Piskun N. Complex of technological processes of induction band melting and welding in solid phase and melting of heat-resistant intermetallic of TiAl system.

The dissertation is devoted The dissertation is devoted to the solution of the scientific and applied problem: in order to optimize the structure and properties of structural intermetallic alloy Ti-44Al-5Nb-3Cr-1.5Zr (at%) of the titanium-aluminum system of conducting zone recrystallization by the method of induction crucible zone melting for its further use technological process of electron beam welding with adjustable cooling rate, which makes it possible to obtain defective welded joint. The problem is solved by establishing the influence of the processes of structure formation in the alloy during induction crucible zone melting on its mechanical properties, as well as the dependence between the conditions of cooling during electron beam welding and structural processes and their relationship with the stress state of the welded connection. The urgency of the work is due to the need to develop new scientific approaches in the creation of modern structural intermetallic alloys, which are promising materials for aerospace engineering, automotive industry and others. fields of technology In the work a detailed analysis of literary sources is considered, in which the questions of structure and properties of structural intermetallics of TiAl system and methods of their production are considered. The requirements for the properties of intermetallics for industrial use are given. The advantages of band melting of intermetallics for optimization of structure and properties are considered. The influence of alloying elements on the structure and properties of the intermetallics of the TiAl system is investigated. The works devoted to the intermetallic welding are analyzed. Methods of thermomechanical treatment of TiAl alloy (Nb, Cr, Zr) alloy after the UPS were obtained sheet semi-finished products for welding. The heat treatment regimes were determined and the structure and properties of the deformed material were investigated. The possibility of welding the intermetallic alloy Ti-44Al-5Nb-3Cr-1.5Zr in the solid phase was studied. Experiments on diffusion welding in vacuum were carried out using various technological methods, both without intermediate layers and with layers in the form of a foil. According to the results of researches the technology of electron beam welding of intermetallide with adjustable cooling is created, which allows to reduce considerably the tendency of welded joint to formation of cold cracks with the use of various technological methods. For the first time, it is found that the cooling rate of the welded compound of intermetallide at the level of 0.7- 0.90C/s and below significantly reduces its tendency to form cold cracks. For the first time, it has been found that the welding with controlled cooling transforms the α-phase into a lamellar (γ + α2) -phase, while the alloy retains some amount of β-phase, which improves the plasticity of the alloy and blocks the origin and propagation of cracks in the α2-phase.