Zhen Lu

Plastic Deformation Behavior of Ti Foil Under Ultrasonic Vibration in Tension

The benefits of ultrasonic vibration auxiliary metal forming have been shown by many studies. In this study, a series of experiments were carried out to investigate the deformation behavior of Ti foils under ultrasonic vibration in tension, and the tensile properties of Ti foils with/without the application of ultrasonic vibration were investigated. Then, the microstructure of different tensile samples was analyzed by transmission electron microscopy (TEM). The results of the tensile experiments showed that the tensile strength of tensile samples was reduced when ultrasonic vibration was applied, while the elongation of these samples increased. The flow stress increased with increasing strain without applying ultrasonic vibration, while it decreased steeply when the ultrasonic vibration was applied, and this reduction of flow stress demonstrated the effect of acoustic softening on the properties of the material. Additionally, the range of flow stress reduction was inversely proportional to the time for which ultrasonic vibration was applied. The TEM images showed that there were remarkable differences in dislocation distribution and tangles with/without ultrasonic vibration. The dislocation distribution was inhomogeneous, and copious dislocation tangles were discovered without ultrasonic vibration. When it was applied, the parallel re-arrangement of dislocations could be observed and the mass of dislocation tangles was mostly absent.

Superplastic Forming/Diffusion Bonding Without Interlayer of 5A90 Al-Li Alloy Hollow Double-Layer Structure

The hollow double-layer structure of 5A90 Al-Li alloy was fabricated by SPF/DB process in this study. The characteristics and mechanism of 5A90 Al-Li alloy with respect to superplasticity and diffusion bonding were investigated. Tensile tests showed that the optimal elongation of tensile specimens was 243.97% at the temperature of 400xa0°C and the strain rate of 0.001xa0s−1. Effect of the surface roughness, bonding temperature and bonding time to determine the microstructure and mechanical properties of diffusion bonding joints was investigated, and the optimum bonding parameters were 540xa0°C/2.5xa0h/Ra18. Through the finite element simulation, it could be found that the SPF/DB process of hollow double-layer structure was feasible. The hollow double-layer structure of 5A90 Al-Li alloy was manufactured, showing that the thickness distribution of the bonding area was uniform and the thinnest part was the round corner. The SEM images of diffusion bonding joints showed that sound bonding interfaces were obtained in which no discontinuity existed.

Dynamic Recrystallization Behavior and Texture Evolution of NiAl Intermetallic During Hot Deformation

B2-ordered intermetallic NiAl was fabricated by hot pressing sintering and studied in terms of dynamic recrystallization behavior and texture evolution during isothermal compression over a temperature range of 1100-1300xa0°C and strain rate of 10−2xa0s−1 as well as strain rate of 10−3 to 10−1 s−1 and temperature of 1250xa0°C. It is found that DDRX mechanism operates predominantly at a high temperature and medium strain rate, while CDRX process is enhanced in the deformation condition of medium temperature and high strain rate yet in a localized way. In particular, progressive subgrain rotation takes place at 1250xa0°C/10−1xa0s−1. Conversely, dynamic recrystallization process is insufficient in the case of 1250xa0°C/10−3xa0s−1 and 1100xa0°C/10−2xa0s−1. Original hot pressing sintered billets are microstructurally homogeneous. Orientation distribution function sections reveal that the strong {110}〈111〉 and {112}〈111〉 texture components appear after deformation. Furthermore, the textures are strengthened with increasing temperature and strain rate.

Numerical simulation on shape distortion of superplastic forming Ti-6Al-4V cylinder

The dimensional accuracy and shape distortion caused by the contraction of ZG35Cr24Ni7N refractory steel die when cooling after superplastic forming were analyzed using MSC. MARC. And the influence of different processing parameters on the shape distortion was also studied. The result show that during the cooling process from 930 to room temperature, when the temperature decreases to 915°, the shape distortion begin to generate, and increasing with the reducing of the temperature up to 800°. The shape distortion increased with the rising of friction coefficient, this is because the Ti-6Al-4V cylinder cant release the volume through sliding but the plastic deformation when the friction exists. So the plastic deformation increased with the rising of friction and leading to the increase of shape distortion.

Superplastic Bulging of Nanocrystalline Ni-Co Alloy with Different Heating Methods

Superplasticity of nanocrystalline materials is a hot spot in the field of scientific research. In this paper, Ni-Co alloy was produced through pulse electrodeposition. Tensile tests were carried out to study the room temperature strength, high temperature plasticity. The superplastic formability under complex stress was evaluated through the superplastic bulging tests. The tests were studied through the methods of resistance heating and furnace temperature heating. The maximum ratios of height and diameter with different heating method were compared. Fracture behavior and microstructure were observed by the method of SEM.

Superplasticity of Nb-Si-Fe and TiAl Intermetallics Synthesized by Powder Metallurgy

Nb-16Si-2Fe alloy were processed by mechanical alloying (MA) and hot pressing sintering (HPS). Microstructure analysis revealed the presence of four phases: Nb solid solution (Nbss), three kinds of intermetallics Nb3Si, Nb5Si3 and Nb4Fe3Si5. The maximum elongation over 500% was obtained at 1450°C and strain rate of 2.31×10-4s-1. TiAl powder pre-alloyed was carried out on pulse current sintering equipment (PCS) with high heating rate. The effect of heating rate on microstructures and high temperature ductility was investigated. The results show that relatively high heating rate is beneficial for obtaining fine grained microstructures. And the resultant intermetallic alloy with equiaxed near gamma structures exhibits superplasticity at relatively low temperature.