X-ray determination of the Debye–Waller factors and order parameters of Ni3Al alloys

Abstract

Integrated intensities of Bragg reflections have been measured at room temperature for Ni3Al alloys containing various amounts of boron, hafnium, zirconium and titanium and the data have been used to evaluate the mean Debye–Waller factors (〈B〉), Debye temperatures (ΘM) and long-range-order parameters (S). The Debye temperatures are observed to show a slight decrease with the decrease of aluminium content within the Ni3Al phase. The results for the Debye–Waller factors indicate that additions of the ternary elements hafnium, zirconium and titanium cause the mean Debye–Waller factor to increase linearly, while boron addition results in a nonlinear increase. The long-range-order parameter of stoichiometric Ni3Al is 0.97, which decreases with decreasing aluminium concentration from the stoichiometric composition. The long-range-order parameter of Ni3Al increases until 0.75 at.% B has been added, beyond that it remains constant. The long-range-order parameter of Ni3Al increases initially with the addition of hafnium, zirconium and titanium up to 0.50 at.% Hf and 0.52 at.%Zr, with further addition of hafnium and zirconium, it decreases. The results are discussed in relation to the crystal structure and chemical bonding in Ni3Al.