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- A dendrite in metallurgy is a characteristic tree-like structure of crystals growing as molten metal solidifies, the shape produced by faster growth along energetically favourable crystallographic directions. This dendritic growth has large consequences in regard to material properties. Dendrites form in unary (one-component) systems as well as multi-component systems. The requirement is that the liquid (the molten material) be undercooled, aka supercooled, below the freezing point of the solid. Initially, a spherical solid nucleus grows in the undercooled melt. As the sphere grows, the spherical morphology becomes unstable and its shape becomes perturbed. The solid shape begins to express the preferred growth directions of the crystal. This growth direction may be due to anisotropy in the surface energy of the solid–liquid interface, or to the ease of attachment of atoms to the interface on different crystallographic planes, or both (for an example of the latter, see hopper crystal). In metallic systems, interface attachment kinetics is usually negligible (for non-negligible cases, see dendrite (crystal)). In metallic systems, the solid then attempts to minimize the area of those surfaces with the highest surface energy. The dendrite thus exhibits a sharper and sharper tip as it grows. If the anisotropy is large enough, the dendrite may present a faceted morphology. The microstructural length scale is determined by the interplay or balance between the surface energy and the temperature gradient (which drives the heat/solute diffusion) in the liquid at the interface. As solidification proceeds, an increasing number of atoms lose their kinetic energy, making the process exothermic. For a pure material, latent heat is released at the solid–liquid interface so that the temperature remains constant until the melt has completely solidified. The growth rate of the resultant crystalline substance will depend on how fast this latent heat can be conducted away. A dendrite growing in an undercooled melt can be approximated as a parabolic needle-like crystal that grows in a shape-preserving manner at constant velocity. Nucleation and growth determine the grain size in equiaxed solidification while the competition between adjacent dendrites decides the primary spacing in columnar growth. Generally, if the melt is cooled slowly, nucleation of new crystals will be less than at large undercooling. The dendritic growth will result in dendrites of a large size. Conversely, a rapid cooling cycle with a large undercooling will increase the number of nuclei and thus reduce the size of the resulting dendrites (and often lead to small grains). Smaller dendrites generally lead to higher ductility of the product. One application where dendritic growth and resulting material properties can be seen is the process of welding. The dendrites are also common in cast products, where they may become visible by etching of a polished specimen. As dendrites develop further into the liquid metal, they get hotter because they continue to extract heat. If they get too hot, they will remelt. This remelting of the dendrites is called recalescence. Dendrites usually form under non-equilibrium conditions. An application of dendritic growth in directional solidification is gas turbine engine blades which are used at high temperatures and must handle high stresses along the major axes. At high temperatures, grain boundaries are weaker than grains. In order to minimize the effect on properties, grain boundaries are aligned parallel to the dendrites. The first alloy used in this application was a nickel-based alloy (MAR M-200) with 12.5% tungsten, which accumulated in the dendrites during solidification. This resulted in blades with high strength and creep resistance extending along the length of the casting, giving improved properties compared to the traditionally-cast equivalent. (en)
- In metallurgia, una dendrite è una struttura ad albero caratteristica di cristalli formatisi nella solidificazione di metalli e leghe metalliche. Tale forma è legata alla rapida crescita del cristallo lungo direzioni cristallografiche energeticamente favorevoli e va ad influire fortemente sulle proprietà del materiale. Solitamente questo tipo di struttura si ha in presenza di leghe metalliche multifase che devono essere raffreddate a temperature molto al di sotto del punto di solidificazione. Infatti, con raffreddamenti rapidi la solidificazione può essere talmente rapida che la composizione della lega che solidifica può essere diversa dalla concentrazione complessiva del fluido di partenza. Differenti concentrazioni implicano differenti punti di fusione.L'aumento di concentrazione del metallo con punto di fusione più basso fa sì che il punto di solidificazione della soluzione ancora liquida diminuisca rendendo più difficile l'ulteriore solidificazione. In questo modo la solidificazione prosegue lungo le zone più sporgenti del fronte dove si ha un migliore smaltimento del calore causando la struttura dendritica. Il raffreddamento rapido produce una maggior nucleazione di nuovi cristalli, in questo modo le dendriti risultano essere di dimensioni ridotte perché la loro crescita è ostacolata dall'accrescersi di quelle limitrofe. Mentre un raffreddamento più lento porta a dendriti di dimensioni maggiori. Dendriti di piccole dimensioni sono caratteristiche di materiali duttili. Inoltre riducono di molto la porosità del materiale, creando anche cristalli ben incastrati e resistenti al creep. La crescita delle dendriti e le conseguenti proprietà del materiale che ne derivano sono facilmente visibili nel processo di saldatura. Anche nei pezzi ottenuti per fusione è possibile vedere le dendriti tramite sezionamento e lucidatura della sezione. (it)
- 金属樹（きんぞくじゅ）とは、樹枝状に析出した金属の結晶のこと。 ある金属単体(MA)を、その金属よりイオン化傾向が小さい金属イオン(MBn+)を含む溶液に浸すと、nMA+mMBn+→nMAm++mMBの反応により、金属単体MAの表面に金属MBが樹枝状に析出する。 析出する金属によって〇樹と呼ばれる。 高等学校化学Ⅰでイオン化傾向の学習にしばしばこの金属樹の生成実験が用いられる。 <例：銅イオンに亜鉛を入れた場合> Zn→Zn2+＋2e- Cu2++2e-→Cu 上記の例では亜鉛が溶け、銅が析出する。 (ja)
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- 金属樹（きんぞくじゅ）とは、樹枝状に析出した金属の結晶のこと。 ある金属単体(MA)を、その金属よりイオン化傾向が小さい金属イオン(MBn+)を含む溶液に浸すと、nMA+mMBn+→nMAm++mMBの反応により、金属単体MAの表面に金属MBが樹枝状に析出する。 析出する金属によって〇樹と呼ばれる。 高等学校化学Ⅰでイオン化傾向の学習にしばしばこの金属樹の生成実験が用いられる。 <例：銅イオンに亜鉛を入れた場合> Zn→Zn2+＋2e- Cu2++2e-→Cu 上記の例では亜鉛が溶け、銅が析出する。 (ja)
- A dendrite in metallurgy is a characteristic tree-like structure of crystals growing as molten metal solidifies, the shape produced by faster growth along energetically favourable crystallographic directions. This dendritic growth has large consequences in regard to material properties. Smaller dendrites generally lead to higher ductility of the product. One application where dendritic growth and resulting material properties can be seen is the process of welding. The dendrites are also common in cast products, where they may become visible by etching of a polished specimen. (en)
- In metallurgia, una dendrite è una struttura ad albero caratteristica di cristalli formatisi nella solidificazione di metalli e leghe metalliche. Tale forma è legata alla rapida crescita del cristallo lungo direzioni cristallografiche energeticamente favorevoli e va ad influire fortemente sulle proprietà del materiale. Solitamente questo tipo di struttura si ha in presenza di leghe metalliche multifase che devono essere raffreddate a temperature molto al di sotto del punto di solidificazione. (it)
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- Dendrite (metal) (en)
- Dendrite (metallurgia) (it)
- 金属樹 (ja)
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