Changes in the microstructure and crystallographic orientations during in-situ heating of folded Al 0.1%Mg have been followed by SEM and EBSD. The folding process results in both strain and texture gradients across the folded region which in turn can influence the recovery and recrystallisation processes as well as crystallographic texture. This work is an extension of ex-situ heating experiments on folded nickel 200, titanium and ferritic steel [1,2]. The present findings illustrates that during isothermal in-situ heating at 295oC nucleation and growth starts close to the surface where the deformation is highest, new grains form and grow in a region about quarter depth of the sheet thickness. After this grain growth occurs resulting in large grains that meet up at the centre line. These results are consistent with those found in ex-situ heated Ni200 alloy [2], where fine grains were found in the compressed and tensile regions with large grains in the middle of the sheet.

The effect of second-phase particles on the deformation and annealing behaviour of metals is re-assessed in the light of some new techniques. Using an EBSD method which provides much improved angular resolution, the effect of small non-deformable particles on the homogeneity of the deformation microstructure has been quantified. The presence of micron sized second-phase particles alters the deformation microstructure adjacent to particles, and a 3-d investigation of the deformation structures associated with large (>1μm) second-phase particles in cold rolled aluminium alloys has been carried out using 3-d FIB sectioning combined with EBSD, and the microstructures compared with the predictions of 3-d CPFEM modelling. The effects of grain orientation, strain and particle size have been investigated, and the results compared with earlier TEM investigations of such microstructures.

A combination of electron backscatter diffraction (EBSD) and focused ion beam (FIB) techniques were used to obtain 3D EBSD data in an investigation of dynamic recrystallization in a Cu-2%Sn bronze alloy. The results of this investigation show the origin of the nucleation sites for dynamic recrystallization and also elucidates the orientation relationship of the recrystallized grains to the deformed, prior grains and between the dynamically recrystallized grains.

High power ultrasonic spot welding (USW) is a low heat input solid-state joining process that may offer a solution for welding difficult dissimilar-material couples, like magnesium (Mg) to aluminium (Al) for automotive body applications. However, the high strain rate dynamic deformation in USW has been claimed to accelerate inter-diffusion rates in dissimilar joints. The interfacial reaction between Al, AA6111, and Mg AZ31 alloys has been studied as a function of welding energy. For the optimum welding condition of 600J (0.4s) the reaction layer thickness was already ∼5μm thick. Intermetallic reaction centres were found to nucleate within microwelds at the interface at very short welding times and spread and grow rapidly to form a continuous layer, composed of two sub-layers of Al12Mg17 and Al3Mg2. Interface liquation was also found for longer welding times at temperatures below the recognised lowest eutectic reaction temperature in the Al–Mg binary system. Modelling has been used to show that the solid state reaction kinetics were over twice the rate expected from parabolic growth predictions made using rate constants obtained under static test conditions. The reasons for this discrepancy and the depressed melting reaction are discussed.

A Nordlys F, fast electron backscatter diffraction camera has been used on a CamScan MX2500 field emission gun SEM in conjunction with a hot stage to study annealing phenomena in metals. The performance of the camera under a wide variety of conditions has been evaluated, and comparison is made with a conventional electron backscatter diffraction camera operating under the same conditions and with the same samples. Examples are given of applications of the system to the annealing of aluminium alloys.

A focused ion beam and electron backscatter diffraction were used to investigate the three-dimensional microstructure of small dynamically recrystallised grains in a deformed Cu–Sn alloy and to determine their orientation relationships. It was found that many of the grains, which form as thin sheets at the prior boundaries, are twin related. It is concluded that dynamical recrystallisation usually starts in regions where plastic deformation has resulted in significant lattice rotations beside the grain boundaries. Once such a new grain has formed, dynamic recrystallisation is propagated by successive twinning from the new grain, along the prior grain boundary, resulting in families of several hundred twin related dynamically recrystallised grains.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

