Dendritic Growth Characteristics of Cu-Rich Zone within Phase Separated Fe50Cu50 Alloy

The undercooled Fe50Cu50 alloy experiences a metastable liquid phase separation and separates into a Fe-rich zone and a Cu-rich zone within the gravity field. The growth characteristics of the Cu-rich zone were investigated by the glass fluxing method, and the achieved undercooling range was 20−261 K. The volume fraction of the Cu-rich zone decreases with the enhancement of the bulk undercooling. The microstructural morphologies of the Cu-rich zone are similar at all the undercooling conditions, that is, αFe dendrites and particles are distributed inside (Cu) phase matrix. The secondary dendritic arm spacing of αFe dendrites decreases with the increase in bulk undercooling. The growth mechanism of αFe dendrites was analyzed by using the LKT/BCT dendritic growth theory. The dendritic growth in the Cu-rich zone is mainly controlled by solute diffusion so that the dendritic growth velocity is only several millimeters per second. Besides, the calculated results indicate that there is only inconspicuous solute trapping during the solidification of Cu-rich zone.

Grain Refinement in Undercooled Metals

ABSTRACTRecently, it was demonstrated that grain refinement in metals can take place through two mechanisms, namely, dynamic nucleation and remelting of initially formed dendrites. In this study, it was found that Ni99.45B0.55 undergoes grain refinement, both by dynamic nucleation or by remelting, depending on the initial bulk undercooling just before crystallization. The nature of the grain refinement process is confirmed by microstructural analysis of the undercooled specimens.

Solidification Front Velocity of Ternary Titanium-Aluminides

ABSTRACTTernary titanium-aluminides with compositions of Ti51Al47Fe2, Ti51A147Cr2 and Ti51Al47Mn2 were investigated with respect to the correlation of their solidification front velocity v and bulk undercooling ΔT. The observation of the solidification front during the recalescence event has been realized using a high speed video system capable of recording up to 12,000 pictures per second. The temperature measurement was carried out by pyrometry, avoiding contact with the sample. The comparison of the experimental data with the LKT-theory (Lipton, Kurz, Trivedi; [1]) refers to a primary (hcp) β-Ti solidification for undercoolings below ΔT≈ 130 K and primary (bcc) α-Ti solidification for ΔT≥ 130 K. For undercoolings ≥ 150 K the theory differs greatly from the experimental results.The maximum undercoolings achieved were 268 K (Ti51Al47Fe2), 285 K (Ti51Al47Cr2) and 280 K (Ti51Al47Mn2), corresponding to a solidification front velocity v ≈ 9-10 m/s for all alloys.