CHALLENGES TO THE IMPLEMENTATION OF HIGH TEMPERATURE AND STRAIN INSTRUMENTATION FOR IN SITU TESTING IN THE SCANNING ELECTRON MICROSCOPE

Abstract

Failure  mechanisms  in  structural  materials  have  been  under  investigation  for  several  years.  Nowadays,  the  implementation  of sophisticated in situ electron microscopy tests is providing new insights in several fields of chemistry, physics, and materials science by allowing  direct  observation  of  a  wide  variety  of  phenomena  at  submicron  and  even  atomic  scale.  These  experiments  may  involve controlled temperature and atmosphere, mechanical loading, magnetic and/or electric field among other conditions that are imposed to the sample while its response or evolution is registered. A novel in situ high temperature-strain test into a Scanning Electron Microscope (SEM) makes possible the real-time observation of phenomena with resolution of 5 µm, providing qualitative and quantitative data. This setup was used to study the Grain Boundary Sliding (GBS)  mechanism and its effect on the high temperature cracking phenomenon known as Ductility-Dip Cracking (DDC). This methodology was applied to study the mechanical behavior of Ni-base filler metal alloys ERNiCrFe-7 and ERNiCr-3, which were evaluated between 700 and 1000 ºC. The DDC susceptibility (threshold strain,  εmin) for both alloys  was  quantified.  The  εmin  of  ERNiCrFe-7  and  ERNiCr-3  alloys  was  7.5  %  and  16.5  %,  respectively,  confirming  the  better resistance of ERNiCr-3 to DDC.