This series on trends and developments in heat-treatment technology continues.

Plasma-Assisted Surface Depositions

The plasma-assisted surface depositions (PASDs) can be subdivided into two groups (Fig. 8). PASDs are applied to the surface of a pre-heat-treated component after the pre-hardening and temper procedure has been completed. The plasma-assisted nitriding procedure has also been completed with a minimal case depth.

For now we have a component that has been heat treated followed by the diffusion treatment of plasma-assisted nitriding. Instead of a diffusion treatment, we now have a deposition treatment. These procedures can be termed in a collected manner as thin-coating deposition technology.

Thin-Coating Deposition Technology

The basis of this technology is to deposit onto a hardened substrate material to produce extremely high surface hardness values, while at the same time retaining the prior metallurgy of the component subjected to this treatment. This technology will produce abrasive-resistant coatings that have been deposited onto a nitrided substrate that has been subjected to a protective method of precleaning and processing.

The procedure ultimately offers low coefficient-of-friction surfaces and good sliding surfaces. The deposited coating is well bonded to the nitrided substrate and necessitates very thin depositions. The two methods of this deposition are identified as CVD and PVD.

CVD (chemical vapor deposition) is conducted under low-pressure conditions (medium vacuum conditions). The deposited coating is produced by chemically starting from a gaseous component at high temperatures. PVD (physical vapor deposition) coating is derived from a metallic vapor that deposits, because of cathodic contact with the process furnace hearth, the extremely hard coating onto the component being treated. Typical applications of both CVD and PVD procedures are usually well suited for hard-wearing and abrasive process conditions.

The procedural process temperatures are higher than those applied to plasma-assisted nitriding and plasma-assisted ferritic nitrocarburizing. The temperatures employed for the CVD and PVD are generally found in the region of 1450-1900°F., so the process-vessel material must be chosen with great care to operate consistently and repeatedly at these high process temperatures.

Plasma-assisted titanium-nitride deposition coatings are used for drills, milling cutter tools, hobs, broaches and punches/dies. The resulting surface hardness after processing by plasma-assisted titanium nitriding can be in the region of 2000 HV (plus), which will assist in wear resistance, corrosion resistance and erosion.

More next time.