19 24 30 P. 13 Laser Shock Peening for Aerospace Applications Investment Casting of Aero Engine Components iTSSe and HTPro Newsletters Included in This Issue NTSB INVESTIGATION OF HYDRAULIC ACTUATOR FRACTURES AEROSPACE MATERIALS AND TESTING APRIL 2025 | VOL 183 | NO 3
19 24 30 P. 13 Laser Shock Peening for Aerospace Applications Investment Casting of Aero Engine Components iTSSe and HTPro Newsletters Included in This Issue NTSB INVESTIGATION OF HYDRAULIC ACTUATOR FRACTURES AEROSPACE MATERIALS AND TESTING APRIL 2025 | VOL 183 | NO 3
THREE EVENTS SUSTAINABLE INNOVATIONS IN THERMAL SPRAY TECHNOLOGY: PIONEERING A GREENER FUTURE MAY 5–8, 2025 VANCOUVER CONVENTION CENTER | VANCOUVER, CANADA REGISTRATION NOW OPEN! REGISTER BY APRIL 1 FOR THE EARLY BIRD DISCOUNT ITSCevent.org CO-LOCATED WITH: 2025
MAY 6–7, 2025 VANCOUVER CONVENTION CENTER | VANCOUVER, CANADA REGISTRATION NOW OPEN! REGISTER BY APRIL 1 FOR THE EARLY BIRD DISCOUNT QDEevent.org 3RD INTERNATIONAL CONFERENCE ON QUENCHING AND DISTORTION ENGINEERING OFFICIAL MEDIA SPONSOR: ORGANIZED BY: ONE LOCATION
56 ASM NEWS The latest news about ASM members, chapters, events, awards, conferences, affiliates, and other Society activities. REVIEW OF NTSB INVESTIGATIONS OF CESSNA 210 HYDRAULIC ACTUATOR FRACTURES FROM FATIGUE Erik M. Mueller, Zoë Keliher, and Timothy Sorensen A persistent failure of main landing gear systems on a series of noncommercial planes was studied at the National Transportation Safety Board’s Materials Laboratory, leading to the discovery of cracks that propagated under cyclic loading of hydraulic actuators. 13 ADVANCED MATERIALS & PROCESSES | APRIL 2025 2 Single engine airplane flying at sunset through a sea of clouds. Courtesy of Dreamstime. On the Cover: 60 ASM STRATEGIC VISION ASM International is focused on fostering strategic collaborations, driving member engagement, and strengthening core foundations. AEROMAT SHOW PREVIEW The 36th AeroMat Conference and Exposition runs from May 6 to 8 in Vancouver, Canada. Photograph by Kristopher Grunert. 28
4 Editorial 5 Research Tracks 10 Machine Learning 6 Metals/Polymers/Ceramics 8 Testing/Characterization 11 Emerging Technology 12 Surface Engineering 67 Editorial Preview 67 Special Advertising Section 67 Advertisers Index 68 3D PrintShop TRENDS INDUSTRY NEWS DEPARTMENTS Check out the Digital Edition online at asminternational.org/news/magazines/am-p ASM International serves materials professionals, nontechnical personnel, and managers worldwide by providing high-quality materials information, education and training, networking opportunities, and professional development resources in cost-e ective and user-friendly formats. ASM is where materials users, producers, and manufacturers converge to do business. Advanced Materials & Processes (ISSN 0882-7958, USPS 762080) publishes eight issues per year: January/February, March, April, May/June, July/August, September, October, and November/December, by ASM International, 9639 Kinsman Road, Materials Park, OH 44073-0002; tel: 440.338.5151; fax: 440.338.4634. Periodicals postage paid at Novelty, Ohio, and additional mailing offices. Vol. 183, No. 3, APRIL 2025. Copyright © 2025 by ASM International®. All rights reserved. Distributed at no charge to ASM members in the United States, Canada, and Mexico. International members can pay a $30 per year surcharge to receive printed issues. Subscriptions: $499. Single copies: $54. POSTMASTER: Send 3579 forms to ASM International, Materials Park, OH 44073-0002. Change of address: Request for change should include old address of the subscriber. Missing numbers due to “change of address” cannot be replaced. Claims for nondelivery must be made within 60 days of issue. Printed by Kodi Collective, Lebanon Junction, Ky. 19 DEVELOPMENTS IN LASER SHOCK PEENING FOR AEROSPACE APPLICATIONS Niall A. Smyth and Michael E. Fitzpatrick An innovative method to add residual stress has demonstrated significant impact in safety-critical applications such as aero engines, while additional research focuses on lowering the cost and increasing equipment flexibility. 24 TECHNICAL SPOTLIGHT INVESTMENT CASTING INNOVATIONS FOR AEROSPACE AND BEYOND Meghan McGrath and Boyd Mueller Single crystal and directionally solidified casting processes are among the most complex techniques available, requiring stringent process control and a thorough understanding of engineered materials and specialty alloys. 30 iTSSe: INCLUDES ITSC SHOW PREVIEW The official newsletter of the ASM Thermal Spray Society (TSS). This timely supplement focuses on thermal spray and related surface engineering technologies along with TSS news and initiatives. FEATURES APRIL 2025 | VOL 183 | NO 3 ADVANCED MATERIALS & PROCESSES | APRIL 2025 3 19 30 43 24 43 HTPro: INCLUDES QDE SHOW PREVIEW The official newsletter of the ASM Heat Treating Society. This supplement focuses on heat treating technology, processes, materials, and equipment.
