The physical and chemical properties of materials are determined in part by microstructure. Grain orientation and size in polycrystalline aggregates affect, for example, yield strength, catalytic efficiency, chemisorption, physisorption, fracture and a host of other properties. The final grain morphology is often determined by thermal processing, addition of a second phase, deformation, etc. However, in order to effectively tailor the microstructure for specific applications, the mechanism and kinetics of grain growth must be known. Unfortunately, present theories predict grain growth kinetics (1–3) which often differ from experimental observation, have little predictive ability with respect to microstructure and are not easily generalized to account for experimentally controllable factors.

The Ostwald ripening of precipitates in Cu-Co alloys was investigated by electron microscopic observation. The variation of the mean particle radius r, and the distribution of relative particle sizes, f(r/r) , were obtained as functions of the aging time at 873K . The shape of f(r/r)was rather sharp and symmetrical around r = T in the early stage. It became broad with the aging and was similar, in the late stage, to the theoretical distribution of Ardell. It appeared that the shape of f(r/r) depends on the volume fraction but the growth rate of F scarcely depends on it. The rate of change of r was proportional to the cube root of the aging time from the early stage of aging.

Consideration of only nearest neighbour pairwise interactions Vij in a binary alloy leads to the classification of the system as ordering (unlike near neighbours) or clustering (like near neighbours), depending upon the sign of Vij However, this simple classification loses meaning when multi-atom correlations, many-body interactions or a longer range interaction are considered. For example, the first nearest neighbour interaction may favour ordering while the second, which may be of comparable magnitude, may favour clustering. By extending the Bragg-Williams model to include second near-neighbour interactions in fcc alloys, it is shown that a miscibility gap may form in the region of the orderdisorder solvus, leading to a complicated sequence of atomicrearrangement upon slow cooling. Despite the well-known failings of the point approximation when applied to fcc alloys, the results are shown to be consistent with the unusual behaviour exhibited by some systems.

The problem of interstitial diffusion in substitutional lattices has been extensively studied due to the practical importance of carbon in ternary austenites, as well as H in alloys.

A new mode of precipitation of the metastable Al3 Zr in Al-Zr-alloys has been investigated. The salient aspects of this precipitation reaction are: (i) The formation of precipitate configurations of a well defined macroscopic morphology, (ii) Each individual precipitate within the colonies grows in crystallographic directions, and (iii) The absence of a high angle grain boundary as a reaction front.

Recent theories make it possible to think that electrical resistivity measurements could provide quantitative informations about the microstructural evolution. These theories are tested by studying the influence of the measuring temperature TM. Our experiments show that when spherical G.P. zones appear in AI-Zn and Al-kg no influence of TM is observed, while the formation of plate-like G.P zones in Al-Cu and Cu-Be alloys induce electrical variations function of TM . This morphology effect is roughly predicted by the theoretical models buv supplementary parameters must be taken into account to obtain a quantitative explanation of experimental results.

During the first stages of decomposition of Al Zn alloys, spherical GP zones are observed. On further ageing of the samples, the precipitates have the shape of flat ellipsoids, the small axis of which are in the various <111> directions.

We have followed such an evolution in single crystals by small angle neutron scattering. From the asymptotic behavior of the cross section, we have calculated the size (c) of the small semiaxis of the ellipsoids. We show that c is almost independent of the initial composition of our samples (5.3, 6.8, 12.1 at Zn %), independent of the other dimensions of the “α'R” precipitates and very sharply distributed around its mean value (c = 24.5 ± 2 Å at 293°C).

The strain field in the matrix must clearly be involved in the limitation of the c value. We have studied the effect of a uniaxial [110] compressive stress applied during ageing. Neutron small angle experiments, carried on an Al-12.1 at % Zn single crystal show that the c value remains the same. The scattering in the [111] and [11] directions is much higher than in the [111] and [111] directions. This is mainly due to the fact that the stress favors the number of [111] and [111] type of α'R precipitates.

