Estimation of thermodynamic stability of isoperiodic epitaxial structures whith GaInSbAs and GaInAsP solid solutions

The work studied the thermodynamic stability of GaInSbAs, GaInAsP heterosystems on different substrates. The isotherms of spinodal decomposition caused by chemical changes in the internal energy of the alloy and by elastic stresses at the layer-substrate interface are obtained with the model of quasiregular solutions. It has been found that elastic stresses lead to an expansion of the region of thermodynamic stability of isoperiodic solid solutions for GaSb substrates and a decrease in the critical temperature. The developed model can be using to selection of the technological modes and parameters of epitaxial growth.

Effect of Heat Treatment Conditions on Microstructures and Mechanical Properties of Cu-9Ni-6Sn-0.22Nb Alloy

Due to its high strength, excellent electrical conductivity and high resistance to stress corrosion, Cu-Ni-Sn alloy has been selected as a kind of advanced metal material which can be used as the manufacture of springs, connectors, bearings and so on. In addition, the addition of Nb can efficiently improve the comprehensive properties of the alloy. In the present work, the effect of heat treatment conditions on microstructure and mechanical properties were studied in a Cu-9Ni-6Sn-0.22Nb alloy by means of optical microscopy (OM), transmission electron microscopy (TEM), tensile test and microhardness tests. The results show that before ageing, a large number of fine γ precipitates with DO22 type structure are distributed on the matrix. With the prolongation of ageing time, the ultimate tensile strength (UTS), yield strength (YS) and Vickers hardness increased firstly, and then decline. The reason can be attributed to the occurrence of spinodal decomposition and the formation of discontinuous precipitation (DP). At first, spinodal decomposition induced the enhanced interaction between dislocations and internal stress field, resulting in an increase of mechanical properties. Then the increased DP at grain boundaries leads to the decline of strength in the material. Finally, the relationship between the microstructure and the electrical conductivity was also analyzed, and the results show that the electrical conductivity increased with ageing time/ageing temperature increasing for the present alloy. Through the analysis of Matthiessen’ s rule, the variation of electrical resistivity depends on precipitates, solute atoms, dislocations, vacancies and grain boundaries, and the precipitates play an important role among them. Besides, more precipitates improve electrical conductivity. Therefore, the increase of ageing time/ageing temperature induced the increase of DP, resulting in an increase of electrical conductivity.

Composition modulation in the GaxIni-xPyAs1-y - InP heterostructure during spinodal decomposition under the conditions of internal energy resonance

The Cahn-Hilliard concepts are generalized and used to the description of the spinodal decomposition of A3B5 quaternary semiconductor solid solutions, when the mixing of components occurs simultaneously in the metallic and metalloid sublattices of the sphalerite structure. The resulting system of differential equations for material decomposition was used to describe the effect of composition modulation observed in the synthesis of GaxIn1-xPyAs1-y - InP heterostructures. Numerical simulation of the spinodal decomposition of the GaxIm-xPyAsuy solid solution is carried out. The intervals of the thermodynamic parameters of the technological process of the synthesis of structures, in which the effect of modulation of the composition should be manifested, are found.

Effect of Stress on Spinodal Decomposition in Binary Alloys: Atomistic Modeling and Atom Probe Tomography

Self-organizing nanostructure evolution through spinodal decomposition is a critical phenomenon determining the properties of many materials. Here, we study the influence of stress on the morphology of the nanostructure in binary alloys using atomistic modeling and atom probe tomography. The atomistic modeling is based on the quasi-particle approach, and it is compared to quantitative three-dimensional (3-D) atom mapping results. It is found that the magnitude of the stress and the crystallographic direction of the applied stress directly affect the development of spinodal decomposition and the nanostructure morphology. The modulated nanostructure of the binary bcc alloy system is quantified by a characteristic wavelength, $$ \lambda $$ λ . From modeling the tensile stress effect on the A-35 at. pct B system, we find that $$ \lambda _{001}< \, \lambda _{111}< \, \lambda _{101}< \, \lambda _{112}$$ λ 001 < λ 111 < λ 101 < λ 112 and the same trend are observed in the experimental measurements on an Fe-35 at. pct Cr alloy. Furthermore, the effect of applied compressive and shear stress states differs from the effect of the applied tensile stress regarding morphological anisotropy.