Transmission Electron Metallography Research Articles

Electron microscopic studies of thermomechanically aged 2218 aluminium alloy

The effect of thermomechanical ageing (TMA) treatment on the microstructure and mechanical properties of 2218 Al alloy has been studied. This was followed by hardness measurements and transmission electron metallography (TEM). The 2218 Al alloy was given various thermomechanical ageing treatments including partial peak ageing, warm rolling and further ageing to peak hardness level. Without thermomechanical treatment the peak hardness value was 130 VHN. With thermomechanical treatment there was an overall improvement in hardness. This is attributed to the combined effect of dislocation precipitate networks and the fineness ofθ′ particles.

The metallography and deformation of the aligned Cd-Zn eutectic

The tensile deformation of the aligned Cd-Zn eutectic alloy has been investigated with particular attention paid to the influence of interlamellar spacing (λ). These tests were supplemented by optical and transmission electron metallography. At plastic strains of 10−6 the stress was independent ofλ, at 10−5 the stress increased with decreasingλ and by 10−4 twinning had become the dominant deformation mode. Twinning stress was found to increase with decreasing cell or grain size, rather than being a function ofλ. Electron microscopy demonstrated that individual twins were continuous through many lamellae of each phase. Differences between tension and compression tests are examined and possible reasons based on dislocation mechanics are discussed.

Structure and properties of free-cutting steels after deformation to high strains

The overall property changes in a high-sulphur free-cutting steel and a lead-bearing high-sulphur free-cutting steel have been determined by compounding the results of tensile tests after cold rolling the steels for differing amounts up to 98% reduction. The structural changes have been determined by optical and thin-foil transmission electron metallography, while the tensile fractures found after cold rolling have been examined by scanning electron microscopy. The high-sulphur steel showed a lower work-hardening rate than the equivalent plain carbon steel at moderate strains, but at high strains a tensile strength of 1700 MN m−2 was obtained. The MnS particles were more plastic than the matrix (plasticity ratio >1) and a fibre-reinforcing effect could give rise to the high strength. For the lead-bearing steel the work-hardening rate was lower than with the lead-free steel. The lead caused the sulphides to fragment and, hence, the final strength level achieved was much lower, but still greater, than that of the equivalent plain carbon steel. The results obtained are discussed in relation to the high-strain work-hardening mechanisms found in plain carbon steel, and to the roles played by MnS and Pb in improving the machinability of steel.

The metallurgical characterization of coatings

This paper reviews some of the metallurgical characterization techniques used at Battelle Northwest for coatings made by high rate sputter deposition methods. The paper includes specific examples and a discussion of problems encountered during characterization. Characterization techniques used include (1) X-ray and electron diffraction for crystal structure determination, (2) X-ray diffraction, optical, scanning electron and transmission electron metallography for microstructural characterization, (3) numerous chemical analysis techniques for bulk alloy composition, gas content, trace impurity analysis and variable composition determinations and (4) a listing of property measurements needed for various purposes. It is hoped that the novelty of these examples will stimulate new approaches to coating characterization at other laboratories.

Transmission Electron Diffraction of Alnico V

By grinding, polishing, and etching it is possible to render Alnico V thin enough for transmission electron metallography. 80-kv electrons penetrated Alnico V metal confirming the two-phase structure found earlier with replica techniques. Transmission diffraction on Alnico V samples reveal the crystal structures of both phases. The development of one phase out of the other was studied on samples from Alnico V at various states of the usual heat treatment.

A technique for obtaining thin foils of aluminium and aluminium alloys for transmission electron metallography

The structural changes produced by ageing aluminium-copper and aluminium-magnesium-zinc-copper alloys have been investigated by examining foils of these alloys in the electron microscope. The foils have been obtained by mechanical reduction in thickness followed by controlled electropolishing and chemical dissolution of the remaining oxide film.