Four Ni-Mn-Ga single crystals exhibiting modulated 10M and 14M martensites were exposed to rotating magnetic fields of 1 and 2 T. Large periodic magnetic-field-induced strains were obtained for crystals that had been subjected to a mechanical stress while the martensite formed on cooling and to deformation in a magnetic field prior to the experiments with rotating field. A reduction of the magnetic-field-induced strain and fracture occurred when the field-induced strain was close to the transformation strain whereas a constant magneto-mechanical response was detected over more than 10 million field cycles when the field-induced strain was small. The cyclic magneto-mechanical response is related to the interaction of groups of twinning dislocations and twin boundaries. If the dislocations move in large groups, they nucleate cracks at twin boundaries. If the dislocations move in small groups, no cracks are formed resulting in a long lifetime.

In-situ small-angle neutron scattering was performed on Ni-(10 to 12) at.% Ti polycrystals and single crystals at temperatures between 870 and 1270 K. During decomposition metastable precipitates of cuboidal shape form with preferred alignement along <100>. The Ti concentration of these precipitates is 17(1) at.% (between 870 and 950 K). Metastable precipitates precede the formation of platelets of the stable η phase even outside the hitherto accepted metastable miscibility gap.

Uniaxially aligned polysynthetically twinned two-phase TiAl/Ti3Al material is produced by induction zone melting and deformed in uniaxial compression. Above 1000 K the strain rate sensitivity is independent of the lamellar orientation and increases strongly with increasing deformation temperature. Results for the strain rate sensitivity parameters are somewhat lower than those obtained for γ-TiAl single- and polycrystals. If the lamellae are oriented parallel or perpendicular to the deformation axis, the flow stress decreases with increasing strain. After plastic deformation the dislocation density in the lamellae is remarkably low indicating recovery processes. At the lamellar interfaces misfit dislocations and periodic arrangements of dislocations with Burgers vectors inclined to the lamellar boundaries are found. In contrast to deformation at lower temperatures, deformation twinning is rare.

The alloy Ti-48.6Al-l.9Cr-l.9Nb-IB with an equiaxed γ microstructure, obtained by heat treatment at 1200°C for 4 h, and with a lamellar mi ero structure, obtained by heat treatment at 1380°C for 1 h, is characterized by compression tests and transmission electron microscopy. A lower activity of superdislocations and a more frequent pinning of ordinary dislocations are detected in the lamellar Ti-Al specimens in comparison with the non-lamellar ones during deformation at room temperature. The activity of superdislocations and the pinning of ordinary dislocations are responsible for the differences in yield stress and brittleness between lamellar and non-lamellar Ti-Al. A very high density of ordinary interfacial dislocations is found in the lamellar structure. These influence the activity of superdislocations and the pinning of ordinary dislocations. At high temperature a change in the deformation mechanism occurs. Above the brittle-to-ductile transition, the material is remarkably softer and the mechanical properties are insensitive to the presence of the lamellar interfaces.

The influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.

The electrical conductivity of 3Y-TZP ceramics containing SiO2 and Al2O3 has been investigated by complex impedance spectroscopy between 500 and 1270 K. At low temperatures, the total electrical conductivity is suppressed by the grain boundary glass films. The equilibrium thickness of intergranular films is 1-2 nm, as derived using the “brick-layer” model and measured by HRTEM. A change in the slope of the conductivity Arrhenius plots occurs at the characteristic temperature Tb at which the macroscopic grain boundary resistivity has the same value as the resistivity of the grains. The temperature dependence of the conductivity is discussed in terms of a series combination of RC elements.

