Hard facing by Plasma Transfer Arc (PTA) relies on a gas-­shielded arc created between a non-consumable tungsten electrode and the workpiece as the primary heat source. The plasma is formed by ionizing the gas flowing in a nozzle sur­rounding the electrode. The electrode gen­erally is recessed into the nozzle, and the plasma gas generally emerges from a con­stricting orifice arrangement. The process can use bare rod or wire as a hard facing consumable, but more often pow­der is used as the consumable. When pow­der is used, the process is referred to as the plasma transferred arc process.

The powder is directed from the torch into the arc ef­fluent, where it is melted and fusion welded to the workpiece. A direct current power supply connected between the tungsten electrode and the workpiece provides the energy for the transferred arc.  The shielding gas is passed through a diffuser and forms a blanket in and around the arc zone.

Powder recoveries as high as 95%, with deposition rates up to 10 lb/h, are possible, depending on the size and shape of the part being hard faced.

Hard facing with the plasma transferred arc process has many advantages.  Hard facing deposits can range in size from ap­proximately 0.01 in. thick by 3/16 in. wide to approximately 1/4 in. thick by 1 1/2 in. wide by simply varying the welding cur­rent, powder-feed rate, oscillation, and travel speed. The process is amenable to automation, which makes it well suited for high production involving a large number of parts.