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| Chemical Vapor Deposition, or CVD, is a
thermal-chemical surface hardening process that can be applied to a wide variety of
ferrous, nonferrous, and cermet materials. The process involves elevating the temperature
of well-cleaned material to the range of 700° to 1000°C (1330°-1830°F) for a period of
1 to 12 hours while in contact with boronacious solid powder, paste, liquid, or gaseous
medium. The CVD process consists of two types of reaction, The first reaction takes place
between the boron-yielding substance and the component surface. The nucleation rate of the
particles at the surface is a function of the boriding time and temperature. This produces
a thin, compact boride layer, containing Iron Boride, Boron Carbide, and Titanium Boride.
The second reaction is diffusion controlled. The boron-containing diffusion zone extends
more than 7 times the depth of the boride layer, up to .020 of an inch deep. CVD
provides surface characteristics that offer numerous advantages over conventional case
hardened surface. The greatest advantage is that boride layers have extremely high
hardness (between 1450 and 5000 HV) with high melting points of the constituent phases.
The typical surface hardness values of borided steels compared with other hard materials
are detailed in the Surface Hardness Table. The hardness of boride layers produced on
carbon steel is much greater than that produced by any other conventional surface
hardening treatments: It exceeds that of hardened tool steel, hard chrome electroplate,
and is equivalent to that of tungsten carbide. The combination of high surface hardness
and low surface coefficient of friction makes a significant contribution in combating the
main wear modes: adhesion, tribooxidation, abrasion, and surface fatigue.
| Material |
Microhardness
(HV) |
Material |
Microhardness
(HV) |
| Borided Mild Steel |
1600 |
Nitrided Steels |
650-1700 |
| Borided H13 Tool Steel |
1800 |
Carburized Low Alloy |
650-950 |
| Hardened/Tempered H13 |
540-600 |
Hard Chrome Plating |
1000-1200 |
| Borided A2 Tool Steel |
1900 |
Cemented Carbide WcCo |
1160-1820 (30Kg) |
| Hardened/Tempered A2 |
630-700 |
TiN |
2000 |
| Quenched Steel |
900 |
SiC |
4000 |
| High-speed Steel BM42 |
900-910 |
BC |
5000 |
| - |
- |
Diamond |
>10,000 |
| - |
| - |
Important Notes |
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Hardness of the CVD layer can be retained at higher
temperatures than that of nitrided steels. |
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A wide variety of steels, including
through-hardenable steels are compatible with the process. |
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CVD can considerably enhance the corrosion/erosion
resistance of ferrous materials in nonoxidizing dilute acids and alkali media |
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Surfaces treated with CVD have moderate
oxidation resistance up to 850°C or 1550°F and are quite resistant to attack by molten
metal. |
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