An increase in the nitriding voltage resulted in a decrease in case depth. This reduction
in case depth may seem anomalous since an increase in voltage results in a higher velocity
of the arriving ions. This however leads also to a high sputtering rate which effectively
reduces the amount of nitrogen diffusing into the surface.
In standard plasma nitriding furnaces, the plasma surrounding the parts is used to heat
them up directly. However, in a large commercial furnace, particularly when fully loaded, it
is almost impossible to ensure that the temperature is the same at the outside of the load as
in the centre. Such a situation is a problem for industry, in that accurate treatment
temperature control is a must to ensure reliability and repeatability of treatments. In order to
reduce this effect many furnaces with auxiliary heat sources were developed and are used
now on a regular basis