**2. Experimental procedure**

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 cooling rate (40°C/min).

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

Brazing filler metal (**Table 2**) in the cast state was placed at the gap (size of fixed brazing gap was 50 μm).

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 scanning electron microscope TescanMira 3 LMU.


**107**

**Figure 2.**

*filler metal: direct (a); reverse (b) fillet.*

*Vacuum Brazing of Dissimilar Joints Mo-SS with Cu-Mn-Ni Brazing Filler Metal*

allowed examining the microsections without chemical etching.

The distribution of chemical elements was examined using the method of a local micro X-ray spectrum analysis applying the energy dispersion spectrometer Oxford Instruments X-max (80 mm2) under the control of the software package INCA. The locality of micro X-ray spectrum measurements did not exceed 1 mm; the filming of microstructures was carried out in back-scattered electrons (BSE), which

For mechanical tests, the plane overlap joints of the 100 × 30 × 3 mm size (three samples for each brazing filler metal) were brazed and tested using the installation

**3.1 Microstructure of brazed joints of molybdenum with stainless steel at the** 

In vacuum brazing of dissimilar materials such as molybdenum-stainless steel by brazing filler metal of Cu-Mn-Ni-Fe-1Si [16] system, good wetting of both the materials is observed, namely, molybdenum and stainless steel. This ensures the

In the central zone (matrix) of the brazed seam, a copper-based solid solution (92.58% Cu) solidifies, which contains a small amount of iron—2.87%, in addition

The more detailed study of chemical inhomogeneity of brazed seam matrix by mapping showed that dispersed particles of 0.5–1 μm size, enriched in iron and

In the peripheral zone of the brazed seam, which borders on molybdenum, two reaction layers are observed, which precipitate in the form of narrow continuous bands along the brazed seam. One of them, based on molybdenum (51.21%), is enriched in iron (31.71%) and silicon (5.88%) and is located closer to molybdenum (**Figure 3(b)**). The second one—based on iron (68.02%)—is also enriched in silicon but contains no molybdenum. It borders on the copper-based solid solution. The width of these reaction layers is variable but does not exceed 5 μm (each). Their common feature is an increased concentration of silicon from 4.83 to 5.88% (**Table 3**). In some areas brazing filler metal penetrates along the grain boundaries

It is evident that during brazing, the liquid brazing filler metal is saturated by steel component elements. Diffusion processes take place at the cooling of

*The appearance of the brazed sample of molybdenum-stainless steel, produced using Cu-Mn-Ni-Fe-1Si brazing* 

Alloys of the copper-manganese-silicon system contain two phases: a solid solution based on copper and manganese silicides [15]. In the presence of iron in the alloy, silicides are compounds having a hexagonal lattice isomorphic to the lattices

to brazing filler metal component elements (**Figure 3(a)** and **(b)**; **Table 3**).

**application of brazing filler metal of Cu-Mn-Ni-Fe-1Si system**

formation of smooth and tight fillets (**Figure 2(a)** and **(b)**).

silicon, precipitate in the copper-based solid solution (**Figure 4**).

of the stainless steel to a maximum depth down to 20 μm (**Figure 3(a)**).

*DOI: http://dx.doi.org/10.5772/intechopen.92983*

MTS-810.

**3. Results and discussion**

Mn5Si3 and Fe5Si3 [17].

**Table 2.** *Used brazing filler metals and brazing modes.* *Vacuum Brazing of Dissimilar Joints Mo-SS with Cu-Mn-Ni Brazing Filler Metal DOI: http://dx.doi.org/10.5772/intechopen.92983*

The distribution of chemical elements was examined using the method of a local micro X-ray spectrum analysis applying the energy dispersion spectrometer Oxford Instruments X-max (80 mm2) under the control of the software package INCA. The locality of micro X-ray spectrum measurements did not exceed 1 mm; the filming of microstructures was carried out in back-scattered electrons (BSE), which allowed examining the microsections without chemical etching.

For mechanical tests, the plane overlap joints of the 100 × 30 × 3 mm size (three samples for each brazing filler metal) were brazed and tested using the installation MTS-810.
