The thesis pertains to establishing of the main regularities and ways of optimization of modes of welded joints fulfillment for Ti - 5 % TiB2 alloy both with each other, and with titanium alloys and other materials (12Х18Н10Т steel, niobium, vanadium), and is aimed at achieving of high mechanical characteristics of all elements of welded constructions, carried out by means of electron-beam welding. It was determined, that the electron-beam welding with utilization of the following operating modes: Uacc=60 kV, Ieb=90 mA, beam sweep - elliptical, transversal (3×4 mm), for all values of veb in the range from 7 to 13 mm·s-1 provides the obtaining of permanent welded joint of specimens of Ti-Ti-B alloy both with alloys of the same composition, and with (α+β) titanium alloy of T110 type.
It is established, that increasing of outlet temperature of subject to welding samples from 20°С до 400°С results in increasing the homogeneity extent of boron-containing phase distribution in transient zone of Ti-TiB alloy and increasing the dimensions of secondary fibers of this phase, both in length and in thickness, both in transient zone, and in welded seam zone. By experimental investigations of structure of welded seam of Ti-TiB alloy with T110 type alloy and fractographic structure of rupture surfaces and mechanical properties of the joint, it is established, that under condition of changing of predominant orientation of TiB reinforcing fiber in Ti-TiB alloy from longitudinal to transversal, the level of mechanical characteristics of "Ті–TiB"-"Т110 type alloy" joint is decreased. From the rupture point of view, the critical in such welded joint is Ti-TiB alloy, in which the brittle rupture is realized with its initiation from reinforcing fibers area. Fulfillment of thermal annealing of welded joint at the temperature 750°С (1 hour, vacuum) permits to reach the ductility of such alloy up to δ=2%. It is demonstrated, that the electron-beam welding of Ti-TiB alloy with vanadium by means of 12Х18Н10Т steel foil utilization permits to obtain the doped laying on base of Ti (63- 68 at.%) V (18-25 at.%) on Ti-TiB alloy surface with retaining of reinforcing microstructure containing TiB microfibers in Ti (63-68 ат.%) V (18-25 ат.%) metal matrix with main doping elements of 12Х18Н10Т steel. Characteristic features of reinforcing boron-containing microfibers in matrix of alloy based on Ti (63-68 ат.%) V (18-25 ат. %) are their doping with vanadium and considerable sizes dimension in comparison with TiB microfibers in Ti-TiB final alloy. It is demonstrated, that for welding by melting of Ti-TiB alloy with titanium allows it is expedient to preserve the micro-composition structure in welded seam and in heat affected zone. Such microstructure obtaining promote maximum rate of crystallization and increased velocity of electron beam movement during electron-beam welding. For the first time the permissibility in welded joint the TiB microfibers disordered or well-ordered predominantly in perpendicular to welded joint direction is confirmed. Investigations of microstructure of welded seam zone and thermal affected zone demonstrated that for Ti-TiB alloy the direction of predominant orientation of TiB reinforcing fibers, formed during eutectic transformation, is determined by direction of temperature gradient in crystallization area and it permits to recommend for future the welded elements cooling in direction from the welding joint and avoiding of its preliminary heating in order to eliminate the predominant orientation of reinforcing fibers along joint of parts subject to welding. For the first time it is proved the possibility of welding of Ti-TiB alloy, containing 5 % of TiB2 in titanium base, with 12Х18Н10Т steel by electron-beam mode, which was provided owing to retaining of reinforcing structure of metal in welded seam in titanium alloys and deciding the problems of inter-metallide laying formation, which frame the welded seam of Ti-TiB alloy with steels, and occurrence of destroying thermal stresses, which are originated owing to considerable difference in thermal expansion coefficients of materials subject to welding, by means of using of double intermediate layings from 10Г2 steel and niobium. Removal of mechanical stresses in material of welding joint of Ti-TiB alloy is proposed by means of annealing fulfillment (550°С, vacuum, 1 hour), which permit to increase and stabilize the mechanical characteristics of welded joints, obtained by electron-beam welding, for all used welding modes (σв=1,050 GPa, δ=4%). It is proposed the utilization of intermediate layers from niobium and 10Г2 steel for electron-beam welding of Ti-TiB alloy, which provides the obtaining of high-quality welded joint for Ti-TiB alloy, containing 5% TiB2 in titanium base, with 12Х18Н10Т steel with such strength limit in the heat affection zone and seam material, which is not worse than yield limits of 12Х18Н10Т steel.
