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The tensile behavior of a Ti–11%Zr–14%Nb–10%Sn alloy with pure orthorhombic α″ phase was studied by in situ X-ray diffraction using synchrotron radiation. It is found that no phase transformation happens during the whole tensile process. The “double-yielding” platforms of this alloy are indeed due to a low stress yielding (∼400 MPa) followed with a significant work-hardening before necking and fracture. In this process, the [0 2 2] orientation of grains more approaches the tensile direction and the [2 0 0] moves to the transverse, causing the lattice parameter a to be shrunk, and b and c elongated, and the formation of texture. The similar texture can also be produced upon cold rolling by which the yield strength of the α” phase is largely improved to be over 900 MPa.

The pressure-induced transitions discovered in metallic glasses (MGs) have attracted considerable research interest offering an exciting opportunity to study polyamorphism in densely packed systems. Despite the large body of work on these systems, the elastic properties of the MGs during polyamorphic transitions remain unclear. Here, using an in situ high-pressure ultrasonic sound velocity technique integrated with x-ray radiography and x-ray diffraction in a Paris-Edinburgh cell, we accurately determined both the compressional and shear wave velocities of a polyamorphous Ce68Al10Cu20Co2 MG up to 5.8 GPa. We observed elastic anomalies of a MG with minima (at ∼1.5 GPa) in the sound velocities, bulk modulus, and Poisson's ratio during its polyamorphic transition. This behavior was discussed in comparison to the elastic anomalies of silica glass and crystalline Ce.

When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various-sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials.

Applied physics letters 102, 051909 (2013). doi:10.1063/1.4790393, Published by American Institute of Physics, Melville, NY

Pressure-induced amorphous-to-amorphous configuration changes in Ca-Al metallic glasses (MGs) were studied by performing in-situ room-temperature high-pressure x-ray diffraction up to about 40 GPa. Changes in compressibility at about 18 GPa, 15.5 GPa and 7.5 GPa during compression are detected in Ca(80)Al(20), Ca(72.7)Al(27.3), and Ca(66.4)Al(33.6) MGs, respectively, whereas no clear change has been detected in the Ca(50)Al(50) MG. The transfer of s electrons into d orbitals under pressure, reported for the pressure-induced phase transformations in pure polycrystalline Ca, is suggested to explain the observation of an amorphous-to-amorphous configuration change in this Ca-Al MG system. Results presented here show that the pressure induced amorphous-to-amorphous configuration is not limited to f electron-containing MGs.

Inhomogeneities in two CuZr-based bulk metallic glasses (BMGs) were studied by using synchrotron radiation x-ray scattering techniques. (Cu(4.5/5.5)Ag(1/5.5))(46)Zr(46)Al(8) BMG was found to be more inhomogeneous than Cu(46)Zr(46)Al(8) BMG on the small length scale, where Cu and Ag atoms form enriched zones. Such heterogeneities are locally favorable for forming close-packed icosahedron-like clusters in three-dimensional space, greatly promoting the glass forming ability of this alloy. Upon annealing near the T(g) temperature, the heterogeneities were reduced initially at low temperature and short time annealing, then regenerated again for temperature increase and time extension. The average environment around Zr atoms almost does not change. However, the heterogeneity increases for Cu, Zr and Ag atoms once nanocrystallization happens.

Using in situ high-pressure x-ray diffraction (XRD), we observed a pressure-induced polyamorphic transition from the low-density amorphous (LDA) state to the high-density amorphous (HDA) state in Ce(75)Al(23)Si(2) metallic glass at about 2 GPa and 300 K. The thermal stabilities of both LDA and HDA metallic glasses were further investigated using in situ high-temperature and high-pressure XRD, which revealed different pressure dependences of the onset crystallization temperature (T(x)) between them with a turning point at about 2 GPa. Compared with Ce(75)Al(25) metallic glass, minor Si doping shifts the onset polyamorphic transition pressure from 1.5 to 2 GPa and obviously stabilizes both LDA and HDA metallic glasses with higher T(x) and changes their slopes dT(x)/dP. The results obtained in this work reveal another polyamorphous metallic glass system by minor alloying (e.g. Si), which could modify the transition pressure and also properties of LDA and HDA metallic glasses. The minor alloying effect reported here is valuable for the development of more polyamorphous metallic glasses, even multicomponent bulk metallic glasses with modified properties, which will trigger more investigations in this field and improve our understanding of polyamorphism and metallic glasses.

