Microstructural evolution of BFe10-1-1 alloy tubes with continuous columnar grains during dieless drawing

The dieless drawing forming of BFel0-1-1 alloy tubes with continuous columnar grains was performed in a temperature range of 750-900℃ at a drawing speed of 0.6-0.9 mm·s^-1. The mierostructural evolution and mechanism of the tubes after the deformation was studied by optical microscopy, transmission electron microscopy, and X-ray diffraction analysis. It is found that the straight grain boundaries of colmnnar grains in the tubes become zigzag after dieless drawing within the process parameters of this paper. The sawtooth depth increases both with increasing drawing speed and temperature. Dislocations tend to pile up adjacent to grain boundaries and then travel over the grain boundaries, leading to gliding steps at the grain boundaries and consequently zigzag grain boundaries. Accompanied with the gliding deformation, thick continuous columnar grains start to rotate, increasing the zigzag degree. The high thermal activation energy and deformation-stored energy failed to release in time are the cause of maintaining continuous columnar grains in BFe10-1-1 alloy.