“Pre-martensitic” phase in nickel-aluminum thin foils

Abstract

Many beta Hume-Rothery alloys which transform martensitically at lower temperatures exhibit anomalies including softening of elastic constants, tweed electron microstructures, and extra spots and diffuse streaking in electron diffraction patterns. At one time it was customary to interpret extra spots as arising from transitional, pre-martensitic phases intermediate between the parent beta phase and the martensite. More recent evidence implicates surface phases on TEM thin foils. It is shown here that extra spots and part of the diffuse intensity in electron diffraction patterns from a Ni-Al alloy are clearly a thin foil artifact, and depend on the foil normal orientation. However, the tweed microstructure and 〈110〉 streaking in diffraction patterns appear to be a bulk effect.