Solute-Derived Thermal Stabilization of Nano-sized Grains in Melt-Spun Aluminum

Thermal stabilization of nanograined metallic microstructures (or nanostructures) can be difficult due to the large driving force for growth that arises from the inherently significant boundary area. Kinetic approaches for stabilization of the nanostructure effective at low homologous temperatures often fail at higher homologous temperatures. Alternatively, thermodynamic approaches for thermal stabilization may offer higher temperature stability. In this research, modest alloying of aluminum with solute (1 pct by mole Sc, Yb, or Sr) was examined as a means to thermodynamically stabilize a bulk nanostructure at elevated temperatures. Following 1-hour annealing treatments at 673 K (400 A degrees C) (0.72 T-m), 773 K (500 A degrees C) (0.83 T-m), and 873 K (600 A degrees C) (0.94 T-m), the alloys remain nanocrystalline (< 100 nm) as measured by Warren-Averbach Fourier analysis of X-ray diffraction peaks and direct observation of TEM dark-field micrographs, with the efficacy of stabilization: Sr a parts per thousand Yb > Sc. The disappearance of intermetallic phases in the Sr- and Yb-containing alloys in the X-ray diffraction spectra is observed to occur coincident with the stabilization after annealing, suggesting that precipitates dissolve and the boundaries are enriched with solute. (C) The Minerals, Metals & Materials Society and ASM International 2016