Refractory metals are a broad category of metallic materials that display excellent durability to thermal and mechanical stress. Their shared properties include resistance to corrosion and wear, high melting points, retention of mechanical strength at high temperatures, and high hardness at room temperature.
Tantalum, niobium, molybdenum, and tungsten are the most commonly used refractory metals.1–4 It is possible to combine these elements, both with other materials and with each other, to create a wide range of high-performance refractory metal compounds and alloys, which are fundamental to several industries.
This article examines the main applications of refractory metals and the range of compounds and alloys in which they are used.
Aerospace and Defense
The defense and aerospace industries require materials with superior thermal and mechanical durability. For defense and aerospace applications, refractory metals are an essential class of materials as they supply a foundation for strength retention to temperatures as high as 2200°C.
Niobium is especially useful for applications in aerospace because of its comparatively low density, which is equivalent to that of nickel.5 Molybdenum, tungsten, niobium, and tantalum all have a range of applications in aerospace, being used in forging dies, thrusters, shields, and balance weights.
While the aerospace and defense industries continue to widely use refractory metals, new opportunities are currently emerging due to developments in additive manufacturing and the production of novel materials with extremely high-temperature capabilities.5,6
Due to its extreme inertness, tantalum is predominantly used in the chemical industry. Spargers, reaction vessels and heat exchangers all utilize tantalum to reject the corrosive effects of nitric, sulfuric, and hydrochloric acids, along with liquid metals and organic chemicals.10
Electronics and Semiconductors
In general, refractory metals have strong electrical conductivity. This means they can be employed to manufacture very hard-wearing and durable electrical components. For example, long-life contact points can be created from refractory metals alloyed with copper, gold, or silver.
Combining thermal expansion coefficients that can be matched to popular semiconductor materials and high thermal conductivity allows molybdenum, W-Cu, and Mo-Cu to be applied to thermally control electronic devices.
The low diffusivity of deleterious elements and good electrical conductivity allows refractory metals to be used as sputtering targets for applications in back contacts, vias, and thin film diffusion barriers in flat panel displays and semiconductor devices.11
Tantalum powder, wire, and sheet materials are often employed in high-performance capacitors as cases, anodes and cathodes. The corrosion-resistant and durable oxide layer that is created on the surface of Ta enables it to yield very high capacitance values.
The high-temperature tolerance and durability of refractory metals make them an ideal solution for industrial parts, which may be exposed to extreme thermal and/or mechanical stress, such as furnace boats, glass melting electrodes, crucibles, shields, tubes, sintering trays, rods, sheets, and nozzles.
In particular, tungsten is widely used in the manufacture of highly durable industrial and mechanical parts. For these applications, tungsten is either combined with carbon in the form of tungsten carbide, used in its pure metallic form, or combined with nickel, iron-nickel, or copper to produce so-called tungsten heavy metals.
Mechanical applications also employ molybdenum, mainly as an alloying component in steel for structural applications. Molybdenum-based alloys like TZM (titanium-zirconium-molybdenum) are mainly utilized in high-temperature applications with heavy mechanical loads, along with hot metal forming dies.14
Refractory metals are frequently used in medical devices. For example, tantalum has applications in dental and medical devices because it is durable and tough and does not impact bodily tissues.
Molybdenum is often employed in medical scanning tools, being used in X-ray detectors and tubes. For radiation shields, tungsten is the material of choice due to its high density of 19.3 g/cm3, which means it delivers notably higher radiation absorption compared to lead.
Refractory metals are also used in MRI scanners, mainly tantalum and niobium, in the form of superconducting magnets.
Applications in the nuclear industry commonly use niobium, molybdenum, and tungsten. Tungsten heavy metals are mainly utilized in radiation shielding, which takes advantage of the heat resistance and high density of tungsten to diminish x-rays and gamma-rays.
Niobium zirconium alloys are employed as structural components in nuclear reactors, where their resistance to liquid metals and low neutron absorption cross-section are beneficial.3 Molybdenum and niobium can additionally be utilized for high-temperature irradiation-resistant equipment in high-temperature reactors.15
Molybdenum, tungsten, niobium, and tantalum alloys are receiving attention for their potential in next-generation nuclear fission reactors because of their capacity to maintain high mechanical strength at extremely high temperatures.
Research indicates that these materials may be applied as structural components in Generation IV fission reactors, while tungsten and its alloys are being thoroughly investigated to be used in high heat-flux applications in fusion reactors.16,17
Niobium and tantalum are often employed in low-temperature superconductor applications, such as MRI machines for medical imaging and additional analytical and experimental equipment, for example, mass spectrometry, particle accelerators, and NMR.