4 ADVANCED MATERIALS & PROCESSES | APRIL 2025 ASM International 9639 Kinsman Road, Materials Park, OH 44073 Tel: 440.338.5151 • Fax: 440.338.4634 Joanne Miller, Editor joanne.miller@asminternational.org Victoria Burt, Managing Editor vicki.burt@asminternational.org Frances Richards and Corinne Richards Contributing Editors Anne Vidmar, Layout and Design Allison Freeman, Production Manager allie.freeman@asminternational.org EDITORIAL COMMITTEE John Shingledecker, Chair, EPRI Beth Armstrong, Vice Chair, Oak Ridge National Lab Adam Farrow, Past Chair, Los Alamos National Lab Yun Bai, Ford Rajan Bhambroo, Tenneco Inc. Punnathat Bordeenithikasem, Machina Labs Daniel Grice, Materials Evaluation & Engineering Surojit Gupta, University of North Dakota Michael Hoerner, KnightHawk Engineering Hideyuki Kanematsu, Suzuka National College of Technology Ibrahim Karaman, Texas A&M University Ricardo Komai, Tesla Krassimir Marchev, Northeastern University Bhargavi Mummareddy, Dimensional Energy Scott Olig, U.S. Naval Research Lab Christian Paglia, SUPSI Institute of Materials and Construction Satyam Sahay, John Deere Technology Center India Abhijit Sengupta, USA Federal Government Kumar Sridharan, University of Wisconsin Vasisht Venkatesh, Pratt & Whitney ASM BOARD OF TRUSTEES Navin Manjooran, President and Chair Elizabeth Ho man, Senior Vice President Daniel P. Dennies, Vice President Pradeep Goyal, Immediate Past President Lawrence Somrack, Treasurer Amber Black Pierpaolo Carlone Rahul Gupta Hanchen Huang André McDonald Victoria Miller Christopher J. Misorski Dehua Yang Fan Zhang Veronica Becker, Executive Director STUDENT BOARD MEMBERS Gladys Duran Duran, Amanda Smith, Nathaniel Tomas Individual readers of Advanced Materials & Processes may, without charge, make single copies of pages therefrom for personal or archival use, or may freely make such copies in such numbers as are deemed useful for educational or research purposes and are not for sale or resale. Permission is granted to cite or quote from articles herein, provided customary acknowledgment of the authors and source is made. The acceptance and publication of manuscripts in Advanced Materials & Processes does not imply that the reviewers, editors, or publisher accept, approve, or endorse the data, opinions, and conclusions of the authors. REGAINING CONFIDENCE IN FLIGHT In the past few months, we have been jolted out of our blissful joy of flight by a sequence of fatal tragedies in the sky. These horrific events have affected our confidence in civil aviation. A recent Associated Press-NORC poll revealed that 64% of Americans feel very or somewhat safe with air travel compared to 71% at the same time last year. How can we regain our trust in the skies? One reassuring factor has been the swift appearance of the teams in blue from the United States National Transportation Safety Board (NTSB) on the scene to research the cause of each accident and make recommendations to prevent similar occurrences in the future. On January 30, the day after the mid-air collision of a passenger jet and a military helicopter near Ronald Reagan Washington National Airport, Jennifer Homendy, chair of the NTSB, spoke at a press conference. She summarized their methodology in this way: “As part of any investigation, we look at the human, the machine, and the environment.” Putting those principles into practice in a series of nonfatal cases, our lead article in this issue provides a snapshot of an NTSB investigation into fatigue cracks found on Cessna 210 hydraulic actuators. From the report summary, we learn how a combination of all three factors that Homendy cited can play a role. An environment can lead to corrosion, human beings can delay recommended maintenance, and as a result, a machine will not operate as originally intended by the manufacturer. But the NTSB has recommendations. In looking for more reasons to regain confidence in air travel, we can turn to the sophisticated R&D program happening at Howmet Aerospace. Boyd Mueller, FASM, received ASM’s Medal for the Advancement of Research last October for his leadership in various metals processing technologies. In this issue, he describes how their complex casting techniques are applied to turbine airfoils that need to withstand harsh environments. He also emphasizes the importance of their onsite training for new engineers (acknowledging the human). Academia is also helping to improve flight systems. An article by authors from Coventry University explains how laser shock peening can significantly reduce residual stress in safety-critical components of aero engines. Attendance at this year’s AeroMat conference will provide more evidence of ongoing developments to improve our 21st century flying machines. With a theme of “Innovations in Materials Engineering: Shaping the Future of the Aerospace Industry” and keynotes from Constellium, Blue Origin, and Airbus, the event features the best minds in the field discussing their recent engineering innovations. Inspired by these promising advancements in aviation technology, and with the hope of industry-wide compliance to safety recommendations, we can find our flight path back to confident air travel. joanne.miller@asminternational.org NTSB Chair Jennifer Homendy.