Hardening of Metals
In materials science, hardness is the ability to withstand surface indentation (localized plastic deformation) and scratching. Hardness is probably the most poorly defined material property because it may indicate resistance to scratching, abrasion, an indentation, or even resistance to shaping or localized plastic deformation. Hardness is important from an engineering standpoint because resistance to wear by either friction or erosion by steam, oil, and water generally increases with hardness.
Hardening is a metallurgical metalworking process used to increase the hardness of a metal. The hardness of a metal is directly proportional to the uniaxial yield stress at the location of the imposed strain. To improve the hardness of the pure metal, we can use different ways, which include:
- Hall-Petch Method
- Solid Solution Hardening (alloying)
- Work Hardening (Cold Working)
- Precipitation Hardening
- Transformation hardening
- Dispersion Hardening
- Surface Hardening
Dispersion hardening involves including small, hard particles in the metal, thus restricting the movement of dislocations and raising the strength properties. It is, in many ways, very similar to age hardening. The difference lies in the precipitates themselves—the particles are chosen because of their thermal stability, that is, their resistance to particle coarsening or growth at high temperatures. Dispersoid particles influence the grain structure, and the increase in strength is due to the grain structure formed due to the presence of dispersoids.