Development Of Deformation Microstructures Research Articles

Effect of strain path on microstructure and texture formation in cold-rolled and annealed FCC equiatomic CoCrFeMnNi high entropy alloy

The effect of strain path on microstructure and texture formation in an equiatomic CoCrFeMnNi high entropy alloy was investigated. For this purpose, the alloy was cold-rolled to 90% reduction in thickness (total equivalent strain (εeq) ∼2.65) using unidirectional cold-rolling (UCR) and different cross-rolling routes. In the MSCCR route, the samples were rotated by 90° around the ND in between each pass. In the TSCCR(90°) and TSCCR(45°) routes, the samples were deformed by unidirectional rolling to half of the εeq (∼1.3) in the first step and the rest half of the strain (εeq ∼1.3) was imparted after rotation around the ND by 90° and 45°, respectively. The development of deformation microstructures in all the processing routes were characterized by fine lamellar type structure intercepted by inclined shear bands. The TSCCR(45°) processed material appeared to be most prone to shear band formation. The UCR processed material showed brass type texture, while the textures of different cross-rolled materials were featured by different rotated brass components. Upon annealing, the UCR processed material showed the lowest grain size while the highest grain size was observed in the TSCCR(45°) processed material. This indicated greater available nucleation sites in the UCR processed material as compared to the TSCCR(45°) processed material. The differences in annealed grain size was presumably higher due to substructure destabilization and misorientation build-up diminishing the number of potential nuclei in the TSCCR(45°) processed material. The annealing textures of the differently processed materials were featured by the presence of α-fiber (ND//<110>) and absence of preferential nucleation and growth.

The effect of strain path reversal on high-angle boundary formation by grain subdivision in a model austenitic steel

The effects of large strain and strain path reversal on deformation microstructure development in austenite below recrystallization temperature were studied by hot torsion using an Fe-30 wt.% Ni model alloy. Results show that high-angle boundaries (HABs) can be generated by both dislocation accumulation and subgrain rotation. Multiple strain reversals lead to less well-developed HABs in the original grains compared to single reversal deformed to the same strain. This is attributed to subgrain rotation mechanism being less effective at small strains.

Deformation-related microstructures in magmatic zircon and implications for diffusion

An undeformed glomeroporphyritic andesite from the Sunda Arc of Java, Indonesia, contains zoned plagioclase and amphibole glomerocrysts in a fine-grained groundmass and records a complex history of adcumulate formation and subsequent magmatic disaggregation. A suite of xenocrystic zircon records Proterozoic and Archaean dates whilst a discrete population of zoned, euhedral, igneous zircon yields a SHRIMP U-Pb crystallisation age of 9.3 ± 0.2 Ma. Quantitative microstructural analysis of zircon by electron backscatter diffraction (EBSD) shows no deformation in the inherited xenocrysts, but intragrain orientation variations of up to 30° in 80% of the young zircon population. These variations are typically accommodated by both progressive crystallographic bending and discrete low angle boundaries that overprint compositional growth zoning. Dispersion of crystallographic orientations are dominantly by rotation about an axis parallel to the zircon c-axis [001], which is coincident with the dominant orientation of misorientation axes of adjacent analysis points in EBSD maps. Less common <100> misorientation axes account for minor components of crystallographic dispersion. These observations are consistent with zircon deformation by dislocation creep and the formation of tilt and twist boundaries associated with the operation of <001>{100} and <100>{010} slip systems. The restriction of deformation microstructures to large glomerocrysts and the young magmatic zircon population, and the absence of deformation within the host igneous rock and inherited zircon grains, indicate that zircon deformation took place within a low-melt fraction (<5% melt), mid-lower crustal cumulate prior to fragmentation during magmatic disaggregation and entrainment of xenocrystic zircons during magmatic decompression. Tectonic stresses within the compressional Sunda Arc at the time of magmatism are considered to be the probable driver for low-strain deformation of the cumulate in the late stages of initial crystallisation. These results provide the first evidence of crystal plastic dislocation creep in zircon associated with magmatic crystallisation and indicate that the development of crystal-plastic microstructures in zircon is not restricted to high-strain rocks. Such microstructures have previously been shown to enhance bulk diffusion of trace elements (U, Th and REE) in zircon. The development of deformation microstructures, and therefore multiple diffusion pathways in zircon in the magmatic environment, has significant implications for the interpretation of geochemical data from igneous zircon and the trace element budgets of melts due to the potential enhancement of bulk diffusion and dissolution rates.

