Ningyuan Zhu

Lubrication is one of the key factors to improve metal-forming quality. In the process of deep drawing, seizing tumors easily occur on the contact surfaces between the tantalum metal and the mold, which greatly affects the forming quality of the deep-drawn parts. Quality-forming quality problems that occur during the deep drawing of tantalum metal are studied from the perspective of lubrication in this paper. Three lubrication media, caster oil, PE (polyethylene) film, and DLC (Diamond Like Carbon) film, were adopted in the deep drawing of tantalum cylindrical cups. A universal testing machine and microscope were used to investigate the effect of lubrication media on the limit-drawing ratio, maximum forming force, and surface topography quality during the deep drawing process of the tantalum sheet. The results reveal that the lubrication of the PE film and DLC film can greatly improve the forming quality of the tantalum metal sheet, in which the DLC film has higher wear resistance and lower friction coefficient and can be used as the lubricating medium in the industrial forming process of tantalum deep-drawn parts.

A two‐dimensional cellular automaton (CA) model of microstructure evolution is developed to visually and quantitatively simulate and predict the dynamic recrystallization (DRX) behavior of a typical Ni‐based superalloy during hot power spinning. The high‐temperature plane strain compression test and hot power spinning experiment are carried out to verify the developed CA model, and results show that the flow stress can be well predicted and the simulated average grain sizes are in good accordance with the experimental ones. The evolution of DRX and dislocation density as well as influence of processing parameters on DRX during hot power spinning are simulated and discussed. It is found that the DRX nucleation starts at grain boundaries when a large thinning ratio of wall thickness is reached. With the increasing of thinning ratio, the growth of crystal nuclei and secondary nucleation occurs. Furthermore, the average grain size and DRX fraction are greatly influenced by the forming temperature and thinning ratio, while the average grain sizes decrease slightly with the increasing of roller feed rate.