Dendritic crystal growth
Dendritic crystal growth forms in undercooled melts due to concentration gradients and directed heat dissipation. It leads to a tree-like branched solidification structure that determines the initial structure.
Physical-Chemical Mechanism of Action
Dendritic crystal growth occurs when concentration gradients and directed heat dissipation are present in a liquid metal melt. The melt constituents condense at cooler spots into crystals that spread like tree roots. This process is influenced by the different diffusion rates of atoms and ions in the melt.
Metallurgical Relevance & Welding Risks
Dendrites can lead to fine, crack-prone structures, especially when they form in cooler areas of the weld. This can impair toughness and mechanical properties of the metal. Excessive dendrite growth can also lead to hot cracks and welding defects, especially at high stresses or with materials of low toughness.
Workshop Practice & Instructions
To minimize dendrite growth, it is important to carefully adjust the cooling rate during the welding process. This can be achieved by optimal arc direction and intensity, as well as by using shielding gases. Some metals require special welding parameters to avoid dendrite growth. It is also important to precisely control the melting time and cooling duration to produce a homogeneous solidification structure.