Magdalena M. Miszczyk

Microstructure and interfacial reactions in the bonding zone of explosively welded Zr700 and carbon steel plates

Abstract The microstructure of an explosive cladding joint formed between parallel Zr700 alloy and carbon steel plates was examined with the use of scanning and transmission electron microscopes equipped with energy dispersive spectrometry. The study focused on near-the-interface microstructural changes and possible interdiffusion between the plates. At the macro-scale, the interfaces were outlined by a characteristic sharp transition, indicating that there was no mechanical mixing between the welded metals in the solid state. At the micro-scale, the melted zones often showed non-uniform swirl-like areas of a similar contrast. The nano-scale analysis revealed that the melted areas were composed of mixed amorphous and nano-crystalline phases. The bonding was always achieved by way of surface melting of the joined materials, which might be invisible for observation methods other than transmission electron microscopy.

Crystallographic aspects of nucleation and growth during primary recrystallization in stable single crystals of Al and Al-1%Mn alloy

The early stages of recrystallization have been characterized in stable, single crystals of Al and an Al-1%wt. Mn alloy to rigorously quantify the orientation relations between nuclei and simple deformation structures. Goss{110} and brass{110} oriented samples were deformed in a channel-die to develop a homogeneous structure composed of two sets of symmetrical microbands and then lightly annealed. SEM/EBSD analyses demonstrate a strong relation between as-deformed orientations and the limited number of recrystallized grain orientations. The misorientation angles across the recrystallization front are mostly grouped in the ranges of 25-55° around axes located near, but not at, the normals of all four {111} planes. In some cases the orientation of the growing grain transforms through the formation of a first generation twin with the twinning plane normal lying near the rotation axis. The intensity of new grain nucleation in near-surface areas is significantly greater than those observed in central parts of the sample. Many new grains grow from the surface into the sample centre mostly along the {111} planes. However, irrespective of the section new grains possess the same type of orientation relationship with respect to the deformed state.

Experimental Investigation of Texture Gradients in Aluminium/Copper Plates Bonded through Explosive Welding Process

In this study, the commercial purity Al/Cu plates were bonded through the explosive welding process. The SEM/EBSD local orientation measurements were conducted to consider the changes in the microstructure and the development of texture gradients for the applied explosive loading. A particular attention was paid to the texture changes across the interface. The detailed local orientation measurements show that the ultra-fine grained layers are formed close to the bonding zone. The layers were characterized by the copper-type rolling texture components. The interface was outlined by a characteristic sharp transition between the two materials. However, in some places, local melted zones were also encountered, mainly in the front slope of the waves.

Effect of Strain Path on Microstructure and Texture Development in ECAP Processed AA3104 Alloy

The objective of the study was to determine the effect of strain path on texture, microstructure and mechanical properties development of severely deformed Al-Mn-Mg alloy. The commercial purity material (AA3104 alloy) was deformed via Equal Channel Angular Pressing (ECAP) up to 10 passes following routes A, B, and C. The deformed and partially recrystallized microstructures and the crystallographic textures were characterized by transmission (TEM) and scanning (SEM) electron microscopy including systematic local orientation measurements (TEM and SEM FEG orientation mapping). The crystallographic texture was determined using X-ray diffraction on a sample section perpendicular to the extension direction (ED). In order to estimate the homogeneity of strengthening the systematic measurements of Vickers micro hardness in the plane perpendicular to the ED was performed. It was found out that different routes led to strong differences in microstructure of billets. In the case of route A and B strong macro cracking appeared after 5 and 3 passes, respectively. A good quality billet after 10 passes was obtained only in the case of route C. Texture evolution turned out to follow nearly the same ‘course’ for different routes of ECAP. However, the intensity of particular texture components was different in each case. TEM observations and local orientation measurements allowed identifying fine and strongly disoriented planar dislocation structure of nanolayers in the case of route A and C. In the case of route B nearly equiaxed structure of fine grains was observed after 3 passes. Moreover, irrespective of the applied deformation routes large, not deformable second phase particles strongly influenced strengthening of the matrix and nucleation during the recrystallization.

Application of orientation imaging to the study of substructural development in cold deformed Al-0.3%Mn single crystal of {110} orientation

A systematic study of the deformation microstructures over 3 perpendicular surfaces was carried out in the present work in order to correlate better the substructure with slip patterns, initial and final crystal orientation, and the macroscopic coordinate system. The microstructure and texture evolution of high purity Al-0.3 wt% Mn alloy of initial near brass {110} (or Bs) orientation, channel-die compressed to the strain level of 1.5, were studied by TEM (including TEM orientation mapping) and high-resolution FEG-SEM/EBSD techniques to observe crystal subdivision deformation patterns at the microscopic scale. The grain orientation dependent structures were analyzed in terms of active slip systems focussing on the crystallography of extended planar boundaries. It was concluded that the type of dislocation structure (one or two sets of microbands) in {110} oriented crystallites, at moderate strains (< 1.5) depended strongly on the crystallographic grain orientation. In this non-ideal initial crystal orientation the applied deformation mode activates a double slip, of which one system predominates and leads to further rotation away from Bs. A general rotation combined with a wide orientation spread is observed after a strain up to 1.5. The microband boundary alignment corresponds very well to the traces of crystallographic {111} planes, on which most of the slip occurs.

