Physical and mechanical properties of the B2 compound NiAl

Abstract

Considerable work has been performed on N iAI over the past three decades, with rapid growth in research on this intermetallic occurring in the past few years because of recent interest in this material for electronic and high temperature structural applications. However, many physical properties and the controlling fracture and deformation mechanisms over certain temperature regimes are still debated. This is due in part to the incomplete characterisation of many of the alloys previously investigated. Fragmentary data on processing conditions, chemistry, microstructure, and the apparent difficulty in accurately measuring composition have made direct comparison between individual studies sometimes tenuous. The purpose of this review is to summarise all available mechanical and pertinent physical properties of NiAI, stressing the most recent investigations, in an attempt to understand the behaviour of NiAI and its alloys over a broad temperature range.1MR/247

Constitutional and thermal point defects inB2NiAl

“…This conclusion is in agreement with the experimentally observed strong tendency of constitutional defects in NiAl to avoid the same kind of defect at the first neighbor distance of their sublattice. 2 In order to determine what kind of ordered structure the constitutional defects form in NiAl, additional information regarding the defects interactions at longer distances is necessary. As Table V shows, Ni Al ϪNi Al and V Ni ϪV Ni interactions beyond the second coordination shell are already very weak.…”

“…49 Thermal disorder in the B2-type intermetallics is often of a triple defect type 50 and the triple defect formed by two Ni vacancies and one antisite Ni atom is considered to be the dominant thermal excitation in NiAl. 1,2 The equilibrium concentrations of thermal defects in NiAl have been investigated by means of semiempirical models 51,34,35,52 as well as on the basis of first-principles calculations 18,19,22 and atomic-scale simulations. [53][54][55] The considerations are commonly based on the model of a gas of noninteracting point defects as proposed by Wagner and Schottky.…”

Modelling the coefficient of thermal expansion in Ni-based superalloys and bond coatings

“…where T is temperature in K and is valid between 300 and 3000 K. The equation was derived by Noebe et al [23] considering a number of published data for polycrystalline materials. It is noted that the CTE of NiAl is a strong function of temperature but not of composition.…”

“…For higher temperatures, isentropic bulk moduli calculated using a first-principles approach by Wang et al [37] Concentration,Temperature were used, after fitting the third-degree polynomial given in Eq. (23). The fitted polynomial coefficients are given in Table 2.…”

“…(29). The density of b-NiAl was given as a function of Ni concentration by Noebe et al [23] using data from a number of sources. The density decreases linearly with decreasing Ni content, although a change in slope of the line occurs at the stoichiometric composition which has a density of 5.9 g cm À3 .…”