Wenlong Xiao

Preparation, mechanical and degradation properties of Mg–Y-based microwire

Mg-Y-based microwire which offers high strength in combination of low degradation rate has been prepared for the first time by a modified melt extraction technique. A circular Mg-Y-based microwire is achieved with an extraction rate of 40m/s, which is composed of Mg matrix and an amorphous phase, and exhibits higher basal texture than that of as-cast sample. The outstanding tensile strength accompanying with an acceptable elongation is obtained with an extraction rate of 40m/s. The improved strength is mainly attributed to high solid solution strengthening, fine grain and the presence of an amorphous phase. In addition, the reduction of secondary phase and homogenous microstructure after melt extraction eliminate both pitting corrosion and micro-galvanic corrosion. A low degradation rate of 0.366mm/y is attained in a simulated body fluid, which is less than 1/10 of that of as-cast sample. These excellent mechanical properties and low degradation rate provide some prerequisites to develop bio-Mg implants. It reveals that this modified extraction technique is one of effective approaches to prepare microwire, which can be directly used for Mg-based stent self-assembly.

Serration Flow Behavior with Abnormal Strain Rate Sensitivity of Fine-Grained Mg-0.8 Wt Pct Ca Alloy

Serration flow is first observed in a fine-grained Mg-0.8 wtxa0pct Ca alloy throughout the deformation history. Strain rate sensitivity (SRS) is sensitive with the deformation temperatures. A positive SRS in combination with a type of downward serration is found at low temperatures, which is mostly attributed to the strong dislocation–dislocation interaction. However, at high temperatures, another upward serration is observed and the SRS is changed to negative as a result of the solute pinning dislocation.

Effect of Strain on Recrystallization of a Ni-Based Single Crystal Superalloy

The effect of strain induced by compression testing on recrystallization (RX) of a single crystal superalloy DD6 was investigated. The evolution of surface structure during annealing at the temperatures of 1000, 1100, 1220 °C was characterized by Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS). The element distribution and microstructure of the oxidation layer after annealing at 1100 °C showed that the main chemical elements were mainly Al, Ta, Cr, Ni, O. This indicated that the formation process of oxides included the inward diffusion of O and the outward diffusion of oxide-rich elements (Al, Cr, etc.). The thickness of RX layer was measured. At 1000 °C, no recrystallization but PFZ (precipitate free zone) was observed under oxidation layer. However, when annealing at higher temperature, the thickness of RX layer increased obviously with the increasing deformation strain. Cellular recrystallization could be detected in the samples annealed at 1100 °C, whereas isometric recrystallization and annealing twin formed in the specimen annealed at 1220 °C.

Enhanced Mechanical Properties of Al7075 Alloy with Graphene Nanoplates Prepared by Ball Milling and Hot Extrusion

In this study, Graphene Nanoplates/Al7075 (GNPs/Al7075) composites were prepared by powder metallurgy and hot extrusion. And the microstructure and mechanical behavior of GNPs/Al7075 composites prepared by ball-milling and hot extrusion were investigated. Compared with the unreinforced Al7075 matrix, these composites possess significantly improved stiffness and tensile strength.