Fu Xuesong

Effect of electropulsing on deformation behavior of Ti–6Al–4V alloy during cold drawing

Abstract Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to investigate effect of electropulsing on microstructure and texture evolution of Ti–6Al–4V during cold drawing. Research results demonstrate that the electropulsing treatment (EPT) can enhance the deformability of the grains with unfavorable orientations, which makes the compatibility of deformation among grains much better. A comparison in texture evolution between conventional cold drawing and EPT cold drawing indicates that the EPT promotes prismatic «a» slip moving, restricts pyramidal «c+a» slip occurring and accommodates the deformation with c-component by grain boundary sliding. The fraction decrease of low-angle grain boundaries for samples deformed with EPT reveals that the application of electropulsing restricts the formation of the incidental dislocation boundaries and the geometrically necessary boundaries.

Microstructure and mechanical properties of 2A12 aluminum alloy after age forming

The comparative experiments of age forming and artificial aging of 2A12 aluminum alloy were carried out. The effect of the age forming on the microstructure and mechanical properties was investigated. The results demonstrate that the grains are further squashed and elongated compared with artificial aging due to the existence of the applied stress during the age forming. Meanwhile, the precipitated phases change from circle shape with random orientation of age forming to long strip shape with uniform orientation of artificial aging. The dislocation configuration in samples changes from ring dislocation or helical dislocation of the artificial aging to long and straight dislocation of the age forming. Otherwise, age forming slightly reduces the tensile properties and fracture toughness of the alloy and enhances its fatigue crack growth rate.

Mechanical properties of strengthened surface layer in Ti–6Al–4V alloy induced by wet peening treatment

Abstract A modified surface layer was formed on Ti–6Al–4V alloy by wet peening treatment. The variations of the residual stress, nano-hardness and microstructure of the modified layer with depth from surface were studied using X-ray diffraction analysis, nano-indentation analysis, scanning electron microscopy and transmission electron microscopy observations. The results show that both the compressive residual stress and hardness decrease with increasing depth, and the termination depths are 160 and 80 μm, respectively. The microstructure observation indicates that within 80 μm, the compressive residual stress and the hardness are enhanced by the co-action of the grain refinement strengthening and dislocation strengthening. Within 80–160 μm, the compressive residual stress mainly derives from the dislocation strengthening. The strengthened layer in Ti–6Al–4V alloy after wet peening treatment was quantitatively analyzed by a revised equation with respect to a relation between hardness and yield strength.

High strain rate superplasticity in oxide ceramics

Oxide ceramic is a structural material with excellent mechanical properties and wide applications. Due to its inbeing brittleness, superplastic forming provides a feasible approach to process the structural oxide ceramics. However, low strain rate is a serious limitation on superplasticity applications of the oxide ceramics in the future. This paper reviewed experimental results and superplastic models in some recent reports, and focused on the major factors limiting the deformation strain rate, such as: Grain size, dynamic grain growth, grain boundary diffusivity, chemical bonding state, grain boundary state, cavity nucleation and growth. Some existing basic and new approaches to achieving high strain rate superplasticity in oxide ceramics were summarized. The superplastic behaviors and enhancement mechanisms were also discussed.