Extraction Replicas of Common Engineering Alloys for Analysis of Small Precipitates

Sammanfattning: Characterization of small precipitates is important for development of new alloys. One inherent  difficulty  in  characterisation  of  small  precipitates  with  electron microscopy techniques  while  the  particles  are  embedded  in  the  matrix,  is  that the surrounding bulk material will contribute to the analysed signal- limiting, for example, the quantification of the composition of particles.  In order to avoid the matrix contribution, the extraction replica technique was developed in the 1950's. Extraction replicas are made by extracting only the particles from a material onto a thin film for further analysis by scanning or transmission electron microscopy. Different types of particles can be examined by this technique, including various carbides, nitrides, oxides and borides, as well as many intermetallic phases.  In this work, direct replication techniques were compared to two-stage replication for low-alloyed steel, concluding that both are suitable for qualitative analysis, but direct replication is preferred for quantitative analysis.  Successful replication of the zirconium-based Zirlo and the stainless steel 254 SMO was performed, where the precipitated phases were isolated and the composition quantified.   Particle extraction was successful also for the zirconium-based Zircaloy-2 and two types of  aluminium  alloys,  but  no  quantification of  composition  could  be  made  due to different problems associated with etching of each alloy, showing that properchoice of etchant is crucial for the quality of the replicas.