High power extended arc plasma spray method and apparatus

In a plasma arc spray process comprising the steps of:

• feeding a plasma producing gas under pressure through a chamber housing a first cathode electrode and from said chamber through a spray nozzle forming a second anode electrode and defining an anode nozzle passage aligned with said first electrode and being spaced therefrom, while creating an electric arc between said first and second electrodes to set up a plasma flame jet exiting said nozzle passage, and feeding material into said flame jet for melting said material and accelerating the same within said flame jet for coating a substrate by impingement placed in front of and downstream of the nozzle exit, the improvement comprising the steps of:
• establishing a vortex flow of plasma-producing gas to create a low pressure core of gas flow extending through the anode passage with said low pressure core, establishing an extended ionized arc column throughout the anode nozzle passage, and adjusting the rate of gas flow and the arc current to the anode nozzle passage diameter to produce a supersonic extended ionized arc column which extends beyond the end of the nozzle by a distance which is approximately four times the nozzle passage diameter.