Steps in Ion/Plasma Nitriding

Ion/plasma nitriding is a thermochemical surface hardening process that significantly improves the wear resistance, fatigue strength, and corrosion resistance of metal parts. Unlike traditional gas nitriding, ion nitriding utilizes a plasma environment, allowing for precise control over the process, reduced distortion, and the ability to selectively nitride specific areas. This makes it a highly versatile and efficient method for enhancing the performance and lifespan of a wide range of industrial parts.

The Steps of Ion/Plasma Nitriding:

1) Cleaning the Parts:
The process begins with cleaning of the workpieces. This is crucial for ensuring uniform nitriding. Contaminants like oils, grease, oxides, and scale can impede the diffusion of nitrogen into the metal surface. Common cleaning methods include solvent cleaning, ultrasonic cleaning, and abrasive blasting.

2) Checking the Hardness Before Nitriding:
Before the nitriding process, the initial hardness of the parts is often measured. This baseline data is essential for comparing the pre- and post-nitriding hardness, verifying the effectiveness of the treatment, and ensuring the material is within the expected parameters.

3) Arrangement in the Chamber:
The cleaned parts are carefully arranged within the vacuum chamber. The arrangement is critical for ensuring uniform plasma exposure and consistent nitriding. Fixtures and supports are used to hold the parts securely and prevent contact that could lead to uneven treatment.

4) Deciding the Recipe Based on the Steel Grade and Requirements:

One of the significant advantages of ion nitriding is its precise control. The process parameters, such as gas composition, temperature, time, and voltage, are carefully selected based on the specific steel grade and the desired surface properties. This "recipe" is crucial for achieving the required case depth and hardness.   

Furthermore, selective nitriding is possible. Areas that do not require hardening can be masked either mechanically (using shields or covers) or by applying a special stop-off paste.  

5) Heating, Nitriding, and Cooling of the Parts:

The vacuum chamber is evacuated, and a controlled gas mixture (typically nitrogen and hydrogen) is introduced. A high voltage is applied, creating a plasma discharge. The positively charged nitrogen ions are accelerated towards the negatively charged workpieces, bombarding the surface and diffusing into the metal.   

The heating of the parts is done by the plasma itself, and by the heating elements in the furnace.
The temperature is carefully controlled during the nitriding process to achieve the desired diffusion depth. After the nitriding cycle is complete, the parts are cooled within the chamber, often under a controlled atmosphere, to minimize distortion and oxidation.

6) Taking Out the Parts and Checking the Achieved Surface Hardness:
Once the cooling cycle is finished, the parts are removed from the chamber. The surface hardness is then measured using appropriate hardness testing methods - most often the Vickers method. This verification step ensures that the desired hardness and case depth have been achieved, and that the process was successful.

Case depth measurement can be further performed by either cutting a sample of the same steel grade, placed with the parts, or cutting one of the parts directly.

Ion/plasma nitriding offers a highly effective and precise method for enhancing the surface properties of metallic components. Its ability to provide superior wear resistance, fatigue strength, and corrosion resistance, combined with the flexibility of selective nitriding, makes it a valuable tool for a wide range of industries. By carefully controlling each step of the process, manufacturers can achieve consistent and reliable results, extending the lifespan and improving the performance of their products.

Check out our video of nitriding parts in our ION-75 Cold-Wall furnace: