Thermal stability of Al20Ti2Nd in rapidly solidified Al-6Nd-2.5Ti alloy byplanar flow casting

Rapidly solidified (RS) Al-6Nd-2.5Ti alloy ribbons 17.5 mm wide by 35 mu m thick were prepared by planar flow casting (PFC), and subjected to heat tre atment for times up to 300 h at 300, 427, 517 and 547 degrees C. The as-spu n and as-heat treated ribbons were investigated by X-ray diffraction, diffe rential scanning calorimetry and transmission electron microscopy. The resu lts show that the as-spun Al-6Nd-2.5Ti ribbon is composed of spherical meta stable Al20Ti2Nd dispersoids (similar to 50 nm) and alpha-Al cells (similar to 0.5 mu m). When the ribbon is heat treated at temperatures above 300 de grees C, blocky alpha-Al11Nd3 particles forms on the metastable Al20Ti2Nd d ispersoids. At 300 and 427 degrees C, the coarsening rates of the metastabl e Al20Ti2Nd dispersoids are 5.01 x 10(-24) and 2.56 x 10(-23) m(3) h(-1), r espectively. At 517 degrees C, the spherical metastable Al20Ti2Nd dispersoi ds begin to transform to the blocky stable ones with twins. Both the metast able and stable Al20Ti2Nd dispersoids possess an Al18Cr2Mg3 structure and s pace group of Fd3m, but the lattice parameter of the former (1.4647 +/- 0.0 006 nm) is smaller than that of the latter (1.4699 +/- 0.0002 nm). Publishe d by Elsevier Science S.A.