Helium ion microscopy and energy selective scanning electron microscopy – two advanced microscopy techniques with complementary applications

Both scanning electron microscopes (SEM) and helium ion microscopes (HeIM) are based on the same principle of a charged particle beam scanning across the surface and generating secondary electrons (SEs) to form images. However, there is a pronounced difference in the energy spectra of the emitted secondary electrons emitted as result of electron or helium ion impact. We have previously presented evidence that this also translates to differences in the information depth through the analysis of dopant contrast in doped silicon structures in both SEM and HeIM. Here, it is now shown how secondary electron emission spectra (SES) and their relation to depth of origin of SE can be experimentally exploited through the use of energy filtering (EF) in low voltage SEM (LV-SEM) to access bulk information from surfaces covered by damage or contamination layers. From the current understanding of the SES in HeIM it is not expected that EF will be as effective in HeIM but an alternative that can be used for some materials to access bulk information is presented

Investigation of microstructural evolution and creep rupture behaviour of 9% Cr MarBN steel welds

The weldments made from the 9-12% Cr tempered martensitic steel are associated with a complex microstructure arising from complicated thermal histories of the fusion and heat affected zones. The complicated microstructural and micro-mechanical states in these critical regions provide a challenge for the determination of creep failure mechanisms. Based on detailed metallographic examination, the microstructural distribution in the heat affected zone of the welds constructed using a recently developed 9% Cr MarBN steel, IBN-1, has been identified and classified into Equiaxed Zone (EZ), Duplex Zone (DZ) and Over-tempered Zone (OZ). Cross-weld testing performed at 650°C has revealed a significant reduction in creep life as compared to bulk material. Creep rupture has been shown to occur in the parent metal region with a ductile manner at a high stress, whereas creep rupture initiates in the DZ region in an intergranular manner at a low stress. Detailed metallographic investigation has further revealed a higher damage susceptibility in the regions along the pre-existing Prior Austenite Grain Boundaries (PAGBs). The diffusional reaustenitisation of local microstructure along the PAGBs leads to a lower strength of matrix in combination with a lack of intergranular precipitates as compared to the surrounding microstructure formed after displacive reaustenitisation

The Effect of Surface Preparation on the Precipitation of Sigma During High Temperature Exposure of S32205 Duplex Stainless Steel

This is an Open Access Article. It is published by Springer under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/Although the formation of sigma phase in duplex stainless steels is reasonably well documented, the effect of surface finish on its formation rate in surface regions has not been previously noted. The growth of the sigma phase precipitated in the subsurface region (to a maximum depth of 120 μm) has been quantified after heat treatment of S32205 duplex stainless steel at 1073 K (800˚C) and 1173 K (900˚C) after preparation to two surface finishes. Here, results are presented that show that there is a change in the rate of sigma phase formation in the surface region of the material, with a coarser surface finish leading to a greater depth of precipitation at a given time and temperature of heat treatment. The growth rate and morphology of the precipitated sigma has been examined and explored in conjunction with thermodynamic equilibrium phase calculations

Energy selective scanning electron microscopy to reduce the effect of contamination layers on scanning electron microscope dopant mapping

We demonstrate that energy selective scanning electron microscopy can lead to substantial dopant contrast and resolution improvements (compared to standard SEM) when the energy selection is carried out based on Monte Carlo modelled secondary electron spectra in combination with detector transfer modelling