are 1800 to 1850 MPa and 500 to 520, respectively, which are higher than those (σ_f=1650 to 1790 MPa and H_v=470 to 480) for the Zr-10%Al–Ni–Cu amorphous cylinders prepared by copper mold casting. The Young’s modulus, elastic elongation and Charpy impact fracture energy are 86 to 92 GPa, 2.0 to 2.2% and 90 to 160 kJ/m², respectively. The highest value of the three point-bending flexural strength is 3900 MPa for Zr₅₅Al₁₅Ni₁₀Cu₂₀. The high impact fracture energy indicates that the cast amorphous alloy sheets have good ductility. Furthermore, the improvement of σ_f and H_v by the simultaneous addition of Ti and Al is presumably due to the increase of the bonding force of the constituent elements resulting from the increase of Zr–Al and Ti–Al pairs with larger negative heats of mixing. The synthesis of the high Al concentration Zr–Al–Ni–Cu and Zr–Ti–Al–Ni–Cu amorphous alloys with higher mechanical strength, higher impact fracture energy and lower density is important for the future progress of high-strength bulk amorphous alloys because the Zr–Al–Ni–Cu amorphous alloys with the 10 at%Al concentration have already been used as new engineering materials.

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Activity of aluminum in platinum-aluminum solid solution was determined by the electrochemical cell technique at temperatures ranging from 913 K to 1050 K. The following cell system was used:
Pt–Al alloys, AlF₃/CaF₂/Co, CoF₂
The values of activity of Al, a_Al, in Pt solid solution with 4.6 mol% Al and 9.4 mol% Al are, respectively, represented by:
Pt-4.6 mol% Al: loga_Al=−1.140−1.337×10⁴T⁻¹±0.152
and
Pt-9.4 mol% Al: loga_Al=−3.167−1.083×10⁴T⁻¹±0.102
The value of a_Al in Pt-13.1 mol% Al alloy, which is comprised of the two-phase region of Pt(Al) solid solution and Pt₃Al, is expressed as follows:
Pt-13.1 mol% Al: loga_Al=−3.523−1.033×10⁴T⁻¹±0.081

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An analysis was made of the X-ray diffraction intensity distribution in a series of single crystal patterns of an equiatomic AgZn alloy recorded at the initial stage of the phase transformation from β′ (B2-type ordered structure) to ζ (trigonal structure). It was shown that the displacements of atoms and the partial disordering, the two atomistic mechanisms involved in the transformation, proceed simultaneously. The ζ phase nuclei grow gradually in the β′ phase matrix with a definite orientation relationship. Two types of the nuclei form; one with a structure similar to the structure proposed for the ζ phase by Edmunds and Qurashi (ζ phase-type structure) and the other with a structure obtained by reversing the direction of the displacements of some of the atoms in the ζ phase-type structure (anti-ζ phase-type structure).

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Rapidly solidified ferromagnetic shape memory Fe-29.6 at% Pd alloy was fabricated to develop a new type of actuator material responded to magnetic field. The thin ribbon samples which were made by the originally designed electro magnetically controlled nozzleless melt-spinning method showed stronger crystal anisotropy and larger shape memory effect. Magnetostriction increased with increasing magnetic field and its value changed with increasing temperature up to about 1800 microstrain at an applied magnetic field, H=8.0×10⁵ A/m (=10 kOe), at just below the inverse phase transformation temperature (A_s). This phenomenon may be caused by the re-arrangements of the activated martensitic twin variants due to applying magnetic field. The dependencies of shape memory effect and giant magnetostriction on metallurgical microstructures are discussed from the viewpoint of the crystal anisotropy and the grain boundary character distribution.

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Deformation and recrystallization during hot working of some polycrystalline metals have been described with a kinetic equation on deformation and Avrami equation respectively. Based on the interactions between deformation region and recrystallization region, a nonlinear differential equation group is suggested to be the kinetic model of hot working. According to the analyses on the stability of the solution of the equation group, if the working temperature, strain rate and other parameters satisfy certain conditions, the volumes of deformation region and recrystallization region will change cyclically and alternatively, which can cause a special fluctuation of the stress-strain curve. The amplitude of the fluctuation will decrease gradually with the increasing strain, when a dynamic equilibrium of deformation and recrystallization is formed finally, a stable stress-strain relation can be expected. A formula is proposed to calculate the frequency of the fluctuation, it can increase with the increasing working temperature or with the decreasing strain rate, initial grain size or solute atoms content. However, when working temperature, strain rate and other parameters go over the critical conditions, the fluctuation of macro-stress can not occur. The calculated results are in better agreement with experiments, and some phenomena associated with dynamic recrystallization can be reasonably explained.

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The most recent and important research results of our group on the microstructure and transformation mechanism of bainite in both ferrous and non-ferrous alloys are reviewed. The objective and popular existence of three-dimensional superledges and nanometre scale edges were confirmed. It was discovered by scanning tunneling microscopy (STM) that the bainitic plates were composed of ultra fine structural units, and their surface reliefs and those associated with Widmanstätten ferrite were tent-shaped. Carbides nucleated in the matrix and grow toward austenite and the model of carbide formation was provided. The sympathetic nucleation and ledgewise growth (SNLG) mechanism of bainite has further been described and applied to interpret the complicated multi-layer substructure. The model of multi-layer structure of bainite has been proposed.

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