On Recrystallization Twinning in Al-l%wt.Mn Single Crystals of Two Stable Orientations

The intensity of recrystallization twinning has been characterized in {110} and {110} oriented single crystals of Al-l%wt.Mn deformed to a strain of 0.5 and then lightly annealed. SEM/EBSD measurements indicate that the quantity of recrystallization twins depends on the sample depth. In partly recrystallized sample of {110} orientation the highest fraction of twinned grains was observed in the Vi sample section, but on the surface in the case of {110} crystals. Most of the grains that fulfil the Brandon criterion for twin-related areas are in fact incoherent twins since the boundary plane does not coincide with a {111} plane. A new algorithm to identify coherent and incoherent twin boundaries was applied. In the case of coherent twins, most of the twinning plane normals lie among the rotation axes of the misorientation relations between the recrystallized grains and their as-deformed neighbourhood. The incoherent twins always appear between the growing grains.

Recrystallization Nucleation and Grain Growth in Al-1%wt.Mn Single Crystals of Stable Orientations

The crystallographic aspects of recrystallization nucleation have been characterized in Al-1%wt.Mn single crystals of Goss{110} and brass{110} orientations. Samples were compressed 40% and then lightly annealed to partial recrystallization. SEM/EBSD orientation maps revealed that boundaries with misorientation angles above 8° are not present in the deformed structures. During annealing high angle boundary segments (>15°) were created at an advanced stage of recovery preceding grain nucleation, i.e. some of the low-angle boundaries evolve into high-angle boundaries. As the dislocation-free subgrains are now partly or completely surrounded by high-angle boundaries, the orientations of nuclei are different from the orientations of their deformed/recovered neighbours. There is also a strong relation between as-deformed orientations and the limited number of recrystallized grain orientations. The results are discussed in terms the creation of twist or tilt grain boundaries of high misorientation by thermally activated, co-ordinated movement of dislocations during recovery.

Recrystallization Twinning in Stable Single Crystals of Cu-2%Al and Al-1%Mn Alloys

The crystallographic aspects of recrystallization twinning have been characterized in {110}<001> and {110}<112>-oriented single crystals of Cu-2%wt.Al and Al-1%wt.Mn alloys. The samples were plane strain compressed to logarithmic strain of 0.52 and then lightly annealed. SEM/EBSD local orientation measurements on partly recrystallized samples demonstrate the appearance of a specific number of new orientation groups of recrystallized grains, which resulted from rotation of the deformed crystal orientations around axes lying near (but rarely at) selected the <111> directions. Then the primary nucleus can transform through the formation of a first generation recrystallization twin. The most frequent situation was that the twinning plane normal was situated near the rotation axis, around which the crystal lattice of the ‘primary nuclei’ rotates. Based on new algorithm to identify coherent and incoherent twin boundaries the influence of free surface on the intensity of annealing twinning was analyzed.

Shear Banding in Polycrystalline Aluminium and Copper Pre-Deformed by ECAP and Subsequently Plane Strain Compressed

The microstructure and texture evolution in commercially pure aluminium (AA1050 alloy) and copper have been characterized after change in strain path to elucidate the mechanisms of shear bands (SBs) formation and propagation across grain boundaries. Samples were pre-deformed in equal channel angular pressing (ECAP) and further compressed in a channel-die to form two sets of macro-SBs. The deformation-induced sub-structures and local changes in crystallographic orientations were characterized by scanning electron microscopy equipped with a high-resolution electron backscattered diffraction facility. It was found that the mechanism of micro-/macro-SBs formation is strictly crystallographic. In all the grains of the sheared zone a strong tendency to strain-induced re-orientation could be observed. Their crystal lattice rotated in such a way that one of the {111} slip planes became nearly parallel to the shear plane and the <011> (or <112>) direction became parallel to the direction of maximum shear. This crystal lattice rotation led to the formation of specific SBs components which facilitates slip propagation across grain boundaries without any visible variation in the slip direction.

Recrystallization Behaviour of Plane Strain Deformed Al-Mn-Mg-Sc-Zr Alloy

Early stages of recrystallization were observed for the Al-Mn-Mg-Zr(Sc) aluminium alloy containing a fine second phase particles. The samples were plane strain compressed to 40%, 60% and 83% and then annealed. The processes of the recovery and the nucleation of new grains were analysed with the use of scanning electron microscopy equipped with a high resolution electron backscattered diffraction facility. The deformed alloy contained a structure of flat grains situated parallel to the compression plane. After annealing, the structure coarsened. However, the growth of the new grains was strongly hindered by the presence of particles, and the elongated shape of the deformed grains was conserved up to the later stages of recrystallization. In the case ofthe samples deformed up to 40%, the structure was transformed by the mechanism of continuous recrystallization, whereas, in the case of the samples deformed up to 60% or 83%, both mechanisms- of continuous and discontinuous recrystallization - were valid. A particular role in the rise of thenuclei and the structure spheroidization is attributed to the thermally activated migration of the low-angle grain boundaries and the movement of the dislocations stored inside the cells. This leads to an increase of the misorientation angles across the pre-existing low-angle boundaries.