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​High-performance materials, fabrication, and complex assemblies: unparalleled know-how to boost manufacturers’ R&D

High Performance Materials/Assembly

Published on 6 October 2016

The French Alternative Energies and Atomic Energy Commission (CEA) has been conducting research in the field of metallurgy since the 1990s, with a focus on implementing specific component fabrication and assembly processes. This research is not targeted to a specific industry; the advances achieved can benefit any industry. Our researchers are working on two processes in particular, hot isostatic pressing (HIP) and brazing, implementing them at scales from the laboratory experiment to mock-ups and prototypes for industrial rollout. Our R&D is backed by equipment that lets us make materials, investigate materials’ microstructures, conduct mechanical testing, and model processes. To qualify a process, we study the relationships between the process, the material’s microstructures, and the material’s properties—one of our researchers’ core areas of expertise.

Hot isostatic pressing (HIP) is a high-temperature, high-pressure (applied by a gas) treatment process. Depending on the material, process temperatures and pressures can range from 500 °C  to 1,300 °C or higher and up to 1,500 bar or more. HIP eliminates all cavities in a material, boosting even very large parts’ mechanical properties. HIP is widely used for the post-treatment of cast metal parts and parts made using powder metallurgy (sintering). Our researchers use HIP to make materials and components by diffusion welding (a solid-state welding process) and powder compaction. The process takes place inside a sealed metal chamber. During the HIP cycle, the chamber transfers the pressure to the materials, which, when heated, allows deformation to occur, eliminating gaps between parts and welds and closing pores. Diffusion welding is suitable for assembling complex parts, such as parts made from several materials, with each material having its own function. For example, one material might provide structural properties, while others might dissipate heat, or resist surface wear. What makes diffusion welding unique is that it is effective at bonding very different materials assumed to be “unbondable.” These include copper and tungsten and steel and titanium. Other parts are considered complex due to their geometry, with shapes that are difficult or even impossible to obtain using machining techniques. Diffusion welding can be used to produce complex part geometries like curved internal cooling channels.

Combining powders and solid parts is another way to obtain assemblies with complex 3D interfaces without resorting to costly machining processes. Our researchers leveraged this technique to make a prototype panel for the “first wall” covering the inside of the ITER reactor. The technique has also been used to create a scale model of a future methane reactor developed at Liten. The stainless-steel reactor/heat exchanger is made of a diffusion-welded stack of grooved plates with rectangular channels where methane is made from carbon dioxide and hydrogen, and cooling channels to control the reaction temperature. We have developed similar reactors, larger in scale, for the energy conversion system for the future ASTRID nuclear reactor.

Brazing is used to bond metal parts by melting a filler material into the joint. Unlike welding, brazing is carried out at a temperature lower than the melting point of the parts to be assembled. Only the filler metal melts; the surrounding material remains solid. The technique is suitable for joining and sealing a broad range of components. Like diffusion welding, brazing forms a very “tight” joint. Our development work focuses on high-temperature brazing of ceramics for energy and other extreme industrial environments like those common in the chemical and aerospace industries. Liten has developed a proprietary process and the associated filler materials (silicon-based brazing alloys), called BraSiC©. It is used to assemble silicon carbide and other similar ceramics. The process has been employed to make telescope mirrors for space applications (it is not currently possible to make silicon carbide structures of this size in a single piece). For example, Liten used the process for the Herschel and Gaia telescopes in conjunction with Airbus Defence & Space. CNES and Safran have also come to Liten for this process for the development of brazed technology for CMC parts for its aircraft engine exhaust systems, with the ultimate goal of reducing weight to save on fuel.

Liten’s other flagship brazing work concerns ceramic-to-metal brazed assemblies. One of the issues that is hindering the widespread use of technical ceramics is the fact that, in the vast majority of cases, they must be coupled—and thus, assembled—with metals. Ceramic-to-metal assembly is particularly complex due to thermomechanical, physical, and chemical incompatibilities between the materials. There is no generic solution for creating such assemblies, and Liten has built up substantial know-how developing custom solutions to respond to each partner’s unique specifications. Current projects cover a broad range of industries, from nuclear energy to aerospace.

Materials and testing know-how
Our researchers draw on the institute’s long-standing research in materials and testing to qualify the processes described above, as well as other manufacturing processes and, in particular, to characterize the mechanical behavior of the materials that make up the assemblies and their interfaces, according to process parameters and the testing environment (with factors like temperature and atmosphere). We can determine the behavioral rules required to model a process and to study the interactions between microstructures, behavior, and damage in order to optimize materials choices and process parameters. And, in the broader context of investigating hydrogen as a new energy vector, we have developed a deep understanding of how hydrogen gas weakens structural materials. We can quantify how sensitive a material will be to damage and study the underlying mechanisms.

BENEFITS

Powerful processes for manufacturing innovative, high-quality products

  • Hot isostatic pressing (HIP) can be used for multi-material assemblies for complex, innovative, and large parts.
  • HIP is a powder metallurgy technique that can also be used to obtain high-performance materials and components.
  • Our researchers also possess know-how in brazing refractory-grade silicon carbide; the process is used to achieve high-performance bonds for extreme environments.
  • Brazed ceramic-to-metal bonds are used to assemble advanced ceramic parts with more conventional system components.
  • Our services cover all stages of research and development, from early-stage scientific research to prototyping and testing.
  • We can address the needs of virtually all industries: new energy technologies, nuclear fission and fusion, aerospace, mechanical engineering, and manufacturing.
PROJECTS
  • The Enerpoudre project (2009–2014), backed by the French Single Interministerial Fund and conducted in conjunction with Areva, Aubert & Duval, Erasteel, and the University of Burgundy, focused on developing HIP powder metallurgy processes to manufacture the metal components used in pressurized-water reactors. The goal was to develop an alternative to traditional forging processes to save on raw materials and shorten lead times. The project looked at the bainite steel used to make the tanks of today’s pressurized-water reactors.
  • ​The Mathryce project to develop a method to assess the fatigue life of pressure equipment for hydrogen systems; the method is based on experimental lab testing. The ultimate goal is to come up with recommendations that take into account fatigue caused by hydrogen gas in international standards and codes.
FACTS & FIGURES

  • Around 30 researchers
  • 44 patents


Publications:

Chaumat V, Roux G. June 18–20, 2013. Multi-staged brazing using the BraSiC® process for the fabrication of very large and/or complex SiC based components. 10th International Conference on Brazing, High Temperature Brazing and Diffusion Bonding (LOET 13). Aachen, Germany.

Bouquet N, Rigal E, Chomette S, Bernard F. June 9–13, 2014. Influence of industrial sheet surface finish on interface formation during HIP-bonding of austenitic stainless steel. 11th International Conference of Hot Isostatic Pressing (HIP ’14). Stockholm, Sweden.

Frayssines PE, Gentzbittel JM, Guilloud A, Bucci P, Soreau T, Francois N, Primaux F, Heikkinen S, Zacchia F, Eaton R, Barabash V, Mitteau R. April 1, 2014. CuCrZr alloy microstructure and mechanical properties after hot isostatic pressing bonding cycles. Physica Scripta 2014: T159.

Briottet L, Moro I, Escot M, Furtado J, Bortot P, Tamponi GM, Solin J, Odemer G, Blanc C, Andrieu E. 2015. Fatigue crack initiation and growth in a CrMo steel under hydrogen pressure. International Journal of Hydrogen Energy. In press.


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