Grain Boundary Wetting in Polycrystals: 2. Percolation Model of the Connectivity of Liquid Phase and Experimental Studies of Zinc–Melt Systems

The notions of percolation theory were used to determine the critical value of the ratio of interfacial and grain boundary energies which provide the liquid-phase inclusions to form the network penetrating polycrystals of any size. Model estimates are compared with the experimental distribution of liquid-phase inclusions over various structural elements of polycrystalline zinc.     

Grain Boundary Wetting Statistic in Zn/Ga System and its Application to Grain Boundary Energy Spectrum Estimation

The grain boundary statistic in zinc polycrystals in contact with saturated Ga(Zn) melt has been studied. The misorientation angle distributions for zinc thin foil and zinc plates were obtained. The influence of the misorientation angle value on the wetting probability p of grain boundaries was observed. The grain boundary energy distribution parameters were obtained by using the p() relationship. The dihedral angles in triple lines of non-wetted zinc samples were also measured and their distribution was used to obtain the grain boundary energy distribution function. The parameters obtained by two different methods correspond to one other.     

Physicochemical mechanics of structural transformations in nitrided steel

It is shown that the orientational anisotropy of intergranular cementite precipitates formed in alloyed steels upon nitriding is due to the presence of an internal stress field which affects the rate of cementite precipitation, predominantly at the nucleation stage. The calculation of the formation work of a new phase with account of both the thermodynamic parameters and stress state makes it possible to estimate the probability of the formation of precipitates on grain boundaries depending on their orientation. The results of calculation are in a good agreement with the experimental data.Translated from Kolloidnyi Zhurnal, Vol. 67, No. 1, 2005, pp. 106–112. Original Russian Text Copyright © 2005 by Traskine, Bochenkov, Skvortsova, Barrallier.     

Experimental and theoretical cooling velocity profile inside laser welded metals using keyhole approximation and Boubaker polynomials expansion

In this paper we are concerned with the t-dependent cooling velocity during laser welding sequences. The temperature profile has been yielded by using keyhole approximation for the melted zone and solving the heat transfer equation. A polynomial expansion has been adopted as a guide to determining the cooling velocity during welding cut-off stage. A thorough comparison with experimental results and recently published profiles has been carried out.     

Percolation models of grain boundary wetting in polycrystalline materials

A model is proposed accounting for grain boundary (GB) wetting in polycrystals. Liquid penetration into GB planes, triple lines, and quadruple points is analyzed. The GB wetting condition (Gibbs-Smith criterion) is generalized by introducing a parameter defined as “characteristic free energy.” In order to find critical values of interfacial/GB energy ratio corresponding to an infinite cluster formation, the percolation theory has been used. Model estimates are consistent with the experimentally observed topology of additives in polycrystalline zinc.