**3. Results and discussion**

*Welding - Modern Topics*

brazing process.

Cu-Mn-Ni system.

**2. Experimental procedure**

cooling rate (40°C/min).

the working space of 1 × 10<sup>−</sup><sup>3</sup>

brazing gap was 50 μm).

tation of several phases takes place.

stresses in brazed joints. The presence of solid solutions characterized alloys based

Proceeding from analysis of binary state diagrams of Cu-Ni, Cu-Mn, and Mn-Ni systems [13], Cu-Mn-Ni ternary system was selected as the base one [14, 15]. This system has a wide range of solid solutions. So, in the Cu-Mn-Ni alloy, additional alloying with silicon should improve the spreading of the surface of stainless steel, and alloying with iron should reduce erosion of stainless steel by brazing during the

This work aims to study the features of the formation of the microstructure of brazed joints, the relationship between the structure, the initial composition of the brazing filler metal, and the strength of dissimilar brazed joints Mo-stainless steel obtained by vacuum brazing using brazing filler metal of the

As the base metal, molybdenum, stainless steel 09Kh18N10, and brazing alloys based on copper-manganese system were applied. The brazing filler metal was applied in the cast form and was produced by melting in the laboratory installation in the shielding atmosphere of argon. The produced ingots were overturned and melted down (up to 5 times) in order to average the chemical composition and provide a uniform distribution of elements. The solidus and liquidus temperatures of cast brazing alloys were determined using the installation of high-temperature differential analysis in the shielding atmosphere of helium at constant heating and

Before brazing, the samples were machined and cleaned (degreased). The prepared samples were overlapped, and the brazing filler metal (**Table 1**) was placed on the surface of the base metal (near the gap) and loaded into a vacuum furnace with radiation heating to conduct capillary vacuum brazing with a rarefaction of

Brazing filler metal (**Table 2**) in the cast state was placed at the gap (size of fixed

**No. Base system of brazing filler metal alloying Brazing temperature, °C/time, min**

1 Cu-Mn-Ni-Fe-1.0Si 1050 /3 2 Cu-Mn-Ni-0.2 Si 1100 /5 3 Cu-Mn-Ni 1084 /3

For metallographic examinations the overlapped joints were brazed, and the specimens were cut out perpendicular to the brazing seam; the microsections were manufactured according to the standard procedure and examined using the scan-

Pa.

ning electron microscope TescanMira 3 LMU.

*Used brazing filler metals and brazing modes.*

The copper-manganese system has a minimum melting point (821°C) at a manganese concentration of 33.7 atom. %. With decreasing temperature, ordering processes occur in the alloys of this system, and the ordered phases Cu5Mn and Cu3Mn precipitate, increasing the strength of the solid solution. Analysis of nickelmanganese binary system is indicative of complete solubility of manganese in nickel in the liquid state at increased temperature but with temperature lowering precipi-

on copper-nickel and copper-manganese systems [13].

**106**

**Table 2.**
