لخّصلي

Influence of Quenching Medium, Specimen Size, and Geometry: The cooling rate depends on the cooling medium.b) rapid cooling across the solvus line to exceed the solubility limit.Fast cooling brings the danger of warping and formation of cracks, since it is usually accompanied by large thermal gradients.Precipitation Hardening: Hardening can be enhanced by extremely small precipitates that hinder dislocation motion. Precipitation hardening is achieved by: a) solution heat treatment where all the solute atoms are dissolved to form a single-phase solution.c) precipitation heat treatment where the supersaturated solution is heated to an intermediate temperature to induce precipitation and kept there for some time (aging).The precipitates form when the solubility limit is exceeded.This is called overaging.

Influence of Quenching Medium, Specimen Size, and Geometry:
The cooling rate depends on the cooling medium. Cooling is fastest using water, then oil, and
then air. Fast cooling brings the danger of warping and formation of cracks, since it is usually
accompanied by large thermal gradients.
The shape and size of the piece, together with the heat capacity and heat conductivity are
important in determining the cooling rate for different parts of the metal piece. Heat capacity is
the energy content of a heated mass, which needs to be removed for cooling. Heat conductivity
measures how fast this energy is transported to the colder regions of the piece.
Precipitation Hardening: Hardening can be enhanced by extremely small precipitates that
hinder dislocation motion. The precipitates form when the solubility limit is exceeded.
Precipitation hardening is also called age hardening because it involves the hardening of the
material over a prolonged time. Precipitation hardening is achieved by:
a) solution heat treatment where all the solute atoms are dissolved to form a single-phase
solution.
b) rapid cooling across the solvus line to exceed the solubility limit. This leads to a
supersaturated solid solution that remains stable (metastable) due to the low temperatures,
which prevent diffusion.
c) precipitation heat treatment where the supersaturated solution is heated to an intermediate
temperature to induce precipitation and kept there for some time (aging).
If the process is continued for a very long time, eventually the hardness decreases. This is called
overaging.