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 5 RESEARCH TRACKS SPINEL HELPS SUPERALLOYS FACE EXTREME TEMPS A multi-institutional team including researchers at Virginia Tech discovered a promising candidate for a lubricant that works at extremely high temperatures: transition metal spinel oxides formed on nickel-chromium- base superalloys. Unlike common lubricants that break down under high heat, spinel oxide maintains lubrication up to 700°C, almost as hot as a metal forge. Enabling metallic materials to withstand higher temperatures could lead to innovations in metals manufacturing for industries like aerospace and nuclear energy. Spinels and spinel- structured oxides belong to a group of semiprecious gemstones sometimes found alongside rubies in rare rocks. The researchers found that the mineral possesses the unusual ability to self- lubricate under heat stress and friction. Yet it only appears to do so under specific circumstances, and only when paired with a certain superalloy. Demand for metal parts that resist wear at extremely high temperatures is becoming increasingly common in many industries. Solid lubricants such as thin layers of molybdenum disulfide and graphite on metal surfaces can help prevent this wear in some cases. However, none withstand temperatures greater than 600°C in tests, and not without corrosion. In the current study, researchers demonstrated a process by which an additively manufactured sample of Inconel 718 is lubricated by spinel at temperatures exceeding 600°C. Using a new approach, the team heat treated its surface before exposing it to these temperatures. The superalloy formed lubricating spinel-based oxides and did not thicken or lose friction tolerance. The scientists note that it could be the unique structure of spinel itself helping it outperform similar oxides as a lubricant. This research was supported by multiple grants from the National Science Foundation. nsf.gov. LEARNING WHY PLATINUM ELECTRODES CORRODE Scientists from Leiden University, the Netherlands, and the DOE’s SLAC National Accelerator Laboratory, Menlo Park, Calif., discovered the mysterious cause behind the rapid corrosion of platinum electrodes. The researchers believe this break- through could lead to applications such as more affordable green hydrogen Hydride formation on a platinum surface. Courtesy of Nature Materials, 2025, doi.org/10.1038/s41563-024-02080-y. production and more reliable electrochemical sensors. With most metals, being negatively polarized protects against corrosion. However, platinum electrodes can rapidly break down under these conditions. “If you take a piece of platinum and you apply a very negative potential, you can dissolve your platinum in a matter of minutes,” says Marc Koper, the Leiden team’s principal investigator. The team knew they would need to observe platinum as it was corroding in an electrolyte while making hydrogen, so they turned to SLAC’s Stanford Synchrotron Radiation Lightsource. There, SLAC researchers developed high- energy-resolution x-ray spectroscopy techniques that could penetrate the electrolyte and filter out other effects, allowing the team to focus on subtle changes in the platinum electrode during operation. Using these methods, researchers made the first-ever observations of platinum actively corroding, recording x-ray spectra from the negatively polarized electrode’s surface. Using computational models of platinum hydrides and platinides, the team simulated the spectra they would expect to see from each structure under the x-ray beam. Comparing the simulated spectra with the results of their experiment confirmed that only platinum hydride could have produced their results. www.universiteitleiden.nl. 2023 launch of NASA’s Crew-6 mission. Some rocket engines use superalloys such as Inconel for certain parts. Courtesy of SpaceX.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 6 METALS | POLYMERS | CERAMICS Carolina Metals Group, Dallas, N.C., and Spartan Recycling Group, Spartanburg, S.C., merged their scrap metal processing businesses in January. The new entity, Southeast Recycling Group, will employ more than 100 people with nearly 100 acres of processing area at three locations in the Carolinas. srgmetals.com. magnetic, and optical properties. Even graphite can rearrange into six different crystalline forms, each with distinct electrical conductivities, infrared responses, magnetizations, and superconducting properties. The main challenge is maintaining the material’s stability while ensuring controlled structural transitions. The team’s latest study proposes new methods to refine this “slidetronics” switching mechanism, which could lead to new applications in electronics, computing, and other fields. https://english.tau.ac.il. SIMPLE PROCESS DECONSTRUCTS POLYMERS Materials scientists at ETH Zurich developed a light-triggered chemical process for breaking down certain polymers into their component monomers, which would enable cheaper and easier