Compressive superplastic behavior of 6Al-4V titanium caused by an applied DC current

Recent research has shown that the flow stress necessary to deform certain metallic materials can be decreased when an electrical current is present in the material while undergoing deformation. As part of this testing, it was found that, under higher current densities, the various metals began to exhibit strain weakening and superplastic behavior (i.e., the stress either remained constant or decreased as the strain increased). During typical compression testing, it is expected that the stress will continually increase as the strain increases. This is due to the increase in the cross-sectional area of the test specimen as well as the frictional effects that are present between the specimen and the fixture throughout the test. Since this strain weakening and subsequent superplastic behavior is opposite of what typically occurs during normal low temperature compression tests, it introduces a new electrical current-related phenomenon. This paper contains a detailed investigation of superplastic behavior using experimental results, focusing on 6Al-4V Titanium in particular. To examine this phenomenon, compression tests are run at different current densities. Some tests are conducted with the electricity present the entire time, while other tests are conducted with the electricity turned off at various points within the superplastic region. Still other tests have a pulsed electrical current present. It will be shown that the superplastic behavior allows significant increases in total deformation to be achieved using extremely low forces.