Equal Channel Angular Pressing (ECAP): Part One

概要:

ECAP is one of the most commonly employed severe plastic deformation process to drive nano or ultrafine grained microstructure at low homologous temperatures.
ECAP is most suitable for materials used in industrial scale application, the process works by introducing a large shear strain by repeated extrusion steps.

Among the different procedures in use for the production of nanostructured materials, only severe plastic deformation (SPD) processes exhibit a potential for producing relatively large samples suitable for industrial applications. Severe plastic deformation is metal forming processes in which an ultra-large plastic strain is introduced into a bulk metal in order to create nano- or ultrafine- grained structure at low homologous temperatures (typically below 0.3 of the melting temperature).

In order to obtain the smallest microstructural sizes plastic strains of more than 600 to 800% are necessary. Such high degrees of plastic deformation are possible because one sample can be subjected several times to SPD in order to accumulate the total amount of plastic strain.

Equal Channel Angular Pressing (ECAP) is one of the most employed methods of Severe Plastic Deformation (SPD); it can be applied to a variety of metals and alloys in order to obtain ultrafine grains and good mechanical and physical properties. The recent literature shows intense and growing interest in some fundamental aspects of SPD techniques, viz., the generation of ultrafine grains and the mechanisms underlying the high levels of strength observed. Aluminum and its alloys, Cu and Ti are the most employed materials in SPD-ECAP studies, with Ti being seriously considered for orthopedic implants.

The current trend in research and development of Ti alloys for biomedical applications is the development of alloys with low elastic modulus, free of toxic and allergic elements such as Al and V, while maintaining the already good mechanical properties of Ti-6Al-4V.

For producing large size stock that is suitable for industrial application, the equal channel angular pressing (ECAP) process is most suitable. This process involves introducing large shear strain in the work piece by pushing it through a die that consists of two channels with the same cross sectional shape that meet at an angle to each other. Since the cross-sections of the two channels are the same, the extruded product can be re-inserted into the entrance channel and pushed again through the die. Repeated extrusion through the ECAP die accumulates sufficient strain to breakdown the microstructure and produce ultra-fine grain size.

The principle of ECAP is illustrated schematically in Figure 1. For the die shown in Figure 1, the internal channel is bent through an abrupt angle, Φ, and there is an additional angle, Ψ, which represents the outer arc of curvature where the two channels intersect. The sample, in the form of a rod or bar, is machined to fit within channel and the die is placed in some form of fuss so that the sample can be pressed through the die using a plunger.

The nature of the imposed deformation is simple shear which occurs as the billet passes through the die. The retention of the same cross-sectional area when processing by ECAP, despite the introduction of very large strains, is the important characteristic of SPD processing and it is this characteristic which distinguishes this type of processing from conventional metal-working operations such as rolling, extrusion and drawing. Since the cross-sectional area remains unchanged, the same billet may be pressed repetitively to attain exceptionally high strain.



Figure 1: Principle of ECAP

ナレッジベース検索

検索したい語句を入力:

検索方法

全文一致
キーワード

前方一致
要約

Total Materia Extended Range(拡張版)には数千種の金属合金塑性域、熱処理、加工温度等における計算に必要な応力‐歪み曲線が収録されております。さまざまな歪み速度に応じた真応力、エンジニアリング応力曲線も表示されます。

簡単でしかも数秒以内でデータベースの応力‐歪み曲線を探せます。

検索対象の材料を入力して下さい。材料入力のフィールドで国/規格を指定し検索を絞る事ができます。


対象材料を選んでから応力‐歪み曲線のリンクをクリックするとデータが御覧になれます。御覧になれる応力‐歪みデータの数はリンクわきのカッコ内に表示されております。


Total Materiaデータベースの応力‐歪み曲線は規格それぞれに中立的なものでサブグループのどれが適切なリンクをクリックしてデータを見て下さい。


他の加工温度に対する応力‐歪み曲線をみることができます。

まず、決められた温度範囲内で新たな温度を’ 温度入力’ のフィールドに入力するだけで構いません。

次に計算ボタンをクリックすると新しい曲線が表示され表の数字が入力された温度に応じて表示されます。 250°Cにて入力した場合の例を御覧下さい。


Total Materiaデータベースをあなたにテスト評価を頂くために15万人以上の方が登録されている無料お試しコミュニティ-へ御招待致します。