**3. Conclusions**

*Welding - Modern Topics*

air pressure.

**Figure 18.**

*circuit.*

software (Japan).

increase of the impact velocity of the particles with the substrate surface, respectively their better fixation in the surface roughness. This aspect determines the increasing the adhesion of the 97MXC deposits with the increase of the compressed

*Variation in the adhesion of 97MXC deposits with the compressed air pressure passing through the primary* 

Porosity is a defining physical characteristic of the deposits obtained by thermal

In **Figure 19** it is presented the variation of the average porosity of the 97MXC deposits with the compressed air pressure passing through the primary circuit - for

As expected, the variation of the average porosity of the 97MXC coatings presents a decreasing tendency both by the increasing of the compressed air pressure value and by the increasing of the current intensity value. Thus, it is observed that

spray, due to the presence of interlamellar voids and interconnection channels between them. It is expressed by the degree of porosity of the deposit, measured in percentages, [48]. In the case of the 97MXC coatings, the porosity was investigated by image analysis of the transversal section of the specimens, using the IQ Materials

different values of the current intensity that supplies the electric arc.

*Average porosity variation of 97MXC coatings with the compressed air pressure.*

*2.2.7 Porosity measurements of the 97MXC coatings*

**154**

**Figure 19.**

The studies, carried out in this paper, demonstrate that qualitative deposits of hard alloys, containing WC and TiC, can be obtained by arc spray process, using a classic spray device equipped with a conical nozzle system.

The increase of the electric arc temperature, due to the increase of the current intensity favors the decomposition of some chemical compounds (TiC, FeB, WC), respectively the appearance of hard chemical compounds of type W2C and of complex carbides of type eta: FeW3C, Fe3W3C and Fe6W6C; the accentuated melting of the additional material and the formation of small particles with low inertia, capable to fix in the surface roughness determine the increase of the adhesion of the deposits of hard alloys and the reduction of the porosity in relatively large limits (up to 28%).

The pressure of the compressed air passing through the primary circuit determines the increase of the velocity of the sprayed particles [33], respectively their better fixation in the asperities of the substrate surface. This aspect justifies the adhesion increasing, the average porosity reducing of the coatings (by up to 12%), and the increasing of the microhardness of the coatings - at the increasing of the compressed air pressure.

The presence, inside the coatings of hard chemical compounds, type WC and W2C - incorporated in the carbide matrix (FeW)xC, as well as compounds TiC, FeCr, and FeB, permits improving the wear behavior of deposits, underlined through the stability of the friction torque, the increasing of the coefficient of friction and obtaining a low wear rate.