The effect of hot deformation on fully recrystallized aluminium-copper alloys (Al-4wt%Cu and Al-33wt%Cu) with different volume fractions of CuAl(2) has been studied. The alloys are Zener pinned systems with different superplastic properties. Strain-induced grain growth, observed in both alloys, was quantitatively estimated by means of electron microscopy and EBSD and compared with the rate of static grain growth. Surface marker observations and in situ hot-deformation experiments combined with EBSD were aimed at clarifying the mechanisms responsible for the changes in the deformed microstructures. A sequence of secondary and backscattered electron images and EBSD maps was obtained during in situ SEM deformation with different testing conditions. Overlaying EBSD maps for the Al-4wt%Cu with channelling contrast images showed that grain boundary motion occurred during deformation, creating a layered structure and leading to an increase in size of some grains and shrinkage of others. Of a particular interest are results related to behaviour of CuAl(2) in superplastic Al-33wt%Cu during deformation, including several problems with the use of EBSD in this alloy.

In situ electron backscatter diffraction microstructural analysis of recrystallizing interstitial free steels deformed to strains of 0.75 and 1.6 has been carried out in a FEG-SEM. The experimental procedures are discussed, and it is shown that there is no degradation of the electron backscatter diffraction patterns at temperatures up to 800 degrees C. Analysis of the surface and interior microstructures of annealed samples shows only minor difference, which suggests that in situ annealing experiments are of value. In addition, it is shown that in situ measurements allow a detailed comparison between the same areas before and after annealing, thereby providing information about the recrystallization mechanisms. Sequential recrystallization phenomena, such as initiation and growth of new grains, are observed at temperatures over 740 degrees C, and depending on the deformation histories, different recrystallization behaviour is observed. It is found that {111}< 123 > recrystallized grains are preferentially formed in the highly deformed material, whereas no strong recrystallization texture is formed in the lower strained material.

Copper, Cu-2%Sn and Cu-4.5%Sn alloys have been deformed in plane strain compression at temperatures up to 700oC and the evolution of the microstructures and textures determined by high resolution EBSD. The effect of the solute is to raise the temperature at which dynamic recrystallization occurs and to significantly reduce the size of the dynamically recrystallized grains. In all the materials, there is a small increase in the cube texture component on dynamic recrystallization. The boundary bulges which precede recrystallization are different in the copper and Cu-Sn alloys, although in both materials there is evidence that local deformation in the boundary regions plays a significant role in dynamic recrystallization.

Tensile tests have been carried out in the rolling and transverse directions of 'interstitialfree' (IF) steel cold rolled to a strain of εh= -0.18. Tests in the transverse direction showed the characteristic features of the orthogonal strain path change effect, with an initially increased flow stress- compared to tests in the rolling direction- followed by a transient regime of very low strain hardening. Tests were also carried out following recovery annealing of the prestrained sheet at 500°C and 600°C. Static recovery had a marked effect on the strain-induced anisotropy, but this was not eliminated even when the cell structure generated by prestraining haD condensed to one consisting of low-angle boundaries. This supports the view that the length scale, with respect to active slip systems, between boundary obstacles is a significant factor in the orthogonal path change effect.

Recrystallization phenomena in an interstitial free (IF) steel have been investigated by in-situ annealing in the SEM, combined with Electron Back Scattered Diffraction (EBSD) mapping. Sequential recrystallization phenomena, such as initiation and growth of new grains, are clearly distinguished by EBSD mapping at temperatures of up to 1070K. More than 70% of the recrystallized grains are of {111}<121>, {111}<123> and {111}<110> orientation. It is found that many recrystallized grains are formed from {111}<123> deformed grains at the beginning of recrystallization. It is observed that some of α-fibre (RD//<110>) orientations have difficulty in recrystallization compared to γ–fibre deformed grains. In particular, many grains of {001}<110> orientation remain un-recrystallized even after holding for 65 minutes at 1050K.

