ON THE STRUCTURAL RELAXATION AND NANOINDENTATION STUDIES OF CHANGES IN FREE VOLUME IN Zr-BASED BULK METALLIC GLASSES

摘要

Real-time diffraction using synchrotron light in transmission and Nanoindentation measurements at displacement rates in the range of 0.02 to 0.1 nm/s have been carried out to track quantitative changes in free volume concentration after compressive deformations generated through brinell indentations below the glass transition temperature Tg and the changes associated with a subsequent annihilation after in situ heating-cooling cycles of Zr_(60)Ni_(10)Cu_(20)Al_(10) and Zr_(65)Ni_(10)Cu_(15)Al_(10) metallic glasses, in the temperature range between 350 K and 670 K. Important structural relaxation occured during in-situ heating and mainly above a critical temperature of T_r = 553 K for both Zr-based amorphous alloys. It was found that heavy deformation produced by an array of ball indentations generate more than 37% increase of free volume in Zr-based glassy ribbons. Plastic instabilities have been observed in the indention loading curves. From the nanoindentation tests, increases in hardness and elastic modulus were observed after annealing low temperatures induces structural relaxation.