Gakh I. Physical-technological peculiarities of electron beam welding of high nickel heat-resistant alloys with single-crystal structure.

The thesis work is devoted to a problem of obtaining of the permanent joints from heat-resistant nickel alloys with single-crystal structure in regard to repair of the blades of gas turbine engines and coarsening of the single-crystals. Current state of a problem of weldability of the heat-resistant nickel alloys was considered and relevance of performance of the study was grounded. Criteria of quality of the welded joints were determined and methods of weldability control for this grade of materials were developed. It was proposed to consider the weldability of single-crystals from point of view of a level of perfection degradation in single-crystal structure. Influence of a position of molten pool in relation to crystallography of fusion surface on a formation of random orientation grains was determined. Conditions of orientation of the welding pool crystallization were established, under which formation of single-crystal structure in the welded joint is achieved. It was determined that the single-crystal welded joint can be obtained at a conjunction of direction of the maximum temperature gradient with direction of the main growth <001> along the front of welding pool crystallization with boundary deviation of not more than 15 deg. Thesis grounds and proposes the modes of welding and technological methods of their fulfillment that allow controlling crystallization of the welding pool during weld formation in welding as well as surfacing. The main problems of welding of heat-resistant nickel single-crystals were solved, including possibility of formation of the random orientation grains in the structure of weld metal and cracks. Principle technology of the electron-beam welding was developed for repair of blades from JS32 alloy for the gas-turbine engine D18T.