The 2212 phase formation during annealing of melt textured Bi–2212 (Bi2Sr2CaCu2Ox) was investigated using differential thermal analysis, thermal gravimetric analysis, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and high resolution transmission electron microscopy. After zone melting, the material is multiphase consisting of 2212, 2201, Sr1−xCaxCuO2, and the eutectic. The 2212 phase formed is highly perfect with less than 5% intergrowths of 2201 layers; the 2201 phase shows no intergrowth of 2212 at all. In the first period of the annealing, remelting of the eutectic leads to fast oxygen diffusion and a high 2212 formation rate. The 2201 → 2212 transformation proceeds via intermediate states of high defect density. The 2212 grains contain up to 30–70% 2201 intergrowths. Further heat treatments lead to an annihilation of the great majority of intergrown 2201 layers. We propose a model for the formation of 2212 grains with a low planar defect density, based on frequent stacking faults, that allows diffusion of Ca- and Cu-atoms over a short distance. The model provides a schematic description of this solid-state process and correlates it to the characteristic microstructural features of melt-processed Bi–2212.

Narrow-gap PbSe and PbSe1−xTex films were grown by MBE on 3n-Si(111) wafers. The layers are used for IR-sensor array applications. Epitaxy was achieved by using an intermediate CaF2/BaF2 bilayer to overcome the large difference in lattice constants (14%) and thermal expansion coefficients (700%). While PbSe is rather soft, the hardness increases with x (x<0.5) in PbSe1−xTex. Thermal stresses are relieved by dislocation glide on (100)-planes, leading to slip lines on the surface. The surface morphology and step heights were studied with the scanning tunneling microscopy technique, and a model for the resulting (111)-surface structure is presented. The value of the remaining strain was determined with precision Rutherford backscattering spectrometry absolute angle measurements, X-ray diffraction and photoluminescence in the temperature range down to 10 K. It is found that no appreciable strain builds up even at cryogenic temperatures and after many temperature cycles. In contrast to PbSe, ternary PbSe1−xTex layers are strained elastically below room temperature owing to solid solution strengthening, and plastic deformation occurs only at higher temperatures.

Quenched equilibrium states of Cu–31.1 at.% Zn and Cu–22.4 at.% Zn single crystals (prepared with the Cu-65 isotope) were investigated by elastic diffuse neutron scattering. The diffuse intensity showed maxima which are attributed to the flat portions of the Fermi surface in the <110> directions. Short–range order parameters and linear displacement parameters were obtained from a fit to the measured data. Pair interaction energies were determined based on the inverse Monte–Carlo method. An ordered low-temperature phase Cu3Zn with the DO23 structure is suggested.

The elastic diffuse neutron scattering from two Al-1.75 at.% Cu single crystals with either the isotope Cu-63 or Cu-65, aged to contain type-I Guinier-Preston zones has been measured along a reciprocal lattice line and evaluated based on an expansion of the atomic displacement scattering up to terms of third order. It is shown that erroneous results for the short-range order term are obtained if the evaluation does not include data from the first Brillouin zone. The most reliable short-range order scattering extracted for both crystals is consistent with essentially single-layered Cu-rich zones.

The decomposition of Ni ∼ 11.5 at.% Ti single crystals was studied for an ageing temperature of 540°C. In this alloy, coherent ordered zones of γ′-Ni3Ti (Cu3Au structure) are formed prior to the stable n precipitates. The early stages of zone formation were investigated by in-beam SANS and transmission electron microscopy (TEM). Electron diffraction, high resolution electron microscopy, TEM analysis of dislocation arrangements in samples deformed after ageing and X-ray measurements of the integrated intensity at L12 superstructure positions show that ordered regions already appear in quenched samples, whereas compositional changes, as determined by SANS measurements, occur only upon ageing.

In Al-Cu alloys containing Guinier-Preston zones, the scattering contributions due to short-range order and atomic displacements vary differently when the scattering contrast between Al and Cu is changed. The diffuse neutron scattering of Al-Cu single crystals containing 63Cu or 65Cu is compared and evaluated to test the current methods of separating the two scattering contributions. - The nature of a sugggtted ordered state in α-brass is also studied by neutron scattering, using Cu to enhance the scattering contrast in a Cu-30 at.% Zn alloy. A broad diffuse peak is found in powdered, appropriately aged samples, confirming that the first Warren-Cowley short-range order parameter is negative.

Recent results on the formation of voids and dislocation substructure in fatigued copper single crystals and on the early stages of decomposition in Ni base alloys are presented to illustrate some of the advances in the application of small-angle scattering techniques.