Precipitation Hardening

1
Precipitation Hardening

• Two requirements
• An appreciable max solubility of one component in
  the other (several )
• solubility limit that rapidly decreases in
  concentration of the major component with reduced
  temperature

2
Based on a Phase Diagram
L
a L
b L
b
a
a b
A
B
3
So conceptually

• Heat treat at a sufficient temperature to create
  one phase (a) with all B dissolved in the A major
  phase.
• Quench (can be to room temp) to saturate a and
  anneal below the solid solubility temperature to
  drive the B rich b phase out of the A rich a
  phase.
• If b is harder than a, the precipitates will
  strengthen the structure

4
For Effective Heat Treatment

• Sufficient thermal conductivity of workpiece
• Sufficient heating capacity of the source (sizing
  sample to source)

5
Other Thermal Processing

• Flame or Torch Exposure
• Laser Exposure
• Electrostatic Discharge
• Welding or heat treatment of a selective zone

6
Localized Heat Treatment

• Welding and other schemes lead to
• Altered microstructure in weld zone
• Heat affected zone with interphase properties
  between the unaffected material weld material
• Potential for cracking and other damage due to
  localized heating
• Can be analyzed by hardness, x-ray diffraction in
  different regions