X-ray diffraction and electrostatic levitation measurements, together with the ab initio molecular dynamics simulation of liquid Al(75)Cu(25) alloy have been performed from 800 to 1600 K. Experimental and ab initio molecular dynamics simulation results match well with each other. No abnormal changes were experimentally detected in the specific heat capacity over total hemispheric emissivity and density curves in the studied temperature range for a bulk liquid Al(75)Cu(25) alloy measured by the electrostatic levitation technique. The structure factors gained by the ab initio molecular dynamics simulation precisely coincide with the experimental data. The atomic structure analyzed by the Honeycutt-Andersen index and Voronoi tessellation methods shows that icosahedral-like atomic clusters prevail in the liquid Al(75)Cu(25) alloy and the atomic clusters evolve continuously. All results obtained here suggest that no liquid-liquid transition appears in the bulk liquid Al(75)Cu(25) alloy in the studied temperature range.

Thermal behaviors of liquid La-based bulk metallic glasses have been measured by using the dilatometer with a self-sealed sample cell. It is demonstrated that the strong glass forming liquid not only has the small thermal expansion coefficient but also shows the slow variation rate. Moreover, the strong glass former has relatively dense atomic packing and also small density change in the liquid state. The results suggest that the high glass forming ability of La-based metallic glasses would be closely related to the slow atomic rearrangements in liquid melts.

A pressure-induced amorphous-to-amorphous reversible transformation was revealed in Pr75Al25 metallic glass (MG) using in situ high-pressure synchrotron x-ray diffraction technique. The transition began at about 21 GPa with a ∼ 5% volume collapse and ended at about 35 GPa. This transition is reversible with hysteresis. Based on the high-pressure behaviors of Ce-based metallic glasses and Pr metal here, we suggest that the pressure-induced polyamorphic transition in Pr75Al25 MG stems from 4f-electron delocalization of Pr metal which leads to abrupt change in bond shortening. These results obtained here provide new insights into the underlying mechanism of the amorphous-to-amorphous phase transition in metallic glasses and will trigger more theoretical and experimental investigations for such transition.

Long-range topological order (LRTO) was recently revealed in a Ce75Al25 metallic glass (MG) by a pressure-induced devitrification (PID) at 300 K. However, what compositions may have PID and an understanding of the physical and chemical controls behind PID are still not clear. We performed in situ high pressure x-ray diffraction measurements on CexAl1−x (x = 65, 70, and 80 at. %) MGs. Combining our experimental results and simulations, we found PID is very sensitive to compositions and can only exist over narrow compositional ranges. These results provide valuable guidance for searching for PID in MGs.

To be structural materials, the critical size is always a bottleneck of bulk metallic glasses (BMGs) due to the cooling rate restriction. Here, we report a developed alloy of Zr46Cu30.14Ag8.36Al8Be7.5, which can be cast into amorphous rods in 73 mm diameter by copper mould casting. The strong glass forming ability of this alloy is closely related to the Be addition, which not only suppresses the phase separation happening in the as-cast Be-free BMG but also sustains low Gibbs free energy difference for crystallization. This finding will stimulate more interests in developing BMGs and their industrial applications.

Atomic configurations of an Mg61Cu28Gd11 bulk metallic glass and its molten state have been investigated. The supercooled liquid and melt have a volume expansion coefficient only two times as large as that below glass transition temperature. Although the dominant polyhedra are 12- and 13-coordinated, the melt has slightly more polyhedra of low coordinated and less of high coordinated than in the as-cast. By Gd addition, half-octahedra with more volume accommodated are likely formed in the polyhedra, causing the local atomic environments of Mg in the melt quite different from the competing crystalline phase, thereby suppressing crystallization upon quenching.

The uniaxial tensile behavior of Zr62Al8Ni13Cu17, Cu46Zr46Al8, Zr48Cu43Al7Ag2, and La62Al14(Cu5/6Ag1/6)14Co5Ni5 bulk metallic glasses (BMGs) has been investigated by using in situ synchrotron radiation diffraction technique. It is found that the local strain is basically homogeneously distributed at low stress. However, heterogeneity appears obviously when the stress is close to the fracture strength. The amplitude of fluctuation in local strain for four BMGs could relate to the distribution of excess free volume within the medium range order.