X-Ray Diffraction Investigation of β′-NiAl Alloys

Abstract

An x-ray diffraction investigation of the structure of β′-NiAl alloys was conducted to define the state of order, identify the lattice sites occupied by compositional vacancies, and measure both static and vibrational components of atomic displacements, all as functions of temperature and composition. Long-range order was found to be virtually complete up to 1000 °C and remained substantial up to the melting points of the alloys. Compositional vacancies present in Al-rich β′ alloys were found to occupy Ni lattice sites only, at least to 1000 °C. Static atomic displacements were minimal at stoichiometry, increased with initial Ni or Al additions, and then decreased with further Ni or Al additions, with the maximum displacement about midway between stoichiometry and the β′ phase boundaries. Vibrational atomic displacements were also minimal at stoichiometry, but in contrast to static displacements, increased continually as either Ni or Al was added. Atomic displacements were correlated with known mechanical properties of β′-NiAl alloys.

Phase and Structural Transformations in the Alloys Based on Monoaluminide of Nickel

“…Характерным признаком сплавов системы Ni-Al является вы-сокая энергия упорядочения: 0,76 эВ на связь [13]. Интерметал-лид NiAl и твердые растворы замещения на его основе обладают высокой степенью дальнего порядка, сохраняющейся во всей температурно-концентрационной области их существования вплоть до температуры плавления [13].…”

“…Интерметал-лид NiAl и твердые растворы замещения на его основе обладают высокой степенью дальнего порядка, сохраняющейся во всей температурно-концентрационной области их существования вплоть до температуры плавления [13]. В решетке β-фазы избыточные 200 С. В. КОСИЦЫН, И. И. КОСИЦЫНА (по отношению к стехиометрии) атомы никеля располагаются в подрешетке алюминия, в общем случае, неупорядоченно.…”

High-Precision Measurement of Temperature Factors for NiAl by Convergent-Beam Electron Diffraction

“…This is probably due to the limited accuracy of powder experiments (Cooper, 1963) or the use of low-order reflections in single-crystal measurements (Hughes, Lautenschlager, Cohen & Brittain, 1971). Very precise powder data have been obtained by Menon & Fox (1996) using an improved extinction-correction scheme.…”

“…For NiA1, TFs have been measured by Cooper (1963), Hughes, Lautenschlager, Cohen & Brittain (1971), Georgopoulos & Cohen (1977) and Menon & Fox (1996). Unfortunately, these data were determined at room temperature, whereas quantitative CBED is preferably performed at liquid-nitrogen temperature.…”

Effect of L1o → Ni5Al3 Reordering on Properties of Martensitic Ni-Al Alloys

“…l a is stable at high temperatures over a wide composition range of 40-68 at.%Ni. For Ni-rich compositions, excess Ni atoms distribute themselves randomly on the A1 sublattice [2]. The B2 phase undergoes a thermoelastic martensitic transformation up on quenching to the tetragonal Llo ordered structure shown in Fig.…”