Microstructure evolution, slip patterns and flow stress

The development of deformation microstructures in medium to high stacking fault energy fcc metals is reviewed illustrating that the basic microstructural element is a cell block. The elongated cell blocks are defined by extended nearly planar boundaries that lie on special planes and enclose a group of approximately equiaxed cells. This duplex structure persists throughout Stage II–IV. What is known about the origins of these structures and the role of the slip pattern is reviewed. Taking all the measurable structural parameters with respect to the cell blocks: spacing, misorientation angle, and dislocation density, and assuming additive strength contributions, flow stress predictions are derived from Hall–Petch and dislocation strengthening. These predictions are in good agreement with the stress values and hardening rates observed experimentally.

Formation of ultrafine scale structures in aluminium containing small amounts of particles by conventional rolling deformation

The development of deformation microstructures during rolling has been studied in polycrystalline aluminium containing 0.8 vol.% of small Al2O3 particles and 2 vol.% of SiC whiskers. The morphology, size and misorientation of the ultrafine scale structures as a function of the imposed strain were characterised using transmission electron microscopy (TEM) technique. The observations were compared to those of cold rolled particle-free pure aluminium reported in the literature. The presence of particles enhances the rate and changes the nature of the development of the overall microstructure in comparison with pure aluminium. With the addition of second phase to pure aluminium, the ultrafine scale microstructure with its size less than 0.5 μm and a fraction of high angle boundaries greater than 30% can be obtained at a comparatively low strain of 2.7. In contrast, complicated processes or severe deformation with a strain of more than 5 are required for obtaining such structures in pure aluminium. The results indicate that there is a considerable potential for extending the present investigation to other particle-containing materials. By selecting second phases with suitable particle size and volume fraction and deformation processes one can expect to develop composites with ultrafine scale microstructure at a comparatively low strain.

Dislocation configurations in metal-matrix composites correlated with numerical predictions

The development of deformation microstructures is reported in reinforced powder-consolidated aluminium. This study discusses observations of the effect of additions of SiC whiskers or particles on the microstructural evolution in the strain range 0.01–0.1. For whisker-containing materials the microstructural changes introduced by thermal cycling have also been investigated, and supplemented by measurements of the dislocation density and microhardness. In plastically deformed specimens the size, shape and microstructure of the deformation zone near the reinforcement have been characterized as a function of the imposed strain. The experimental observations have been compared to finite element model predictions of the stress and strain distribution in the uniaxially loaded composite, and good qualitative agreement has been found. This comparison also points to areas for future model development.

Automated EBSP studies of deformation microstructures

Measurements of the crystallographic orientation within selected local areas of the microstructure is important to achieve further understanding of the development of deformation microstructures and texture; for example for studies of grain subdivision and texture formation. Different techniques may be applied. The most clear and precise results relating directly specific microstructural features to given orientations (or misorientations) are obtained by TEM methods. However, better statistical data may be obtained by the electron back scattering pattern (EBSP) technique in the SEM. The present paper concentrates on the EBSP technique and result obtained thereby.Characterization of the distribution of orientations in the deformation microstructures by EBSP generally requires measurements of hundreds or more orientations. Automatic techniques are therefore very adequate. By using a modified Hough transform routine, lines in an EBSP are easily and rapidly identified. Figure 1 shows an example of computer identified lines in an EBSP of aluminum. Based on this data the crystallographic orientation is calculated by standard routines.

Influence of carbon on development of deformation microstructures in Hadfield steels

AbstractThe microstructural development during rolling is compared in two Hadfield steels, one having low carbon content (0·65 wt-%) and the other high content (1·35 wt-%). Differences in substructure are observed which are due not to small changes in stacking fault energy, but to carbon segregation, which occurs in the low carbon steel (through vacancy diffusion) but not in the high carbon steel. This is demonstrated using Mossbauer spectroscopy and is in agreement with systematic characterisation of microstructures by optical and transmission electron microscopy. In the low carbon steel mixed microstructures are formed which contain intrinsic stacking faults, deformation twins, and brass type shear bands. In the high carbon steel mixed substructures of dislocation tangles, deformation twins, and shear bands (both copper and brass type) are found to develop. In spite of the difference of substructure development during rolling in the two steels, the difference in stacking fault energy is measured to be s...

Influence of carbon on development of deformation microstructures in Hadfield steels

Influence of carbon on development of deformation microstructures in Hadfield steels