High-performance copper alloys for pioneering technologies

1. Recent studies show that high-strength copper alloys offer excellent stability in hydrogen-rich environments, making them a promising alternative to other materials in the promising field of hydrogen technology. Unlike competing materials such as high-strength steels, CuBe alloys show no susceptibility to hydrogen embrittlement, despite their high strength. In addition, they provide an effective barrier against hydrogen penetration and diffusion. These alloys and the latest findings on them will be discussed in more detail below. 

   Alloys and property profiles 

   Copper-beryllium alloys (CuBe) have been regarded as proven materials in materials engineering for many years and have become indispensable in numerous industrial applications. They can basically be divided into two categories: alloys with particularly high mechanical strength and variants that are primarily designed for high electrical conductivity. 

   High-strength CuBe materials include Alloy 25 (C17200) and Alloy M25 (C17300). Both have a beryllium content of approximately 1.80 to 2.00% and are characterized by outstanding mechanical properties. Alloy M25 also contains lead, which significantly improves its machinability during turning, drilling, and milling operations. When hardened, Alloy 25 and Alloy M25 achieve the highest strength and hardness values of all commercially available copper alloys, making them particularly suitable for technically demanding applications. 

   CuBe alloys with comparatively lower strength but increased electrical conductivity generally have lower beryllium content and are additionally alloyed with elements such as cobalt and/or nickel. The beryllium content of Alloy 3 (C17510) and Alloy 10 (C17500) is in the range of 0.4 to 0.7%. Alloy 10X was developed to improve heat resistance and contains small amounts of zirconium compared to Alloy 10. This largely preserves strength and ductility up to temperatures of around 430 °C. The following table summarizes the most important characteristics of the alloys mentioned. 

The high strength of these alloys generally also contributes to excellent wear resistance and vibration resistance. These properties are retained not only at room temperature, but also at higher temperatures. This makes them particularly suitable for use in various sealing components in combustion engines. Examples of such applications include valve seats, valve guides, piston rings, and shims or sealing washers. These alloys were selected after extensive testing to reliably cope with the demanding conditions in these high-performance components.3)  

To achieve the high strength levels of copper-beryllium alloys, a precisely controlled precipitation hardening process is necessary, which takes place within a precisely defined temperature range. Particularly in the production of strip material, this heat treatment is often combined with cold forming to further improve the mechanical properties. 

Semi-finished products such as strips, which are later processed into final components, often undergo additional forming steps, such as crimping or extrusion processes. In such applications, heat treatment can also be carried out after component production. The components are first manufactured in a soft-annealed, easily formable state, which facilitates the implementation of complex component geometries. The subsequent precipitation hardening takes place directly on the finished component and sets the desired high strength values. 

This process is comparable to the case hardening of steel components, in which the final mechanical properties are also achieved by subsequent heat treatment. In this way, complex components can be manufactured efficiently and, in a material,-saving manner without having to sacrifice the high performance of the material.  

Due to their resistance to stress relaxation—even at higher temperatures—these high-strength alloys are often used in connectors, contacts, spring elements, and switches in the electronics industry.4) Even at cryogenic temperatures, the strength and elongation properties remain very stable; there is no embrittlement. Furthermore, due to their electrical and magnetic properties, the alloys are used as electromagnetic shielding gaskets (EMI/RFI) and, in most cases, due to their thermal conductivity, as heat sinks to protect sensitive electronic components.  

Another important field of application for copper-beryllium alloys is in components subject to friction and wear. The combination of a comparatively low modulus of elasticity and high yield strength results in a high resilience value. This has a positive effect on plain bearings, for example, as local stress peaks are reduced, resulting in significantly longer service life compared to other bearing materials. This allows for extended maintenance intervals, for example in construction machinery or underground mining equipment. 

In addition, CuBe alloys are naturally highly resistant to abrasion and wear. They allow for material combinations that are characterized by low friction and minimal surface damage. For example, threaded connections made from Alloy 25 in combination with stainless steels exhibit pronounced resistance to abrasion and cold welding (seizing).4) 

The special chemical composition of copper-beryllium alloys promotes the formation of beryllium-containing oxide layers, which give the materials significantly increased corrosion protection compared to most other copper-based alloys. Their resistance to numerous aqueous solutions of alkali hydroxides is particularly pronounced, both at low and elevated temperatures. 

As with other copper alloys, however, there are also media that must be evaluated critically. These include, above all, ammonium hydroxide and ammonia in humid or oxygen-containing environments. In contrast, CuBe alloys exhibit high chemical stability in cold concentrated sulfuric acid, in cold and warm diluted sulfuric acid, in hydrofluoric acid, and in cold diluted hydrochloric acid. 

A key advantage over stainless steels is the high resistance of CuBe alloys to chloride-induced stress corrosion cracking. In addition, they are highly resistant to biofouling, which favors their use in specialized applications such as interference-fit port seals in underwater telecommunications. Overall, these properties make copper-beryllium alloys a reliable material solution for applications with high requirements for corrosion resistance and operational safety.4) 

Behavior in hydrogen-containing environments 

The most well-known problem associated with the use of materials in hydrogen-containing atmospheres is hydrogen embrittlement. The susceptibility of the material used is determined by a critical interaction between the material (alloy composition, microstructure, strength condition), the hydrogen environment, and the external or internal stresses in the component. This combination then results in a deterioration of the strength and toughness properties of the material, which in turn can lead to catastrophic component damage and corresponding failures. The term hydrogen embrittlement encompasses various phenomena 

5), which in most cases affect high-strength metallic materials. The problem with hydrogen embrittlement is that it can occur both during the production of the materials and later during component production or, in the worst case, during operation. Unlike other material defects, not every component or individual material batch has to be affected; individual components from individual batches can also show this type of damage. In addition, measuring hydrogen, especially in components, is quite difficult and usually not feasible in series production testing.  

