Dislocation - Teni

In a crystal, a part where the atomic arrangement is partially deviated from the normal one is called a defect, and when this defect is linear, it is called a dislocation. The vector of the deviation from the normal arrangement is called the Burgers vector, which indicates the size and nature of the dislocation. When the Burgers vector is perpendicular to the defect line (dislocation line), the dislocation is called an edge dislocation, and when it is parallel, it is called a screw dislocation. In a crystal, it is in an intermediate state between these two, with both edge and screw components. Almost all plastic deformation of a crystal is the result of the movement of dislocations, and by using dislocations, it is possible to theoretically study deformation resistance, deformability, work hardening, etc. The concentration of dislocations is expressed as the total length per unit volume, and in the case of metal crystals, a considerable amount is generated from the time of melting and solidification, and is reduced by annealing. However, 10 ^-6 cm cm ^-3 of dislocations still remain. When stress is applied to a crystal, dislocations move, but at the same time, they increase to 10 ¹³ cm cm ^-3 due to the Frank-Reid mechanism, etc. Whereas edge dislocations can only move in specific slip planes, screw dislocations have no such restrictions. However, when they intersect with other dislocations, an edge is created, and due to the Burgers vector relationship, it becomes more difficult for the dislocation to move. Since dislocations can move much easier than the slip of a perfect crystal, a material without dislocations (or more accurately, without mobile dislocations) should be very strong. In fact, whiskers are such a material, where mobile dislocations are eliminated by carefully arranging very fine crystals, and in Cu, an increase in yield strength of nearly 3000 times is observed.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

結晶体のなかで原子の配列が部分的に正規のものからずれている部分を欠陥とよぶが，この欠陥が線状をなしているときこれを転位という．正規の配列からのずれのベクトルをバーガースベクトルとよび，これは転位の大きさと性質を表す．バーガースベクトルが欠陥線(転位線)と直角のとき，この転位を刃状転位，平行のとき，らせん転位という．結晶中ではこれらの中間の状態にあり，刃状成分とらせん成分をもつ．結晶のほとんどすべての塑性変形が転位の移動の結果であり，転位を用いることで変形抵抗，変形能，加工硬化などを理論的に検討できる．転位の濃度は単位体積中の延べ長さで表すが，金属結晶の場合，溶解凝固時からかなりの量が発生し，焼なましによって減少する．しかし，なお 10^－6 cm cm^－3 の転位が残る．結晶に応力が加わると転位の移動が起こるが，同時にフランクリードの機構などにより 10¹³ cm cm^－3 まで増殖する．刃状転位は特定すべり面中のみを移動できるのに対して，らせん転位にはこのような制約はない．しかし，ほかの転位と交差すると刃状部分ができ，そのバーガースベクトルの関係により動きにくくなる．転位の移動は完全結晶のすべりよりはるかに容易であるため，転位のない(正確には可動転位のない)物質は非常に強いはずである．事実，ひげ結晶はこのような材料で，非常に細かい結晶を注意深く調整することにより可動転位をなくしているが，Cuでは3000倍近い降伏強さの上昇がみられる．

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