Reasearch
Field of Research
The Surface Chemistry and Laser Processing group concentrates on the laser-based synthesis of nanomaterials designed explicitly for new (powder) feedstock formulations in additive manufacturing (AM). As polymer and metal powder feedstocks have material-related limitations regarding their flowability, thermal properties, laser absorption, and melting-solidification kinetics affected by the laser-based AM, nanoparticle additives have great potential to optimize this process. They can further include controllable microstructural and functional properties in the printed parts.
To fully exploit the potential of these innovative materials, this group focuses on laser-based synthesis via laser ablation (LAL) and laser fragmentation (LFL) in liquids of various nanomaterials. The main goal is hunting for targeted surface chemistry to further support the produced nanoparticles on polymer, metal, or ceramic powder feedstocks. The large variety of materials (carbon, metal, metal-oxide/sulfide/boride nanoparticles in a different colloidal environment) gives access to a fundamental understanding of how nanoparticles interact with the support feedstock material, a prerequisite for the laser-based manufacturing process.
Project 1: Project within the Collaborative Research Centre Transregio 270
Title: Nano-functionalization of magnetic microparticles for engineering grain boundaries during additive manufacturing to build magnets with maximized hysteresis
It is hard to imagine the 21st century without permanent magnets. They are used in various applications such as electric power generation, transportation, and telecommunication and thus play an essential role in everyday and industrial applications. However, the high cost of rare-earth magnets, their supply, and availability represent critical factors, and novel technologies that avoid or minimize the use of such rare elements in permanent magnets need to be developed immediately. Here, additive manufacturing is a promising approach, as it allows the production of complex structures under low waste conditions, which will minimize the need for rare earth elements. However, the successful printing of magnet powders is still under investigation as printed magnets are often brittle and exhibit low magnetic properties.
This project addresses this issue and points out why nano-functionalization of rare-earth micro-powders with diamagnetic (Ag) or paramagnetic (ZrB2) nanoparticles may significantly improve the final magnetic properties. Here, we characterize the whole process chain, from the nanoparticle synthesis by pulsed laser ablation or fragmentation in liquids to the nano-additivated magnetic powder and the properties of the printed parts.
See also: SFB CRC/TRR 270, Subproject A11
Project 2: Method Development and Validation of In-situ Optical Emission Spectroscopy During Laser Powder Bed Fusion for 3D Reconstruction of Chemical Composition of Additively Manufactured Metal Parts
Understanding the elemental distribution in metal parts produced by additive manufacturing (AM) is essential for quality control and traceability. Our project focuses on developing an in-situ method using optical emission spectroscopy (OES) to track and document the chemical composition during powder bed fusion with a laser beam (PBF-LB/M). Currently, advanced in-situ techniques for PBF-LB/M are unavailable. Our goal is to create a PBF-LB/M-integrated OES method to analyze and record quality control information in five dimensions (space, element emission wavelength, and intensity). This method will enable 3D composition reconstruction of the manufactured parts, validated by ex-situ analyses. By focusing on structural (Scalmalloy) and functional (NdFeB) model materials, we aim to expand the knowledge gained from our previous research on permanent magnets to a broader range of materials and applications.
See also: SFB CRC/TRR 270, Transferproject T1
Important literature:
A. R. Ziefuß, P. Gabriel, R. Streubel, M. Nachev, B. Sures, F. Eibl, S. Barcikowski, In-situ composition analysis during laser powder bed fusion of Nd-Fe-based feedstock using machine-integrated optical emission spectroscopy; Materials & Design, 2024, 11321
Project 3: How surface chemistry affects the electronic heating at liquid-metal interfaces
All projects described above require the addition of nanoparticles (to either metal or polymer microparticles) which we produced free of organic molecules via a laser-based synthesis route in liquids. A precise understanding of this process is a prerequisite for precisely tuning the surface chemistry of the produced nanomaterials. Besides, tuning photophysical interactions at the liquid-nanoparticle interface provides significant insights into electronic processes, particularly in determining the lifetime of the optically induced hot electron population. Such understanding is essential for a variety of applications, ranging from hot-electron electrochemical catalysis to biomedical optoporation. In this context, a quantitative understanding of processes like the electron-phonon coupling (EPC) is fundamental since it influences the lifetime of the optically induced hot electron population, determines electronic transport, and is responsible for transferring excess electronic energy to the lattice, resulting in heat generation. However, it is still an open and controversially discussed question to which extent and by which mechanisms EPC is affected in nanoscale material systems. While the influence of particle size on the EPC is described in the literature, the effects of the colloidal environment on the early relaxations of nanoparticles (NPs) remain controversial. The influence of an inorganic chemical environment on electron relaxation is, however, currently unexplored which the surface chemistry and laser processing group will address.
