WETTING AND PREMELTING PHASE TRANSITIONS IN 43° <100> TILT GRAIN BOUNDARIES IN Fe-5at.% Si

Penetration of Sn and Zn along a 43° tilt grain boundary (TiGB) in a body-centred cubic (bcc) Fe - 5 at.% Si alloy is studied in the temperature range of 652 - 975°C. Wetting transition of GB by the Sn-rich melt is observed at TW = 810 ± 5°C. For Zn penetration along the GB, the wetting film is observed at all temperatures studied. The region behind the wetting film is observed to have an unusually high GB diffusivity of Zn (by two order of magnitude), followed by a region of "usual" GB diffusivity. The transition from usual to anomalous GB diffusivity D'δ, where D' is the GB diffusion coefficient and δ is the GB width, takes place at the concentration Cbt. The value Cbt is independent of the annealing time, but depends strongly on the temperature. Such a phenomenon may be explained in terms of the so-called premelting phase transition "GB → thin wetting film on the boundary"

CONCENTRATIONAL PHASE TRANSITION ON THE INTERPHASE BOUNDARIES Sn/Ge AND ON THE GRAIN BOUNDARIES IN TIN : INDIUM DIFFUSION

The diffusion of indium along [001] tin-germanium interphase twist boundaries and [001] twist grain boundaries in tin has been studied in the vicinity of the β - γ' transition in the Sn-In system. The temperature of the β - γ' transition in the interphase boundaries and in the grain boundaries is lower than that in the bulk and depends on the boundary misorientation angle. In the tin-germanium interphase boundaries, near the temperature of β - γ' boundary transition, strong violations of the arrhenius law were observed. The observed decrease of the phase transition temperature at grain boundaries and interphase boundaries is explained in terms of a prewetting transition at the boundaries

PRESSURE EFFECT ON PREMELTING TRANSITION IN A TILT GRAIN BOUNDARY IN AN Fe-Si ALLOY

The effect of pressure on the diffusion of zinc along a 43° tilt grain boundary in an Fe-6at%Si alloy was investigated. Zinc penetrated into the grain boundary from a 100 µm thick liquid layer on the surface of the bicrystal. It was found that penetration of zinc causes a premelting phase transition in the grain boundary. The phase transition was suppressed for pressures higher than 0,5 GPa

THE ISOTOPE EFFECT BY ZINC DIFFUSION ALONG 43° [100] TILT GRAIN BOUNDARY IN Fe-5 at.% Si ALLOY

The distribution of stable zinc isotopes in the regions of bulk and grain-boundary diffusion of zinc in bicrystals of Fe+5 at.% Si with tilt grain boundary [100] 43° is studied by means of local secondary ion mass-spectrometry. Two-dimensional images are obtained which evidently show the existence of regions of wetting rapid diffusion (premelting region) and common diffusion on the grain boundary. The isotope effect is determined for bulk diffusion and diffusion along premelting layer for zinc isotope pairs 64/66, 64/67 and 66/67