Thermal stability of Al20Ti2Nd in rapidly solidified Al–6Nd–2.5Ti alloy by planar flow casting

Rapidly solidified (RS) Al–6Nd–2.5Ti alloy ribbons 17.5 mm wide by 35 μm thick were prepared by planar flow casting (PFC), and subjected to heat treatment for times up to 300 h at 300, 427, 517 and 547°C. The as-spun and as-heat treated ribbons were investigated by X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The results show that the as-spun Al–6Nd–2.5Ti ribbon is composed of spherical metastable Al20Ti2Nd dispersoids (∼50 nm) and α-Al cells (∼0.5 μm). When the ribbon is heat treated at temperatures above 300°C, blocky α-Al11Nd3 particles forms on the metastable Al20Ti2Nd dispersoids. At 300 and 427°C, the coarsening rates of the metastable Al20Ti2Nd dispersoids are 5.01×10−24 and 2.56×10−23 m3 h−1, respectively. At 517°C, the spherical metastable Al20Ti2Nd dispersoids begin to transform to the blocky stable ones with twins. Both the metastable and stable Al20Ti2Nd dispersoids possess an Al18Cr2Mg3 structure and space group of Fd3m, but the lattice parameter of the former (1.4647±0.0006 nm) is smaller than that of the latter (1.4699±0.0002 nm).