The discontinuous precipitation reaction has been studied in an Al-28a/o Zn solid solution. It appears that the diffusion rates determined by us for migrating grain boundaries are of the same order of magnitude as the values determined by Häβner (1974) for stationary grain boundaries. To the same statement have led results from the discontinuous coarsening reaction in an Al-29a/o Zn alloy (Fournelle et al., 1982) as well as from the eutectoid reaction in an Al-60a/o Zn alloy (Cheetham et al., 1971).

The influence of plastic deformation on the kinetic of precipitation and the morphology of precipitates in an Al-Zn 4.4 % at. studied by T.E.P. and SAXS is reported. Some results can be pointed out ; after a given amount plastic deformation at room temperature by tensile strength:

i - the precipitates have a flat shape (instead of the spherical or ellipsoidal shape usualy observed in this alloys.

ii - the precipitate volume fraction is a function of strain (ε) and strain rate (ė). For a given ė, the higher precipitate volume fraction is obtained with the higher ε. For a given ε, the lower ė the higher the volume fraction of precipitates.

iii - the scattering intensities at small angle for three orientations of the sample (α =0,45°, 90° where α is the angle between the axis of tensile and the scattering vector- are different. A calculation for an anisotropic orientation of flat discs shows that precipitates have a preferential texture. The orientation is about 50° from the tensile axis.

The clustering in Cu-Be alloys lead to large modifications of the X-ray scattering curves and to increases of both electrical resistivity and thermopower. The microstructure is investigated in the initial stages of precipitation : small clusters exist in the quenched state, but no spherical precursor precipitates are observed before the formation of plate-like G.P. zones. The evolution of the transport properties is qualitatively analyzed and the deformation effect induced by anisotropic particles is considered.

The pseudo-binary alloy system extending between copper and the intermetallic NiMn was first shown by Dean et al. [1,2] to yield a series of age hardenable alloys. The alloy containing 20% each of Ni and Mn has the best combination of strength and toughness and has been the subject of more recent studies [3,4]. The phase transformation associated with ageing in quenched Cu-NiMn alloys is precipitation of the ordered tetragonal (Llo) phase, (⊖) based on NiMn, from an fcc solid solution. Generally three modes of transformation occur depending on composition and temperature. An intragranular precipitate of fine coherent particles of ⊖, or a cellular or discontinuous precipitation reaction emanating from the grain boundaries, or heterogeneous precipitation of ⊖ at the grain boundaries.

The effect of stress on spinodal decomposition in Cu-15Ni-8Sn alloy was investigated at various temperatures and stresses. As the aging temperature approached the coherent spinodal temperature about 500°C, the anisotropy among the three equivalent <100> modulations of the stress aged specimens became pronounced. The wavelength of the [001] modulation along the tensile stress axis was smaller than that of the [100] or [010] modulation perpendicular to the stress axis. TEM diffraction patterns also showed the anisotropy effect of the applied stress to the composition modulation. A theoretical model based on micromechanics concepts was employed to explain the experimental results.

Spinodal decomposition in iron-chromium alloys has been studied for various compositions and aging temperatures by several workers using small angle neutron scattering. The data of the present study and that of previous workers are reviewed in order to better define the coexistence curve of this system as well as to provide an experimental basis for comparison with current nonlinear theories of spinodal decomposition. Regarding the coexistence curve, it is argued that the qualitative changes in the scattering pattern with composition and aging temperature are consistent with the experimentally determined boundary, rather than those calculated for this system. Quantitative analysis of the kinetic development of scattering from Fe-32Cr samples allows direct comparison with predictions of nonlinear theories of spinodal decomposition. The time dependence of the position of the peak maximum has been given by several theories as t−. The value of ø found for Fe-32Cr increased with increasing aging temperature, extrapolating near the value of 1/6 at the estimated spinodal temperature.

Continuous phase separation or spinodal decomposition occurs within a miscibility gap through the selective amplification of long wavelength concentration waves to produce a two-phase modulated microstructure. To comprehensively study the formation of these modulated microstructures and the kinetics of continuous phase separation the behavior of the composition fluctuations in the decomposing material should be monitored directly. The atom probe field-ion microscope is an ideal instrument for this type of investigation of fine-scale microstructures because of its ultra-high spatial resolution and microchemical analysis capability.

