Concentration gradient
Concentration gradients are local changes in the alloy content of a material. They occur during diffusion processes and affect phase transformation.
Physical-Chemical Working Mechanism
Concentration gradients arise from the uneven exchange of atoms or ions between different areas of a material. This exchange is driven by diffusion, where atoms or ions move from high-concentration to low-concentration regions.
Metallurgical Relevance & Risks in Welding
Concentration gradients can cause local stresses and cracking, especially during phase transformation. These stresses result from different expansion rates of phases. In the weld, this can lead to hot cracks or 'zinc' (probably 'zinc' is a typo, but we keep as is) especially at high temperatures and long cooling times.
Workshop Practice & Actions
To minimize concentration gradients, it's important to control the cooling rate of the weld. Too fast cooling can lead to brittle phase transformation and cracks (t8/5 < 5 s). Too slow cooling can cause coarse grain and 'zinc' (t8/5 > 25 s). For critical components, consider continuous cooling with water spray or similar.