Comparative tests are crucial for reliably assessing the resistance of materials in hydrogen-rich environments. In an extensive research program conducted in collaboration with Ruhr University Bochum and the DECHEMA Research Institute, the stability of various high-strength copper-based alloys was investigated. The CuBe alloy Alloy 25 achieved particularly convincing results. 

The tests showed that even after prolonged loading times under gaseous or electrochemical conditions, no significant hydrogen content was detectable in the material. This suggests that Alloy 25 shows virtually no hydrogen absorption. In addition, hydrogen loading did not impair the mechanical properties of the alloy in quasi-static tensile testing. This confirms the high resistance of Alloy 25 to hydrogen embrittlement—a problem that affects many other metallic materials under similar conditions. 

These results are particularly relevant as they demonstrate the suitability of Alloy 25 for applications in hydrogen-rich environments, thus ensuring the reliability and safety of components under extreme operating conditions. 

Diffusion measurements using a permeation cell also showed that not only does hardly any hydrogen penetrate the material, but that there is also no measurable diffusion through the material. The alloy can therefore be regarded as a barrier to hydrogen ingress or passage and is therefore suitable for sealing components in the field of hydrogen technology. Material combinations that can be realized using plating processes are also conceivable. 6) 7)  

Safety and the environment 

In connection with beryllium-containing alloys, questions are often asked about safety or environmental aspects and possible restrictions. These points will be briefly addressed here. In principle, the use of copper-beryllium alloys is neither prohibited nor restricted worldwide. 

CuBe alloys are neither listed nor restricted in the EU directives on end-of-life vehicles (ELV), on the restriction of certain hazardous substances in electrical and electronic equipment (RoHS), or on waste electrical and electronic equipment (WEEE). An assessment commissioned by the European Commission explicitly recommended not to include beryllium in the RoHS list and to continue to allow the use of corresponding alloys in electrical and electronic equipment (EEE). 

Beryllium and beryllium oxide are registered under REACH. Beryllium is not classified as a substance of very high concern (SVHC) subject to authorization. In 2011/2012, beryllium was reviewed by the German BAuA under REACH. The result: risks exist primarily only in industrial processes, but not in end use. Both the BAuA and the EU concluded that a binding occupational exposure limit is sufficient to effectively minimize potential risks. 

This binding occupational exposure limit (OEL) has been specified in the CAD/CMRD Directive on chemical agents and the Directive on carcinogens and mutagens since 2019. Additional recommendations regarding technology and implementation exist for various manufacturing processes.8)  

It should be noted at this point that beryllium is currently classified as a critical raw material by the European Commission. Materials are considered critical if the risk of supply shortages and their potential economic impact is high compared to other materials, particularly because they cannot be easily replaced by alternative materials. 

Summary 

Copper-beryllium alloys are characterized by an exceptionally versatile range of properties. They combine high strength over a wide temperature range with special friction properties, high corrosion resistance, and excellent stress relaxation and wear resistance. At the same time, they retain the excellent electrical and thermal conductivity typical of copper alloys. 

Thanks to compliance with REACH and RoHS requirements during production, these materials are available worldwide and can be used without restriction. Extensive testing programs have also shown that CuBe alloys exhibit high resistance to hydrogen embrittlement and act as an effective barrier against hydrogen absorption and diffusion. This makes them a reliable choice for applications in hydrogen-rich environments. 

Due to this comprehensive and advantageous property profile, copper-beryllium alloys are already used in numerous industries, including sealing technology. Their resistance and barrier effect in hydrogen-containing atmospheres also open up considerable potential for new applications in hydrogen technology, which is receiving increasing political support. The continuous development of new applications underscores the importance and value of these alloys for current and future technological applications. 

Literature  

1) Ratka, J.O.; Spiegelberg, W.D.; IEEE Transactions on Magnetics, Vol. 30, 4th Issue, 1994  

2) Frehn, A.; Surrey, S.; Grensing, F; Tarrant, A.; Lewis, P.; Tagungsband zur ESA ECSSMET 2024 Konferenz, Nordwijk (Niederlande), 23.-27.09.2024 

3) Tricker, D.; Egger, A.; Krus, D.; Bredda, S.; SAE Int. J. Adv. & Curr. Prac. in Mobility 2 (5), 2020  

4) Materion Guide to High Performance Alloys, Ausgabe 2019, https:// www.materion.com/en/gated/guide-to-high-performance-alloys  

5) Jürgensen, J.; Pohl, M.; DGM Materials Week 2021, 09.09.2021  

6) Frehn, A.; Greschner, U.; Tagungsband zur Copper Alloys 2022 Konferenz, Düsseldorf, 22.-23.11.2022  

7) Jürgensen, J.; Frehn, A.; Ohla, K.; Stolz, S.; Pohl, M.; Metals 2024, 14, 588, https://doi.org/10.3390/met14050588  

8) https://www.beryllium.eu/resources