Segregation - Henseki (English spelling) Segregation

Japanese: 偏析 - へんせき（英語表記）segregation

The solute concentration becomes inhomogeneous inside the solidified alloy. It can be divided into the following categories based on the phenomenon and cause. (1) Normal segregation Normally, the solid components that crystallize first during the solidification of an alloy are different from the components of the liquid. Therefore, if solidification proceeds from the part in contact with the mold toward the inside, a solute concentration distribution parallel to that direction is formed. This is normal segregation, which depends on the type and concentration of the alloy components, the cooling rate, etc., and generally deteriorates the material. Sulfur segregation in steel ingots (→sulfur printing) is a well-known problem that causes red brittleness. (2) Reverse segregation When the outer periphery of the solid solid solidifies first, the columnar crystals shrink when cooled, and if gaps are formed between the crystal grains, the inner solution with a high impurity concentration is absorbed into them, resulting in a higher impurity concentration at the periphery than at the inside. This is reverse segregation, which often occurs in aluminum bronze and bronze. (3) Gravitational segregation When the mutual solubility of the liquid phases is low, the components with a higher specific gravity sink to the bottom and solidify. Gravitational segregation is common in high-concentration non-ferrous alloys such as bronze, lead bronze, and aluminum bronze. (4) Microsegregation When considering the solidification of a single crystal grain, dendrites form first, and the solidification proceeds as the solution fills the spaces between the dendrites (→ polycrystalline structure). However, since the concentration of the solution between the dendrites and the branches is usually different, segregation occurs at a microscopic level even within a single crystal grain. This is also called microsegregation or intragranular segregation. It is particularly likely to occur in solid solution alloys with a large difference in the melting points of the components, such as cupronickel (→ copper-nickel alloy).

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

合金の凝固固体の内部で，溶質濃度が不均質になること。現象と原因により次のように分ける。 (1) 正常偏析　通常，合金の凝固時において最初に晶出する固体の成分は液体の成分と異なる。したがって，鋳型に接する部分から内部に向って凝固が進行すれば，その方向に平行な溶質濃度分布が形成される。これが正常偏析で，合金成分の種類，濃度，冷却速度などに依存し，一般に材質を劣化させる。鋼塊の硫黄の偏析 (→硫黄印刷 ) はよく知られた難物で，赤熱脆性の原因となる。 (2) 逆偏析　凝固固体の外周部が先に凝固する結果，柱状晶が冷却により収縮し，結晶粒間にすきまができると不純物濃度の高い内部溶体がそこに吸込まれ，結果的に内部より外辺のほうが不純物濃度が高くなることがある。これが逆偏析で，アルミ青銅，青銅にしばしば起る。 (3) 重力偏析　液相の相互溶解度の低い場合は，比重の大きいほうの成分が底に多く沈んで凝固する。この重力偏析は青銅，鉛青銅，アルミ青銅など，高濃度の非鉄合金に多い。 (4) ミクロ偏析　1個の結晶粒の凝固を考えると，まず樹枝晶ができてその枝間を溶体が埋めつつ凝固が進行するが (→多結晶組織 ) ，通常，樹枝晶と枝間の溶体の濃度は異なるので，結果的に1結晶粒内でさえ顕微鏡的レベルで偏析が生じている。これをミクロ偏析，または粒内偏析ともいう。特に成分の融点の温度差の大きい固溶体合金に起りやすく，白銅 (→銅ニッケル合金 ) などにみられる。

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