Webel Johannes, Weber Louis, Vardo Emina, Britz Dominik, Kraus Tobias, Mücklich Frank
Institute for Functional Materials, University of Saarland, Campus D3 3, 66123 Saarbrücken, Germany; MECS - Materials Engineering Center Saarland, Campus D3 3 66123 Saarbrücken, Germany.
INM - Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany.
Ultramicroscopy. 2021 Apr;223:113219. doi: 10.1016/j.ultramic.2021.113219. Epub 2021 Jan 30.
Atom probe tomography (APT) provides sub-nm resolution in the analysis of complex industrial steels. It can resolve the carbonitride precipitates in Nb-Ti microalloyed high-strength low-alloy (HSLA) steels that strongly affect material performance and illuminate the complex precipitation sequence before and during the thermo-mechanical controlled process (TMCP). However, the precipitate concentration is low in HSLA steels during austenite conditioning, especially at temperatures > 850 °C, so that the probability of detecting precipitates via APT is below 5%. Here, we demonstrate two encapsulation-based approaches that increase the precipitate concentration in the APT sample volume sufficiently to enable the analysis of sparse precipitates. The first method is based on metallographic etching and direct targeting of precipitates in the steel. A focused ion beam was used to mark precipitation sites. Encapsulation with nickel-phosphorus (Ni-P) enabled localized APT and increased the yield by a factor of 10. The second method relies on the chemical extraction of precipitates and subsequent encapsulation in a silicon oxide (SiO) network at a very high particle density. Analysis of tips cut from the encapsulated particles increased the yield by a factor of >15. We discuss and compare the spatial and chemical accuracy obtained in the analysis of pure Nb-, Ti- and mixed Nb-Ti carbonitrides.
原子探针层析成像（APT）在复杂工业钢的分析中提供亚纳米级分辨率。它能够分辨出铌钛微合金化高强度低合金（HSLA）钢中的碳氮化物析出相，这些析出相对材料性能有强烈影响，并能阐明热机械控制过程（TMCP）之前和期间复杂的析出顺序。然而，在奥氏体调质过程中，HSLA钢中的析出相浓度较低，尤其是在温度>850 °C时，因此通过APT检测析出相的概率低于5%。在此，我们展示了两种基于封装的方法，这些方法可充分提高APT样品体积中的析出相浓度，从而能够分析稀疏的析出相。第一种方法基于金相蚀刻并直接针对钢中的析出相。使用聚焦离子束标记析出位点。用镍磷（Ni-P）进行封装可实现局部APT，并使产率提高了10倍。第二种方法依赖于析出相的化学萃取，随后以非常高的颗粒密度封装在氧化硅（SiO）网络中。对从封装颗粒上切割下来的针尖进行分析，使产率提高了>15倍。我们讨论并比较了在分析纯铌、钛以及混合铌钛碳氮化物时获得的空间和化学精度。
