Effects of alloy stoichiometry on environmental embrittlement in Ll 2-ordered (Co,Fe) 3V alloys

Abstract

Recent studies have demonstrated that a large number of ordered intermetallics exhibit environmental embrittlement in air at ambient temperatures. The embrittlement involves the decomposition of water vapor at metal surface, resulting in the generation of atomic hydrogen that diffuses into the alloys and causes brittle intergranular fracture. The authors' recent studies have shown that Ll[sub 2]-ordered (Co, Fe)[sub 3]V alloys containing 25 at. % V exhibit the environmental embrittlement. For instance (Co[sub 78]Fe[sub 22])[sub 3]V alloy showed a high ductility of 36% when tested in vacuum at room temperature, whereas the ductility decreased to 20 and 16% when tested in air and distilled water, respectively. In this paper, the study of environmental embrittlement in (Co,Fe)[sub 3]V is extended to include effects of alloy stoichiometry. Hypostroichiometric alloys containing less than 25 at.% V were prepared and tensile tested in various environments at room temperature. The results are compared with those from the stoichiometric (CO,Fe)[sub 3]V alloy and other Ll[sub 2] intermetallics and discussed based on available models predicting the grain-boundary cohesive strength.