Abstract:To further understand the alloying behavior for Ni₃Al, the alloying behavior of boron and carbon in Ni ₃Al has been studied by X ray powder diffraction analysis. The results show that boron and carbon occupy the octahedral interstitial site with six nearest neighboring nickel atoms in the L1₂ type structure, and the additives can increase the degree of long range order for Ni ₃Al, the degree of long range order for Ni ₃Al varies with the stoichiometry; the effects of boron and carbon on the lattice parameter of Ni ₃Al are also evaluated. Comparatively, the degree of the long range order is highest for Al rich Ni ₇₄ Al ₂₆ and it is lowest for Ni rich Ni ₇₆ Al ₂₄ . The order degree for stoichiometric Ni ₇₅ Al ₂₅ stands between them. Furthermore, the role of boron in increasing the degree of long range order is more significant in Al rich Ni ₇₄ Al ₂₆ than in Ni rich Ni ₇₆ Al ₂₄ or stoichiometric Ni ₇₅ Al ₂₅ . With boron and carbon content increasing, the lattice parameter of Ni ₃Al increases linearly, and the increment caused by carbon is more pronounced than that by boron. Moreover, the increasing trend of the lattice parameter by boron addition is followed by the stoichiometric sequence of Ni ₇₆ Al ₂₄, Ni ₇₅ Al ₂₅, Ni ₇₄ Al ₂₆ .  

Key words: intermetallics Ni ₃Al stoichiometry solid solution alloying lattice parameter