Wenbin Dai

Microstructure evolution in metals induced by high density electric current pulses

Abstract In this paper, microstructure evolution in metals induced by high density electric current pulses (ECPs) treatment, such as grain refinement, formation of oriented microstructure and redistribution of inclusions, is carefully reviewed. The mechanism for these microstructure evolutions is discussed. It is suggested that there are usually several factors working during ECP: Joule heating (including temperature rise, the heating rate and the cooling rate), stress (including thermal compressive stress, skin effect, electron wind force) and free energy change caused by the current. The Joule heat and the stress usually affect the dynamics, enhance the microstructure evolutions rate, while the free energy change affects the thermodynamics and lowers the barrier of the phase transformation or recrystallisation. The experimental results indicate that high current density ECP provides an effective approach to refine the microstructure of polycrystalline materials and to improve the mechanical properties of the materials.

Refinement of inclusions in molten steel by electric current pulse

Abstract The refinement of inclusions in molten steel induced by a continuous electric current pulse was investigated at 1823 K. The results revealed that due to the application of electric current, the melted sulphide inclusions in molten steel were refined. Analysed from the thermodynamic theory, the refinement mechanism was ascribed to the decrease in the system free energy that resulted from the formation of the refined sulphide inclusions in molten steel at 1823 K. Hence, the electric current pulse treatment may be a new method to refine inclusions in molten metallic materials in the future.

Improvement of pitting corrosion resistance of stainless steel by electric current pulse

ABSTRACT The electric current pulse (ECP) was applied on the liquidus of 304 stainless steel during solidification and the pitting corrosion of the water-quenched specimens was explored in the present work. The results revealed that the utilisation of ECP can inhibit manganese sulphide from segregating around oxide inclusions during solidification and consequently, the pitting corrosion resistance of ECPed steel was significantly improved. Hence, the application of ECP during solidification might be an efficient way to improve the pitting corrosion resistance of the 304 stainless steel. This paper is part of a themed issue on Materials in External Fields.

A Method to Distinguish Twinning Variants and Second Twins by EBSD Measurements

This paper proposes a direct and simple method to identify the second twins from twinning variants by electron back scattered diffraction (EBSD). To clarify the orientation relationship between the neighboring crystals, the misorientation calculation by MATLAB software based on the EBSD data is also used. This method is generally applicable to predict the variants occurring in the nucleation and growth of the recrystallization or phase transformation process.

Effect of electric current pulse on preparation of nano Y2O3

ABSTRACT The effect of electric current pulse (ECP) on preparing nano Y2O3 powder was initially investigated in this paper. From the determination of thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction, it was revealed that the composition of non-calcined precursor had changed due to the application of ECP. In addition, the scanning electron microscope results indicated that Y2O3 powders fabricated by ECP treatment had less aggregate and were in nano size. Therefore, the ECP treatment is a promising way to prepare nano Y2O3 powder. This paper is part of a themed issue on Materials in External Fields.

Twins Evolution During the Recrystallization Induced by Electric Current Pulses in a Cu‐Zn Alloy

A high current density (up to 104 A•mm−2) electric current pulse (ECP) is used to cause recrystallization of a cold-rolled single phase Cu-Zn alloy directly. Since the whole treating time is the discharge time of ECP, and the duration time is very short, it is very easy to remain the non-equilibrium phase at high temperature to the room temperature to investigate the microstructural evolution during the recrystallization process. By the determination of TEM, it is found that due to the application of ECP, the original deformed twins are greatly decreased while a lot of incomplete annealing twins are emerged. Interestingly, the various morphologies of annealing twins are revealed, and the different growth directions are also observed. This phenomenon would contribute to study the variant selection of the twin in the early stage of recrystallization process.

Effect of calcia additive on the grain growth of yttria

The effect of calcia on the grain growth of yttria was investigated in present work. The results shown that by adding calcia, yttria was sintered as low as 1300°C and abnormal grain growth model was observed over 1500°C. When higher than 1600°C, lots of closed pores were formed in the coarse yttria grains and the relative density was decreased with the increasing temperature and prolonging soaking time. Through theoretical analysis, it was known that oxygen vacancies were formed during the solid solution of Ca2+ into Y3+ and they were ascribed to the increasing of grain boundary diffusion of yttria. The developed yttria might be an applicable material for vacuum induction melting process to produce high purity titanium and its alloys.