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Researchers at Pohang University of Science and Technology (POSTECH) in South Korea have developed a new type of steel with improved tensile strength and lightness. In their approach, they effectively utilized a brittle intermetallic compound (B2) that metallurgists usually try to suppress by modifying B2 morphology and dispersion in the steel matrix.
The specific tensile strength and ductility of the developed steels improve on those of the lightest and strongest metallic materials known, titanium alloys, the researchers said. The results, reported in a paper in the journal Nature, demonstrate how intermetallic compounds can be harnessed in the alloy design of lightweight steels.
There is a growing demand for lightweight structural materials as an alternative to conventional steels which are heavy and impractical for future energy-efficient vehicles. The share by weight of steel and iron in an average light vehicle is now gradually decreasing, from 68.1% in 1995 to 60.1% in 2011, the authors of the paper noted.
This has been driven by the low strength-to-weight ratio (specific strength) of iron and steel, and the desire to improve such mechanical properties with other materials.
While high-aluminium low-density steels are actively under study as a means of increasing the specific strength of an alloy by reducing its density, increasing aluminium results in poor ductility, due to the formation of brittle intermetallic compounds forming in the resulting alloys.
Until now, low-density steel has been studied mostly in systems based on Fe-Al and Fe-Al-Mn-C. In particular, low-density steel with fairly high specific strength has been produced with alloys based on Fe-Al-Mn-C (the so-called TRIPLEX steels) using a microstructure consisting of austenite (face-centered cubic) matrix and finely dispersed nanometre-sized κ-carbides of the (Fe,Mn)3AlC type. However, the level of specific strength attainable by this microstructure was not comparable to those of light materials such as aluminium and titanium alloys. This was due to the low strain hardening rate of the Fe-Al-Mn-C alloys containing κ-carbides, which are easily shearable by gliding dislocations.
One of the general concepts employed until now in the alloy design of Fe-Al-Mn-C-based, high-aluminium, low-density steel has been the suppression of ‘brittle’ intermetallic compound formation by stabilizing the ‘ductile’ austenite matrix (this stabilization is achieved by alloying carbon and manganese). Instead, here we have actively utilized the brittle intermetallic compound B2 by modifying its morphology in the steel matrix. Despite their poor plasticity at ambient temperature in the bulk state, FeAl-based intermetallic compounds offer an attractive combination of physical and mechanical properties such as low density and good corrosion, oxidation and/or wear resistance.
To take advantage of B2, we devised an alloy design in which B2 is dispersed as a second phase in the austenite matrix on the basis of the ‘divide and rule’ principle, which is analogous to harnessing ‘brittle’ martensite as a strengthening second phase in the ferrite (body-centered cubic) matrix of dual-phase steels.—Kim et al.
To expand the stability domain of B2, the research team at the Graduate Institute of Ferrous Technology (GIFT) at POSTECH modified the alloying recipe of an austenitic low-density steel comprising iron, aluminium, manganese and carbon by adding 5 wt % nickel (Ni)—one of the most effective elements for forming B2 with aluminium.
The addition of Ni to low-density steel may appear to conflict with the collective wisdom of ferrous alloy design; Ni has been regarded merely as a well-known austenite stabilizer like Mn and C; and Ni has been little noticed in low-density steel design, mainly because it is not a critical determinant of the density in ferrous alloys.—Kim et al.
Modumetal: taking steel into the next generation
Early-stage company Modumetal is developing a lightweight nanolaminated alloy its says is stronger and lighter than steel.
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They found that alloying of nickel catalyzes the precipitation of nanometer-sized B2 particles in the face-centered cubic matrix of high-aluminium low-density steel during heat treatment of cold-rolled sheet steel. The brittle but hard B2 particles thus were effectively used as a strengthening second phase in the high-aluminium, low-density steel, while alleviating the harmful effect of B2 on ductility by controlling its morphology and dispersion.
With this innovative approach, stronger and more ductile lightweight steels have been created. The team plans to work with South Korean steel manufacturer POSCO later this year to produce high-specific-strength steels that will be lightweight and strong enough to produce fuel efficient vehicles.
Sang-Heon Kim, Hansoo Kim & Nack J. Kim (2015) “Brittle intermetallic compound makes ultrastrong low-density steel with large ductility” Nature 518, 77–79 doi: 10.1038/nature14144
Researchers at RMIT University in Australia have developed a talking drone that can interact with air traffic controllers like a human pilot. The development, they say, is a critical step towards the full integration of unmanned aircraft systems into civil airspace.
The project, part of a larger research initiative that aims to address safety and efficiency issues related to drones and air traffic management, is the result of a partnership between RMIT, Thales Australia and the company’s Centre for Advanced Studies in Air Traffic Management (CASIA), and UFA Inc.