The factors which determine the angular resolution in electron backscatter diffraction (EBSD), and the operating conditions which optimise it are considered. On suitable samples the angular resolution may be substantially improved by data averaging using an edge preserving Kuwahara filter. It is shown that measurements of misorientation by direct comparison of diffraction patterns can reduce the angular resolution to below 0·02°, and the application of this method to linescans and EBSD maps is discussed. It is concluded that the applicability of pattern comparison methods for EBSD maps is limited by time and microstructural considerations, but linescans using this method are shown to produce high quality data in material containing small misorientations, which cannot readily be analysed by the conventional Hough transform EBSD method.

A method of accurately measuring misorientations by electron backscatter diffraction (EBSD), which is an extension of that proposed by Wilkinson and based on the comparison of diffraction patterns, is described. The method has been applied to linescans, and found to improve the angular resolution by a factor of more than 30. The consequent improvement in determining misorientation axes is also analysed. Small changes of orientation very close to some low-angle boundaries were investigated and found to be artefacts of the analysis. Measurements of the area from which diffraction patterns are generated show this to be much larger than the effective spatial resolution of EBSD, and it is concluded that this may be a limiting factor in the use of EBSD for microstructural characterization.

Three high density polythylenes with widely differing molecular weights have been subjected to a fast fracture process and studied by scanning electron micrography. Two polymers in the low to medium molecular weight range show evidence of substantial melting during facture, in support of some previous work. On the other hand the ultra high molecular weight material seems to deform on a more massive scale without recognisable relics of a melting process.

The technique of combining in situ hot-deformation and high resolution electron backscattered diffraction (EBSD) has been applied to study the mechanisms operating during the thermomechanical processing of metals. A simple hot tensile-straining stage is installed in a field emission gun scanning electron microscope equipped with an EBSD system and has been used successfully for a number of preliminary investigations. These investigations include substructure formation, dynamic subgrain and grain growth, superplastic deformation in aluminium alloys, and dynamic recrystallization in copper. Despite the surface topography, which inevitably increases during plastic deformation, channelling contrast backscattered electron micrographs have been successfully obtained after strains of up to approximately 50%. Good quality EBSD maps have been obtained after strains of up to 100%. Most observations and measurements from the in situ experiments are consistent with what is known about the mechanisms occurring in the bulk. The microstructures revealed in the centre of the in situ samples after later repolishing are generally similar to those at the surface.

Electron back-scattered diffraction (EBSD) patterns are produced by inelastically scattered electrons and are intimately related to the local crystal orientation and quality. Analysis of the EBSD patterns is a rapid, non-destructive technique, which we have used to follow the regrowth of amorphised silicon-based heterostructures. The effective spatial resolution is 80nm, and we show that the technique can detect buried amorphous and oxide layers. Cross-sectional transmission electron microscopy (XTEM) studies confirm the EBSD results. A gas source MBE-grown Si1−xGex (x=14.5%) multi-quantum-well structure with good optical properties was implanted with an amorphising dose of either Si or Er, or Si followed by Er. The structure was annealed at 560°C under flowing N2 and regrowth was monitored at intervals by EBSD. It was found that structures implanted only with Er regrew faster than those implanted only with Si. As expected, the sample implanted with both Si and Er showed regrowth kinetics in between the two.

The grain structures formed during friction stir welding of a typical aluminium aerospace alloy have been studied by high resolution EBSD analysis. The grain structures reflect the local deformation conditions, and due to the high temperatures and strains, show characteristics typical of different stages of dynamic recrystallisation. The large strains and high density of second phase particles in the nugget zone result in a very fine 2-3 mu m equiaxed grain size. There is an abrupt transition in grain structure between the nugget and the TMAZ at the side of the weld. A very fine grain structure was also observed near to the top surface of the weld that was in contact with the tool shoulder. The nugget zone, "onion ring" structure was attributed to bands of different densities of second phase particles, rather than any significant difference in the local grain structure or texture.