High-energy Ball Milling Preparation And Structural Characterizations Of Metallic Nanoglasses

Nanoglass is a new kind of glassy materials that exhibits a microstructure consisting of nanometer-sized glassy regions connected by glass/glass interfaces with an enhanced free volume (relative to the free volume in the glassy regions). Because microstructure of nanoglass is different from the known crystalline and conventional galssy structure, nanoglasses may exhibit properties different from or better than the properties of crystalline and conventional glassy materials. So nanoglasses may be of importance in some applications. On the one hand, research and development of nanoglasses will deepen the understanding of the nanoglass structure, the development of preparation technology. On the other hand, research and development of nanoglass will be important scientific and technical significance in pioneering new materials research and development of new ideas and new areas to enhance the capability of independent innovation of new materials.There are two main preparation strategies of nanoglass:high-pressure compaction of glassy nanoparticles and inhomogeneous plastic deformation of metallic glasses. The former is the preparation of monodisperse glassy nanoparticles and the compaction of monodisperse glassy nanoparticles into nanoglass in ultrahigh vacuum by a high pressure. The latter is the introduction of high-density shear bands in metallic glasses by inhomogeneous deformation. Because metallic glasses have unique physical, chemical, and mechanical properties, metallic glasses show a good application potentials as advanced materials and become one of the hot spots of materials research of the recent decades Nanoglasses prepared by the inhomogeneous plastic deformation of metallic glasses have structures different from those of conventional metallic glasses and thus exhibit properties different from ever more excellent than the properties of metallic glasses.At low temperatures and high strain rates, plastic deformation of metallic galss occurs in an inhomogeneous mode; and plastic flow is localized in narrow regions called "shear bands". Most inhomogeneous plastic deformation of metallic glass with different loading methods (such as tensile, bending, quasi-static compression, rolling, indentation, punch, etc) introduces shear bands in materials with minimal spacings in the order of several micrometers. And high-density of shear bands with minimal spacing below100nm were introduced in some metallic glasses by inhomogeneous deformation in a few reports. There are rare reports on inhomogeneous plastic deformation by high energy ball milling. Various types of stresses (compression stress, shear stress, or a combination of compression and shear stresses) and stochastic loading directions on the metallic glass samples can be induced by balls during the ball milling process, and multiple deformation on the metallic glass samples can occur during the ball milling process. Small geometric size constraint of ribbon samples may be another reason which leads to high density of shear bands.Because shear bands in metallic glasses have a lower atomic density and enhanced free volume relative to undeformed region, as shear bands form and propagate during inhomogeneous plastic deformation, more free volume is created. Shear bands can serve as the glass/glass interfaces in nanoglasses. Free volume is an important factor affecting structure and properties of metallic glasses. Most reported analyses of the variation in free volume in metallic glasses are qualitative analyses. Enhanced free volume associated with a high density of shear bands introduced by ball milling has not been quantitatively studied so far.In this study, high-energy ball milling was employed to induce plastic deformation of Cu45Zr30Ti10N15、Cu60Zr30Ti10、Zr70Cu20Ni10metallic glass ribbons. The aim of this work is to prepare metallic nanoglass by introducing high-density shear band in metallic glasses. The enhanced free volume induced by ball milling was also qualitatively analyzed and quantitatively determined.(1) The inhomogeneous plastic deformation of Cu45Zr30Ti10Ni15、Cu60Zr30Ti10、Zr70Cu20Ni10metallic glass ribbons was induced by high-energy ball milling with different milling speed on a planetary ball milling. Both XRD and electron diffraction results show that the samples are maintained amorphous and do not crystallize during ball milling process.(2) Both the surface SEM and the TEM observations of the Cu45Zr30Ti10Ni15、Cu60Zr30Ti10、 Zr70Cu20Ni10metallic glass ribbonss ball-milled for different durations show that a high density of intersected and branched shear bands with spacings below100nm and a minimal spacing of about30nm was introduced by high-energy ball mill. These are much smaller than those observed in metallic glasses deformed by tensile, bending, quasi-static compression, rolling, indentation, punch, etc. And it is suggested that inhomogeneous deformation induced by high-energy ball milling may be a new and feasible approach to prepare nanoglasses.(3) XRD was applied to detect free volume change in Cu45Zr30Ti10Ni15、Cu60Zr30Ti10、 Zi70Cu20Ni10metallic glass through the variation of the maximum diffraction wave-vector. The results show that the maximum diffraction wave vector decreases with increasing ball-milling duration. So the average atomic spacing and the average atomic volume of samples increase with increasing ball-milling duration. This implies that free volume in the ball-milled ribbon samples increases with increasing ball-milling duration.(4) DSC measurements for the as-spun and ball-milled Cu45Zr30Ti10Ni15、Cu60Zr30Ti10、 Zi70Cu20Ni10metallic glass samples were conducted to determine their free volume changes. Qualitative results show that structural relaxation exothermic enthalpy increases with increasing ball-milling duration. This suggests that free volume increases with increasing ball milling duration. Quantitative determinations of absolute free volume contents shows that free volume in the Cu60Zr30Ti10and Zr70Cu20Ni10metallic glass ribbons ball-milled for different times with different rotational speed are at least20%higher than that in the as-spun metallic glass.