Proceedings of the 2nd International Congress on 3D Materials Science

The measurement of 3D displacement fields experienced by a sample that has been reconstructed in its reference state can be achieved from much less projections than needed to image the sample itself. The principle of the approach is discussed together with proposed extensions.

Plastic deformation generates cellular/subgrain structures in many types of metals, and these features have a pronounced influence on mechanical behavior as well as subsequent recovery and recrystallization processes. These features can be observed by electron backscatter diffraction (EBSD) but are challenging to identify automatically. For example, no threshold misorientation angle may adequately capture gradual orientation transitions without noise dominating the result. A more robust technique, fast multiscale clustering (FMC), partitions a data set with attention given to local and global patterns. With FMC, individual data points are combined iteratively into clusters. To determine similarity of clusters during the aggregation process, the method requires an appropriate distance metric. We have adapted FMC to EBSD data, quantifying distance with misorientation and using a novel variance function to accommodate quaternion data. This adaptation is capable of segmenting based on subtle and gradual variation as well as on sharp boundaries within the data, while maintaining linear run time. The method is useful for analysis of any EBSD data set for which the structure of grains or subgrain features is required, and it has been incorporated into the open-source quantitative texture analysis package MTEX. The sensitivity of a segmentation is controlled by a single parameter, analogous to the thresholding angle. To balance the desired identification of subtle boundaries with erroneous oversegmentation, a method to quantitatively optimize this free parameter has been developed. Since the FMC process does not depend on the spatial distribution of points, data can be in either 2D or 3D and organized with any geometry. In fact, the data points may have arbitrary placement, as is the case after correcting for instrument drift. Often investigation of the relationship between structure and formation mechanisms requires extraction of coherent surfaces from cluster volumes. FMC has been further modified to group closed 3D boundaries into distinct surfaces based on local normals of a triangulated surface. We demonstrate the capabilities of this technique with application to 3D EBSD data with subtle boundaries from a deformed Ni single crystal sample. In addition, a recrystallizing steel microstructure with three magnitudes of boundaries is analyzed to show how FMC can be used to characterize both sharp grain boundaries and more subtle features within the same data set.

A comprehensive three-dimensional (3D) stochastic model for simulating the evolution of dendritic crystals during the solidification of binary alloys was developed. The model includes time-dependent computations for temperature distribution, solute redistribution in the liquid and solid phases, curvature, and growth anisotropy. 3D mesoscopic computations at the dendrite tip length scale were performed to simulate the evolution of columnar and equiaxed dendritic morphologies and compared then with predictions obtained with 2D mesoscopic computations.

This poster presentation gives an overview of the great potential of X-ray micro computed tomography (CT) to cast light on the evolution of the microstructure in construction materials. Prevention of damage is of major economic and social importance in the development of suitable construction materials such as concrete and asphalt. Therefore a non-destructive testing method such as CT is an appropriate tool for visualization of the inner structure. Its combination with other test methods allows understanding the damage processes such as crack propagation or corrosion. We show examples of internal structure analyses on a wide range of materials: Automatic 3D crack detection and the visualization of corrosion products inside of steel reinforced concrete, pore and shape analysis of lightweight aggregates and the visualization of deformation of high-pressure loaded aerated concrete specimens, distribution of aggregates inside concrete, and determination of the surface of porous asphalt core samples. Segmented structures serve, e.g., as input data for simulation of transport phenomena or virtual load tests.

New composites based on a matrix of silica aerogel grains are currently being developed to answer the expectations of thermal renovation. One of the key parameters for their commercial use is the control of their porous network. In this study, we aim to propose a three-dimensional characterization from the nanometer to the millimeter scale of the silica aerogel particles themselves. Transmission electron microscopy (TEM) is used to characterize the mesoporous network within the aerogel grain. The arrangement in three dimensions of the grains and the voids within the aerogel grain pileup is investigated at the micron scale by X-ray tomography.

Micro-computed tomography (µCT) yields three dimensional reconstructions of the microstructures of materials down to a spatial resolution of about 1 µm. Based on the resulting image data, many mechanically relevant geometric parameters can be computed using three dimensional image analysis. These parameters include fiber density, orientation, homogeneity and thickness. We show how to fit stochastic fiber models to this image data. Such models take into account fiber densities, orientations, radii and inhomogeneities. These geometries can be realized, thus enabling numerical homogenization methods based on the Lippmann-Schwinger equations in elasticity. These yield the full elastic tensor and even nonlinear elastic behavior. With appropriate damage models, the material strength can be characterized. Such an approach has various advantages over mechanical testing. For example, it characterizes a material in every direction, instead of only the direction in which a tensile test was performed. Furthermore, material models open the path to virtual material design, where one can use computer experiments to identify the microstructural geometry which best fulfills the requirements in some given application. In this contribution, we demonstrate the entire chain consisting of image analysis, geometric and mechanical modeling for glass fiber-reinforced thermoplastics.

