Measurements of relative bond energies in some ordered nickel-based alloys by field-ion microscopy

Abstract

The field‐ion images from stoichiometric Ni3Fe, Ni3Al and Ni3Mn are analysed in detail on the assumption that the binding of the surface atoms can be described in terms of the nearest neighbour interactions. It is found that this simple approach is capable of yielding useful information on the relative bond energies which is correlated with the ordering behaviour. For Ni3Fe and Ni3Al first nearest neighbour interactions are dominant, whilst for Ni3Mn the second nearest neighbours assume some importance.

The mechanism of ordering in Ni3Fe: Modular ordering

“…It is ex- pected that the variations in local order (or "nuclei") after this heat treatment would be of the order of 3 nm in extent, which is comparable with the diameter of the topmost { 220) plane ring in a typical 6 kV specimen [ 181. The small evaporation sequence extended about 13 nm through the material, but no contrast was observed which could be ascribed to a well ordered particle [9]. A further increase in the number and regularity of the high index planes is apparent after a 5 h anneal, (Fig.…”

“…The relative stability to field evaporation of successive superlattice planes in Ni,Fe depends on the chemical composition of the plane [9], that is, on the degree of order in the structure. Although this effect is difficult to detect in the images from partially ordered specimens, it is possible to measure the effect by t,he field evaporation technique and obtain quantitative comparisons of the local degrees of order in the specimens.…”

“…A detailed analysis of the contrast mechanisms in ordered Ni,Fe has already been presented [9]. Fig.…”

Observations of the fine structure of superdislocations in Ni3Al by field-ion microscopy

“…At higher imaging temperatures (-77°K) both the (200) and (220) poles show alternate bright and dim rings, corresponding to all nickel and mixed planes, respectively. The factors controlling this contrast have been discussed by Taunt et al (1973).…”

“…Southworth and Ralph 1966), the overall symmetry and pole prominence of field-ion images from binary ordered alloys are consistent with the Bravais lattice of the ordered material. The field-ion contrast from Ni,AI has been analysed in detail elsewhere (Taunt, Sinclair and Ralph 1973) and only the features relevant to the present discussion will be summarized here.…”