The Paton Welding Journal, 2022, №05



2022 №05 (04)

DOI of Article 10.37434/tpwj2022.05.05

2022 №05 (06)

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The Paton Welding Journal, 2022, #5, 33-39 pages

Features of the structure of molybdenum‒covar brazed joints

S.V. Maksymova, P.V. Kovalchuk, V.V. Voronov

E.O. Paton Electric Welding Institute of the NAS of Ukraine 11 Kazymyr Malevych Str., 03150, Kyiv, Ukraine. E-mail: office@paton.kiev.ua

Abstract
The work presents the results of metallographic and X-ray microspectral studies of molybdenum‒Kovar overlap joints, which were produced by vacuum brazing with application of brazing filler metal based on Cu‒Mn‒Co system. The influence of soaking at brazing temperature on brazed seam structure formation was studied. Local X-ray microspectral analysis was used to determine the number of structural components of the brazed seam: copper-based solid solution, individual single iron-based grains, reaction layer in the form of a continuous band on molybdenum‒brazing filler metal interface. It was found that longer soaking at the brazing temperature promotes an increase of the reaction layer width from 1 to 3 μm and leads to formation of a faceted morphology from the brazed seam side and to microcracks initiation in it, but it does not affect molybdenum concentration, which at different soaking (1‒15 min) is in the range of 55.81‒59.05 wt.%. In the solid solution (matrix) manganese concentration decreases with longer soaking, copper concentration rises, but the quantity of iron practically does not change, and it is in the range of 4.52‒4.95 wt.%. In single grains of the dark phase, observed near the interface with Kovar, longer soaking promotes an increase of iron and nickel concentration and lowering of manganese and copper content.
Keywords: Kovar, molybdenum, vacuum brazing, brazing filler metal, structure, brazed seam, soaking, reaction layer, X-ray microspectral analysis

Received: 07.04.2022
Accepted: 08.08.2022

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