Page 151 - The Tribology Handbook

Table 27.2 Types of surface treatments and coatings
General bpe Materials ruhich can be coated or Examples
treated
Modifying the [material at the Ferrous materials, steels and cast Induction hardening See Table 27.3
surface without altering its irons Flame hardening
chemical constituents Laser hardening
Shot peening

Adding new material to the Ferrous materials Carburising See Table 27.4
surface, to change its chemical Nitriding
composition and properties Boronising
C hromising
Aluminium alloys Anodising

Placing a layer of new material on Ferrous materials Electroplating See Table 27.5
the surface Non-ferrous materials Physical vapour deposition
Plastics Chemical vapour deposition
Plasma spraying
Flame spraying
Vacuum deposition

Table 27.3 ,Surface treatment of ferrous materials

Process Mechanism Hardness and desicn debth Asbects
Induction hardening of Rapid heating followed by Up to 600 Hv at depths up to Provides a hard layer deep
medium carbon alloy steels quenching produces 5 mm enough to contain the high
martensite in the surface sub-surface shear stresses
which occur in concentrated
load contacts. Very large
components can be treated
Flame hardening of medium Surface heating followed by a Up to 500 Hv at depths up to Provides a hard wear-
carbon alloy steels quenching process produces 3 mm resistant surface layer.
martensite in the surface Particularly suitable for
components with rotational
symmetry that can be spun
Laser hardening of medium A scanned laser beam focused Up to 800 Hv at depths up to Suitable for local hardening of
carbon steels and cast irons on the surface. The very 0.75 mm small areas of special
local heated area is self components
quenched by its
surroundings

Shot peening of lferrous Work hardens the surface and Up to 0.5 mm approx Gives increased resistance to
materials leaves it in compression fatigue and stress corrosion

A27.2