Complex(Mn,X)S compounds-major sites for graphite nucleation in grey cast iron

Despite the cubic system, the ability of sulphides to nucleate graphite can be enhanced by inoculating elements which transform them in complex compounds with a better lattice matching to graphite, a low coagulation capacity, good stability and adequate interfacial energy. （Mn,X）S compounds, usually less than 5.0 μm in size, with an average 0.4-2.0 μm well defined core （nucleus）, were found to be important sites for graphite nucleation in grey irons. A three-stage model for the nucleation of graphite in grey irons is proposed： （1） Very small microinclusions based on strong deoxidizing elements （Mn, Si, Al, Ti, Zr） are formed in the melt; （2） Nucleation of complex （Mn,X）S compounds at these previously formed micro-inclusions; （3） Graphite nucleates on the sides of the （Mn,X）S compounds with lower crystallographic misfit. AI appears to have a key role in this process, as Al contributes to the formation of oxides in the first stage and favors the presence of Sr and Ca in the sulphides, in the second stage. The 0.005-0.010% Al range was found to be beneficial for lower undercooling solidification, type-A graphite formation and carbides avoidance.

Self-Learning Algorithm for Coiling Temperature Controlling

A novel model of the evolution of microstructure during continuous cooling with the formation of proeutectoid ferrite in steel was proposed from a Voronoi construction for the austenite grains, based on the Rappaz′s integral nucleation model and the assumption that the ferrite nucleates at the edges of the original austenite grains and the successive growth of the ferrite grain is radial. The model can be used to calculate the fraction of ferrite as a function of time or temperature during continuous cooling, and to determine the microstructure of ferrite. The calculated results are in agreement with experimental results investigated in 0 38C-0 28Si-0 55Mn-0 92Cr-0 20Mo steel under continuous cooling using a Gleeble 1500 thermomechanical simulator.

The asymptotic solution of particle growth in the convective undercooled melt driven by a biaxial straining flow

A dynamical system of particle growth in the con vective undercooled melt driven by a biaxial straining flow is modeled. A uniformly valid asymptotic solution for the in terface evolution in particle growth is obtained by means of the multiple variable expansion method. The analytical so lution as a function of both azimuth angle and polar angle shows that the interface shape of particle growth in the bi axial straining flow is significantly deformed by the biaxial straining flow. The biaxial straining flow results in higher lo cal growth rate near the surface where the flow comes in and leads to lower local growth rate near the surface where the flow goes out. Due to the difference in local growth rate, an initially spherical particle will evolve into a prolate barrel like shape in the biaxial straining flow.

Simulation of secondary nucleation of polymer crystallization via a model of microscopic kinetics

We present simulations of the mechanism of secondary nucleation of polymer crystallization,based on a new model accounting for the microscopic kinetics of attaching and detaching.As the key feature of the model,we introduced multibody-interaction parameters that establish correlations between the attaching and detaching rate constants and the resulting thickness and width of the crystalline lamella.Using MATLAB and Monte Carlo method,we followed the evolution of the secondary nuclei as a function of various multibody-interaction parameters.We identified three different growth progressions of the crystal：（i） Widening,（ii） thickening and（iii） simultaneously thickening and widening of lamellar crystals,controlled by the corresponding kinetic parameters.

Modelling the Effect of Initial Grain Size on Dynamic Recrystallization Using a Modified Cellular Automata and a Adaptive Response Surface Method

A modified cellular automata （CA） model of dynamic recrystallization （DRX） and a flow stress-based nucleation parameter identification method have been developed. In the method, the modified CA model, which takes the role of deformation degree on nucleation behavior into consideration, is coupled with an adaptive response surface model （ARSM） to search for the optimum nucleation parameter. The DRX behavior of an oxygen free high conductivity （OFHC） copper with different initial grain sizes has been taken as an example to validate the model. Good agreement is found between the simulated and the experimental results, which demonstrates that the new method can effectively improve the simulation accuracy.

Analytical Description for Solid-State Phase Transformation Kinetics:Extended Works from a Modular Model, a Review

Solid-state phase transformation plays an important role in adjusting the microstructure and thus tuning the properties of materials. A general modular, analytical model has been widely applied to describe the kinetics of solid-state phase transformation involving nucleation, growth and impingement; the basic conception for iso-kinetics which constitutes a physical foundation for the kinetic models or recipes can be extended by the analytical model. Applying the model, the evolution of kinetic parameters is an effective tool for describing the crystallization of enormous amorphous alloys. In order to further improve the effectiveness of this kinetic model, recently, the recipes and the model fitting procedures were extended, with more factors （e.g., anisotropic growth, soft impingement, and thermodynamic driving force） taken into consideration in the modified models. The recent development in the field of analytical model suggests that it is a general, flexible and open kinetic model for describing the solid-state phase transformation kinetics.

Mechanism and mitigation of spontaneous Ga whisker growth on Cr2GaC

Spontaneous growth of A-element whiskers on Mn+1AXn(MAX for short) phase materials poses a barrier to their practical applications, since it casts doubts on their stability. In this study, Ga whisker growth on sintered Cr2GaC samples was investigated. The elemental source for spontaneous growth of Ga whiskers is identified as the free Ga contained in the Cr2GaC material, not the lattice atoms from Cr2GaC grains, which removes the doubts on the stability of Cr2GaC material. The growth behavior and morphologies of the Ga whiskers follow a new catalysis-based model, with cleavage planes of Cr2GaC grains involved as nucleation sites. This model explains and predicts well the growth behavior of the whiskers. The mitigation strategy based on this model is in principle simple: to prevent free Ga in Cr2GaC material or limit it to a certain level;to avoid cleavage plane of Cr2GaC grains;to achieve high density of the Cr2GaC material.