Microstructural processing of steel at ambient surface temperature

Abstract

We provide evidence that microstructural processing of metallic materials can be achieved at lower temperatures by passing dc current and simultaneously cooling the specimens. As the Joule heat is removed, the electron wind force due to transfer of momentum to defects become the predominant stimulant for grain boundary and defect migration. We demonstrate this technique on nominally 50 μm thick additive manufactured 316 stainless steel specimens, electrically biased at around 200 A/mm2 current density while actively cooled to maintain ambient surface temperature. The microstructural analysis involved electron backscattered diffraction, grain boundary misorientation plots, and grain size analysis. Experimental results indicate that both grain growth and grain refinement are possible, depending upon the controlled temperature and processing time. The results also showed significant changes in misorientation angle distributions for both grain growth and grain refinement with almost all low angle grain boundaries being converted to high angle grain boundaries. These results are encouraging for further development of the electron wind force as a driver for low temperature post processing of metals and alloys.