recycling. The new process involves placing the polymer in a dichlorobenzene solvent and then shining a violet light on it as reactions in the solvent take place, with no reagents or SLIDETRONICS AND POLYTYPE MATERIALS Researchers at Tel Aviv University, Israel, are exploring the idea of turning graphite into diamond since they are both made entirely of carbon atoms. The main difference between the two involves how their atoms are arranged. Converting graphite into diamond would require extreme temperatures and pressures to break and reform chemical bonds, making the process impractical. A more realistic transformation, according to Professor Moshe Ben Shalom, involves reconfiguring the atomic layers of graphite by shifting them against relatively weak van der Waals forces. In this case, the value of these newly engineered “polytype” materials could surpass that of both diamonds and gold. “We are developing new methods to slide the layers into different arrangements and study the resulting materials. By applying an electric field or mechanical pressure, we can shift the layers into various stable configurations. Since these layers remain in their final position even after the external force is removed, they can store information— functioning as a tiny memory unit,” says researcher Simon Salleh Atri. The team also explored how different numbers of layers influence materials properties. For example, three layers of a material with two types of atoms can create six distinct stable materials, each with unique internal polarizations. With five layers, this number increases to 45 possible structures. By switching between these configurations, researchers can control electrical, Ball Corp., Westminster, Colo., acquired Alucan, Barcelona. The purchase complements Ball’s existing extruded aluminum aerosol and bottle business by adding two manufacturing facilities located in Spain and Belgium. ball.com. BRIEFS Layers research team from the School of Physics and Astronomy. Courtesy of Tel Aviv University. Graphic of the reversion of commercial Plexiglas to its starting materials, the monomer. Courtesy of Hyun Suk Wang and Athina Anastasaki/ETHZ.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 7 other catalysts required. As part of the process, vat temperature must be kept above 90°C and the light must remain on the entire time. Once complete, the result is a vat filled with monomers and other chemicals, which can be easily separated and recycled. The technique was discovered by accident, so the team tried to explain why it worked so well. They found that dichlorobenzene, when exposed to the polymer, produced chlorine radicals under the light. The radicals then pulled hydrogen atoms from seemingly random parts of the polymer backbone, causing it to break. In addition, when it broke, a new radical was formed, kicking off even more reactions. The researchers acknowledge that the reaction is slow, but note that it has a high yield and that it is simple, easy, and inexpensive to conduct. Further, they believe it could transform the recycling of plastics around the world. www.ethz.ch/en. COPPER NANOPARTICLE COATINGS FOR IMPLANTS Scientists at Nottingham Trent University, (NTU) U.K., developed copper oxide nanoparticles that can be coated onto implanted medical devices to reduce the risk of infection. As part of their study, the team created the nanoparticles as an anti- pathogenic coating suitable for use on a range of medical-grade materials, including silicone, stainless steel, and titanium. Research results show that both dip and spray coating techniques are effective at protecting against a range of clinically relevant bacteria, including multidrug-resistant strains. The new coating also remained non- toxic to human cells. In recent years, there has been a growing interest in nanoparticle technologies and the application of anti- microbial metals, particularly silver nanomaterials, which have applications ranging from food storage to wound dressings. The scientists report that copper has emerged as a viable alternative to silver, which is susceptible to oxidation and a related reduction in antimicrobial properties. On a global scale, several million implants are placed in patients each year, including intravascular and cardio- vascular devices as well as ortho- pedic and dental implants. The researchers say that these medical materials within the body provide an ideal scaffold for microbial contamination and infection. “Nanoparticles offer excellent surface area to volume ratios, as well as having excellent interaction rates with bacterial cells,” says researcher Gareth Cave. “Our coating method can be applied during manufacturing, or for ad hoc modifications, enhancing the antimicrobial properties of medical devices.” www.ntu.ac.uk. Copper oxide nanoparticles shown in solid and solution form. Courtesy of NTU. WORLD-LEADING ELECTRON BEAM TECHNOLOGY pro-beam.com PRECISE. QUICK. HIGH QUALITY. Welding with the electron beam offers these and many other advantages - find out more about it here: Electron microscope image of copper oxide nanoparticles. Courtesy of NTU.
