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The production of a solid-phase diffusion bond in OT4-1 alloy on the basis of a cold forced fit of components in a shaft–hole configuration is considered. The influence of the maximum stress–strain state in the cold forced fit and subsequent heat treatment (in autonomous vacuum) on the structural evolution and properties of the contact region is investigated. In cold plastic deformation of the alloy with the formation of a solid-phase diffusion bond, deformational relief (traces of grain-boundary slip) is observed in the microstructure of the contact region. In addition, decrease is noted in the area of the contact surfaces, and fewer bulk interactions are noted in the contact plane (grain distortion) and in the contact volume (regions of dislocation departure). The basic characteristics of the structural interface—the unit parameter of structural organization, the grain density, the mean grain-boundary density, and the development of the grain boundaries—exceed by factors of 10, 4, 1.8, and 1.5, respectively, those of the basic metal in the initial state. Heating in autonomous vacuum in the range of α → β phase transitions leads to stepwise structural changes in the basic metal and in the contact region of the solid-phase diffusion bond. Initially, a globular component appears in the microstructure. With further heating, this component reverts to the initial acicular structure (with some increase in microhardness). The formation of globular structure on heating plastically deformed metal is observed not only at temperatures corresponding to phase transition but also at higher temperatures; this has not previously been noted. With increase in temperature, the duration of this stage decreases. In addition, with less developed plastic deformation, the formation of globular structure is observed close to the polymorphic-transformation temperature Tpt, with shorter holding. For the basic metal (with little deformation), the globular structure disappears practically completely after heating for 10 min at 950°C. In the cold-deformed contact region of the solid-phase diffusion bond, the globular structure disappears on heating for 1 h at 950°C, for 40 min at 975°C, and for 20 min at 1000°C. At those temperatures the sealing of discontinuities is practically complete. In other words, the weld line disappears: the metal with continuous microstructure in the contact region does not differ from the basic metal, except for a slight enlargement of the microstructure. Quantitative assessment of the structural changes in terms of the basic characteristics of the structural interface permits determination of their mechanism and kinetics and also the dependence of the structure on the plastic strain and the heat treatment. On that basis, it is possible to identify conditions such that the discontinuities are eliminated, the boundaries disappear, and the properties of the solid-phase diffusion bond are no worse than those of the basic metal.

Titanium alloys are widely used in the aerospace industry on account of their high strength, fatigue strength, impact strength, and corrosion resistance. Airplane components such as ribbed panels must satisfy strict requirements on the quality of weld joints and the dimensional precision. The welding of titanium alloys leads to the formation of flaws at the joint and impairs the performance of the part; their geometric dimensions are distorted on account of the welding stress; pores and microstress appear in the seam; and the mechanical and other characteristics are impaired. That calls for comprehensive analysis of the manufacture of ribbed titanium panels, all the way to the heat treatment of the final product, so as to discover the processes that are most likely to generate defects. The manufacture of the workpieces—including their preparation for welding, the welding conditions, and subsequent heat treatment—affects the static and cyclic strength of welded ribbed panels, with variation in the number of weld-seam defects and their total area. The results obtained in the present work permit prediction of the properties and reliability of welded structures and the maintenance of identical properties of the basic metal and the seam metal, with the guaranteed absence of external and internal effects, on the basis of the selected production processes. It is found that the properties and reliability of weld joints will match those of the basic VT20 titanium alloy in ribbed panels in the following conditions: welding with specific cooling rate in the phase-transition temperature range; final milling, turning, degreasing, and drying of the surface of the joined edges; light annealing after welding in air; subsequent sandblasting; and gas-laser layout cutting in a nitrogen or argon atmosphere, with or without milling.

The residual stress due to welding in steel and alloy structures is analyzed. The greatest residual stress is produced by cooling of the welded structure. The results of calculations are in satisfactory agreement with the experimental deformation of the structure in welding on a test bench. The tests reveal the direction of the internal stress and permit assessment of the geometry of parts on the basis of a model of the temperature fields in the butt welding of steel and titanium-alloy workpieces. A coercimeter may be used to assess the stress state of the material and its defect content. By that means, it is possible to predict the structural state and properties of weld joints. The dynamics of welding deformation may be understood on the basis of the internal residual stress and the structural transformations produced by the welding process.