THE EFFECT OF MEGAPLASTIC DEFORMATION IN THE BRIDGMAN CHAMBER ON THE PHASE TRANSFORMATIONS, CORROSION BEHAVIOR, AND MICROHARDNESS OF PURE VT1-00 AND VT1-0 TITANIUM

Due to the combination of lightness, high specific strength and corrosion resistance, titanium and its alloys are highly interesting for applying in many areas of industry (mechanical engineering, shipbuilding, and aircraft manufacturing). Technically pure titanium is the first choice to be used in medicine because of its high biocompatibility and lack of toxic elements. Pure titanium has high ductility and corrosion resistance but it is inferior to titanium alloys in other mechanical characteristics, such as tensile strength, yield strength, and hardness. Megaplastic deformation (MPD) is a promising method for increasing the strength of titanium to the level of highly alloyed alloys. The paper deals with the study of the influence of MPD in the Bridgman chamber on the structure (phase transformations occurring in technically pure VT1-00 and VT1-0 titanium), corrosion resistance, and microhardness. Using the high-pressure torsion (HPT), the authors obtained samples with different degrees of deformation: from 0.25 to 4 revolutions of the movable anvil. The authors carried out the X-ray diffraction analysis and electrochemical tests of samples and studied the phase composition of titanium samples of two grades containing 0.1 and 0.3 % of impurities before and after MPD. The study identified that the HPT led to the formation of a two-phase mixture a+ɷ. The results showed the positive effect of MPD on the mechanical properties of titanium. The microhardness of the deformed material increases in comparison with the initial state, while there is no deterioration in the corrosion resistance in the studied environment. Under all deformation modes, titanium stays in a passive state. For the VT1-0 alloy, the stationary corrosion potentials of samples after HPT have a more positive value compared to the original undeformed material.

ultra-pure titanium, technically pure titanium, megaplastic deformation, Bridgman chamber, phase transformations, corrosion resistance, microhardness, high-pressure torsion, VT1-00, VT1-0