Havrysh I. Formation of high-strength structural and phase states in fasteners made with titanium VT22 alloy treated at non-equilibrium conditions.

The thesis is dedicate to the solution of important scientific and technical problem - development of scientific approach and industrial technology of high-strength (having Ultimate Strength not less than 1350 MPa) titanium fasteners production for aerospace application. New data on the structural and phase transformations in the VT22 alloy were obtained for the first time for conditions of its thermomechanical processing and heat treatment under essentially non equilibrium conditions, including severe hot plastic deformation by rolling - forging and rapid heat treatment. It is shown that the main condition for obtaining high-strength state in titanium VT22 alloy ensuring high service performance of aerospace products is based on the necessity to ensure via technological methods applied uniform and high-disperse microstructure with optimal crystallographic texture in the direction of the major external loads. Due to developed technology strength level of VT22 alloy was improved up to UTS = 1350 - 1550 MPa, which is almost 30% more than the accepted in the aircraft industry for fasteners (UTS = 1050MPa according to TU -92-22-74 1). The levels of static and fatigue strength of experimental bolts made with VT22 alloy are essentially higher than in traditionally used for these purposes steel analogs, indicating that the existing reserve of ductility. Industrial technology of VT22 fasteners having UTS not less than 1350 MPa were developed employing available technological equipment.