Project 4: Nonequilibrium thermal processing of nanoparticles: Laser melting and fragmentation in liquid
Over the years, researchers have been fascinated by the interaction between pulsed lasers and matter. Depending on the laser fluence (typically over several J⋅pulse-1⋅cm−2) and target dimension, this interaction can lead to laser ablation in liquid (LAL) or laser fragmentation in liquid (LFL), resulting in the production of nanoparticles (NPs), observable by a clear size change of matter. Laser melting in liquid (LML) differs significantly from LAL and LFL methods. Unlike LAL and LFL, LML operates at much lower laser fluences, typically ranging from several tens to hundreds of mJ⋅pulse-1⋅cm−2, one to two orders of magnitude less than fluences required for LAL and LFL. LML has shown promise in generating sub-micrometer spheres in a volume-conserving process. However, the LML of micrometer particles dispersed in pure water remains underexplored. However, the full extent of this capability remains unexplored and will be the primary focus of this study.
Project 5: Mechanistic Insights into Nanocluster Formation via Microparticle Laser Fragmentation in Liquids: Unravelling Photothermal and Photomechanical Processes for Controlled NCs Synthesis
This research project aims to investigate and optimize the mechanisms of microparticle laser fragmentation in liquids (MP-LFL) to produce nanoclusters (NCs) and nanoparticles (NPs) with high purity and precise size control. MP-LFL combines the advantages of laser ablation in liquids (LAL) and nanoparticle laser fragmentation in liquids (NP-LFL) while overcoming their limitations. This positions MP-LFL as a promising method for scalable nanomaterial synthesis with applications in catalysis, energy technologies, and advanced materials.
Although the three main fragmentation mechanisms—photothermal phase explosion, photomechanical spallation, and central cavitation—have been identified, key questions remain about their influence on particle size distributions and yield. In particular, it is unclear how laser parameters, such as fluence and pulse duration, can be optimized to selectively achieve monomodal particle size distributions with high yield and enhance microparticle fragmentation efficiency.
The project leverages the complementary expertise of the two applicants: Prof. Heinz Huber (HM) focuses on time-resolved single-particle studies to decipher the dynamics of MP-LFL processes. At the same time, we conduct multi-particle experiments under realistic conditions to investigate scalability. This dual-method approach provides a comprehensive analysis, bridging fundamental mechanisms and practical implementation.
The project outcomes aim to establish MP-LFL as a precise, scalable technology. This will contribute to a deeper understanding of laser-matter interactions and enable the development of high-purity nanomaterials with optimized properties. The findings will serve as a foundation for future innovations in nanomaterial synthesis and industrial applications.
Project 6: Surface and Volume-Sensitized Polymer Powders for Diode Laser Powder Bed Fusion
Understanding how the modification of commercial polymer feedstocks with near-infrared (NIR)-absorbing nanoparticles (NPs) influences the diode-laser-based powder bed fusion (PBF-LB/P) process is essential for addressing current challenges. Issues like inadequate laser absorption in unmodified polymer materials necessitate a thorough investigation into how these modifications can enhance energy transfer during printing. This project will explore the impact of NP distribution—whether on or in the surface or throughout the polymer matrix—on heat generation, heat distribution, and light scattering during PBF-LB/P.
Consequently, the knowledge transfer project aims to jointly develop a comprehensive understanding of how the type, distribution, and loading of NPs can optimize the NIR-PBF-LB/P process, thereby improving the aging resistance of the powders and the quality of printed components. The project's core is a joint work program focused on the intensive mutual exchange of scientific knowledge and application-related challenges. The research will systematically study NIR-sensitizing NP-modified polymer powders, at the example of PA12, to evaluate their printability and resultant part quality. Additionally, the project seeks to develop aging-resistant PA12 through surface modification with NIR-absorbing NPs, aiming to reduce thermal and oxidative degradation and enhance long-term stability and mechanical properties.
This project expands the knowledge of PBF-LB/P with diode lasers and corresponding feedstock modifications generated within the DFG SPP 2122 to surface-adsorbed, surface-encapsulated, and volume-additivated NP/PA12 feedstocks. Material-related determinants during PBF-NIR-LB/P are investigated to pave the way for new materials required for effective and efficient additive manufacturing with diode lasers.