Characterization of the internal microstructure of paper, consisting of a dense network of wood fibres, is an important tool for determining the properties of paper and for optimizing the papermaking process. A novel two step approach for segmentation of wood fibres in high resolution micro CT images of paper has been developed that is able to isolate the individual wood fibres even with cracks and openings in their fibre walls, and is thus a first step in quantifying the fibrous microstructure of paper. The approach uses an extended 2D connected components method to track the lumen or hollow within the fibre in a fully automated manner, followed by labeling of the fibre walls using a distance transform. The result is a robust 3D fibre segmentation that preserves the surface topology of the papermaking fibres.

The modelling of three-dimensional composite carbon fibers-resin materials for a multi-scale use requires the knowledge of the carbon fibers localization and orientation. We propose here a mathematical method exploiting tomographic data to determine carbon localization with a Markov Random Field (MRF) segmentation, identify carbon straight cylinders, and accurately determine fibers orientation.

The dynamic deformation of metallic polycrystalline materials leading to ductile damage and failure events involves a complex series of physical processes which are poorly understood. This lack of understanding prevents us from properly formulating and offering the appropriate physically based theories for accurate and robust representation of the ductile damage and failure response of ductile materials. This paper briefly describes and illustrates a coupled experimental and computational methodology to develop greater physical insight linking the structural details of the material to its formation of damage sites. Results from examinations of both tantalum and copper are presented to illustrate the types of methodologies that will be needed in the future to better understand the critical physical processes occurring in polycrystalline metallic materials leading to their catastrophic failure.

The multi-phase-field (MPF) method has attracted attention as a very promising tool for simulating microstructure evolutions in polycrystalline materials. However, because of the heavy computational cost incurred by three-dimensional (3D) MPF simulations, simulating realistic microstructure morphology in three dimensions has been difficult. In our research, we developed a multiple-GPU computing technique and an overlapping method that facilitate efficient 3D MPF simulations. Using the technique developed, we performed 3D MPF simulations of polycrystalline grain growth on a GPU-cluster and on the TSUBAME2.5 supercomputer at the Tokyo Institute of Technology. The results obtained indicate that our multiple-GPUs computing technique combined with the overlapping method significantly reduce the elapsed time of simulations and easily facilitate the performance of very large-scale 3D simulations with up to 1024³ computational grids.

The co-continuous ceramic/metal composite (referred to as C⁴ composites) are becoming an important class of materials as the result of the development of a number of new techniques for fabricating composites with interpenetrating macrostructures. In this paper, the fatigue endurance behaviors of three three-dimensional (3-D) continuous SiC ceramic network reinforced ZL111 Al alloy composites (T6-treated SiC_n/ZL111Al) were simulated by the finite element method (FEM). The finite element simulation showed that the stress concentration, due to the presence of continuous SiC ceramic network reinforcements, produces controlled crack growth and higher stresses, which are related to regular energy release by the material during fracture. The need for higher stresses for a crack to propagate reveals the material’s microstructural strength. Experimental analysis showed fatigue life for specimen was 4.8×10⁵ cycles for 200 MPa, R=−1.0, and 6.5×10⁵ cycles for 95 MPa, R=−0.05. The number of cycles to failure predicted numerically is higher than the experimental one. This difference is attributed mainly to an upper stage of fatigue crack growth, particularly, the interaction between fatigue crack growth and growth that cannot be accounted for in the numerical model.

Aluminum alloy automotive parts produced by the Lost Foam Casting (LFC) process have coarser microstructure and porosity defects than parts produced with conventional casting processes at faster cooling rates. This coarse microstructure has a major influence on the fatigue properties and crack initiation. In order to study its influence upon the mechanical behaviour, an experimental protocol has been set up using X-ray tomography and 3D Digital Volume Correlation (DVC). The present work focuses on the use of this protocol to study the influence of the casting microstructure upon the tensile behaviour. The 3D cracks were observed to initiate at large pores and microshrinkage cavities and then to propagate along the hard inclusions towards the free surface when cracks originate from a subsurface pore. The validated experimental protocol is presently applied to in-situ fatigue tests realized with synchrotron tomography and a newly developed DVC platform in order to analyze the damage micromechanisms of this alloy subjected to low cycle fatigue test.

Inhomogeneous deformation in polycrystalline material is important matter, because the concentration of deformation relates with the origins of yield, fracture and recrystallization. Plastic strains in three-dimension during tensile deformation have been investigated by using the marker tracking method in synchrotron X-ray microtomography. Three-dimensional position of grains was detected by grain-boundaries visualizing method. The variation of deformation was measured for each grain. We investigated how much external deformation deformed grains heterogeneously.

Creep failure of materials under service conditions strongly rely on the formation and growth of cavities, encouraging the characterization and modelling of the cavitation process. In the present work pre-existing pores from manufacturing process are investigated in 9Cr steel creep loaded for up to 9000 hours. Scanning electron microscopy (SEM) is used for 2D analysis while Computer tomography (CT) is employed for 3D exploration. Nearest neighbours distances in 3D are calculated from 2D measurements and are decreasing with creep exposure time. The pore growth is studied applying a physical growth model, and experimental results are compared with numerical simulation. From this research it is deduced that damage occurs by agglomeration and growth of pre-existing cavities. The developed model can predict the growth of pores as a function of temperature and load at service.

