Abstract:

Tensile properties and fractographic features of ordered and disordered Ni₃Fe alloys with different Fe stoichiometry tested in vacuum and gaseous hydrogen were investigated. The results show that the phase structure of the alloys does not change, but both tensile properties and sensitivity to H₂induced embrittlement change when the Ni₃Fe alloy component deviates from stoichiometry. Compared with the stoichiometric Ni₃Fe alloy, ductility of the nonstoichometric Ni₃Fe alloys increases when tested both in vacuum and gaseous hydrogen. The hydrogen embrittlement factor (I_H2) of the ordered alloys decreases when tested in gaseous hydrogen for the nonstoichiometric Ni₃Fe alloys. The difference in sensitivity to environmental embrittlement depends on the degree of order for Ni₃Fe alloys with different stoichiometry. The ordered stoichiometric Ni₃Fe alloy has the highest degree of order and is the most sensitive to environmental embrittlement among the used alloys. The degree of order and the sensitivity to environmental embrittlement decrease at the same time for the ordered nonstoichiometric Ni₃Fe alloy. 

Key words: Ni₃Fe intermetallics; environmental embrittlement; fractographic feature; stoichiometry; degree of order