Sergio F. Gueijman

Semi-empirical modeling for columnar and equiaxed growth of alloys

The columnar and equiaxed growth of low-melting point binary alloys (Pb–Sn) was studied in a wide range of concentrations. From temperature measurements a number of important dynamic parameters were derived, such as cooling rates, profiles, grad ients andthe position andvelocity of liquid us andsolid us fronts. These parameters were correlatedwith the structure-like length of columnar grains andsize of equiaxedgrains. These correlations were usedto predict the solidification structure with the aid of a thermal model of solidification. An original feature of the thermal model is the way the latent heat is calculated and released. The nucleation and growth of equiaxed grains is assumed to follow the supercooling from the liquidus temperature. The main observation from the model is the high number of equiaxedgrains, which compete with the columnar growth in the transition. r 2002 Publishedby Elsevier Science B.V.

Tracking Interphases in Directionally Solidified Zn-Al Binary Alloys

In the present work, we investigated the movement of [liquid/(solid + liquid)] interphases [L/(S + L)], [(solid + liquid)/(eutectic + solid + liquid)] interphases [(S + L)/(E + L)], [(eutectic + solid+ liquid)/solid] interphases [(E + L)/S], and [(solid + liquid)/solid] interphases [(S + L)/S], running in a binary Zn-Al alloy system from the chilled ends of a hemicylindrical sample. We found that under specific solidification conditions, new [(S + L)/(E + L)] and [(S + L)/S] interphases can be created in the center of the sample, and then move toward the ends of the probe and collide with the solidification advancing fronts. In a horizontal setup with chilled ends we determined the speeds and accelerations of the four imposed interphases, two of which moved from left to right and two of which moved from right to left. We were also able to detect the creation of new [(S + L)/(E + L)] and [(E + L)/S] or [(S + L)/S] interphases created near the center of the sample, and to calculate their speeds and accelerations from the near beginning of the creation to the instant in which they collided with the imposed solidification fronts.

Macroestructuras de solidificación versus parámetros térmicos y electroquímicos en aleaciones zinc-aluminio (za)

Los materiales bimetalicos se fabrican por una diversidad de razones, entre ellas podemos mencionar el reemplazar aleaciones costosas, mejorar el aspecto superficial, obtener mayor resistencia mecanica, resistencia al desgaste o a la corrosion. La presente investigacion se realiza en aleaciones zinc – aluminio (Zn-4%Al, Zn-16%Al y Zn-27%Al) en sus diferentes estructuras (columnar, equiaxial y con transicion, TCE), a fin de estudiar la vinculacion entre los parametros de solidificacion, estructurales y de resistencia a la corrosion de las mismas. Los resultados son fuertemente dependientes de la concentracion de aluminio en la aleacion, como asi tambien del tipo de estructura que las mismas presentan.

CORRELACIONES ENTRE PARÁMETROS TÉRMICOS, ESTRUCTURA Y MICRODUREZA EN ALEACIONES ZINC-ALUMINIO (ZA).

In the present research we investigate correlations between thermal parameters (cooling rate, velocity and position of solidification fronts, temperature gradients), type of structure (grain size, dendritic spacing) and microhardness in directional solidified samples of Zn-Al (ZA) alloys. We present correlations between cooling rate and the width of columnar grains, velocity of solidification fronts versus length of columnar grains, density of equiaxial grains versus temperature gradients, grain size, primary an secondary dendritic spacing and the variations in microhardness.