Heating of TEM specimens during ion milling

Abstract

Sample heating during preparation of electron-thin specimens for observation in transmission electron microscopy (TEM) can produce artefacts which invalidate observations. This is particularly true of two-phase materials such as metal matrix composites, for which sample cooling with liquid nitrogen cannot be used to preserve the substructure during milling. A series of experiments is conducted using an age-hardenable aluminium alloy which produces a trace of peak temperature attained by TEM specimens during ion milling. It is shown that peak temperatures of the order of 650 K can be attained using conventional milling parameters; the technique must therefore be used with caution with materials such as metal matrix composites. A simplified one-dimensional heat transfer analysis of the problem is conducted to show that the most critical parameter is heat transfer along the sample holder legs and across interfaces along the heat path. Temperature differentials within the TEM specimen are shown to be less significant, yet these alone are capable of reaching 60 K within a dimpled specimen under usual milling conditions. #

Size dependent strengthening in particle reinforced aluminium

“…That the rate of dislocation accumulation is highest for strains up to this fixed and scale-independent strain could result from a lack of cross-slip ability of thermal dislocations, which are predominantly prismatic and thus edge in character. This interpretation is of course tentative and needs confirming by further experimentation (at lower temperatures for example, in order to increase the thermal strain), coupled with TEM investigations of the matrix structure (though this would prove difficult with the present matrix [57]). …”

Quasistatic and dynamic compression of aluminum-oxide particle reinforced pure aluminum

“…This slight temporary increase in flow stress manifests a difference in the dislocation substructure developed during high and low rate deformation. Qualitative differences in dislocation substructures as a consequence of quasistatic and dynamic deformation were indeed found in a low volume fraction composite with a pure aluminum matrix [14] (there is significant risk of producing artifacts when preparing TEM specimens from metal matrix composites, particularly with unalloyed aluminum [58]; hence direct observation of dislocation structures was not pursued in this study).…”

Measurement and estimation of temperature rise in TEM sample during ion milling

“…Sample heating by the ion milling has been a well-known phenomenon and many reported about related issues, loss of grain boundary segregation [5], micro-structural change [6,7], estimation of the temperature using low-meltingpoint metals [8], and measurement using temperature probe [9][10][11]. The operational manuals of ion-milling system provide only a rough estimate of the thermal power, which can be as much as 300 mW at a high milling rate [12].…”