Thermal plasma spraying is a popular process because of its ability to create a top-quality coating on a variety of materials, including tungsten and zirconium. This versatility means that this process is widely used to apply thermal spray coatings for a number of different applications.
Additionally, as this ScienceDirect article notes, thermal spray processes are highly productive, robust and cost-effective. Plus, the properties of this type of coating are highly predictable, which allows for the consistent finish that is often required across all the industries and sectors in which this process is used.
A brief overview of the thermal plasma spray process
A DC electric arc is used during the thermal plasma spray process. It is this electric arc which produces a steady stream of ionised plasma gas at a high temperature and acts as the heat source for the spray.
What are thermal plasma spray guns made out of?
Thermal plasma spray guns are composed of a tungsten cathode and a copper anode. Both of these elements are cooled by water during the process.
How do thermal plasma spray guns work?
Plasma gas, which is a combination of helium, nitrogen, argon and hydrogen, passes through the anode which is carefully shaped to form a directional nozzle.
The process begins with a high-voltage discharge. This burst of power stimulates ionisation and also creates a path for the arc, which passes between the anode and the cathode, to form. The arc then creates resistance heating, which prompts the gas to ionise and form plasma. The shaped anode nozzle then allows the plasma to exit as a neutral or free plasma flame, which does not carry any electrical current.
Are all materials suitable for the thermal plasma spray process?
Temperatures reach 15,000 degrees Celsius during this process and this, combined with the plasma jet’s high thermal energy levels, means that only materials that have a high melting point are suitable for thermal plasma spray. This means that this process is suitable for ceramic materials such as zirconium, as well as refractory metals such as tungsten.