Studies of Heterogeneous and Diffusion-Influenced Nucleation for Improved Processing of Nanostructural Materials

Abstract : The high strength to weight ratio of amorphous and nano-structured Al-based alloys make them particularly interesting for aerospace applications. The purpose of this grant was to identify a suitable glass for studies of the nucleation processes leading to nanostructure formation and to investigate the possibility of using TiB2 for enhanced microstructure refinement during crystallization. The goals of the grant were met and exceeded. We (i) identified Al88Y7Fe5 as a model glass for study; (ii) discovered that microalloying significantly improved glass formation and stability with the substitutions of small amounts (=0.5 at %) of Ti, Zr and V for the Al; (iii) discovered amorphous Al(85.35)Y7Fe5Ti(0.5) by the addition of TiB2 particles, producing a final grain density of approximately 10(exp 24/cu m on the surfaces of the particles. In addition to demonstrating the technological usefulness of microalloying and the indication that evenly dispersed nanoparticles of TiB2 should lead to a significant nanostructure refinement during crystallization, these results also raise new fundamental questions, such as the mechanism of microalloying.