Observations of changing fine structure in nanoscale EELS analysis of grain boundaries in stainless steels

Abstract

SUMMARYIncreasingly sophisticated demands placed on metals in the modern world have stimulated the use of tailor‐designed multi‐component alloys in many applications. Solute segregation, whether due to thermodynamic or non‐equilibrium processes, can dramatically alter the alloy composition near the grain boundary leading to drastic (and often detrimental) change in the properties of the alloy. The solute segregation profile is often a nearly singular function centred at the boundary, leading to great difficulty in analysis. The traditional method of depth profiling using Auger electron spectroscopy can only examine fractured surfaces and, because of limited spatial resolution, yields laterally averaged information. Recent improvement in the efficiency of electron‐microscope‐based electron energy‐loss spectroscopy has allowed a new high‐resolution approach in analysing the chemical and electronic properties of buried interfaces on a nanometer scale, i.e. we can study the complicated details of the alloy boundary itself. As an example, we will present the result of a study on stainless‐steel alloys used in the U.K. nuclear industry. The effect of irradiation on the structure of the alloy boundary is investigated. The nanoscale change in the chemical state of the alloying element at the grain boundary is observed for the first time in situ. The result can be potentially utilized to predict the corrosion‐resistance of the stainless steels.