BROADER IMPACTS

1. A quantized hierarchy of shear transformation zones in a metallic glassMichael Atzmon, University of Michigan Ann Arbor, DMR 0605911 Unlike in crystalline metals, the deformation of metallic glasses is poorly understood. One of the challenges is in defining and characterizing flow defects in an ill-defined structure. Simulations and artificial models indicate that macroscopic plastic deformation of metallic glasses involves microscopic shear transformation zones (STZs). We have measured anelastic, i.e., time-dependent and reversible, strain relaxation in amorphous Al87Ni4Y9on time scales of 1 s to one year. The resulting relaxation-time spectra indicate a series of distinct processes. These correspond to a quantized hierarchy of STZs with increments of a single atomic volume. The significance of these results may turn out to be similar to that of early dislocation studies to crystalline materials. Relaxation time spectra obtained by a combination of bend-stress relaxation measurements ((a) above) and cantilever bending in a nanoindenter ((b) above). STZ volume in units of atomic volume of Al, calculated for each peak in the relaxation time spectrum for each STZ type.

2. Fundamental aspects of plasticity in metallic glassesMichael Atzmon, University of Michigan Ann Arbor, DMR 0605911 • BROADER IMPACTS • Graduate students have received education and training in research that includes experiment and modeling. A woman and member of underrepresented minority were among these students. • The PI has given numerous invited talks at national and international meetings, which include a combination of tutorials on basic topics, e.g., modeling of anelastic solids, and their application to current research. Colleague feedback has indicated the benefit to graduate students from other U.S. institutions. • Considering the significance and simplicity of the research results, it is expected that they will be incorporated into classroom teaching at the PI’s and other universities.