8 ADVANCED MATERIALS & PROCESSES | APRIL 2025 properties affect battery operation. The team applied their framework to investigate ion transport, which affects how efficiently a battery can charge and discharge. The work focused on two-phase composites commonly found in solid- state batteries, using Li7La3Zr2O12- LiCoO2 as a model system. The new method helped generate many digital representations of distinct material microstructures with different grain, grain boundary, and interface configurations. The team then extracted the features of the generated microstructures and used a machine learning model to pinpoint specific microstructural features that critically impact ionic diffusivity. The new approach allowed for a comprehensive analysis of highly complex microstructural and interface features and their implications for material properties. The findings confirmed that microstructural feature diversity can significantly impact effective transport properties. Notably, the interface between the two phases played a critical role in determining those properties. “Our established modeling framework can be extended to investigate other critical microstructural and chemical features (e.g., pores, additives, and binders), representing TESTING | CHARACTERIZATION FRESH FRACTURE ENERGY FINDINGS Researchers at MIT, Cambridge, Mass., are studying the energy required to fracture various materials networks used to construct everything from car tires and human tissues to spider webs. These networks are diverse in composition but all contain interconnected strands. “Our findings reveal a simple, general law that governs the fracture energy of networks across various materials and length scales,” says Professor Xuanhe Zhao. “This discovery has significant implications for the design of new materials, structures, and metamaterials, allowing for the creation of systems that are incredibly tough, soft, and stretchable.” Until now, no physical model effectively linked strand mechanics and connectivity to predict bulk fracture. The new study reveals a universal scaling law that bridges length scales and makes it possible to predict the intrinsic fracture energy of diverse networks. To test their results, the team 3D-printed a giant, stretchable network, allowing them to demonstrate fracture properties in practice. They found that despite differences in the networks, they all followed a simple and predictable rule. Beyond changes to the strands themselves, a network can also be toughened by connecting the strands into larger loops. The scientists explain that this work represents progress in the field of architected materials, where the structure within the material itself gives it unique properties. They say the discovery provides clues about how to make these materials even tougher, by focusing on designing the segments within the architecture to be stronger and more stretchable. Further, the team believes the strategy is adaptable to many materials, such as improving the durability of soft robotic actuators or building resilient lattices for aerospace applications. mit.edu. MODELING BETTER SOLID-STATE BATTERIES Researchers at Lawrence Livermore National Laboratory (LLNL), Calif., developed an integrated modeling ap- proach to improve the key interface and microstructural features in complex materials used for advanced batteries. The study helps decode the relationship between a material’s microstructure and its essential properties, and better predicts how those Illustration of the integrated computational framework used to design materials for solid-state batteries. Courtesy of LLNL. The researchers 3D-printed this giant, stretchable network of interconnected strands to test its fracture properties. Courtesy of MIT. Ipsen, Cherry Valley, Ill., announces the graduation of its inaugural class of field service engineers (FSEs) from the new Ipsen FSE Academy. The engineers completed an intense 20-week training program focused on heat treatment furnace repair and service. ipsenglobal.com. BRIEF
ADVANCED MATERIALS & PROCESSES | APRIL 2025 9 the broader impacts and practicality of this approach for materials in energy storage applications and beyond,” says researcher Tae Wook Heo. llnl.gov. ACCURATE ATOM-BASED THERMOMETER Researchers at the National Institute of Standards and Technology (NIST), Gaithersburg, Md., developed a new thermometer using atoms boosted to such high energy levels that they are 1000 times larger than normal. By monitoring how these so-called “Rydberg” atoms interact with heat in their environment, scientists can measure temperature with extreme accuracy. The thermometer’s sensitivity could improve temperature measurements in fields ranging from quantum research to industrial manufacturing. Unlike traditional thermometers, a Rydberg thermometer does not require factory calibration because it relies on the basic principles of quantum physics. These quantum principles yield precise measurements that are also directly traceable to international standards. To create the thermometer, researchers filled a vacuum chamber with a gas of rubidium atoms and used lasers and magnetic fields to trap and cool them to nearly absolute zero. This means the atoms were essentially not moving. Using lasers, they then boosted the atoms’ outermost electrons to very high orbits, making the atoms approximately 1000 times larger than ordinary rubidium atoms. In Rydberg atoms, the outermost electron is far away from the core of the atom, making it more responsive to electric fields. Scientists can then measure temperature by tracking these energy jumps over time. Rydberg thermometers can measure the temperature of their Noah Schlossberger monitors how giant Rydberg atoms interact with heat in their environment. Courtesy of R. Jacobson/NIST. environment from about 0° to 100°C without needing to touch the object being measured. Beyond precision science, the new thermometer could have applications in challenging environments from spacecraft to advanced manufacturing plants, where sensitive temperature readings are essential. nist.gov. STAY AHEAD OF YOUR PROFESSIONAL JOURNEY WITH ASM EDUCATION & TRAINING. EARN CEUs, ENJOY DISCOUNTS, NETWORK, AND LEARN FROM INDUSTRY EXPERTS. SCAN TO ENROLL TODAY Education