The new system, presented by researchers in a paper at the Australian International Aerospace Congress this week, enables a drone to respond to information requests and act on clearances issued by an air traffic controller using ATVoice, UFA’s voice recognition and response technology.
Flight-testing of a prototype system was completed late last year, demonstrating integration to Thales’ Top Sky Air Traffic Control System. Further studies are now underway to better understand the benefits, and explore the human factor issues associated with the automation of drone to air traffic controller communications.
Dr. Reece Clothier, leader of the RMIT Unmanned Aircraft Systems (UAS) Research Team, said drones needed to be able to fly safely alongside other airspace users without causing disruption to air traffic management.
The majority of air traffic control services are provided to aircraft by voice radio – aircraft controllers speaking directly to pilots. Our project aimed to develop and demonstrate an autonomous capability that would allow a drone to verbally interact with air traffic controllers. Using the system we’ve developed, an air traffic controller can talk to, and receive responses from, a drone just like they would with any other aircraft.—Dr. Reece Clothier
Drones are the fastest growing sector of the aviation industry, with worldwide sales expected to top $US6 billion in 2015. The RMIT UAS Research Team addresses the safety, regulatory, social and technical challenges facing the emerging industry.
A new study from the Energy Department’s National Renewable Energy Laboratory (NREL) demonstrates the conversion of lignin-derived compounds to adipic acid, an important industrial dicarboxylic acid produced for its use as a precursor to nylon, plasticizers, lubricants, polyesters, and other popular products and chemicals.
Published in the RSC journal Energy & Environmental Science, the research demonstrates how lignin-derived compounds can first be converted to muconic acid via a biological process. Muconic acid can then be separated from the biological culture and catalytically converted into adipic acid. A patent application has been filed on this research, and the NREL Technology Transfer Office will be working with researchers to identify potential licensees of the technology.
Lignin is an alkyl-aromatic polymer present in plant cell walls for defense, structure, and water transport. Despite exhibiting a high-energy content, lignin is typically slated for combustion in modern biorefineries due to its inherent heterogeneity and recalcitrance, whereas cellulose and hemicellulose are converted to renewable fuels and chemicals. However, it is critical for the viability of third-generation biorefineries to valorize lignin alongside polysaccharides. To that end, we employ metabolic engineering, separations, and catalysis to convert lignin-derived species into cis,cis-muconic acid, for subsequent hydrogenation to adipic acid, the latter being the most widely produced dicarboxylic acid.—Vardon et al.
The demonstration is an important step toward the goal of garnering more uses from lignin, which could be crucial for the economic success of the biofuels industry. It also shows that adipic acid can be produced from a renewable resource, which might have important ramifications for mitigating greenhouse gases.
Approximately 2.5 million tons of adipic acid are produced each year, mainly as a precursor for the production of nylon, and this global demand is expected to increase by up to 3.5% annually. Nylon is one of the most abundant materials in the world, used in everything from carpet and ropes to clothing and toothbrushes. With more than 4 million metric tons of nylon manufactured annually around the world, capitalizing on the production of adipic acid from lignin-derived aromatic molecules could one day have a significant impact on the bottom line of lignocellulosic biorefineries.
The current industrial pathway to produce adipic acid involves oxidation of cyclohexanol and cyclohexanone with nitric acid, which is a harsh process that produces nitrous oxide that must be cleaned up. The development of a new process toward converting renewable lignin feedstocks to adipic acid could potentially provide positive economic benefits and greenhouse gas offsets, but, certainly, major technology improvements must still be made.
While our research is still in the concept stage, this gets us one step closer to improving the technology to expand the slate of molecules that can be viably produced from lignin. As more lignocellulosic biorefineries come on line, large quantities of lignin will be generated, and valorization of these waste streams could eventually play a key role for the economic viability and environmental sustainability of biorefineries.—Gregg Beckham, senior engineer at NREL and a co-author of the study
Lignin is one of the most abundant organic materials on Earth (second only to cellulose), and it potentially offers a vast, renewable source for the sustainable production of fuels, chemicals, and materials. Valorization of lignin has been shown by techno-economic analysis conducted at NREL to be essential to the development and success of the biofuels industry. However, because it is inherently difficult to remove from biomass, lignin is currently underutilized in fuel and chemical production.
The work reported in Energy & Environmental Science was funded by the Energy Department’s Bioenergy Technologies Office.
Vardon, Derek R., Franden, Mary Ann; Joh;son, Christopher W.; Karp, Eric M.; Guarnieri, Michael T.; Linger, Jeffrey G.; Salm, Michael J.; Strathmann, Timothy J.; Beckham, Gregg T. (2015) “Adipic acid production from lignin” Energy Environ. Sci. doi: 10.1039/C4EE03230F