Non-equilibrium primary crystallisation in silver–germanium alloy under microgravity conditions

Abstract

T he influence of convection on the morphology of primary dendrites and on the distribution of germanium in primary crystals of hypoeutectic Ag-Ge alloy was studied. T he experiment in microgravity provided conditions for the suppression of melt flow. Both the morphology of the primary dendrites and their chemical composition profiles were found to vary considerably depending on the intensity of convection. Primary crystals in specimens solidified in the space laboratory exhibited strong supersaturation with germanium. T his supersaturation is associated with a decrease of solute in the eutectic. T he overall segregation of germanium between crystals and the melt during the growth of primary dendrites is strongly promoted by convection. T he influence of convection on the non-equilibrium primary crystallisation, particularly on the solute trapping process, the occurrence of which is likely in the initial stage of primary crystallisation (solute rich core), is discussed. A higher solute gradient close to the core in the space sample implies a higher melt stability below the liquidus when convection is suppressed.MST /4234

Microgravity Crystal Formation

“…If the authors in the reference discussed improved uniformity specifically in their text, often providing statements such as "improved morphology" [19] and "high isotropy" [20], it was reported as improved in our database. Due to structural enhancement, microgravity-grown crystals were described as having "fewer flaws" [18] and being "better developed" [21]. Improvements in the numerical measure of mosaicity, as in [20], and resolution limit, as in [22], where lower numbers were better, were used to determine whether comparative data were provided.…”