Abstract
Tailored heterogeneous distributions of microstructural features enable extraordinary material performance in biological and physiological structures such as trees, the aortic arch, human teeth and dinosaur skulls. In ductile iron, a heterogeneous distribution in size and morphology of graphite nodules and variations of the fractions of ferrite and pearlite are created during solidification, and varies as a function of parameters such as local cooling rate, segregation and flow. In the current work, the size distribution as well as the orientation and relation between graphite nodules is obtained by a three-dimensional reconstruction of a ductile iron microstructure from X-ray tomography. The effect of the nodule morphology and clustering on the localization of plastic strains is studied numerically using finite element analysis of the reconstructed microstructure. Real castings have a variation in geometry, solidification conditions and are subjected to variations in loads. A framework for optimized geometry and solidification conditions in order to design and deliver castings with tailored local material performance is proposed.
Highlights
Nature is filled with examples of structures where heterogeneous distributions of sub-scale features have been tailored to enable extraordinary performance when the structure is subjected to load
A heterogeneous distribution in size and morphology of graphite nodules and variations of the fractions of ferrite and pearlite are created during solidification, and varies as a function of parameters such as local cooling rate, segregation and flow
This paper aims to highlight current and future research in the area and demonstrate how increased knowledge about the formation and effect of graphite nodules can be utilized in an integrated simulation methodology to enable the use of tailored heterogeneous material behaviour in the design process for ductile iron castings
Summary
Nature is filled with examples of structures where heterogeneous distributions of sub-scale features have been tailored to enable extraordinary performance when the structure is subjected to load. Local microstructure variations are visibly seen as annual rings, but are present as large-scale variations throughout the tree This enable large deformations and absorption of energy when the tree is subjected to strong winds, and makes the tree insensitive to damage initiation and crack propagation [1]. Most metallic alloys solidify in a non-isothermal transformation through the nucleation and growth of phases, where factors such as chemical composition and local cooling rate affects the final morphology, refinement and amount of different phases. In shape casting, this inevitably leads to heterogeneous microstructures
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