A neutron scattering study on a number of CuNi(Fe)-alloys has been undertaken in order to test some recent theories on the relaxation of short-range clustering and decomposition with special emphasis on scaling properties. The structure functions S(k,t), have been determined for samples, which had undergone a large number of different heat treatments resulting in different thermodynamic states. The analysis of the structure functions during relaxation of short-range clustering showed that even in these cases the assumption of small concentration fluctuations made in Cook's theory for spinodal decomposition is not always valid. Moreover, for the relaxation of short-range clustering and the very early stages of decomposition no scaling behaviour could be found. However, for some particular cases close to the spinodal, after a certain transient time, the structure function could be transformed into a time-independent function.

The main conclusion is that the kinetics of relaxation above as well as within the miscibility gap show similar characteristics, but there is no universal description applicable to all different regimes.

Several authors have modeled the order-disorder transformation as a continuous process, not occurring by nucleation and growth. Their approaches are based either on treating the transformation as a second-order chemical reaction [1,2], or on discrete formulations of the phenomenological diffusion equations [3–8]. Extending the work of Gorsky [9] and of Bragg and Williams [10], Dienes [2] used the chemical reaction model with absolute reaction rate theory to derive numerically the time-dependence of the longrange order parameter. As his thermodynamic model he used the Bragg-Williams (B-W) approximation, assuming that the solid was uniformly ordered and ignoring inhomogeneity effects such as the excess interface and coherency strain energies that arise if antiphase domains exist.

Experimental studies on deformation behavior of Cu-10Ni-6Sn spinodal alloy specimens subjected to different aging treatments were carried out at various temperatures ranging from 77°K to 353°K, using a micro-tensile device. It was found that the total elongation was independent of aging time as long as the modulated structure was coherent. Observed slip distribution and activation energy obtained in these investigations are presented. Transmission electron microscopy of deformed specimens showed straight dislocations in as-quenched samples; they were curved and wavy in aged samples. Burgers vector analysis of the dislocations present in the deformed aged samples indicated that they were of mixed character. Preliminary theoretical results on the role of wave-squaring of the internal stress field on CRSS are also presented.

Earlier investigations of short range clustering (SRC) and long range decomposition (LRD) in Cu-Ni alloys upon electron irradiation [1,2] have been extended to alloys containing 0.5 and 2 at.% Fe. Moreover, quenching instead of furnace cooling was applied to achieve a well defined homophase equilibrium state with a small degree of SRC. Under subsequent irradiation at temperatures between 373 K and 623 K the decomposition kinetics of the alloys have been followed by diffuse and small angle neutron scattering experiments within a momentum transfer range of 0.001 < κ(Å−1) < 8. The addition of Fe is found to extend the miscibility gap to higher temperatures. The observed scattering curves are discussed in terms of the existing models for the initial stages of spinodal decomposition, irradiation enhanced diffusion and phase stability under irradiation.

An attempt is made to investigate theoretically the kinetics of ordering accompanying phase separation in an alloy as a continuous medium. A set of coupled equations for the local composition and the degree of order are derived from the first principles of thermodynamics of irreversible processes, under an appropriate assumption as to the free energy of the system. Under certain circumstances a periodic deviation of local order parameter in the disordered state induces that of the composition, leading to a spinodal decomposition, and the resonance conditions for enhancement of such an induction are examined in the perturbation approximation. In a uniform state of imperfect degree of order disturbances of the local composition and degree of order develop in-phase.

We discuss some the physical issues involved with the adsorption of several layers of a solid adsorbate on a strongly attractive substrate. The experimental observation at low temperature of vertical risers (the “layering transitions”) in the plot of coverage versus pressure can be understood using a one-layer 2D lattice-gas model. The behavior at higher temperature is described in terms of a coarse-grained interface hamiltonian which emphasizes the role of long-wavelength interface fluctuations. A simple variational theory predicts that the coverage in the nth layer is a continuous function of pressure above a critical temperature Tc,n which depends weakly on n and has as its large n limit the bulk roughening temperature TR.