Towards a metadata scheme for the description of materials - the description of microstructures

Abstract

The property of any material is essentially determined by its microstructure. Numerical models are increasingly the focus of modern engineering as helpful tools for tailoring and optimization of custom-designed microstructures by suitable processing and alloy design. A huge variety of software tools is available to predict various microstructural aspects for different materials. In the general frame of an integrated computational materials engineering (ICME) approach, these microstructure models provide the link between models operating at the atomistic or electronic scales, and models operating on the macroscopic scale of the component and its processing. In view of an improved interoperability of all these different tools it is highly desirable to establish a standardized nomenclature and methodology for the exchange of microstructure data. The scope of this article is to provide a comprehensive system of metadata descriptors for the description of a 3D microstructure. The presented descriptors are limited to a mere geometric description of a static microstructure and have to be complemented by further descriptors, e.g. for properties, numerical representations, kinetic data, and others in the future. Further attributes to each descriptor, e.g. on data origin, data uncertainty, and data validity range are being defined in ongoing work. The proposed descriptors are intended to be independent of any specific numerical representation. The descriptors defined in this article may serve as a first basis for standardization and will simplify the data exchange between different numerical models, as well as promote the integration of experimental data into numerical models of microstructures. An HDF5 template data file for a simple, three phase Al-Cu microstructure being based on the defined descriptors complements this article.

Keywords: 100 Materials; 200 Applications; 300 Processing/Synthesis and Recycling; 3D microstructures; 402 Multi-scale modeling; 403 CALPHAD/Phase field methods; 404 Materials informatics/Genomics; 500 Characterization; 60 New topics/Others; HDF5; Metadata; hierarchy; interoperability; multiphase materials; multiscale modelling; nomenclature; ontology; simulation chains.

Graphical abstract

Figure 1.

The four core ontologies for the description of materials (middle) as ingredients of any component (left column), adapted from [16, 17]. The term ‘substance’ in [17] is replaced by ‘microstructure’ for the current purpose. The term ‘performance’ indicating the evolution of properties under environmental/operational conditions has been added for the component. The present paper aims at providing a detailed and comprehensive description of substances/microstructures (right column) as a part of the description of a material (middle column).

Figure 2.

Structure classifying the phase state of a material. Any of the depicted phase states can occur in multicomponent systems (i.e. systems comprising multiple chemical elements). Single component systems (i.e. pure elements) only occur as single phase materials except at critical points, where e.g. solid and liquid phases may coexist only in a very narrow temperature range. Multiphase single crystals are to be understood as a single crystalline matrix containing secondary phases. The present article focuses on solids only (light gray) but the concepts can readily be extended to fluids (dark gray). This structure provides the basic and generic concept of classifying materials according to their phase state as detailed in the text.

Figure 3.

Dimensional hierarchy of the description of the geometry of a microstructure. Each dimension group has different subsets, which correspond to different levels of detail. The RVE in the 3D description, for example, provides average values and statistical information, while Field/Cell corresponds to the highest resolution. See text for further details and explanations of the terms in the boxes.

Figure 4.

Hierarchical structure of materials.

Figure 5.

Illustration of the basic descriptors for the geometry of an RVE.

Figure 6.

The major descriptors for the composition of an RVE.

Figure 7.

Equilibrium Volume_Fractions of different phases in an RVE with a defined overall composition can be calculated for given conditions (e.g. temperature, pressure). There is no information about the spatial distribution of these phases. Shown is the example of the α, Θ and Liquid phases in a binary Al-Cu alloy.

Figure 8.

Major descriptors for the phases being present in an RVE.

Figure 9.

Major descriptors for an ensemble/a phase. The phases (blue and red) are already depicted here in a spatially resolved way.

Figure 10.

Descriptors for Features in an RVE. Note the similarity with the descriptors for the RVE geometry.

Figure 11.

Descriptors for a discretized simple geometry.

Figure 12.

FeatureID: Graphical scheme of a Feature indicator function in a 1D representation. The finite volume corresponds to a NumericalElement.

Figure 13.

Construction of volumetric NumericalElements (Cells) from vortices, edges, and surfaces (left: element object), further assembly of a number of NumericalElements forming a Feature (middle: feature object), and eventually an Ensemble of Features filling the entire RVE in this case.[10]

Figure 14.

Some major descriptors for Faces.

Figure 15.

Surface of a Feature 3 being composed from different interface areas identified by different FaceFeatureLabels. Feature 4 (liquid) is not shown. FaceFeatureLabels to be combined are FaceFeatureLabel(3,*) and FaceFeatureLabel(*,3) where * denotes all FeatureIDs except 3.

Figure 16.

FaceFeatureLabels for the different Features of the example. Feature 4 (Liquid Phase) is not shown. Note the negative FeatureIDs representing Features outside the RVE boundaries.

Figure 17.

Excerpt of an HDF5 file drawing on some of the descriptors being defined in this article and their hierarchical structure. This file is based on the Al-Cu example used throughout this article. It is available as a template for download from [32] along with this publication. Visualization of the file structure proceeds e.g. by HDF5-view.[12]