Precipitation evolution in Al–Zr and Al–Zr–Ti alloys during aging at 450–600 °C
The transformation of Al3Zr (L12) and Al3(Zr1?xTix) (L12) precipitates to their respective equilibrium D023 structures is investigated in conventionally solidified Al–0.1Zr and Al–0.1Zr–0.1Ti (at.%) alloys aged isothermally at 500 °C or aged isochronally in the range 300–600 °C. Titanium additions delay neither coarsening of the metastable L12 precipitates nor their transformation to the D023 structure. Both alloys overage at the same rate at or above 500 °C, during which spheroidal L12 precipitates transform to disk-shaped D023 precipitates at ca. 200 nm in diameter and 50 nm in thickness, exhibiting a cube-on-cube orientation relationship with the ?-Al matrix. The transformation occurs heterogeneously on dislocations because of a large lattice parameter mismatch of the D023 phase with ?-Al. The transformation is very sluggish and even at 575 °C coherent L12 precipitates can remain untransformed. Mechanisms of microstructural coarsening and strengthening are discussed with respect to the micrometer-scale dendritic distribution of precipitates.
Keith E. KniplingaEmail:knipling@anvil.nrl.navy.mil?David C. Dunandb?David N. Seidmanb
[a]Naval Research Laboratory, Code 6356, 4555 Overlook Avenue, SW, Washington, DC 20375-5320, USA;[b]Department of Materials Science; Engineering, Northwestern University, 2220 Campus Dr., Evanston, IL 60208-3108, USA;[c]Northwestern University Center for Atom-Probe, Tomography (NUCAPT), Northwestern University, 2220 Campus Dr., Evanston, IL 60208-3108, USA
