Materials Science Forum Vols. 702-703

Abstract: Texture, structure, and magnetic and mechanical properties of thin tape substrates fabricated of ternary nickel alloys with chromium, tungsten, molybdenum, and vanadium have been investigated. It has been shown that in Ni_93.8Cr_4.0Mo_2.2, Ni_88.5Cr_6.2V_5.3 and Ni_88.4Cr_9.2W2.4 alloys a sharp cube texture can form, which is stable up to high annealing temperatures. In the Ni_87.6Cr_8.0Mo_4.4 alloy, other weak orientations are present, along with the strong cube component. The possibility of obtaining a sharp cube texture after primary recrystallization is controlled by the quantitative relationship between the texture components in a cold-rolled tape, which is determined by the method of orientation-distribution functions. Three alloys studied are non-magnetic at 77 K.

Abstract: Optical microscopy on the etched cross-section of a nanocrystalline Ni-18 wt.% Fe electrodeposit revealed the existence of a banded structure perpendicular to the growth direction. To evaluate if the banded structure is affecting grain growth and texture development, EBSD orientation maps were obtained after annealing for 30 min at 300, 350, and 400°C. Grown grains were found to be random in shape and no preferential sites for grain growth were observed. The texture of the grown grains is changing upon annealing and the final fibre texture parallel to growth direction of the electrodeposit can be obtained from texture components found at lower annealing temperatures when performing one or two consecutive twinning operations.

Abstract: GaAs nanopillars show promise for energy applications. Understanding, characterizing and modifying the structure of the pillars will be very important for optimizing the properties of the assemblies. EBSD was used to investigate the orientations of these nanometer structures.

Abstract: The texture evolution in the plastic deformation layer of the pure iron sample after the surface mechanical attrition treatment (SMAT) was discussed through electron backscattering and X-ray diffraction (XRD) analysis. The results showed that: the surface layer of the iron sample can be subdivided into four sub-layers along the depth from the top surface: nano-sized regime, submicro-sized regime, micro-sized regime and deformed coarse-grained regime. Nano-sized regime possesses random crystallographic orientations. But in submicro-sized regime and micro-sized regime, the //ND fiber texture is the prominent texture with a strong orientation of (110)[1-11]. Increasing treatment time during SMAT process does not change the components of texture in plastic deformation layer, only strengthen their orientation density.

Abstract: High resolution EBSD analysis was carried out under specific experimental conditions (15 to 5 kV) on the skeleton of the modern carbonate brachiopod Gryphus vitreus and resolved nano- to microscale preferred crystallographic orientation patterns undetcted so far. As biologic superstructures are formed by controlled nanoparticle assembly it is essential to resolve their internal structure and texture with the highest possible spatial resolution. Low kV EBSD (15 kV and at 5 kV) provides the required resolution. We observe in the investigated carbonate skeletons a strongly interlocking microstructure of concave/convex grains. The interface topology of the interdigitating structure reaches below the micrometer scale. Individual grains reach sizes up to 20 µm (or even more) in one dimension. They show a mosaic spread of several degrees such that they must be addressed as mesocrystals. Even though the shell consists of three different microstructures with completely different crystal morphologies and grain boundary topologies the crystallographic texture of the three layers is similar. This indicates that distinct control mechanisms prevail when the shell is formed.

Abstract: Organic additives such as saccharin have been frequently used in electroplating operations to moderate deposit growth rates and to control film quality. In this study, texture development upon annealing of pulse-electroplated Nickel produced without additives is analyzed by use of electron backscatter diffraction technique. Plating without additives results in a microstructure with slightly elongated grains and a fibre texture in growth direction and this texture is conserved upon annealing up to 600°C. Structural units in form of groups of elongated grains possessing a common zone axis in growth direction and twin relationships between themselves are found in the microstructure. For revealing the influence of additives, the observations are compared with results obtained for Ni and Ni-Fe plated in the presence of additives where during abnormal grain growth the initial fibre texture changes to an energetically more favourable texture by twinning. The lack of additives is assumed to be responsible for the observed differences in texture and microstructure development.

Abstract: In this paper, a multiscale modeling approach has been developed to simulate the intergranular crack propagation in textured polycrystalline materials. Embedded Atom Method (EAM) and Molecular Dynamics (MD) simulations were carried out to determine the energy and fracture strength of different types of grain boundaries in Ni₃Al. Subsequently, the atomistic model has been integrated with the microstructure based model of crack propagation using the Voronoi-Markov Chain-Monte Carlo approach. The model has been utilized to evaluate the crack length for various scenarios and reasonable results are obtained.

Abstract: Bainitic steels, which are transformed at very low temperatures, offer an excellent combination of strength and ductility where the strength comes from the nano-structured bainitic plates and thin-film of austenite sandwiched between two bainite sheaves offers the ductility. The main drawback of this structure is the long transformation time which is not ideal for industrial application. Through the microstructural engineering, the extent and kinetics of transformation can be manipulated by judicious selection of alloy composition and process variables. The main challenge is to delay the transformation till the coiling stage and allow the formation of bainite only during the cooling of the coil. In the current work, an approach will be shown, starting from the alloy design based on thermodynamics till the cooling after coiling, which can satisfy the requirements to develop such steel with 1300 MPa UTS combined with 20% elongation (min).

Abstract: Effects of electric current densities on recrystallization texture evolution in cold-rolled Fe-3%Si steel were investigated by using a high current density electropulsing treatment. Results showed that the orientation density of α fiber and  fiber varied with the specimen thickness during current passing. However, with the current density increasing, the difference from layer thickness almost vanished. In addition, Goss component texture was the final sharper one but no relation with the specimen thickness at 9.96kAmm-2. By the texture evolution analysis, it was found that the preferred nucleation always occurred in the surface layer due to the high storied energy coursed by previous cold rolling. Combined with the corresponding microstructures, it could be found that though there was an apparent texture evolution along specimen thickness, the microstructure had no change with thickness. In addition, due to the application of electropulsing, the recrystallization nucleation was greatly increased.

Abstract: MMCs (Metal Matrix Composite) are very useful in the different branch of application like aerospace, automobile engineering and defense application. Of late surface modification of variety of materials is gaining importance. Various surface modification techniques are being used some at research scale and some at industrial scale. In the present study, an attempt has been made to modify the surface of Al-Si/SiCP metal matrix composite using KrF Excimer laser and to study the microstructural changes using optical microscopy and SEM imaging and EDS analysis. Results from the study are presented and discussed.