Regularities of Formation and Degradation of the Microstructure and Properties of New Ultrafine-Grained Low-Modulus Ti–Nb–Mo–Zr Alloys

Abstract

Abstract—Regularities of the formation of ultrafine-grained (UFG) and submicrocrystalline (SMC) structures in new nickel-free low-modulus Ti–Nb–Mo–Zr titanium β alloys under the action of plastic deformation have been studied. Temperature–time ranges of the development of dynamic recrystallization processes under the simultaneous action of temperature and plastic deformation are determined. A type-II recrystallization diagram of the Ti–28Nb–8Mo–12Zr alloy is constructed and analyzed. It is shown using scanning electron microscopy and the electron backscatter diffraction method that the UFG structure with an average grain size of no more than 7 μm and high fraction of high-angle grain boundaries is formed in the investigated alloys as a result of longitudinal rolling, followed by annealing for quenching. It is found that the formation of the UFG structure leads to a significant increase in the strength and plastic characteristics of these alloys. The regularities of the formation of UFG and SMC structures in titanium β alloys Ti–28Nb–8Mo–12Zr and industrial VT30 under the action of plastic deformation by the helical rolling method are studied. It is shown that the helical rolling of the VT30 alloy leads to the formation of the homogeneous UFG state as opposed to the Ti–28Nb–8Mo–12Zr alloy, where this method causes structure softening with micropores and microcracks formed in the central region. It is possible to form a nanostructured state with an average grain size of about 100 nm in Ti–Nb–Mo–Zr titanium β alloys using the high-pressure torsion method.