ADVANCED MATERIALS & PROCESSES | APRIL 2025 10 MACHINE LEARNING | AI MACHINE LEARNING IMPROVES TUNABLE METAMATERIAL Engineers at the University of California, Berkeley developed a tunable metamaterial microwave absorber that can switch between absorbing, transmitting, or reflecting microwaves on demand by mimicking the color- changing mechanism of a chameleon. “A key discovery was the ability to achieve both broadband absorption and high transmission in a single structure, offering adaptability in dynamic environments,” explains principal investigator Grace Gu. According to Gu, creating materials that can efficiently absorb electromagnetic waves has been a longstanding technological challenge. Aiming to develop a material that could dynamically change how it interacts with electromagnetic waves, researchers looked to chameleons for inspiration. These reptiles change color by adjusting the spacing between photonic crystals in their skin to modulate light reflection. Gu and her team worked to adapt a similar tuning mechanism to their metamaterial design. The result was a crisscross truss structure that can mechanically transform to control its electromagnetic properties. By collapsing or expanding its truss system, the metamaterial can vary its electromagnetic response from broadband absorption to transmission mode. Using machine learning and genetic algorithms, researchers optimized the design for specific electromagnetic responses, achieving a level of programmability. Next, they fabricated the structure using 3D printing and tested its ability to switch between absorbing and transmitting microwaves. Researchers say the new electro- magnetic material could enhance technologies in defense, wireless communications, energy, and smart infrastructure. In addition, it could be used to improve the efficiency of electromagnetic energy harvesting systems that help power sensors and batteries. “The tunable nature of the design allows it to adapt to changing needs, providing a versatile solution for electromagnetic wave management,” says Gu. berkeley.edu. AI HELPS GENERATE CRYSTAL STRUCTURES Scientists at the University of Reading, U.K., and University College London, developed a new artificial intelligence model that can predict how atoms arrange themselves in crystal structures. The technology, named CrystaLLM, works like an AI chatbot—learning the “language” of crystals by studying Generated structures of various inorganic compounds: (a) Ba2MnCr; (b) CsCuTePt; (c) YbMn6Sn6; (d) AuO2; and (e) Sm2BS4. Courtesy of Nature Communications, 2024, doi.org/10.1038/s41467-024-54639-7. millions of existing structures. The new system soon will be distributed to the scientific community to aid the discovery of new materials for everything from advanced batteries and solar panels to faster computer chips, say researchers. The current process for deter- mining how atoms will arrange themselves into crystals relies on computer simulations of physical interactions between atoms. In contrast, CrystaLLM learns by reading millions of crystal structure descriptions contained in Crystallographic Information Files, the standard format for representing crystal structures. CrystaLLM treats these descriptions like text. As it reads each one, it predicts what comes next, gradually learning patterns about how crystals are structured. The system was never taught any physics or chemistry rules, but instead figured them out on its own. It learned things such as how atoms arrange themselves and how size affects crystal shape, just from reading these descriptions. When tested, CrystaLLM could successfully generate realistic crystal structures, even for materials it had never seen before. www.reading.ac.uk. A chameleon’s color-changing mechanism (top) and the bioinspired tunable metamaterial microwave absorber (bottom).
ADVANCED MATERIALS & PROCESSES | APRIL 2025 1 1 EMERGING TECHNOLOGY BETTER BATTERIES THROUGH NEUTRONS Researchers at Duke University along with scientists at the national labs discovered a way to make batteries that are safer, charge faster, and last longer. The team used neutrons at the DOE’s Oak Ridge National Laboratory (ORNL) to understand how lithium moves in lithium phosphorus sulfur chloride (Li6PS5Cl), a promising solid-state battery material. Using neutrons at ORNL’s Spallation Neutron Source and machine-learned molecular dynamics simulations at Lawrence Berkeley National Laboratory, they found that lithium ions easily diffused in the solid material, as they do in liquid electrolytes, allowing faster and safer charging. The results could enhance solid-state electrolytes (SSEs), enabling next-generation batteries. While SSEs have known advantages over liquid electrolytes, such as improved energy density, liquid electrolytes are more prevalent in battery materials because SSE materials are more challenging to create. Similarly, ions move more freely through liquid electrolytes than they do SSEs. The team used neutrons to study the lithium behavior in Li6PS5Cl because neutrons see lighter elements, allowing the scientists to gain new insights into solid-state superionic material for future energy storage technologies. Researchers used neutron spectro- scopy to measure molecular and atomic motions with lattice vibrations and magnetic excitations in materials. The team measured and modeled lithium diffusion in the solid material, finding that lithium easily diffused. “Our findings are impactful because they open the door to optimizing conductivity of the ions inside the material, therefore unlocking a path to increasing battery performance,” says ORNL scientist Naresh Osti. ornl.gov. FROM FUNGAL TISSUE TO CIRCUIT BOARDS Researchers at Johannes Kepler University Linz, Austria, are transforming fungal tissue into circuit boards that match traditional materials in performance while decomposing completely after use. Their approach involves targeting fundamental material properties instead of trying to replicate standard manufacturing processes. The team chose Ganoderma lucidum, a fungus that grows on dead hardwood, harvesting its mycelium before