Pengfei Yu

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

Abstract Nanoindentation 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.

Effect of Voronoi volume on fluctuation at initial deformation of amorphous alloys

Quasi-static compressive behaviors of three amorphous alloys (Cu 50Zr50, Pd80Si20, and Ni 67Zr33) are investigated via molecular dynamics simulations. Compared to the crystalline counterpart, when the strain is below 1%, significant fluctuations can be observed in the stress-strain curves. Further analysis of the simulated data indicates that the fluctuations are associated with the variations of Voronoi volume. A gradient reduction model is proposed to explain the process of the evolution of Voronoi volume at the initial stage of the deformation.

Effects of Aspect Ratio on the Shear Band Arrangements of Zr-Based Metallic Glasses

Effects of aspect ratios of Zr-based metallic glasses on the shear band arrangements are investigated through molecular dynamics simulations and experiments. It is found that as the aspect ratio decreases, the dense multiple shear bands form, effectively depressing the formation of the penetrating shear bands, which improves plasticity and strength of metallic glass. Simulation reproduces the images of the evolution of the shear bands in metallic glass, explaining the experimental observation. It is found that as the aspect ratio decreases, shear transformation zones disperse evenly in the entire model, restraining connecting into penetrating shear bands.

Preparation of high-strength Al-Mg-Si-Cu-Fe alloy via heat treatment and rolling

An Al-Mg-Si-Cu-Fe alloy was solid-solution treated at 560°C for 3 h and then cooled by water quenching or furnace cooling. The alloy samples which underwent cooling by these two methods were rolled at different temperatures. The microstructure and mechanical properties of the rolled alloys were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, and tensile testing. For the water-quenched alloys, the peak tensile strength and elongation occurred at a rolling temperature of 180°C. For the furnace-cooled alloys, the tensile strength decreased initially, until the rolling temperature of 420°C, and then increased; the elongation increased consistently with increasing rolling temperature. The effects of grain boundary hardening and dislocation hardening on the mechanical properties of these rolled alloys decreased with increases in rolling temperature. The mechanical properties of the 180°C rolling water-quenched alloy were also improved by the presence of β″ phase. Above 420°C, the effect of solid-solution hardening on the mechanical properties of the rolled alloys increased with increases in rolling temperature.

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 ΔT = 145 K achieved for this melt corresponds to a comparatively large relative undercooling of 0.15 times the melting-point temperature of Tm∼ about 953 K(ΔT/Tm = 0.15). 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 140 K 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...

Effects of Forming Pores on Mechanical Property of Zr70Cu30 Metallic Glass

Effects of forming pores in Zr70Cu30 metallic glass on the deformation behaviour is investigated through molecular dynamics simulations. The formation of pores leads to only a small reduction in strength, but dramatically enhanced plasticity in compression. The large plasticity of glass is attributed to the large effective free space induced by forming pores. It can also promote formation of crystalline phases in the amorphous matrix during deformation. Simulation reproduces the images of the evolution of pores in the metallic glass. The simulation results are in good agreement with experimental results.