*2.2.7 Porosity measurements of the 97MXC coatings*

Porosity is a defining physical characteristic of the deposits obtained by thermal 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 software (Japan).

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

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

**155**

*Hard Alloys with High Content of WC and TiC—Deposited by Arc Spraying Process*

for the same value of the intensity of the electric current, when the compressed air pressure increases, the average porosity of the deposits decreases by up to 12%. The effect of increasing the temperature of the arc achieved by increasing the electric current determines the reduction of the average porosity by a maximum of 28%. It can be stated that between the two process parameters: compressed air pressure and electric current intensity, the latter has a "dramatic" influence on the deposition

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

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

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

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

classic spray device equipped with a conical nozzle system.

*DOI: http://dx.doi.org/10.5772/intechopen.94605*

density of 97MXC.

**3. Conclusions**

(up to 28%).

compressed air pressure.

**Conflict of interest**

friction and obtaining a low wear rate.

The authors declare no conflict of interest.

**Figure 19.** *Average porosity variation of 97MXC coatings with the compressed air pressure.*

for the same value of the intensity of the electric current, when the compressed air pressure increases, the average porosity of the deposits decreases by up to 12%. The effect of increasing the temperature of the arc achieved by increasing the electric current determines the reduction of the average porosity by a maximum of 28%. It can be stated that between the two process parameters: compressed air pressure and electric current intensity, the latter has a "dramatic" influence on the deposition density of 97MXC.
