AmorFeTa

Amorphous metals in additive manufacturing

Aim of the development

Advances in rocket and computer technology, particularly through reusable rocket stages and the miniaturization of sensor systems, enable complex tasks to be carried out using constellations of many small satellites. The market for small satellites (up to 500 kg) is set to grow from $3.3 billion (2020) to $13.7 billion by 2030. A key driver is the goal of providing global mobile internet, especially in remote regions, through satellite constellations consisting of thousands of satellites. This technology can improve internet connectivity in previously untapped areas, provided that costs remain low. Fast internet connectivity is essential for economic development, particularly in regions that have not yet been adequately served, which is why this project is of great importance.

To keep signal propagation times short and avoid space debris, satellites are positioned in low Earth orbits. However, efficient propulsion technology is needed there to counteract air resistance and prevent collisions. Effective electric propulsion systems, such as Hall thrusters powered by solar energy, are used. These require only a small amount of support mass, but still require the storage of noble gases such as krypton or xenon, which are difficult to accommodate in small satellites because the tanks cannot be refilled during their service life (approx. 5 years). Fuel tanks must meet high requirements: mechanical strength, corrosion resistance, tightness, radiation resistance, and low weight. They are often made of titanium alloys or CFRP composites. To reduce transport costs, it is essential to keep the empty mass as low as possible. In addition, a lower mass reduces fuel consumption during launch and thus pollutant emissions at high altitudes.

When it comes to tank geometry, conflicting requirements must be met: Spherical tanks are ideal for pressure vessels, but usually do not fit into the flat space available in satellites. Cuboid tanks make better use of space, but are heavier and require stronger walls. Modern approaches use topology optimization and additive manufacturing to produce customized, lightweight tanks that make optimal use of the volume. Materials such as titanium-based alloys and, in particular, bulk amorphous metals (BMGs) offer high strength at low weight. BMGs, also known as solid metallic glasses, are isotropic, have high surface quality, good low-temperature properties, and are corrosion-resistant. Due to their higher density compared to titanium alloys, they can achieve smaller wall thicknesses with the same strength, which further reduces the tank mass.

The component size is limited by the build platforms in the additive process, but large structures (up to 800x400x500 mm) are feasible. BMGs also offer potential for use in mobile fuel cells, e.g., for hydrogen storage in drones, enabling longer operating times. The miniaturization of such tanks is complex, but advantageous in applications such as transport drones, rescue systems, or solar park inspections. Another promising area of application is the development of solid-state joints made of amorphous metals. These enable complex movements with few components, are wear-free because they do not require friction surfaces, and function in a vacuum without lubrication – ideal for space travel and aviation. Due to their elastic properties, they are suitable for grippers, space pointing, adaptive wings, or rotor systems. They offer greater adjustment ranges with little effort, making them attractive for high-precision control systems.

The investigation of the use of BMGs and additive manufacturing for both applications, tanks and joints, based on BMGs, had the overall goal of achieving significant weight savings in both application areas compared to the state of the art through higher strengths and lower wall thicknesses.

Advantages and Solutions

For the successful development of lightweight yet highly resilient components manufactured from amorphous metal using the powder bed fusion laser-based process (PBF-LB), it was crucial to take numerous factors along the process chain into account. The quality of the manufactured components depended on process parameters such as scanning speed, laser power, track spacing, focus diameter, and possible negative influencing factors such as foreign powder residues and residual oxygen content in the protective gas atmosphere during additive manufacturing, but also in the powder material itself.

When processing BMGs in particular, it is essential to control these parameters precisely in order to achieve high mechanical strength. Investigations were therefore carried out into the relationships between the process parameters and the resulting mechanical properties, as well as into the occurrence of oxygen introduction and other harmful contaminants along the entire process chain, starting with the delivered powders. Methods such as XRF (elemental composition), laser diffraction (particle size distribution), and SEM (particle shape) were used to characterize the powdered starting material. These analyses were intended to establish previously insufficiently investigated correlations between material properties and process parameters in order to enable replication of the process on other plants.

Based on this, track tests are carried out in which small quantities of material are processed at different scanning speeds, laser powers, and focus diameters. The resulting tracks were examined microscopically for homogeneity, continuity, and density. The most promising parameters were then used to derive the next steps in the optimization process, in which fine bulk structures with varying track spacings are produced. The quality of these structures was assessed by means of optical evaluation, computer tomography, and criteria such as density and porosity. In addition, the occurrence of residual crystallinity was checked by X-ray diffraction (XRD) and indirectly by hardness values (Vickers), and the influence on the mechanical properties was investigated. Based on this, special hatch patterns were developed to reduce residual crystallinity by remelting (re-melting scan strategy) to increase the relative density and reduce the cooling times of the melt pool. Special patterns with large distances between the individual melt tracks were used to minimize heating and oxygen uptake.