The fatigue crack propagation behavior in an Al-Zn-Mg-Cu alloy was investigated by amalgamating X-ray diffraction (XRD) with grain boundary tracking (GBT). The integrated technique, Diffraction-Amalgamated Grain Boundary Tracking (DAGT), provides new possibilities for mapping grain morphologies and crystallographic orientations in three-dimension (3D). 3D crack morphologies at different propagation stages in the bulk of metallic materials were successfully obtained by using Synchrotron Radiation X-ray Microtomography (SRCT). Using 2D slices of the 3D crack, the crack length increment was measured to calculate the crack growth rate which varies significantly. Typical crack morphology, such as crack tilt, is detected by the observation of 2D tomographic slice image. The observed interaction between fatigue crack and polycrystalline microstructures can be analyzed in 3D. Through this synthesis of techniques, DAGT, a detailed direct assessment of microstructure and crack propagation behaviors has been achieved.

In cast aluminum alloys used in the automotive industry the microstructure inherited from the foundry process has a strong influence upon the fatigue behavior. In the cylinder heads produced by the Lost Foam Casting process, the microstructure consists of hard intermetallic phases and large gas and microshrinkage pores. In order to study the influence of this complex 3D microstructure on fatigue crack initiation and propagation, an experimental protocol using laboratory and synchrotron tomography, Finite Element simulation and 3D Digital Volume Correlation has been used. Full field measurements at the microstructure scale were performed during a low cycle fatigue test at room temperature performed in situ under synchrotron X-ray tomography (TOMCAT beamline, SLS). Synchrotron tomography allowed characterizing the eutectic Al-Al₂Cu, iron based intermetallics phases and above all eutectic Si, which could not be distinguished with laboratory tomography; these constituents were proved a suitable natural speckle for Digital Volume Correlation.

The 3D cracks were observed to initiate at large pores and then to propagate along the hard inclusions towards the free surface. The DVC of in-situ fatigue tests allows observing the relations between cracks and displacements discontinuities and strain localizations in measured field. The experimental protocol proposed will be further improved for a validation at a temperature characteristic of in-service conditions of cylinder heads (250°C).

In-situ time- and temperature-resolved synchrotron radiation techniques like ultrafast synchrotron X-ray tomographic microscopy and powder diffraction are unique tools for the dynamic characterization of materials processing by microwave heating. The absorption of microwave energy is typically a very fast process, with heating rates of the order of hundreds of degrees per second being no exception. The microwave energy absorption efficiency changes significantly with increasing temperature. Another unique feature of microwave heating is the intrinsic dielectric and/or magnetic selectivity, which often translates into the preferential deposition of microwave field energy only into specific specimen regions. For inhomogeneous materials in particular, complex patterns for the dynamic electromagnetic and temperature field distributions can be expected thus making the use of 3D monitoring methods not only meaningful but also necessary. We report on our recent progress with the in-situ characterization of microwave heating of metallic, ceramic and composite materials at very high heating rates. Experimental methods with subsecond temporal resolution, in particular high-temperature time-resolved X-ray scattering and time-resolved X-ray microtomography using synchrotron radiation, are discussed. Examples include microwave-assisted structural phase transitions and sintering in Al-alloys, foaming of construction materials, microwave processing of ceramics and composites.

The variant distribution and three-dimensional (3D) configurations of the heterogeneously formed S (Al₂CuMg) precipitates at dislocations were studied by means of high resolution transmission electron microscopy (HRTEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) tomography. The preferred S variant pair along dislocation was proved to be S1 & S4 or its counterparts, and the inherent characteristic of the crystal structure of the S phase, i.e. the symmetry of pentagonal subunit, was considered to be the fundamental factor determining the preference of variant pair. The obtained 3D reconstructions of the S precipitates formed at helical dislocations can clearly reveal both the morphology of individual S precipitates and the overall configuration of the S precipitates nucleated at these dislocations.

The use of focused ion beam (FIB) microscopes to characterise the microstructure of materials in three dimensions, by reconstruction of serial sections, has rapidly grown during the last decade. This is due to improved capabilities in material characterisation and more effective control of the ion beam to cut cross sections in a wide range of materials. It is easy to assume that a visual reconstruction of a stack of images produced by FIB is a fairly accurate representation of the true 3D structure and subsequently carry out measurements based on these data. However, it will be shown that this is not straightforward and in practice, errors or uncertainties in the sectioning, imaging or mapping, and reconstruction can combine to produce misleading results. This paper discusses the metrological challenges faced, but often disregarded, in measurement of the errors and uncertainties that occur throughout FIB 3D characterisation of materials. This was done by studying image stacks and 3D reconstructions from purpose-made structures of known geometries and composition.

In the present work we analyze the growth history of individual grains and grain boundary junctions. Based on a mean-field theory this enables us to calculate from stochastic fluctuations of individual junctions during grain growth the average growth law of the ensemble of grains, which we find to be in very good agreement with the growth law simulated by the Monte Carlo Potts model.