National Research Nuclear University “MEPhI”, Moscow, Russia:

P. V. Morokhov, Engineer Department No. 9 “Physical Problems of Materials Science”, e-mail: morokhov@mail.ru
A. A. Ivannikov, Senior Lecturer, Department No. 9 “Physical Problems of Materials Science”, e-mail: ivannikov7@rambler.ru
N. S. Popov, Masters Student, Department No. 9 “Physical Problems of Materials Science”, e-mail: NSPopov@mephi.ru
O. N. Sevryukov, Associate Professor Department No. 9 “Physical Problems of Materials Science”, e-mail: Sevr54@mail.ru

The article was attended by the staff of the Department No. 9 “Physical Problems of Materials Science” NRNU MEPhI — Sidorenko A. A.

Two titanium alloys, OT4 and VT6-c, with a pseudo-α and α + β structure, respectively, were brazed using transient liquid phase (TLP) bonding. To obtain high strength joints an amorphous foil (Ti – 12Zr – 22Cu – 12Ni – 1.5 Be – 0.8V wt.%) was used. Based on microstructural studies and analysis of two- and three-component phase diagrams, the mechanism of the microstructural evolution of the brazed seams of titanium alloys OT4 and VT6-c is described. Brazing at 800 °C with exposure for 0.5 h leads to the formation of a heterogeneous structure consisting of Widmanstätten, eutectoid, and eutectic. Brazed OT4 and VT6-c joints with the presence of a eutectic layer in the centre show low mechanical properties; their ultimate strength lies in a range from 200 to 550 MPa. Increasing the brazing temperature to 840 °C and the exposure time to 2 h, leads to the disappearance of the brittle eutectic component from the seam. This structure typically consists of Widmanstätten with a small number of eutectoid fractions. Joints with the absence of a eutectic layer in the brazed seam demonstrate a strength equal to the base titanium alloys. In this case, failure occurs in the base metal. For brazed samples from the OT4 alloy, the tensile strength value is σ_b = 750 ± 3 MPa, and for samples from VT6-c, σ_b = 905 ± 3 MPa.

This work was supported by Competitiveness Growth Programme of the Federal Autonomous Educational Institution of Higher Education National Research Nuclear University MEPhI (Moscow Engineering Physics Institute).

The authors express a gratitude to the staff of "MEPhIANETO" for providing brazign foils".

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