Dresden 2011 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 45: Topical Session Heterogeneous Nucleation II

MM 45.2: Talk

Friday, March 18, 2011, 10:45–11:00, IFW B

Peritectic solidification in Al-Ni alloys — •Hai-Lin Chen and Rainer Schmid-Fetzer — Institute of Metallurgy, TU Clausthal, Robert-Koch-Str. 42, D-38678 Clausthal-Zellerfeld, Germany

This work aims at a better understanding of the mechanism of peritectic solidification, including the four stages of heterogeneous nucleation, peritectic reaction, peritectic transformation and direct growth of the peritectic phase, and their roles in phase transformation and microstructure evolution. Directionally solidified, non-directionally solidified, quenched and specially heat treated alloys, relevant to the two peritectic reactions, L+NiAl->Ni2Al3 and L+Ni2Al3->NiAl3 in the Al-Ni model system, were investigated. A peritectic "reaction" is believed to occur instantly after a single nucleus of β forms on the primary phase α and result in a very thin peritectic rim, which may have different orientations. Generally, the primary phase α is mainly consumed during peritectic transformation and the amount of consumption may be defined as the "yield" of this step. It depends on the solid-state diffusion across the peritectic envelope and the composition relation between α and β. The diffusion, however, is hindered by the direct growth of β, which can become significant especially if β is located close to the peritectic liquid point and/or if the nucleation of β is difficult and the liquid is deeply undercooled. A new method is presented to tentatively predict the rate of a peritectic transformation according to phase diagram features, and it well accounts for the present experimental evidence that the transformation in L+NiAl->Ni2Al3 is extremely fast while that in L+Ni2Al3->NiAl3 extremely slow.