Concentration Gradient
A concentration gradient is the difference in composition of alloying elements across a region. It drives diffusion, moving elements from rich to poor areas.
Physico-Chemical Mechanism of Action
A concentration gradient arises from differences in the number of atoms or ions of different alloying elements at different locations. These differences create a driving force that moves elements from richer to poorer areas to reach equilibrium.
Metallurgical Relevance & Risks in Welding
A strong concentration gradient can occur during welding and leads to diffusion of elements like carbon or oxygen. This can distort the microstructure, cause porosity, or worsen mechanical properties. In strongly concentrated gradients, grain formation can also be affected.
Workshop Practice & Action Items
To minimize concentration gradients, it's important to ensure uniform heating and cooling of the weld. This can be done with shielding gases or special welding processes. With highly temperature-unstable alloys, careful control of heating and cooling times is essential to avoid gradients.