Volume 7, Issue 3 (March 2010)
Hydrogen Embrittlement in Metallic Amorphous Alloys: An Overview
In hydrogen-related energy technologies, the selection of materials is critical since hydrogen can modify the initial microstructure and induce damage that could result in the reduction of mechanical properties and embrittlement. In this context, metallic amorphous alloys are viable candidates due to their high hydrogen solubility. Earlier studies demonstrated the positive interaction of hydrogen with amorphous alloys. However, similar to crystalline metals, embrittlement by hydrogen was also reported. In order to clarify the role of hydrogen in this class of alloys, we present an overview on the hydrogen interaction and embrittlement, encompassing results from published studies and from our own investigations on several Zr-, Ni-, and Ti-based amorphous alloy systems. The importance of the constituent elements and composition in determining the structure, hydrogenation kinetics, and hydrogen absorption capacity were brought out. The resistance to embrittlement varies upon the alloy system, constituent elements, and atomic packing of the amorphous alloy. In metalloid-free amorphous alloys, the bending ductility and tensile fracture strength of thin ribbons could be preserved up to a critical concentration beyond which hydrogen degradation occurs. The value of this critical concentration was found to vary from a few percent to about 45 at. % H. The mechanism of embrittlement induced by hydrogen was identified from the correlation of the observed changes in structural, thermal, and mechanical properties. It was found that hydrogen plays a prime role in altering the local atomic structure by reordering the nearest neighbor atomic configuration. The structural dilatation so produced was found to be the source of hydrogen-induced failure in these amorphous alloys. Also a “hydrogen concentration versus dilatation” map has been proposed, which would serve as a tool to predict the hydrogen-induced ductile-to-brittle transition in these alloys.