*Hard Alloys with High Content of WC and TiC—Deposited by Arc Spraying Process DOI: http://dx.doi.org/10.5772/intechopen.94605*

The substrate material can be of any nature: ferrous, non-ferrous, plastic, ceramic, textile, glass, wood, but the coating material is limited by its capacity to be transformed into a liquid state, or to be processed into of powder, wire, cord or wand, [12–13]. Usually, spraying processes allow the deposition of a diverse range of materials: pure metals and metal alloys, cermets, ceramics and under certain conditions polymers, [2, 14, 15].

The thermal spraying methods, recognized in the specialized technical literature as synergetic and versatile [16], have as objectives:


Recognized as the cheapest process for obtaining spray coatings, two-wire arc spraying finds numerous industrial applications that aim to obtain both surfaces with new properties and the restoration of used surfaces. [11–13].

The spraying method consists of making an electric arc between two consumable metal wires, followed by the atomization of the molten material with the help of a compressed air jet and the spraying of those particles on the substrate surface - **Figure 2**, [17]. Although the functional principle constructive of electric arc spraying devices is apparently simple, it must to allow the correlation between the wire feed speed, the intensity of the electric current in the circuit and the pressure of the compressed air, in the purpose of obtaining qualitative coatings and maximum yield, [11].

The electric arc coating devices also called spraying guns, are powered by direct current generators which have a rigid characteristic, develop voltages between 25 and 45 V and high currents with values in the range of 100–500 A, [18]. They are characterized by a modulated design, composed of:


**Figure 2.**

*Schematic representation of electric arc coating method, [17].*

*Welding - Modern Topics*

Depending on the melting method of the coating material, the thermal spraying

processes can be classified into four main categories, as presented in **Figure 1**. The thermal spraying processes are realized with the help of installations and equipment capable to develop the necessary heat for the CM melting, to achieve the dispersion of the formed droplets into fine particles and to transfer to them

**1.1 Background**

kinetic energy.

**138**

**Figure 1.**

*Classification of thermal spray methods, [11].*

The wire feed mechanism is positioned directly on the gun or outside of it and has the role of directing the wire from the coils towards the area of electric arc formation.

The spray head includes the wire guides and the nozzle through which the compressed air passes - symbolically called carrier gas, [2]. During the device functioning, the nozzle is placed in the lower part of the melting zone, before the contact point of the wire electrodes, usually called "arc point". The role of the spray head is to direct the entrainment gas in the area where the electric arc is formed, in order to produce the division (atomization) of the droplet of molten filler material into particles, which it propels on the surface of the substrate, [19].

The dispersion of the molten droplets determines the interrupting of the circuit respectively of the electric arc. The electric arc priming is carrying out by advancing the wires in the melting area, where the medium is strongly ionized. The phenomenon has a periodic character, being composed of melting sequences of the input material followed by interruptions. In this case, the electric arc is a short-circuit arc, intermediate between the usual arc and the "breaking" arc produced at the interruption of a circuit, [20, 21].
