Understanding Annealing: Reversing Cold Work In Dental Alloys

Understanding Annealing: Reversing Cold Work In Dental Alloys

Write a short note on annealing.
Answer:

The effect associated with cold working (for example, Strain, Hardening) can be reversed by simple heating of the metal. The process is called annealing. The more severe the cold working the more readily annealing occurs. Annealing is generally comprised of three stages which are as follows:

• Recovery: In the recovery stage, the properties of the cold worked metal begin to disappear before any significant changes are observed under microscopic examination.
• Recrystallization: When a severely cold worked metal is annealed recrystallization occurs after recovery. This involves a radial change in the microstructure.
• Grain growth: The average grain size of the recrystallized structure depends on the initial number of nuclei. The more severe the cold working, the greater the number of such nuclei, and the grain size for the recrystallized metal can range from fine to fairly coarse.
  • This grain growth process is simply a bounded energy-minimizing process.
  • The annealing is a relative process, the higher the melting point of the metal, the higher is the temperature needed for annealing.