Table of contents
Properties and significance of refractory alloys
Refractory alloys made from materials such as tungsten, molybdenum, niobium, tantalum, rhenium and vanadium play a key role in extreme applications in the aerospace industry. aerospacenuclear technology, the high-temperature industry, medical technology and electronics (1). These high-performance materials are characterized by exceptional properties that make them essential for innovative technologies.
The characteristic features of these alloys include
- Particularly suitable for operating temperatures above 1200 °C
- Melting points mostly above 2000 °C
- High strength and exceptional resistance to wear, creep and distortion
- Excellent temperature and load resistance
Despite their outstanding properties, these materials present researchers and developers with major challenges. Classic alloys such as MoNbTaW often exhibit poor machinability, high density and, above all, oxidation problems (2). Tungsten and molybdenum in particular form volatile oxides when in contact with air or oxidizing atmospheres, while tantalum and niobium develop solid protective layers but are also susceptible.
Innovative manufacturing processes
The processing of refractory metals requires specialized manufacturing processes, as these can usually no longer be processed by melting metallurgy. Powder metallurgical processes have established themselves as the industrial standard and enable the targeted adjustment of porosity, structure and alloy composition (3).
Modern powder metallurgical variants offer considerable advantages:
- Hot Isostatic Pressing (HIP) for very dense, fine-jointed materials
- Spark Plasma Sintering (SPS) with low processing temperature
- Minimization of process-related oxygen uptake
- High material utilization due to minimal loss during pressing and sintering
The additive manufacturing of refractory alloys using laser powder bed fusion or electron beam melting offers potential for complex geometries and customized components. Advances in process control, such as optimized atmospheres or in-situ reaction control, are continuously pushing the application boundaries (4). In recent research, targeted in-situ alloy formation and local reinforcement with carbides and oxides have increased component quality.
Refractory High-Entropy Alloys (RHEA)
High-entropy alloys with several main components, in particular Refractory High-Entropy Alloys (RHEA) such as HfNbTaZr or MoNbTaVW, are being developed specifically for extreme environments (4). These innovative materials exhibit characteristic properties that distinguish them from conventional alloys and open up new possibilities in high-temperature technology.
RHEA are characterized by the preferred formation of single-phase, solid solutions that exhibit very high yield stresses and exceptional corrosion resistance. Particularly noteworthy is their resistance to radiation, which makes them ideal for nuclear applications, as well as their self-healing properties in the event of radiation damage. These properties result from the complex interaction between the various alloying elements, which leads to a unique microstructure.
Modern design strategies are increasingly using computer-aided methods:
- Machine learning to predict optimal compositions
- Monte Carlo simulations for structural analysis
- Multiscale modeling for property optimization
RHEA based on Mo, Ta, Nb and W in particular show great potential for nuclear technology applications due to their exceptional radiation resistance and could represent the next generation of reactor materials.
Industrial applications and areas of use
The special properties of refractory alloys make them indispensable for a wide range of industrial applications. Components such as turbine blades, rocket structures, valves or heat-resistant radiation shields benefit directly from these properties (4). High entropy alloys show significant advantages over classic nickel-based superalloys at operating temperatures above 1200°C.
Special areas of application include:
- Aerospace: Turbine blades, rocket structures
- Nuclear technology: radiation shielding, structural components
- Medical technology: Biocompatible implants (tantalum, niobium)
- Electronics: imaging systems, electrical contacts
- High-temperature industry: radiant heaters, heat-resistant valves
Tantalum and niobium are used in implants and electronic components in particular, as they are biocompatible, corrosion-resistant and radiopaque. Tungsten and molybdenum are used in imaging systems and as heat emitters or electrical contacts (5).
Comparison: Powder metallurgy vs. additive manufacturing
Both manufacturing processes offer specific advantages and disadvantages for tungsten and molybdenum alloys and are used specifically depending on the application and component geometry. Powder metallurgy enables the production of dense, fine-grained alloys with high purity and a uniform microstructure with minimal material losses. Pressing and sintering minimizes material loss, which reduces raw material costs and at the same time allows good control over the alloy composition. The targeted selection and mixing of the powders allows precisely defined material properties, even for difficult-to-mix systems such as TZM (molybdenum-titanium-zirconium-carbon). The method is also very well suited to the mass production of small to medium-sized components of the same geometry with narrow dimensional deviations.
Additive manufacturing, on the other hand, enables complex geometries, internal channels and bionic structures that would be impossible or very costly to implement using powder metallurgy. Additive processes such as laser powder bed fusion or binder jetting offer geometric flexibility that brings decisive advantages in the development of innovative component designs. Individual parts and small batches can be produced quickly and without expensive tools, which is ideal for research and prototype development. Complex or functionally integrated components are often significantly cheaper, as machining and assembly are no longer necessary and designs can be optimized without regard to milling or punching capabilities.
However, both processes face significant technical challenges. Defect and process control requires the utmost attention with both technologies, in particular the control of cracking and porosity with tungsten is problematic due to high melting points and brittle solidification. Material losses due to evaporation of low-melting alloy components such as nickel or iron can lead to uncontrollable alloy loss during melting. The need for post-processing, such as de-powdering, smoothing or post-heat treatment, usually remains, and components do not always achieve the density and mechanical quality of classic powder metallurgical components
Solutions for processing challenges
Pre-alloying powders in additive manufacturing significantly reduces evaporation and thus the loss of volatile alloying elements such as nickel or iron, as these are already homogeneously integrated and chemically bound within each individual powder particle (6). With pre-alloyed powders, the desired alloy composition is already set in the melt and the powder is then produced by atomizing the completely molten alloy.
Other important solutions include
- Improvement of oxidation resistance through protective coatings
- Doping with aluminum or silicon
- Innovative surface modifications
- Modern additive processes with controlled atmosphere
- Computer-aided methods and multiscale simulations
The avoidance of oxygen absorption and the production of homogeneous, fine-grained structures remain key challenges that can be overcome through precise process control and modern process technology.
Conclusion
The efficient production and application of refractory alloys in highly stressed industries can only be achieved through the interplay of advanced powder metallurgy, additive manufacturing and innovative material design. Refractory high-entropy alloys offer particular potential for extreme applications in nuclear technology and aerospace. Despite existing challenges in processing and oxidation resistance, targeted alloy development, protective coatings and highly developed manufacturing processes offer a way to continuously lead these high-performance materials into new application spheres. The development of pre-alloyed powders and optimized process parameters will play a key role in their future industrial use.
List of sources
(1) Zhuo, L. et al.: A review on recent progress of refractory high entropy alloys. Journal of Materials Research and Technology 33:1097-1129 (2024).
https://www.sciencedirect.com/science/article/pii/S2238785424021355
(2) Pacchioni, G. et al.: Designing ductile refractory high-entropy alloys. Nature Reviews Materials (2025). https://www.nature.com/articles/s41578-024-00763-1
(3) Mukherjee, P. et al.: Additive manufacturing of refractory metals and carbides for extreme environments: An overview. Science and Technology of Welding and Joining. 29.
(4) Rodriguez, S. et al: Application of Refractory High-Entropy Alloys for Higher Performance in Advanced Nuclear Reactors and Aerospace (2021). DOI: 10.2172/1822585
(5) Leading Edge Metals: Exotic & Refractory Metals in the Medical Equipment Industry (2025).
https://leadingedgemetals.com/industrie-exotic-refractory-metals/medical-equipment-industry/
(6) Tungsten industry: Tungsten alloy for 3D printing of complex components
https://medizin-und-technik.industrie.de/3d-druck/wolframlegierung-fuer-3d-druck-komplexer-bauteile/
