Spinodal decomposition of beta brass

An electron microscopy study has been carried out to determine the origin of diffuse satellite reflections appearing in the electron diffraction patterns of the metastable CsCl type phase in Cu-38.9 and Cu-47.3 at. pct Zn alloys. It has been shown that two different kinds of satellite reflections appear: one set arises because of spinodal decomposition at low temperatures near room temperature, and the other is related to a soft phonon mode. The observed basket weave microstructure is formed by a spinodal decomposition of the ordered phase. The spinodal curve in the ordered CsCl type phase is discussed on the basis of a regular solution model, and the morphology of the spinodally decomposed structure and its dependence on specimen thickness is discussed in terms of elastic energy. The spinodal product is characteristic of thin foils only, being found in elastically soft {100} specimens, but not in foils with {110} or {111} orientations. In comparison with previous observations, the present results indicate that thin foils in other β-phase materials may decompose spinodally, and the effect may be of general significance. formerly with the Department of Metallurgy and Mining Engineering and Materials Research Laboratory, University of Illinois.     

Spinodal decomposition of a Co-Ti-Nb alloy

The microstructural evolution on aging a Co-3 wt pct Ti-2 wt pct Nb alloy has been followed by transmission electron microscopy and diffraction to show that the solid solution decomposed by the spinodal mode. The strengthening observed has been correlated with the differences in lattice parameters of the coexisting phases. The several stages of coarsening have been documented to yield information about their kinetics and morphological changes. Formerly Visiting Assistant Professor, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1206 West Green Street, Urbana, IL 61801, is with .     

Spinodal decomposition during aging of Fe-Ni-C martensites

A collaborative study of the aging of virgin Fe-Ni-C martensites has combined the techniques of transmission electron microscopy (TEM), atom-probe field-ion microscopy (APFIM), and electrical resistometry. Aging at room temperature leads to the rapid development of a finescale structural modulation along 〈203 〉 lattice directions. Atom-probe analysis of Fe-15Ni-lC martensite reveals the formation of carbon-rich regions whose carbon concentration increases with time and approaches 11 at. pct C on prolonged aging. The early stage kinetics of this process are composition-dependent and are consistent with carbon-diffusion control. The morphological features of the aging reaction are explained by elastic strain-energy considerations. In accordance with previous thermodynamic models, it is concluded that virgin Fe-C martensites are unstable and that phase separation occurs by a spinodal mechanism. The martensitic substructure does not appear to exert any substantial influence on this decomposition behavior. Due to tetragonality of the martensites in this paper, it should be noted that the third Miller index (representing the c-axis) is not interchangeable with the other two indices when obtaining equivalent variants. K.A. Taylor, formerly with the Massachusetts Institute of Technology L. Chang, formerly with the University of Oxford G.B. Olson, formerly with the Massachusetts Institute of Technology     

Spinodal decomposition in nickel based nickel-titanium allols

The earll stages of the decomposition process in Ni based Ni-Ti allols have been studied bl means of transmission electron microscopl. It was found that the supersaturated solid solution of Ti in Ni decomposes bl the spinodal mechanism into periodic and aligned regions lhich are Ti rich and Ti lean. After a critical amount of Ti enters the Ti rich regions, thel order continuousll to the Ll₂ (Cu₃Au) structure. The tlo processes then continue together until the fulll ordered metastable γ′ particles are formed.     

Spinodal decomposition in the Fe−Cr system

Fe?Cr binary alloys ranging from 20 to 50 pct Cr have been analyzed by Mössbauer spectroscopy, in the queached state and after aging respectively at 470° and 540°C. A clear distinction could be made in this way between the nucleation and growth, and the spinodal process of decomposition during aging. When the alloy lies inside of the miscibility gap but outside of the spinodal, a pramagnetic precipitate clearly appears right from the beginning of the aging process, while when the alloy lies inside of the spinodal, no paramagnetic phase appears even after 1050 hr of aging at 470°C. This certainly indicates that the spinodal decomposition is very slow. One more point is shown: aging outside of the miscibility gap shows clearly a clustering of the chromium atoms and a large departure from the concept of an ideal solid solution.     

Spinodal decomposition in a Cu-9 wt% Ni-6 wt% Sn alloy

Decomposition of a Cu-9 Ni-6 Sn (composition by wt.%) supersaturated solid solution has been investigated at 350°C by resistivity measurements, X-ray diffraction and transmission electron microscopy. Concomitant effects on mechanical properties have also been evaluated. The presence of side bands on X-ray and electron diffraction patterns and modulated microstructures indicate that the supersaturated solid solution initially decomposes spinodally. These structural features persist even after aging for 80 hr; discontinuous precipitation is also observed in these samples. However, after aging for 160 hr, only discontinuous precipitates are present. Yield strength is observed to increase by ∼ 75,000 psi (517 MN/m²) during the aging sequence. The incremental strengthening is not thermally activated.Fracture ductility begins to drop rapidly after ∼ 45 min at 350°C and in the peak yield strength condition was less than 5 per cent. The change in ductility can be correlated with the presence and development of grain boundary precipitates.     

A simple method for the determination of isoelectric points of ampholytes with closely spaced pKa values using pressure-mediated capillary electrophoresis

A simple method, based on a modified version of pressure-mediated capillary electrophoresis (PreMCE) has been developed for the determination of the isoelectric points of ampholytes which have closely spaced pKa values. This new pI-determination PreMCE method (i) can be easily executed on most commercial capillary electrophoresis instruments; (ii) it can use small, impure samples, (iii) unlike isoelectric focusing methods in natural pH gradients, it does not require a linear pH gradient, and (iv) it eliminates the pI errors that are due to chromatographic retention on the walls of the separation chamber.