Structural metallographic studies on the welded joints zones of the samples obtained by inertial friction welding

Machine-building Engineering and Machine Science


DOI: 10.34759/vst-2022-2-211-219

Аuthors

Fozilov T. T.1*, Shumskaya S. A.1**, Kudryavtsev E. A.2, Babaitsev A. V.1***

1. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
2. United engine corporation (UEC), 16, Budyonny avenue, Moscow, 105118, Russia

*e-mail: fozbourne@yandex.ru
**e-mail: bratinaaa@gmail.com
***e-mail: ar77eny@gmail.com

Abstract

The article presents the results of the study of inertial friction welding of the EP741NP nickel heat-resistant alloy. Since not all metal materials can be welded by melting methods, there are alternatives, for example, mechanical welding, namely friction welding. A literature review oriented to studying the preceding similar experience on optimal welding modes selection, which was the prime task was accomplished. Due to the friction welding optimal parameters selection more strong and qualitative joints are being produced at the lower temperatures and less heat-affected zones (HAZ) than while fusion-welding methods employing. The major part of works was being conducted on the foundry alloys, since their grain structure is more pliable for these kind of impacts, while our work studied the alloy, being obtained by the metallurgy of granules method. The task is being aggravated by the fact that the alloy itself is liable to the great risk of crack formation while moulding methods employing in view of utterly complex chemical composition. Based on the above said we come to the conclusion that the purpose of the presented work consists in achieving stable, high level of strength, no less than that adduced in the said review. It was established in the course of the study that this welding process allows obtaining the joints, which are not being obtained by the melting welding methods. Welding was being performed on the PSTI-120SW installation. Afterwards, rods were cut out for the samples production and templates for the obtained joint structure studying. Further, experimental study of the samples’ mechanical properties was conducted. The experiments were being performed with the Instron universal breaking machine. The samples were being subjected to the tests on the short-time strength at the room temperature, and the long-time strength (for 100 hours) under the load of 900 Mpa at 650C. As the result of the test, the samples demonstrated rather high qualities as it was predicted. This fact allows our alloys and equipment competing with their foreign counterparts. In the course of this research, the authors studied the microstructure of the weld seams and weld-affected zones. Transverse metallographic samples containing welded joint were prepared for the research. The microstructure analysis was being performed with metallographic microscope. The structure of the samples from the EP741NP alloy is granular. Three types of the strengthening -phase are being observed, and it is noted that no defects on the macrostructure are detected in both joint and weld-affected zones. The study of the weld workblanks from the EP741NP alloy revealed the absence of porosity and cracks in the basic material and thermally affected zone. The welded joint up to 200 microns, irrespective of the final material shortening. Transition zone (a zone of the thermal affect) of 500 microns to 1000 microns is being observed. The heat treatment conducting after the welding contributes to the strengthening phase exudation in both seam and weld-affected zone. As the result, the welded joints become equal in strength to the basic material, which will be the next stage of materials treatment in the further research.

Keywords:

weld-affected zone, sub-cuboid, rotational friction welding, inertial friction welding

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