Gong Li

Compressibility and hardness of Co-based bulk metallic glass: A combined experimental and density functional theory study

An incompressible Co54Ta11B35 bulk metallic glass (BMG) was investigated using in situ high-pressure synchrotron diffraction and nanoindendation. The elastic constants were deduced from the experiments based on the isotropic model. The Vickers hardness was measured to be 17.1u2009GPa. The elastic moduli and hardness are the highest values known in BMGs. The theoretically calculated elastic properties by density-functional study were well consistent with experimental measurements. The analysis of charge density and bonding character indicates the covalent character of Co-B and B-B bonds, underlying the unusually high elastic modulus and hardness in this material.

Nanoindentation Creep Behavior of an Al0.3CoCrFeNi High-Entropy Alloy

AbstractnNanoindentation creep behavior was studied on a coarse-grained Al0.3CoCrFeNi high-entropy alloy with a single face-centered cubic structure. The effects of the indentation size and loading rate on creep behavior were investigated. The experimental results show that the hardness, creep depth, creep strain rate, and stress exponent are all dependent on the holding load and loading rate. The creep behavior shows a remarkable indentation size effect at different maximum indentation loads. The dominant creep mechanism is dislocation creep at high indentation loads and self-diffusion at low indentation loads. An obvious loading rate sensitivity of creep behavior is found under different loading rates for the alloy. A high loading rate can lead to a high strain gradient, and numerous dislocations emerge and entangle together. Then during the holding time, a large creep deformation characteristic with a high stress exponent will happen.

Enhancement of the Thermal Stability and Mechanical Hardness of Zr-Al-Co Amorphous Alloys by Ag Addition

The thermal and mechanical properties of Zr57Al15Co28-XAgX (Xxa0=xa00 and 8) amorphous alloys were investigated using differential scanning calorimetry, in situ high-pressure angle dispersive X-ray diffraction measurements with synchrotron radiation, and nanoindentation. Results show that Ag doping improves effective activation energy, nanohardness, elastic modulus, and bulk modulus. Ag addition enhances topological and chemical short-range orderings, which can improve local packing efficiency and restrain long-range atom diffusion. This approach has implications for the design of the microstructure- and property-controllable functional materials for various applications.

Atomic clusters triggering nucleation and solidification of the metallic glass melt

The Zr41Ti14Cu12.5Ni10Be22.5 (atomic percent, at. %) melts embedded in a flux of the dehydrated B2O3 were under cooled by the repeated treatment of melting. The maximum melt undercooling of ΔTu2009=u2009145u2009K achieved for this melt corresponds to a comparatively large relative undercooling of 0.15 times the melting-point temperature of Tm∼ about 953u2009K(ΔT/Tmu2009=u20090.15). The solidification and nucleation behaviors of the Zr41Ti14Cu12.5Ni10Be22.5 undercooled melts triggered by Ni, Ti, Cu, and Zr clusters introduced by sputtering these pure metal targets are studied. An anomalous solidification triggered by Zr-atomic clusters above the Zr41Ti14Cu12.5Ni10Be22.5 melting temperature of 140u2009K is observed. The instability of a metallic-glass (MG) liquid near the thermodynamic critical temperature is present. The nucleation in the undercooled Zr41Ti14Cu12.5Ni10Be22.5 is investigated by Monte Carlo simulations and analyzed by the classical nucleation theory. This letter reveals an effective research method on investigating the...

Special Orientation Relationships of CuZr2 in the Annealed Zr64.5Cu35.5 Metallic Glass

The amorphous Zr64.5Cu35.5 alloy ribbon was prepared and annealed in a high vacuum furnace at 645xa0K (372xa0°C) for different times. It was found that the main crystallization phases in the alloy ribbon are CuZr2 and CuZr3. The grains of CuZr2 show special orientation relationships. The grains in opposite dendrites show the same orientation, and adjacent dendrites behave as a twinlike orientation with a (103) twin plane. The CuZr3 with a superstructure is discovered in annealed ZrCu metallic glasses.