Definition - What does Surfacing mean?
Surfacing is the process of altering the surface characteristics of a component to achieve an improvement in properties by depositing a coating or modifying the surface structure. In metallurgy, it is depositing filler metal on a metal surface by welding or spraying.
For a successful hard surfacing or overlaying operation, a welding procedure should be established. It should specify:
- Welding process to be used
- Method of application
- Pre-welding operations such as cleaning, undercutting, etc.
Corrosionpedia explains Surfacing
Surfacing is the action or process of giving a finished surface to something. It makes possible the design and manufacture of components with a combination of bulk and surface properties unobtainable in a single-component material.
Surfacing processes are numerous. They include more traditional methods like:
- Weld overlaying
- Thermal spraying
- Thermochemical treatments (carburizing, nitriding)
Newer surfacing technologies include:
- Physical vapor deposition (PVD)
- Chemical vapor deposition (CVD)
- Laser surface modification
- Plasma thermochemical diffusion
- Cold spraying
The thickness of the surfacing deposit is extremely important. It varies from several millimeters for weld overlays to a few microns for PVD and CVD coatings, while the surface modification depth can vary from 0.5 microns or less for ion-implantation to more than a millimeter for nitriding. Coating properties can also vary considerably. For example, surface hardness can be modified to 1000HV for nitrided steels and up to 3500HV with the deposition of a TiN PVD coating.
Available surfacing coatings and treatments are numerous, and still increasing, making selection a difficult task for the non-specialist. Cost and practicalities of the treatment must be considered in the final selection, taking into account the composition, size and shape of the component concerned.
Surfacing for corrosion resistance is recommended for use of one layer only. However, for certain applications such as pump linings and wear areas a second layer of surfacing is applied. Hardfacing alloys should be restricted to two layers. Some types of alloys can be used in three layers.