RESEARCH NEWS
Preventing component failures in metals
When a metal is stressed far below its yield strength at elevated temperatures , a process known as creep can occur . Creep , the time-dependent deformation of materials , is responsible for many component failures at high temperatures . Scientists know that eliminating grain boundaries in materials is a useful way of resisting high-temperature creep in metals . However , a Chinese team of researchers has developed a different strategy for inhibiting creep by using stable grain boundary networks . Their findings were published in the journal ‘ Science ’ in November 2022 .
The team ’ s strategy for a property enhancement differs fundamentally from that of traditional strategies .
“ The behaviours of grain boundary networks may be fundamentally alerted when structural relaxation of grain boundaries is triggered through their interaction with partial dislocations below a critical grain size ,” said Li Xiuyan , a professor at the Institute of Metal Research , Chinese Academy of Sciences . Using its new method , the team obtained “ unprecedented creep resistance that outperformed that of conventional superalloys .” Creep is a costly problem . A great number of failures of materials and components at high temperatures are attributed to creep or to its combination with other degradation processes . These failures cost billions of dollars annually for the repair and replacement of parts in advanced devices . The demand for higher fuel efficiency and more reliable turbines , nuclear reactors and devices in chemical industries continues to grow . With this increasing demand , there is a growing need for improved high-temperature creep resistance in advanced alloys .
“ The traditional development of alloys for high-temperature applications primarily relies on the skilful addition of various alloying elements for strengthening the matrix or interfaces , or for forming reinforcing precipitates ,” said Li . “ Such a strategy faces the dilemma of limited property improvement with intensifying alloying and elevated cost .”
A new approach
Grain boundaries , defects in the crystal structure , are the interfaces where two crystals that have different orientations meet . Although conventional wisdom points to the elimination of grain boundaries to counter the problem of creep , the research team proposed introducing abundant grain boundaries to form stable grain boundary networks in metal to inhibit creep by suppressing atomic diffusion and hardening at high temperatures , simultaneously . This was inspired by recent studies on grain boundary relaxation in metals .
The team found that grain boundaries can be used for strengthening alloys at elevated temperatures , contrary to the conventional wisdom that they always weaken the alloys at high temperatures . It is known that grain boundaries in metals and alloys are usually considered as a “ weak component ”, as they may migrate or slide upon loading at elevated temperatures .
“ We found that grain boundaries in the nanograined single-phased alloy can be effectively stabilised through a structural relaxation , and the creep performance of the alloy is significantly enhanced at elevated temperatures ,” said Li . Distinct from the traditional alloying approach , the grain boundary relaxation offers a novel and sustainable strategy for advancing the properties and performance of alloys for hightemperature applications .
Next steps
For future research , the team sees room for stability enhancement by tailoring grain boundary networks in metals and alloys .
“ The next step of this study is to extend this principle to other engineering alloy families for high-temperature applications , including nickelbased alloys and steels ,” said Li . The team plans to perform processing development to further promote the stability of grain boundary networks and prepare large-size samples for measurements of more properties and performance at high temperatures ,” said Li .
“ Ultimately we hope to realize industrial applications of the high-performance engineering alloys with stable grain boundary networks ,” he concluded .
The research team includes B . B . Zhang and Xiuyan Li from the Shenyang National Laboratory for Materials Science ( SYNL ), Institute of Metal Research , Chinese Academy of Sciences ; Y . G . Tang from the Institute of Metal Research , Chinese Academy of Sciences and from the School of Materials Science and Engineering , University of Science and Technology of China ; Q . S . Mei from the School of Power and Mechanical Engineering , Wuhan University ; and K . Lu from the SYNL , Institute of Metal Research , Chinese Academy of Sciences and from the Liaoning Academy of Materials .
The research is funded by the Ministry of Science and Technology of China , the National Natural Science Foundation of China , and the Chinese Academy of Sciences . n
German-Dutch aviation cooperation
German research and technology centre ECOMAT and Royal NLR ( Netherlands ) confirmed their cooperation and exchange of knowledge in sustainable aviation in a Memorandum of Understanding ( MoU ) during the Paris Air Show .
The focus is on four topics such as the reuse and circularity of materials used as economically as possible . It also included the development of ( liquid ) hydrogen applications , so that both the Netherlands and Airbus ZeroE can develop future aircraft that no longer emit CO₂ .
The MoU also describes agreements on future space technology , in which developments in aerospace can complement each other such as the ( re ) use of lighter materials and on digitisation . The latter can contribute to sustainability by testing and certifying aircraft components without the need for ( destructive or full-scale ) tests . CO₂ emissions can also be reduced by simulating flight movements in a computer program .
“ We have been talking to each other since last year ,” confirmed Collin Beers , Vice
President Aerospace Vehicles , Royal NLR . “ After a visit to Bremen , we were inspired and very much impressed by the entire setup of ECOMAT and the aerospace knowledge and experience of companies such as Airbus , Ariane , Testia and fellow institutes DLR and Fraunhofer . It was clear that joining ECOMAT would be of great value to us and we believe that NLR can also bring a lot to ECOMAT .” The MoU follows the recently signed contracts for office and workspace for NLR at ECOMAT and cooperation between the participants in ECOMAT with NLR in sustainable aviation and space . n
https :// ecomat-bremen . de / en / home /
22 | ismr . net | ISMR September 2023