Körnungswachstum

Körnungswachstum, also known as grain growth, is a phenomenon in materials science where the average grain size of a polycrystalline material increases over time. This process occurs during annealing, a heat treatment process. At elevated temperatures, atoms within the material have enough energy to move. Grain boundaries, which are the interfaces between individual grains, are regions of higher energy. To reduce the total grain boundary energy of the material, larger grains grow at the expense of smaller ones. This is driven by the reduction of the overall surface energy of the material.

The rate of grain growth is influenced by several factors, including temperature, time, and the initial microstructure of the material. Higher temperatures and longer annealing times generally lead to more significant grain growth. The presence of impurities or alloying elements can also affect the process by pinning grain boundaries and slowing down growth.

Grain growth has a substantial impact on the mechanical and physical properties of materials. In general, larger grains lead to lower yield strength and hardness but can improve ductility and toughness. This is because grain boundaries act as obstacles to dislocation movement, which is the primary mechanism of plastic deformation. Therefore, controlling grain size through processes like annealing is a crucial aspect of material processing to achieve desired properties. For instance, in metals, fine grain sizes are often preferred for high strength applications, while coarser grains might be acceptable or even desirable for other uses.