Broad Beam Ion Milling for Microstructure Characterization

Abstract

Abstract Optimum sample preparation is essential to obtain reliable data in microstructure analysis. Whereas traditional metallographic preparation techniques, using mechanical polishing and chemical etching, are sufficient for many applications, these methods can be unsatisfactory for high-technology materials, complex assemblies, and smaller components. Broad-beam argon ion milling (AIM), using high-energy ion bombardment to remove material or modify the surface of a specimen, can provide a substantial improvement in specimen quality for many difficult materials and components. Directing energetic argon ions toward the specimen at a low angle of incidence gradually removes material at the atomic level to produce flat surfaces with no deformation or other disturbance of the material microstructure. Especially for multi-phase materials with low hardness or soft constituents, polishing by ion milling at low-angles results in optimum surfaces for light microscopy, scanning electron microscopy (SEM), or electron backscattered diffraction (EBSD). Surface modification to produce contrast between phases or reveal other microstructural features can be realized with higher milling angles. This provides a great advantage for components consisting of noble metals, like gold and platinum, or corrosion-resistant alloys bonded to less noble metals, which are frequently difficult or impossible to prepare with chemical etching. Microstructure contrast with ion milling is also useful for extremely fine structures, such as ultra-fine grains, that can be obscured by chemical etching.