Ostwald Ripening (Precipitate Coarsening)
Precipitate coarsening is the growth of larger particles at the expense of smaller precipitates due to prolonged thermal exposure. This leads to a loss of strength and toughness.
Physical-Chemical Mechanism
Precipitate coarsening occurs when metallic precipitates (such as copper or nickel) in the weld slowly grow and enlarge. This happens through the diffusion growth of larger particles from the smaller ones. Coarsening leads to an uneven microstructure.
Metallurgical Relevance & Welding Risks
Increased coarsening can significantly reduce the strength and toughness of the weld. The tendency for cracking increases, especially under mechanical loads. In addition, resistance to chemical corrosion can worsen.
Workshop Practice & Actions
To avoid precipitate coarsening, it is important to ensure optimal welding time and temperature. The cooling time should not be too long (t8/5 < 20 s) to prevent microstructural coarsening. Use appropriate shielding agents or filler materials that stabilize precipitates and limit their size.