An Overview of the Hydrogen Embrittlement of Iron Aluminides

Abstract

New technologies often lead to the development of new materials with better mechanical, thermal and chemical behaviors. Recently, transition metals (TM), or aluminide intermetallics, for example TiAl, NiAl, FeAl, and Fe3Al, have attracted considerable interest due to their unique properties such as high melting points, enhanced corrosion resistance, relatively low density, and utility as soft magnetic materials [Baker and Munroe (1997); Noebe et al. (1993); Sundararajan et al. (1995)]. The main problem of these alloys, however, is their limited ductility at ambient temperature especially in presence of water vapor, and limited strength and creep resistance at high temperatures. In order to evaluate the reasons of the embrittlement in iron aluminides at room temperature, the brand new method of in-situ nanoindentation is used for the Fe3Al intermetallic with a DO3 structure.The results of nanoindentation, under cathodic and anodic charging, show the influence of hydrogen on the reduction of Young's moduli of alloys in agreement with the hydrogen-enhanced decohesion (HEDE) model; whereas measurements of the pop-in load indicate a drastic decrease after cathodic charging in samples with low Cr content. This is thought to be due to the decrease of the energy needed for homogeneous dislocation nucleation (HDN) in the dislocation free samples based on the Defect Acting Agents (defactants) concept. Additionally, the effect of hydrogen on hardness or the mobility of dislocations was noted. This paper explains in detail some aspects that are necessary for the performance of in-situ nanoindentation.