Revisiting the applications of the extraction replica sample preparation technique for analysis of precipitates in engineering alloys

The extraction replica technique is a useful sample preparation method to fabricate transmission electron microscopy samples for subsequent studies of small particles, such as precipitates, in different types of alloys. With other sample preparation methods, such as thin foil fabrication, the surrounding matrix might influence compositional or crystallographic analysis in the TEM. The extraction replica technique omits that problem, as the precipitates are extracted onto a thin, amorphous film (most commonly carbon) and the influence of the matrix is thus eliminated. The replica can be produced in a direct manner, by a two stage-method or in certain cases by the oxide replica method. A variety of precipitates from common engineering alloys including carbides, nitrides, oxides and various intermetallic phases in steels, nickel-, zirconium-, aluminium-, copper-, and magnesium-based alloys, can be extracted and the techniques are summarized in this work. The choice of etchant is crucial for the end result, as is also showcased experimentally in this work. Furthermore, the direct replica and two-stage replica method are directly compared with each other by new experiments on a low alloyed steel and a zirconium alloy. There are indications that the direct method has a greater particle extraction efficiency of smaller particles compared to the two-stage method. Moreover, the direct method also facilitates the analysis of other features, such as grain boundaries, in special cases.

Automated summary

The extraction replica technique is a useful method for preparing transmission electron microscopy samples, which eliminates the influence of the surrounding matrix on compositional or crystallographic analysis. This study summarizes the techniques for extracting various precipitates from different alloys and compares the efficiency of the direct replica method with the two-stage replica method. The results indicate that the direct method has a higher particle extraction efficiency for smaller particles and also facilitates the analysis of other features in certain cases.