it matures. They then developed a precise chemical treatment sequence using sodium hydroxide and acetic acid that fundamentally alters the material’s cellular structure. The treatment collapses the fungal networks into a dense and uniform material with a surface roughness of 2.7 µm. The treated material withstands temperatures up to 250°C without degrading, allowing manufacturers to use standard soldering techniques for attaching components. To protect the material during use, researchers applied a coating of shellac. This coating prevents moisture absorption that would disrupt electrical signals, provides an adhesive layer for copper circuit components, and enables end-of-life recycling. When submerged in ethanol, the shellac dissolves, allowing recovery of valuable metals while the fungal material composts naturally. www.jku.at. Purdue University, West Lafayette, Ind., recently hosted the National Science Foundation’s launch of the CHORUS Center, whose goal is to create resilient safetycritical cyber-physical systems. Examples of such systems include driverless cars and smart traffic lights as well as smart power grids and health care/medical device networks. purdue.edu. BRIEF Neutron scattering was used by researchers to see how lithium ions (glowing orbs) move through a diffusion gate (gold triangle) in a solid-state electrolyte. Courtesy of Phoenix Pleasant/ORNL, U.S. DOE. Eco-friendly fabrication of mycelium-based substrates for electronic circuits. Image follows the harvest of pure mycelium skin. Courtesy of Advanced Functional Materials, 2024, doi.org/10.1002/adfm.202412196.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 12 SURFACE ENGINEERING LASER SURFACE TEXTURING KEEPS BACTERIA AT BAY Researchers from the Hopkirk Research Institute, New Zealand Food Safety Science & Research Centre, and Applied Technologies Group in New Zealand are developing a new approach to keep work surfaces free of bacteria in meat processing facilities. Instead of trying to prevent bacteria buildup, they created surfaces that stop bacteria from attaching in the first place. This is essential because bacteria from meat can attach, grow, and build into a biofilm that is difficult to remove, even on stainless steel surfaces. It can also aggregate, clumping together into an invisible mass stronger than its individual cells, which makes it harder to kill with antibacterial surface cleaners. Using lasers to etch the metal surface, researchers were able to create micro or nanoscale textures that make it difficult for microbial cells to attach. This laser-induced surface texturing also changes the metal’s water-repellent properties, another key to halting bacterial growth. “These nanoscale and microscale surface textures mimic natural antimicrobial surfaces, such as those found on cicada wings and shark skin,” says researcher Sebastiampillai Raymond. His team found the lasertexturing technique to be highly effective for carefully controlling and tuning textures on metal. Scientists are also working on developing machine learning models that could help manufacturers optimize and automate laser surface texturing. www.nzfssrc.org.nz. ART MEETS SCIENCE IN COLOR-SHIFTING COATINGS Researchers at Cornell University, Ithaca, N.Y., along with the KoreanAmerican artist Kimsooja are working to recreate the natural iridescence of things like peacock feathers and butterfly wings in synthetic materials. Unlike traditional pigments that absorb specific wavelengths of light, these natural materials use microscopic structures to split light into different colors. This structural color approach creates vibrant hues that do not fade over time and require no toxic pigments. The challenge lies in creating and maintaining precise structures that are just hundreds of nanometers thick across surfaces many meters wide. The Cornell team developed a new method for creating large-scale iridescent coatings, demonstrated through a 46-ft-tall installation titled, “A Needle Woman: Galaxy was a Memory, Earth is a Souvenir.” Initially exhibited at Cornell, the piece now resides at Yorkshire Sculpture Park in Wakefield, U.K., where it has maintained its optical properties for over a decade. The scientific breakthrough relies on custom-designed plastic molecules that automatically arrange themselves into regular patterns. These molecules consist of two different types of plastic chemically bonded together— polystyrene and poly(tert-butyl methacrylate). When properly designed, thousands of these dual-component molecules spontaneously stack into alternating layers, creating a natural grating that splits light into different colors. cornell.edu. Inspired by the antimicrobial surface of shark skin, micro and nanoscale textures at the scale of bacterial cells resist bacteria attachment. Courtesy of Sebastiampillai Raymond. This installation of “A Needle Woman” features window panels coated with iridescent self-assembled lamellar block copolymer film. Courtesy of Wiley-VCH Verlag. Researchers at Nagaoka University of Technology, Japan, developed a method for synthesizing surfacemodified apatite nanoparticles that results in improved cell adhesion, offering new possibilities for the next generation of biocompatible medical implants. www.nagaokaut.ac.jp. BRIEF
