純鐵小顆粒中的馬氏體相變
doi: 10.13374/j.issn1001-053x.1983.03.002
The Martensitic Transformation in Small Pure Iron Particles
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摘要: 當使用Ar+離子轟擊Cu-Fe合金薄膜試樣時,試樣中所存在的fcc亞穩狀態小鐵顆粒將發生馬氏體相變。定量立體電子顯微術的試驗結果表明:(a)馬氏體相交只限于在那些臨近試樣表面的小鐵顆粒內發生(b)盡管試樣的下表面不受Ar+離子的轟擊,也浸有幅射缺陷存在,但靠近下表面的小鐵顆粒仍然發生了馬氏體相變。可見,由于離子轟擊所引起的彈性表面波(Rayleigh Waves)是促成相變產生的原因。
受轟擊試樣的高分辨率晶格象表明上述的馬氏體相變又可分為二種類型:部份型轉變(Partially transformation)和整體型轉變(fully transformation)。其中,整體型轉變后的小鐵顆粒具有孿晶型組織,使用一般的透射電子顯微鏡也能看到;而部份型轉變后的小顆粒里則含有很薄的馬氏體片層,這些馬氏體片平行于未轉變區內奧氏體的致密排列面。整體型轉變只是在試樣表面處的小鐵顆粒內發生,原因可能是這里的小鐵顆粒有著足夠的自由表面。而部份型轉變則是在被銅基體完全包裹著的顆粒內發生。Abstract: When Thin foil Specimens of Copper-iron alloys Containing metastable fcc r-iron are bombarded with argon ions the precipitates are induced to transform martensitically to bcc iron. Using stereo microscopy technigues it was established that (1) transformation is limited to those particles near the Surfaces of the Specimen, (2) Particles on the non-irradiated Surface Can transform even when the irradiation damage does not extend so far. The transformation is therefore thought to be initiated by elastic Surface (Rayleigh) waves Set up by the ion impacts.
High resolution lattice fringe electron microscopy of bombarded Specimens Showed that both partially transformed and fully transformed Precipitates exist. The fully transformed precipitates have the twin structure already Seen with Conventiond TEM, but the partially transformed precipitates Contain Very thin laths or plates of martensite Parallel to the Close-packed planes of the untransformed fcc regions. Complete transformation is thought to be associated with partides that have a substantial amount of free Surface, while Partial transformation is probably Characteristic of particles that are fully constrained by the copper matrix. -
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