Prof.  Yilong  Han
The Hong Kong University of Science and Technology,  China

Title: Mechanical properties of crystalline-amorphous composite and crystal-to-glass transformations

Abstract:

Crystalline-amorphous composites are characterized by two fundamental geometric parameters: the mean diameter of the crystalline grains (D) and the mean thickness of the amorphous grain boundaries (l). While the influence of grain size on mechanical properties has been extensively studied, the role of grain boundary thickness—an equally critical parameter—has remained largely unexplored. For the first time, we present a systematic investigation of material strength, ductility, and elastic moduli across the complete (D, l) parameter space [1,2]. We generalize the conventional Hall–Petch and inverse Hall–Petch relationships of strength, σ y (D), to σ y (D, l). Our findings reveal that maximum strength in face-centered cubic (fcc) composites is achieved at an optimal geometry of (D, l) ≃ (50, 6) particles. These results provide a quantitative explanation for recent alloy experiments and offer new principles for designing materials with superior properties, such as simultaneous high strength and high ductility. A polycrystal can transition into a glass through two distinct pathways: by reducing the crystalline grain size or by increasing the thickness of the amorphous boundaries.This raises fundamental questions about the nature of the polycrystal-glass transition: is it a sharp phase change or a gradual crossover? These questions have been difficult to address experimentally due to the instability of ultrafine-grained polycrystals. Our simulations circumvent this challenge by compressing binary single crystals into polycrystals and further into glasses in both 2D and 3D [3]. We identify a sharp polycrystal-glass transition accompanied by distinct structural, mechanical,dynamical, and thermodynamic signatures. In contrast, we find that progressively expanding the grain boundary thickness induces a continuous crossover from a polycrystal to a glass. These simple model systems provide a novel perspective on glass formation and establish a new framework for studying crystal-glass transitions.

REFERENCES

1. Z. Xu, M. Li, and Y. Han, National Science Open 2, 20220058 (2023)

2. Z. Xu, M. Li and Y. Han, National Science Review 12, nwaf336 (2025)

3. H. Zhang and Y. Han*, Phys. Rev. X, 8, 041023 (2018)

Biography: