Investigation Of Atomic Structure Of Metallic Glasses By Synchrotron Radiation Techniques

Microstructure of metallic glasses has been largely researched for such work may benefit understaning their forming mechanism and excellent properties. Till now, several explanations or atomic structural models have been presented. Generally speaking, there is an evolvement for understanding of microsructure of metallic glasses, from atoms random dense-packing to clusters oder-packing, short-range to medium-range order. But a mass of deep work is needed in such field, because microsructure of metallic glasses is far away from clear. In the present paper, Zr- and Cu- based metallic glass systems are selected for microstructure exploring, which are formed with simple composition. Especially, synchrotron radiation techniques are widely used in such work, including XANES, EXAFS and XRD diagnostic methods.Local atomic structures of Pd, Cu and Zr atoms in as-prepared Zr₇₀Cu₂₉Pd₁ glassy alloy and the annealed samples containing icosahedral quasicrystal have been investigated by Pd, Cu and Zr K-edge EXAFS measurements. It is found that Cu and Zr atoms have an icosahedral atomic surrounding. Cu atoms could locate at both center position and shell sites while Zr atoms most likely occupy the shell sites of icosahedron. Its short-range range is probably due to such distored icosahedron unit. Pd atoms neither substitute Zr atoms nor Cu atoms. They sit at octahedral interstices, which link up icosahedron and promote the growth of icosahedron into long-range order icosahedral quasicrystal in the ternary Zr₇₀Cu₂₉Pd₁ glassy alloy during annealing treatment. Free of octahedral interstices may result in missing of icosahedral quasicrystal in the binary Zr₇₀Cu₃₀ metallic glass during annealing treatment.Basic optimal polyhedral clusters were derived for intermetallic compounds at near-eutectic composition by considering several criterions, such as dense-packing, random arrangement of atoms at shell sites. Using such building units, bulk metallic glasses can be formed. This strategy was verified in the EXAFS research for Cu-Zr binary system, where we have demonstrated the existence of Cu₈Zr₅ icosahedral clusters centered with Cu atoms in Cu_64.5Zr_35.5 and Cu₆₄Zr₃₆ amorphous alloys. Furthermore, novel ternary bulk metallic glasses can be developed by doping the basic Cu-Zr alloy with a minority element. This hypothesis was confirmed in the system (Cu_0.618Zr_0.382)_100-xNb_X) where x = 1.5 and 2.5 at.%. The present results may open a route to preparing novel amorphous alloys with improved glass forming ability.The short-range structure of the Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass prepared by shock-wave treatment was investigated by x-ray diffraction using synchrotron radiation. Theradial distribution function was obtained from S(Q) with a large Q value up to 20 A^-1. The oscillation in S(Q) of the glass definitely persists up to Q:14 A^-1. The shoulder on the high Q side of the second peak is observed in the bulk glass. It is found that the glass has higher coordination numbers in the range of r:2.4-5.6 A and lower numbers in the range of r:5.6-9.5 A than those for the water-quenched glass while the shell distances are similar in both glasses. Under shock-wave treatment, i.e., rapid solidification under high pressure, atomic configurations in the first, fourth, or fifth coordination shells are modified, i.e., the atoms in glass are packed even denser in the first two coordination shells and less (or more free volume) in the third and fourth coordination shells as compared to those for conventional water-quenched glass. This atomic configuration for shock-waved glass might have different physical properties, which are in progress.The origin of pre-peak in the low Q range of S(Q) in Zr₇₀Cu₂₉Pd₁ metallic glass was investigated together with Zr₇₀Cu_30-xPd_x (x =0, 5, 10, 20, and 30 at.%) samples by high resolution XRD and RMC. It is found that in Zr₇₀Cu₂₉Pd₁ metallic glass the Pd atoms occupying octahedral-like interstices could form medium-range (about 4.5 A) order. Pd-M (M = Zr or Cu, whose atoms are on the second shell) interatomic correlations contribute to the pre-peak in S(Q) for the Zr₇₀Cu₂₉Pd₁ metallic glass at about 1.4 A^-1. When the medium-range order is destroyed, no pre-peak exist in the samples containing higher amounts of Pd in Zr₇₀Cu_30-xPd_x (x = 5, 10, 20 and 30 at.%). We believe that when pre-peak in S(Q) exists for metallic glasses containing heavy metal elements with low concentration (such as noble metal or rare earth elements), medium-range order, centered with such atoms, might occur in metallic glasses. This work extends our understanding of atomic structures for a body of metallic glasses.RMC simulation combined with synchrotron radiation XRD and EXAFS data was performed to research mirocstructure of Zr₇₀Ni₃₀ metallic glass. Voronoi tessellation was used to extract Voronoi clusters based on the result from RMC simulation. Distribution of atomic coordination number and Voronoi clusters shows that Z11 Kasper-like clusters (with 18 faces) and distorted icosahedral-like clusters are dominant in the present sample, which is much different with those in fcc Zr2Ni and icosahedral phase, resulting in existence of only one phase transition during annealing precess. Microstructure of Zr₇₀Cu₃₀ and Zr₇₀Pd₃₀ metallic glass and their corresponding crystal phases are analysed too.