Technology： Other surface modification technologiesPTA process

Overlay welding by PTA

Principle of PTA

Figure 1 shows the PTA overlay welding mechanism. First, a pilot power supply is used to produce an electric arc, which is carried to argon gas flow between a tungsten electrode and a water-cooled nozzle. The argon gas transforms into plasma, and the hot plasma gas converges under the thermal pinch effect of the water-cooled nozzle to flow to the substrate as a high-energy plasma arc. When the arc reaches the substrate, the main power is supplied to maintain the status, and the arc current flows to the substrate where it forms a molten pool on the surface. At the same time, the welding-powder material is force-fed into the plasma arc by a carrier gas such as helium or argon. The material melts and is infused to the molten pool on the base metal surface to form the overlay layer.

Figure 2 compares the temperature distribution of the convergence of plasma arc and the TIG arc. The water-cooled nozzle intensively compresses the plasma arc and creates high-energy density, thus enabling powder with high melting points to be used as the filler material.

Main alloy powders employed

Main carbide powders used

Section macrostructures of overlaid alloy with various carbide particles dispersing in it

SEM structure of overlaid alloy with various carbide particles dispersing in it

PTA process flow