Microstructural Changes during Annealing of Work-Hardened Mechanically Milled Metallic Powders (Overview)

Yuuji Kimura, Setsuo Takaki

Research output: Contribution to journalArticle

88 Citations (Scopus)

Abstract

The behavior of work-hardening which occurs during mechanical milling (MM) treatment in metallic powders, and the process of recovery and recrystallization which occurs during annealing in the MM powders were over-viewed showing the results obtained by the authors using an industrial pure iron powder. Through the MM treatment, metallic powders stores extremely large strain energy, and this results in the marked work-hardening and the formation of a fine structure with nanocrystalline grains. In the case of iron, the hardness of powder can be increased to DPH1024 in practice, and the crystalline grain size is to be reduced to the limiting value of 3.4 nm in principle. The polycrystallization of dislocation cells and subgrains also proceeds on the grain refining process. When the MM powders are annealed, the powders undergo different microstructural changes depending on the degree of work-hardening subjected by the prior MM treatment. In the case that powders are not work-hardened so much, usual recovery and recrystallization occur with raising annealing temperature. However, when powders are extremely work-hardened to the level where crystalline grain size nearly reaches the limiting value, only the process of normal grain growth occurs during annealing and this results in the softening of MM powders. Under the usual milling conditions, the degree of work-hardening of powders is in the middle stage, so that both of the above two processes are possible with overlapping each other. It was confirmed in both of MM iron powders and annealed iron powders that the relation between hardness and polycrystalline grain size gives a good fit to the Hall-Petch relationship in a wide grain size range up to 6 nm. In addition, some examples are introduced at the end, in order to excellent properties of materials produced from MM powders.

Original languageEnglish
Pages (from-to)289-296
Number of pages8
JournalMaterials Transactions, JIM
Volume36
Issue number2
DOIs
Publication statusPublished - Jan 1 1995

Fingerprint

Powders
Annealing
annealing
Strain hardening
work hardening
Iron powder
grain size
iron
Hardness
Crystalline materials
Recovery
hardness
recovery
Strain energy
Grain growth
Refining
refining
Iron
softening
fine structure

All Science Journal Classification (ASJC) codes

  • Engineering(all)

Cite this

Microstructural Changes during Annealing of Work-Hardened Mechanically Milled Metallic Powders (Overview). / Kimura, Yuuji; Takaki, Setsuo.

In: Materials Transactions, JIM, Vol. 36, No. 2, 01.01.1995, p. 289-296.

Research output: Contribution to journalArticle

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