Thermodynamic Equilibrium
Thermodynamic equilibrium: State where Gibbs free energy is minimal and the material no longer undergoes phase changes. This is typical for materials with metastable structures.
Physical-Chemical Mechanism of Action
A material is in thermodynamic equilibrium when Gibbs free energy is minimized and no further phase changes or chemical reactions occur. This usually happens at low temperatures and high pressures.
Metallurgical Relevance & Risks in Welding
In welding, thermodynamic equilibrium means the material no longer changes its chemical properties. This is important for the stability of materials like alloys with metastable structures. An example is martensitic structures in high-strength steels that form when cooling too fast and retain their hardness.
Workshop Practice & Action Instructions
To ensure thermodynamic equilibrium, you should:
• Cool the weld slowly (e.g., t8/5 > 25 s) to avoid metastable structures.
• For high-strength steels, control the cooling rate precisely to prevent cracking and hardness issues.