Due to its electronic characteristics and durability, tantalum is especially useful in superconductors in the form of sheets, which offer a durable and stable diffusion barrier between tin and copper layers, stopping direct contact between the tin and copper.
Tantalum and niobium are additionally used in rods for creating superconducting wires.
High-Performance Refractory Metals
Drawing on decades of expertise in metallurgy, H. C. Starck Solutions offers a full range of refractory metal fabricated parts tailored to all applications. The company offers complex assemblies, machined products and fabrications from refractory metals.
Prepared powders and additive manufacturing powders are also offered by H. C. Starck Solutions, such as molybdenum, tungsten, niobium and tantalum, along with compounds and alloys of each (for example, MHC, TZM and further alloys on request). 18
References and Further Reading
- Bauccio, M. ASM Metals Reference Book, 3rd Edition. (ASM International, 1993).
- Snead, L. L., Hoelzer, D. T., Rieth, M. & Nemith, A. A. N. Refractory Alloys: Vanadium, Niobium, Molybdenum, Tungsten. in Structural Alloys for Nuclear Energy Applications 585–640 (Elsevier, 2019). doi:10.1016/B978-0-12-397046-6.00013-7.
- Harvell, M. B. What are Refractory Metals. https://www.pickpm.com/wp-content/uploads/2016/08/What-Are-Refractory-Metals.pdf.
- International Journal of Refractory Metals and Hard Materials.
- Wadsworth, J., Nieh, T. G. & Stephens, J. J. Recent advances in aerospace refractory metal alloys. International Materials Reviews 33, 131–150 (1988).
- Satya Prasad, V. V., Baligidad, R. G. & Gokhale, A. A. Niobium and Other High Temperature Refractory Metals for Aerospace Applications. in Aerospace Materials and Material Technologies (eds. Prasad, N. E. & Wanhill, R. J. H.) 267–288 (Springer Singapore, 2017). doi:10.1007/978-981-10-2134-3_12.
- Aslan, E., Sarilmaz, A., Ozel, F., Patir, I. H. & Girault, H. H. 1D Amorphous Tungsten-Based Ternary Refractory Metal Sulfides for Catalytic Hydrogen Evolution at Soft Interfaces. ChemNanoMat 5, 1461–1466 (2019).
- Ma, Z., Liu, Y., Zhou, J., Liu, M. & Liu, Z. Recovery of vanadium and molybdenum from spent petrochemical catalyst by microwave-assisted leaching. Int J Miner Metall Mater 26, 33–40 (2019).
- polyak, D. E., John, D. A. & Seal II, R. R. Rhenium. (2017).
- Koivuluoto, H., Näkki, J. & Vuoristo, P. Corrosion Properties of Cold-Sprayed Tantalum Coatings. J Therm Spray Tech 18, 75–82 (2009).
- Vetrano, J. B. & Boom, R. W. High Critical Current Superconducting Titanium‐Niobium Alloy. Journal of Applied Physics 36, 1179–1180 (1965).
- Mineta, K. & Okabe, T. H. Development of a recycling process for tantalum from capacitor scraps. Journal of Physics and Chemistry of Solids 66, 318–321 (2005).
- Methods of fitting heavy metal to counterweights. High Power Media https://www.highpowermedia.com/Archive/methods-of-fitting-heavy-metal-to-counterweights.
- Harimon, M. A. et al. High temperature fracture toughness of TZM alloys with different kinds of grain boundary particles. International Journal of Refractory Metals and Hard Materials 66, 52–56 (2017).
- Palmer, A. J. & Woolstenhulme, C. J. Brazing Refractory Metals Used in High-Temperature Nuclear Instrumentation. 6 (2009).
- Muroga, T. Refractory metals as core materials for Generation IV nuclear reactors. in Structural Materials for Generation IV Nuclear Reactors 415–440 (Elsevier, 2017). doi:10.1016/B978-0-08-100906-2.00011-2.
- Rieth, M. et al. Recent progress in research on tungsten materials for nuclear fusion applications in Europe. Journal of Nuclear Materials 432, 482–500 (2013).
- Additive Manufacturing | HC Starck. (2019). https://www.hcstarck.com/additive_manufacturing_w_mo_ta_nb
This information has been sourced, reviewed and adapted from materials provided by H.C. Starck Solutions.
For more information on this source, please visit H.C. Starck Solutions.