In order to clarify the effect of alloy stoichiometry on the grain boundary strength and fracture behavior of L12-type A3B compounds, the mechanical properties of Ni3Al, Ni3Ga, Co3Ti and Ni3(Al0.52Mn0.48) compounds were investigated at room temperature. Also, the effect of interstitial atoms of boron and hydrogen and the interaction of its effect with alloy stoichiometry were observed. The result indicated that the magnitude of compositional dependence of alloy stoichiometry on the elongation, the ultimate tensile strength and fracture behavior varied as Ni3Al > Ni3Ga > Co3Ti > Ni3(Al0.52Mn0.48). It was also revealed that the effect of interstitial atoms on the grain boundary cohesive strength is independent on and then additive to the effect of alloy stoichiometry. The significance of the grain boundary structure and related electronic environment in the grain boundary region was, in the geometrical frame, emphasized to interpret the present behavior.
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