Controlled environment transmission electron microscopy

Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum

Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.

A (S)TEM gas cell holder with localized laser heating for in situ experiments

The advent of aberration correction for transmission electron microscopy has transformed atomic resolution imaging into a nearly routine technique for structural analysis. Now an emerging frontier in electron microscopy is the development of in situ capabilities to observe reactions at atomic resolution in real time and within realistic environments. Here we present a new in situ gas cell holder that is designed for compatibility with a wide variety of sample type (i.e., dimpled 3-mm discs, standard mesh grids, various types of focused ion beam lamellae attached to half grids). Its capabilities include localized heating and precise control of the gas pressure and composition while simultaneously allowing atomic resolution imaging at ambient pressure. The results show that 0.25-nm lattice fringes are directly visible for nanoparticles imaged at ambient pressure with gas path lengths up to 20 μm. Additionally, we quantitatively demonstrate that while the attainable contrast and resolution decrease with increasing pressure and gas path length, resolutions better than 0.2 nm should be accessible at ambient pressure with gas path lengths less than the 15 μm utilized for these experiments.

Kinetic measurements from in situ TEM observations

Environmental transmission or scanning transmission electron microscope is ideally suited to observe gas solid interactions at nanoscale. It is shown that the time and temperature resolved data, obtained from in situ observations, can be used to obtain reaction rates and understand the kinetics of the processes. Low or high magnification images provide the change in length, area or volume with time at constant temperature and pressure conditions during nitridation of Cu-Cr thin films, deposition of Au particles, growth of Si nanowire and carbon nanotubes. Effect of electron beam is estimated by making observations with and without constant electron beam exposure. Quantitative electron energy loss spectroscopy is employed to measure the reduction rate of Ce(+4) in pure ceria, mixed oxides (ceria-zirconia) and catalyst (Rh-ceria-zirconia) powders.