One of the many advantages of plasma nitriding is that the ratio of nitrogen to hydrogen can be varied to suit the steel being processed in relation to the appropriate required surface metallurgy. In other words, the process technician now has the ability to control the nitride potential and reduce the serious risk of nitride networking. (Please be aware that nitride networking can also be controlled and reduced with new gas nitride techniques.)
Nitride networks are simply a saturated solution of nitrogen in the surface of the steel, which can be limited by the control of the nitrogen to hydrogen ratio. High-alloy steel requires only a low volume of nitrogen to hydrogen, whereas low-alloy steels require a high volume of nitrogen to hydrogen.
This will also help control the thickness of the compound layer and the phases present in the compound layer. It will now be the surface metallurgy that will dictate the nitrogen-to-hydrogen ratios.
This means that on the ramp-up to the selected process temperature, the generated plasma and hydrogen (no nitrogen on the heat-up stage) can be used to sputter clean (which is likened to atomic shot blasting) the workload. As the workload approaches the selected process temperature for nitriding, the appropriate process gas of nitrogen begins to flow into the process chamber. The flow rate of nitrogen is then determined by the surface metallurgy that was required for the workpiece.
Further to the reduction of the voltage necessary to generate the plasma, the plasma is now pulsed during the complete process cycle. This means that the process technician can now adjust the process voltage as well as the pulse time on and the pulse time off of that voltage. The system is now controlling the following: process temperature, process cycle time at temperature, process plasma generation voltage, pulse time on, pulse time off, process amperage, process current density, process current and process gas volume (nitrogen and hydrogen).
This means that there is more detailed control of the process operating parameters, which further means the introduction of the PC/PLC control system in order to accurately control all of the process parameters.
Pulsed-plasma generation technology will virtually eliminate the risk of arc discharging to the workpiece. The introduction of the PC/PLC control for both data acquisition and process control also offers a very accurate nitriding process system.
The process metallurgy can be accurately controlled in relation to the surface metallurgy that is necessary to suit the workpiece application as well as producing uniform case-depth control and an effective, efficient method of nitriding.