Abstract
This paper considers the influence of the technology to finish and strengthen compressor blade tips made of EP718-ID alloy on the characteristics of the surface quality, surface layer, and bearing capacity. Taking into consideration the special role of the finishing-strengthening treatment in the formation of the quality of the surface layer, various options for blade tip processing were investigated. The blade tips were shaped by high-speed line milling. The finishing-strengthening stage of tip machining included manual polishing and ultrasonic hardening operations with steel balls in various combinations. The basic regularities have been established in the formation of the roughness of tip surfaces, the maximum height of micro-irregularities, the surface microhardness, and the propagation depth of the hardened layer, depending on the combination of finishing-strengthening machining techniques. The results of tests are given for multi-cycle fatigue of blade batches treated according to various variants of the technological process. The efficiency of polishing the surface of the tip after strengthening treatment has been established. To restore the quality characteristics of the surface layer after polishing, it is proposed to perform repeated strengthening treatment. It is shown that the use of double deformation hardening technology with intermediate polishing at the finishing-strengthening stage of blade manufacturing makes it possible to increase the endurance limit from 320 MPa to 400 MPa while increasing durability. Technology for the finishing-strengthening stage of machining blades made from nickel alloys, characterized by significant viscosity, has been devised. It is shown that based on the criteria of minimum labor intensity of machining and maximum endurance of blades, it is effective to use double deformation hardening with steel balls in an ultrasonic field with intermediate polishing.
Highlights
The primary role of the condition of the surface and the surface layer of parts operating under variable loads is to provide their bearing capacity; that predetermines the use of finishing-strengthening operations at the final stage of the technological process of manufacturing
By controlling them at the finishing-strengthening stage of the technological process when manufacturing, for example, compressor blades for gas turbine engines (GTE), it is possible to achieve an increase in the endurance limit up to 50...70 %
Based on the analysis of the effect of manual polishing on the roughness of the surface of the blade tip, the quality of the surface layer, and the labor-intensity of the operation in various combinations, it was found that it reduces the average height of micro-irregularities from 5 μm after high-speed milling and 2.5 μm after ultrasonic hardening to 0.6...0.8 μm
Summary
The primary role of the condition of the surface and the surface layer of parts operating under variable loads is to provide their bearing capacity; that predetermines the use of finishing-strengthening operations at the final stage of the technological process of manufacturing. Despite the cumulative role of each of the factors that determining endurance, the technological support of their rational values for nickel alloys, as well as alloys that are similar in the set of their physical and mechanical properties, is associated with a number of difficulties One feature of such materials is high strength at relatively low hardness and a high tendency to deformation hardening. Formed as a result of 3D printing, for example, the aerodynamic surfaces of the tip of the blades made of the EP718-ID alloy have characteristic surface defects and require mandatory finishing-strengthening treatment In this regard, it should be noted that despite existing body of research, the task to control the quality characte ristics of the surface layer is relevant and is exacerbated in connection with the development of new materials and manufacturing technologies
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