High strength and ductility across size scales: 3D printed metal materials with microscale heterostructure

icaf2023 Tracking Number 87

Low-weight design is pursued by aeronautical manufacturing since the very beginning. Additive Manufacturing (AM, also known as 3D printing) provides a method to build novel composite materials as well as high-performance structures from conventional materials. AM makes it possible for aeronautical structures to bear large loads with a low weight (examples shown in figures below). However, due to the microscale heterogeneity caused by AM process, AM metal materials exhibit different mechanical properties from conventional cast/wrought materials. The heterogeneity of AM metal products is nearly unavoidable, even if the printed materials is designed to be homogeneous. This phenomenon extensively occurs from microscale (grain boundaries, domain of different grain sizes) to mesoscale (structural or periodical micro-design) or even macroscale (product structures). These heterogeneities, especially the micro and mesoscale ones, always involve significant size-effect of materials. The author applies numerical simulations based on a modified strain gradient theory to find the strength-ductility relationships of heterostructured metal materials [1], the simulation result coincides well with the experiment and literature. Both statistically stored dislocations and geometrically necessary dislocations are combined in a mechanism-based theory to depict the mechanical response across size-scales. The Taylor stress and back stress are found dominating the high mechanical performance of materials with heterogeneous structures. And a hetero-zone boundary affected region, whose width seems to be a constant depended on the materials of the two phases, is revealed to be the key factor of such microscale heterogeneous materials. Results show that heterostructured metals possess superior mechanical properties exceeding the prediction by the rule-of-mixtures. Though the AM materials cannot achieve the performance of conventional manufactured ones in many cases, these efforts indicate that there is an opportunity for AM materials to bridge this gap and even get better. Many related researches together shed lights on the mechanisms of the strength-ductility of heterostructured materials across size scales, and this will help promote the design and manufacture of aeronautical AM structures to a higher level.