ФОРМУВАННЯ СТРУКТУРИ ТА МЕХАНІЧНИХ ВЛАСТИВОСТЕЙ З'ЄДНАНЬ З ІНТЕРМЕТАЛІДНОГО СПЛАВУ TiAlNb ПРИ ДИФУЗІЙНОМУ ЗВАРЮВАННІ

The impact of technological measures in vacuum diffusion welding on formation of the structure and mechanical properties of joints of TiAlNb intermetallic alloy was studied in the work. It is shown that welding of intermetallic alloy by the method of vacuum diffusion welding at temperature T_w = 1050 °C, pressure Pw = 10 MPa, for 20 min does not ensure producing sound joints. After welding, the joint line is visible in the butt, along which there is a considerable number of defects in the form of pore lines. Increase of welding parameters up to the temperature T_w = 1200 C, pressure P_w = 30 MPa, welding time of 30 min, as well as application of a ductile interlayer from NbTi alloy 1 mm thick allows improving the conditions of welded joint formation and greatly reducing the number of defects in the butt joint. During welding, common grains and diffusion zone 25 - 35 ~m thick form between the interlayer material and intermetallic alloy. Application of nanolayered interlayer of Al-Ti system of the total thickness of 25 ~m in welding of TiAlNb intermetallic alloy, combined with cyclic loading in the form of 3 cycles of loading-unloading leads to a change of the nature of the structure in the joint zone. In the microstructures of welded joints obtained by optical metallography, the joint line is not visible. Application of electron microscopy allows detecting in the butt joint a diffusion zone 15 to 20 ~m thick, close by its chemical composition to that of the intermetallic alloy. Investigation of the compressive strength of welded joints demonstrated that the average strength of joints of TiAlNb intermetallic alloy, produced using an interlayer from NbTi alloy, is equal to 988.2 MPa, and application of a nanolayered insert of Al-Ti system in welding allows increasing the average strength of the samples up to 1279.8 MPa. [ABSTRACT FROM AUTHOR]