This was followed by optimization of the contour paths to improve surface quality (roughness, shape deviations), which is particularly important for the mechanical properties of relatively hard and brittle materials. The surface quality was assessed using laser scanning microscopy. Ultimately, the targeted local use of specialized scanning strategies for thin-walled and thick-walled component sections resulted in an optimal combination of mechanical properties. While a scanning strategy with a particularly high resulting surface quality was optimal for the thin-walled component sections, a scanning strategy with a greater focus on avoiding residual crystallinity was developed for thicker-walled sections in order to prevent brittle fracture failure. With regard to the topology optimization of lightweight structures, it was important to take into account both the special mechanical properties of amorphous metals and the imaging possibilities in the PBF-LB process. Topology optimization was carried out with the aim of completely eliminating non-removable internal support structures, for which, on the one hand, optimization of the laser parameters for the production of the overhanging component sections (to be supported) secondly, optimized alignment of the components, and thirdly, the use of load-bearing reinforcement structures inside as possible solutions for achieving the project goal.

In summary, the use of the developed, optimized process routine and adapted topology-optimized structures resulted in significant weight savings of over 10 percent compared to the use of steels (for solid joints) and titanium alloys (for pressure tanks).

Target market

The AMPOWER Report 2024 estimates the global industrial market for additive manufacturing in 2023 at around €10.5 billion, with an expected growth rate of 13.9%. The report highlights a clear trend toward the use of additively manufactured end components, particularly in industries with high requirements for mechanical properties, wear resistance, and surface quality.

Zu den wachstumsstärksten Segmenten zählen Luft- und Raumfahrt, Medizintechnik, Energie und Werkzeuge/Formsätze, also jene Bereiche, in denen die hohen Festigkeiten, elastischen Eigenschaften und die Korrosionsbeständigkeit amorpher Legierungen hohe Anwendungspotenziale besitzen. Im Bereich PBF-LB wird ein zunehmender Einsatz spezialisierter Legierungen jenseits der etablierten Werkstoffe wie Ti-6Al-4V, Inconel-Legierungen und rostfreien Stählen beschrieben. Dabei wird der Bedarf an „advanced materials with tailored properties“ als einer der wichtigsten Wachstumstreiber identifiziert. Dies unterstützt die Marktchance für Werkstoffe wie Zr-basierte BMGs, die durch ihr metastabiles Gefüge für Anwendungen mit extremen Belastungen prädestiniert sind. Die Wettbewerbssituation im AM-Sektor wird als zweigeteilt beschrieben: Einerseits existiert eine große und wachsende Anzahl kleiner Anbieter die zu einer Fragmentierung des Marktes beiträgt. Andererseits dominieren im Metall-AM-Sektor weiterhin wenige große Unternehmen, insbesondere im Maschinen- und Pulversektor.

Since amorphous powders are currently only available in very small quantities and there are only a few specialized manufacturers, this suggests a favorable competitive situation: The market for highly specialized metal powders is small, innovation-driven, and offers new suppliers opportunities for differentiation. At the same time, the report shows that demand for novel high-performance materials is growing faster than their availability, which increases the chances of entering niche markets. Overall, the trends presented in the AMPOWER Report indicate that the customer markets for amorphous alloys produced using the PBF LB process represent a dynamic and growing environment with clear demand for materials with above-average performance. The knowledge gained in the project on the processing of Zr-based amorphous alloys using the PBF LB process will be transferred in a targeted manner with a view to the widest and most effective use possible, particularly in sectors where the specific material properties of amorphous metals offer clear added value. Amorphous metals are characterized by a combination of high strength, high elasticity, and corrosion resistance.

The materials have been tested for biocompatibility and meet the requirements of ISO 10993-5 and ISO 10993-12, making them suitable for medical applications. The combination of these material properties with the geometric freedom of additive manufacturing opens up a wide range of applications, from medical technology and precision mechanics to aerospace and lightweight construction. Based on these fundamentals, the transfer pursues the following strategy: By providing validated PBF-LB process parameters and proven powder and material quality, small and medium-sized enterprises (SMEs) and specialized service providers are given direct access to the production of amorphous components.

At the same time, cooperation with established companies is to be intensified. One focus is on medical technology applications: since amorphous alloys are already qualified for surgical instruments and implants, the project results can be directly transferred to medical components. The combination of AM processes and amorphous materials can offer a clear competitive advantage, particularly for components with complex geometries, filigree structures, or increased material performance requirements.

In addition, applications in areas such as robotics, sensor technology, aerospace, and lightweight structures are clearly addressable: the high specific strengths, elasticity, corrosion and wear resistance, and isotropic material behavior of amorphous metals offer advantages over conventional materials in these areas. The collaboration with Heraeus AMLOY and other industrial partners also opens up the possibility of further developing the powder and processing technology. This means that the methodology can be gradually extended to new alloys and applications, further increasing innovation and competitiveness.

This transfer and marketing strategy ensures that the project results are not only scientifically documented, but also transferred directly into industrial applications with realistic market access, high material and process quality, and clear differentiation thanks to the special advantages of amorphous metals.