INFLUENCE OF THE CONDITIONS OF SOLID-PHASE PRESSURE WELDING AND HEAT TREATMENT ON THE STRUCTURE AND PROPERTIES OF JOINTS OF THE INTERMETALLIC ALLOY VKNA-25 Mono WITH SUPERALLOY EP975. I. INFLUENCE OF THE VACUUM DEPTH AT SOLID-STATE JOINTS

The article is devoted to the development of a method for producing solid-state joints (SSJ) of blades with a disk in «blades and disks» type parts operating under conditions of high tensile, bending and thermal stresses (static, re-static, fatigue, etc.). The quality of SSJ depends on such factors as the atmosphere (degree of vacuum) during pressure welding (PW), preparation of the welded planes, temperature, magnitude and duration of pressure application during PW. The first part of the article is devoted to the study of the effect of the degree of vacuum in the PW process on the quality of welded joints, which was evaluated by the tensile strength of welded samples at room temperature. The study of the influence of SSJ conditions under conditions of superplasticity of only a disk alloy on the structure and properties of welded joints showed that samples with a specially prepared surface obtained under low vacuum conditions during SSJ demonstrate tensile strength, which, apparently, can be considered sufficient to ensure long-term operation of such a part as «blisk» in gas turbine engines. Carrying out PW under conditions of high vacuum made it possible to obtain a welded joint with tensile strength exceeding that of the least strong at room temperature welded high-heat-resistant alloy VKNA-25 with a single-crystal structure. Carrying out heat treatment (1200 °C / 6 h + 950 °C / 6 h) after PW, necessary for the formation of a coarse-grained structure in a disk alloy, ensuring its high heat resistance characteristics, does not affect the mechanical properties of welded joints.