Many metallic alloys (with a combination of different metal and/or metalloid elements) can be frozen into so called “metallic glass” or “glassy metals", by cooling the liquid melt fast enough to avoid nucleation and growth of crystals. Nevertheless, solid pure metals have all remained in a crystalline state in reality, until the recent success in obtaining super high cooling rates on the order of 10^13 K/s (Li et al., Nature 512, 177, 2014) on small specimens in the form of nano-tips. This cooling rate was sufficient to quench a handful of pure metals into the glassy state, among which tantalum showed surprisingly high stability against (re-)crystallization at room temperature. This talk presents a computational (molecular dynamics) study of the structural evolution in the supercooled tantalum liquid, with the aim to shed light on the origin of the glass forming ability and the glass stability of this exceptional metal. We will focus on two dominant structural features, icosahedral and BCC (body-centered-cubic) clusters, and how they fight to control the resulting glassy or crystalline state upon quenching and isothermal annealing.
Speaker professional affiliation:

Donghua Xu (Materials Science Program)
School of Mechanical, Industrial and Manufacturing Engineering
Oregon State University, ext. X7-7027
http://research.engr.oregonstate.edu/mmdg/