Phase-field modeling of eutectic structures on the nanoscale: the effect of anisotropy

This is a post-peer-review, pre-copyedit version of an article published in Journal of Materials Science. The final authenticated version is available online at: https://doi.org/10.1007/s10853-017-0853-8A simple phase-field model is used to address anisotropic eutectic freezing on the nanoscale in two (2D) and three dimensions (3D). Comparing parameter-free simulations with experiments, it is demonstrated that the employed model can be made quantitative for Ag-Cu. Next, we explore the effect of material properties, and the conditions of freezing on the eutectic pattern. We find that the anisotropies of kinetic coefficient and the interfacial free energies (solid-liquid and solid-solid), the crystal misorientation relative to pulling, the lateral temperature gradient, play essential roles in determining the eutectic pattern. Finally, we explore eutectic morphologies, which form when one of the solid phases are faceted, and investigate cases, in which the kinetic anisotropy for the two solid phases are drastically different

Microscopic origin of demixing in Ge20SexTe80−xGe_{20}Se_{x}Te_{80-x} alloys

International audienceThe structure of Ge20SexTe80−x (x = 5, 10, 15, 20) glasses has been investigated by X-ray and neutron diffraction as well as Ge and Se K-edge extended X-ray absorption fine structure (EXAFS) measurements. Experimental datasets have been fitted simultaneously by the reverse Monte Carlo simulation technique. It has been found that all components obey the 8-N rule. Se binds preferentially to Ge. At x = 20, experimental data can be fitted without Se-Te bonding, but Se-Se bonds appear, and the Te-Te coordination number starts to increase. These observations show that though Se and Te are completely miscible in the liquid and in the solid phases the presence of Ge induces nanoscale phase separation

Ultrafine Fe-Fe2Ti eutectics produced by laser metal deposition: processing and characterization

Additive manufacturing (AM) presents advantages over the traditional production methods such as the ability to produce near net-shape components with reduced material usage and a weight-optimized component design. Laser-based AM process methods, i.e. Laser Metal Deposition (LMD) and Selective Laser Melting (SLM), provide rapid and directional solidification in the melt pool and hence the possibility to produce ultrafine microstructures. These conditions hold great promise for the production of novel eutectic materials with ultrafine microstructural length scales. Eutectics can benefit immediately and dramatically from rapid solidification, since it has been shown [1, 2] that the reduction of the eutectic spacing leads to increasing the materials strength along with increasing ductility and fracture toughness. In this presentation, we describe our research on Fe-Fe2Ti eutectics produced by Laser Metal Deposition (LMD). We will discuss the effect of process parameters such as Laser scanning velocity and Laser power on the microstructure on distinct length scales, encompassing features such as eutectic grain size, interlayer boundary morphology and eutectic spacing. We will show that the lamellar eutectic consisting of hexagonal Laves-phase Fe2Ti and the BCC a(Fe) can be processed to above 99.8 % density, while reaching lamellar spacing in the range of 50 to 200 nm. Furthermore, mechanical properties will be discussed based on microhardness measurements and in-situ micromechanical testing inside an SEM

Silver environment and covalent network rearrangement in GeS3–AgGeS_{3}–Ag glasses

The structure of Ag-doped GeS3 glasses (0, 15, 20, 25 at.% Ag) was investigated by diffraction techniques and extended x-ray absorption fine structure measurements. Structural models were obtained by fitting the experimental datasets simultaneously by the reverse Monte Carlo simulation technique. It is observed that Ge has mostly S neighbours in GeS3, but Ge–Ge bonds appear already at 15% Ag content. Sulfur has ~2 S/Ge neighbours over the whole concentration range, while the S–Ag coordination number increases with increasing Ag content. Ag–Ag pairs can already be found at 15% Ag. The Ag–S mean coordination number changes from 2.17 ± 0.2 to 2.86 ± 0.2 between 15% and 25% Ag content. Unlike the As–S network in AsS2–25Ag glass, the Ge–S network is not fragmented upon Ag-doping of GeS3 glass

Phase-Field Modeling of Polycrystalline Solidification: From Needle Crystals to Spherulites—A Review

Advances in the orientation-field-based phase-field (PF) models made in the past are reviewed. The models applied incorporate homogeneous and heterogeneous nucleation of growth centers and several mechanisms to form new grains at the perimeter of growing crystals, a phenomenon termed growth front nucleation. Examples for PF modeling of such complex polycrystalline structures are shown as impinging symmetric dendrites, polycrystalline growth forms (ranging from disordered dendrites to spherulitic patterns), and various eutectic structures, including spiraling two-phase dendrites. Simulations exploring possible control of solidification patterns in thin films via external fields, confined geometry, particle additives, scratching/piercing the films, etc. are also displayed. Advantages, problems, and possible solutions associated with quantitative PF simulations are discussed briefly