It is most interesting to note that the process technology of gaseous nitride (as developed by Adolph Machlet in the early 1900s) is still being used in today’s surface-treatment processing world.

However, some significant process-control development has taken place to ensure better process control, such as the development and understanding of the Lehrer diagram and its influence on the thermal decomposition of the process gas in relation to a better control of the phase formation of the immediate surface compound zone.

 

Lehrer Diagram

The Lehrer diagram provides process-gas analysis utilizing sensory probes in conjunction with PC/PLC control systems to ensure the compound surface phase analysis of both epsilon and gamma prime.

Should there be an excessive use (without good control) of the process gas flow in relation to the intended use of the component and in relation to the steel analysis, the risk of surface cracking of the compound zone can occur (Figures 3 and 4). Another example of nitride networking is seen in Figure 5.

There is, therefore, an absolute necessity to control the process gas flow to ensure the control and prevention of nitride networking. This means that the following process parameters must be accurately controlled: process temperature and ammonia process gas flow.