Origin of Ordering Coupled Tweed Microstructures in Alloys with Large Atomic Size Factors

A theoretical study is developed on the evolution and mechanism of an ordering coupled phase separation, and on the origin of a resultant tweed microstructure. It is found that long-range elastic interaction among atoms with different atomic sizes plays a key role in the phase separation, and that the evolution of the phase separation is very similar to that of conventional spinodal decomposition except that the separation is dependent on an elastic interaction ordering (EIO). This ''EIO coupled spinodal decomposition'' is shown to exhibit a periodical or tweed microstructure being accompanied by an EIO. It is also found that a large atomic size factor yields a large positive contribution of EIO to spinodal decomposition. Generally, it is thermodynamically and kinetically favorable for the EIO to precede the onset of spinodal decomposition, though the former is not separable from the latter as a whole. We suggest that an initially disordered solid solution undergoes an EIO first, and then the partially ordered solid solution starts to decompose via a spinodal mechanism. Solute-enriched regions increase their degree of order along with an increase in solute content, and solute-depleted regions decrease their degree of order together with a decrease of solute content. The final microstructure is characterized by a periodical array of highly ordered solute-enriched regions and nearly disordered solute-depleted regions. The notion of EIO coupled spinodal decomposition is in general agreement with the transformation behaviour of a large number of alloy systems.

Effect of Elastic Energy due to Atomic Size Factor on Ordering and Decomposition Behaviour of Binary Solid Solutions

A theory recently developed by the present authors is applied to the study of the effect of elastic energy due to atomic size factor on the transformation behaviour of binary solid solutions. It is found that elastic interaction energy (EIE), which is a part of the total elastic energy, plays a key role in both ordering elastic interaction ordering (EIO) and spinodal decomposition. The present study gives a reasonable explanation to the historical dilemmas, ''elastic energy paradox'' and ''atomic size factor paradox''. By solving these confusing problems, the coexistence of ordering (EIO) and decomposition, which has been regarded as impossible by conventional theories, can be well understood. The mechanism is as follows: lowering of elastic energy demands EIO, and such an ordering provides a driving force for spinodal decomposition. Therefore, in alloys with large atomic size factor, spinodal decomposition is preceded and induced by ordering. Ordering and spinodal decomposition are thus closely related processes to each other.

Elastic Energy and Elastic Interaction Ordering of Binary Solid Solutions

A theory in the framework of continuum elasticity has been developed to calculate the total contribution of ''atomic size effect'' or ''strain energy effect'' to free energy of binary solid solutions. It is found that elastic free energy consists of two parts: elastic self energy (ESE), and elastic interaction energy(EIE). The former is a function of composition alone, the latter is also a function of atomic configuration. Minimization of total elastic free energy with respect to atomic arrangement results in an ordered arrangement of atoms, which is called elastic interaction ordering (EIO), as it originates from elastic interaction among atoms. EIO is a kind of local ordering within a ''characteristic range'', and it is found to be important in determining the state of solid solutions and structures of superlattices. The present theory also gives good explanation to the coexistence of ordering and decomposition which can not be understood in conventional theories.

Emission spectra produced by pulsed laser ablation of metal Al at different ambient pressures

INTERACTION between laser and material is closely related to background besides properties oflaser and material. The interaction process can be influenced to a great extent by ambient at-mosphere and pressures. In the present work, a time and space resolved diagnostic tech-nique was used to study the emission spectrum from the plume produced by a pulsed laser on

8-chloroadenosine induces apoptosis in human MOLT-4 cell line

THE 8-chloroadenosine (8CA) is a novel analog of adenosine synthesized in the National Research Laboratories of Natural and Biomimetic Drugs. Fang et al. reported that 8CA is capable of inhibiting the cell growth in vitro of mouse liver cancer cells and human