Effects of electric pulse heat treatment on microstructures and dynamic deformation behaviors of Ti6441 alloys

With respect to a newly developed titanium alloy Ti-6Al-4V-4Zr-Mo (Ti6441), electric pulse heat (EPH) treatment is innovatively employed to modulate lamellar microstructure details. It is interesting to find that, without mechanical processing such as forging, the EPH treatment can significantly decrease the prior beta grains size down to 390 μm from its original size of 520 μm. Further microstructure analyses show that alpha colonies, as well as alpha plates, are also refined correspondingly. The refinement behaviors are contributed by the unique effects of electric pulses, such as the acceleration of nucleation rate and the retard of grain growth. Especially, the EPH treatment has the orientation of alpha colonies tailored to be regularly 60°-intersected, different from the irregularly oriented lamellar structure treated by conventional heat-treatment furnace. Dynamic compression test results show that the fracture strain of the EPH-treated specimen is obviously increased from 23% to 29%, owing to the attenuation of local stress concentration, and the fracture strength retains a fairly high level. According to the forced shearing experiment results, the susceptibility to the adiabatic shear bands (ASBs) of the Ti6441 alloy after the EPH treatment is declined, because of the apparent ASBs' deflection and bifurcation.