Amorphous precipitates in a crystalline matrix; precipitation of amorphous Si3N4 in α-Fe
Amorphous precipitates in a crystalline matrix; precipitation of amorphous Si3N4 in α-Fe
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结晶基体中的非晶态沉淀；α-Fe 中非晶态 Si3N4 的沉淀
DOI：
10.1016/s1359-6462(99)00143-8
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发表时间：
1999
影响因子：
6
通讯作者：
F. Tichelaar
中科院分区：
文献类型：
--
作者：
E. Mittemeijer;M. Biglari;A. Böttger;N. Pers;W. Sloof;F. Tichelaar
在实践中，由于相变而引起固体的微观结构变化，从而产生特定的、所需的性能。到目前为止，已经观察到在结晶过饱和固体中形成的沉淀颗粒，并假设其是结晶的。当然，应用“强力”，例如通过离子注入，可以导致结晶基质中的非晶区域/颗粒。从过饱和结晶固溶体中可能发展出非晶态沉淀颗粒是违反直觉的，因为非晶态的体能大于晶态的体能。据我们所知，这封信首次直接观察到沉淀初始阶段的非晶态沉淀颗粒。钢工件的渗氮用于改善机械和/或化学表面相关性能，如疲劳、摩擦和腐蚀性能。氮化时在钢基体中以氮化物形式沉淀的合金元素有助于其强化。渗氮过程中铁素体 (-Fe) 中常用合金元素如 Cr 和 Al 的影响已得到广泛研究 (1-6)。硅通常作为合金元素存在于钢中。硅对氮有很大的化学亲和力。因此，如果向含硅铁中添加氮，则预计会析出氮化硅。尽管氮化时样品的质量增加表明氮化物沉淀，但以前尚未以直接（微观）方式识别沉淀物的性质；在任何情况下，始终假设沉淀物是结晶 Si3N4 (7, 8)。本研究项目的重点是开发含硅 Fe 中氮化硅沉淀的动力学模型，或多或少与我们之前针对 CrN 和 AlN 沉淀所做的一样 (2, 5)。与我们过去的早期初步工作（8）相反，我们坚决致力于揭示氮化物的结构。令我们惊讶的是，我们发现沉淀物是无定形的、化学计量的 Si3N4。此处提供了这一发现的证据。此外，根据我们最近对界面能建模的工作 (9)，将建议
Microstructural changes in solids due to phase transformations are induced in practice to bring about specific, desired properties. Until now precipitate particles developing in crystalline supersaturated solids have been observed, and assumed, to be crystalline. Of course, application of “brute force,” eg by ion implantation, can lead to amorphous regions/particles in a crystalline matrix. A possible development of amorphous precipitate particles from a supersaturated crystalline solid solution is counter-intuitive as the bulk energy of the amorphous state is larger than that of the crystalline state. This letter presents, to our knowledge, the first direct observation of amorphous precipitate particles in an initial stage of precipitation.Nitriding of steel workpieces is employed to improve the mechanical and/or chemical surface dependent properties, as fatigue, tribological and corrosion properties. Alloying elements that can precipitate as nitrides in the steel matrix upon nitriding contribute to its strengthening. The effect of normally used alloying elements as Cr and Al in ferrite (-Fe) during nitriding has been investigated extensively (1–6). Silicon is often present as an alloying element in steel. Silicon has a large chemical affinity for nitrogen. Therefore one expects the precipitation of silicon nitride if nitrogen is added to silicon containing-Fe. Although the mass increase of the specimen upon nitriding suggests that nitrides precipitate, the nature of the precipitates has not been identified before in a direct (microscopical) way; in any case it has always been assumed that the precipitates are crystalline Si3N4 (7, 8). The present research project focused on the development of a kinetic model for the precipitation of silicon nitride in silicon containing-Fe, more or less as performed earlier by us for the precipitation of CrN and AlN (2, 5). In contrast with our earlier preliminary work from the past (8), a determined effort to reveal the structure of the nitrides was undertaken. To our surprise it was found that the precipitates were amorphous, stoichiometric Si3N4. The evidence for this finding is presented here. Further, on the basis of our recent work on the modelling of interface energies (9), it will be suggested