Improved FIB milling process for TEM preparation of NiAlPt bulk alloy samples containing residual stress

Abstract

NiAlPt alloys which undergo complex martensitic and twinning transformations during thermal cycling were prepared for Transmission Electron Microscopy (TEM) analysis using the Focused Ion Beam (FIB) milling process. Coupons of alloys that underwent cyclic heating, with no prior isothermal heat treatment contained a build-up of residual stress that caused sections of the foil to crack or buckle during the thinning process, rendering them useless. The solution was to mill strain isolation trenches perpendicular to the area of interest. These trenches acted as reservoirs for the released residual stress. This step was conducted in conjunction with reducing the beam current much earlier in the thinning process, thus ensuring minimum damage to the section being thinned. These two modifications of the standard FIB milling process, with emphasis on the strain isolation trenches, allowed for successful preparation of TEM samples from a bulk alloy containing residual stress.