- Pack carburizing
- Drip-feed carburizing
- Gas carburizing
- Vacuum carburizing
- Low-pressure carburizing
- Plasma carburizing
When considering surface treatments, the principal question has always been: Should it be deposition, or should it be diffusion?
The success of deposition methods of surface treatments has always been, and always will be, the degree of surface cleanliness in preparation for the deposition metal. Without the appropriate precleaning and surface preparation, no matter how good the deposition material might be, it will not be successful because the adhesion will not present between the deposited material and the substrate material.
Diffusion treatments, on the other hand, do not necessitate the same degree of pre-surface cleaning. However, that is not to say that precleaning is not required. Adequate precleaning can and will lead to process atmospheric contamination, and perhaps cause and create surface oxides, surface chlorides and surface sulfides, which in turn will lead to poor quality diffusion and formed case.
New techniques of surface-diffusion procedures are moving beyond the state of developmental work and into the field of commercialization. Process techniques such as the diffusion of aluminum, vanadium, molybdenum, tungsten and other metallic diffusion methods are now becoming commercially available process techniques. The next step will be that of discovering applications for these diffused metals.
For example, consider AISI 8620 steel having been carburized for the first portion of the cycle followed by the diffusion of aluminum into the surface. A hydrocarbon-based atmosphere would be used for the carburizing procedure, which would be followed by the addition of a nitrogen source to form aluminum nitrides in the immediate surface. This will give excellent wear-resistant characteristics, particularly for gear applications, and will improve the surface corrosion-resistance level.
There are many developments taking place in the field of induction heat treatment that include new power-generation systems and control of those systems by PC/PLC combinations, which are leading to more precise and distinct areas of heat treatment.
Other surface treatments for precision hardening by phase transformation can be attributed to the technology of laser heat treatment. Laser heat treatment is simply the manipulation of a focal point of a light beam in relation to the surface of the steel. With any surface phase-change technology, it is necessary to have the following process prerequisites: carbon, temperature and cooling rate.
Without the above prerequisites, phase-change surface treatment cannot occur other than by diffusion techniques such as by carburizing, nitriding, Boronizing and other similar techniques.
The technology of surface treatment by either diffusion, deposition or phase change is exciting. Diffusion techniques will have a continuing future in the field of engineering.