ADVANCED MATERIALS & PROCESSES | APRIL 2025 13 AEROSPACE FAILURES *Member of ASM International A persistent failure of main landing gear systems on a series of noncommercial planes was studied at the National Transportation Safety Board’s Materials Laboratory, leading to the discovery of cracks that propagated under cyclic loading of hydraulic actuators. REVIEW OF NTSB INVESTIGATIONS OF CESSNA 210 HYDRAULIC ACTUATOR FRACTURES FROM FATIGUE Erik M. Mueller, FASM,* Zoë Keliher, and Timothy Sorensen National Transportation Safety Board, Washington, D.C.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 14 The United States National Transportation Safety Board (NTSB) is an independent federal agency charged with investigating all civil avia- tion accidents and significant surface transportation events. The NTSB is not a regulatory agency but determines probable causes of accidents and issues safety recommendations to prevent them from recurring. Among the largest numbers of transportation accidents that the agency investigates are those in the general aviation category or those not defined as commercial aviation (Federal Aviation Regulations Part 121). A recurring issue in general aviation that the NTSB Materials Laboratory has investigated involves the hydraulic actuators that extend and retract the main landing gear of Cessna 210 Centurion airplanes. This vehicle is a six-seat, high-performance, retractable- gear, single-engine, high-wing general- aviation light aircraft. Originally produced from 1960 to 1986, the airplane is widely used by private operators, air-taxi and commercial charter, and private companies. A hydraulic fluid leak caused by a rupture of a hydraulic actuator would prevent the pilot from fully extending the landing gear, impacting their ability to land the airplane safely. BACKGROUND The NTSB investigated multiple accidents of hydraulic actuators integral to the 210 Centurion landing gear system, as detailed in Table 1. Many of the events leading up to each accident were similar. For example, the sequence of events for a Cessna 210B (N9674X) accident in Tacoma, Washington, began in flight as the pilot was completing the landing checklist. The pilot noticed the landing gear would not fully extend/retract. After trying to repeat the procedure, the pilot noted that the main landing gear (MLG) would not lock, and other control surfaces, like the flaps, could not be actuated. However, the nose landing gear (NLG) did extend and lock. The pilot circled over a field near the runway, contacting emergency ground personnel to diagnose and remedy the problem. After trying unsuc- cessfully to hand pump the MLG for over an hour, the pilot attempted an emergency belly landing. While the pilot could control the plane to some degree with the NLG during the landing, the aircraft slid to the left and eventually stopped in the grass left of the runway. The initial examination found hydraulic fluid, colored red, leaking from the actuator, as shown in Fig. 1. This actuator was removed and sent to the NTSB Materials Laboratory TABLE 1 — LIST OF RECENT ACCIDENT INVESTIGATIONS OF CESSNA 210 LANDING GEAR FAILURES CAUSED BY FRACTURED HYDRAULIC ACTUATORS NTSB accident number Accident location (United States) Accident date Airplane Registration number Actuator P/N ANC15LA048 Juneau, AK 12/10/2015 Cessna 210 N3607Y 1280501-1 ANC18LA019 Juneau, AK 7/6/2018 Cessna 210C N3607Y 1280501-2 CEN22LA378 Clinton, AR 8/9/2022 Cessna 210B N9637X P/N damaged WPR23LA213 Tacoma, WA 5/30/2023 Cessna 210B N9574X 1280501-1 CEN24LA018 Pueblo, CO 10/18/2023 Cessna 210B N9597X 1280501-2 Fig. 1 — View of hydraulic fluid (red) leaking from a cracked actuator housing from a 210B (N9674X) accident scene in Tacoma, Washington. Fig. 2 — Rotated views of the fractured hydraulic actuator from a 210C (N3607Y) showing (a) the longitudinal and (b) the circumferential aspects of the barrel crack. (b) (a)
ADVANCED MATERIALS & PROCESSES | APRIL 2025 15 for examination. The hydraulic actuator is an assembly that converts hydraulic pressure into linear movement of a piston, which then rotates a spindle, extending the landing gear leg until it reaches a locked position. If fluid pressure is lost in the cylinder, actuation cannot occur. As shown in Fig. 2, these actuators were 14.5 in. long with a diameter of 2.25 in. The cracked barrel was made of 7075-T6 aluminum. Each failed actuator exhibited near identical cracking patterns with two segments through the barrel: a circumferential crack (130° to 300° long) and a longitudinal crack that extended partway along the housing (typically 2.5 to 4 in.). LABORATORY EXAMINATION After initial photography, the barrel of the actuator was disassembled by removing the set screws and any safety wire present. Subsequently, the flange opposite the endcap typi- cally separated past the clip, either being held by a small filament or falling off entirely from the housing. These conditions were consistent with nearly or complete circumferential fracturing. In most cases, the retaining or snap ring also fell out—this ring was made of cadmium-coated alloy steel. To examine the longitudinal crack on the side of the barrel, an angled cut was made with a handheld cutoff wheel and then intentionally overstressed just outside of the crack tip. This process created a small exemplar area of overstress features to compare with pre-existing cracks, and the region was visually distinguishable, consistent with lack of prolonged exposure to outdoor service environments. Optical and scanning electron microscopy (SEM) examinations revealed distinct regions in the circumferential crack. As shown in Fig. 3, the fracture surface area nearer to the housing groove that held the retaining ring exhibited a smoother, more reflective visual appearance, whereas the outer regions were darker and dull, with a rough, fibrous texture. The inner region, annotated in Fig. 3b, exhibited striations, as typified in Fig. 4. Outside the fatigue crack, the fracture surface exhibited equiaxed dimpled rupture, consistent with overstress fracture. The longitudinal crack also showed dimpled rupture, with more directional quality as this crack was parallel to the part grain direction. A closer examination of the fatigue region found the cracks had originated at multiple initiation Fig. 3 — View of (a) the circumferential portion of the crack on the hydraulic actuator, after disassembly, with (b) the areas of fatigue cracking and overstress annotated. (b) (a) Fig. 4 — Secondary electron (SE) micrograph of a typical view of fatigue striations in the propagation region of the circumferential crack.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 16 sites. As illustrated in Fig. 5, a corrosion pit was located at the center of one such site. In most cases, the initiation sites contained pitting. These pits were located along a thin layer containing higher oxygen content, as demonstrated by the darker surface layer in the backscattered electron micrographs. When probed using energy dispersive x-ray spectroscopy (EDS), the pits were found to be comprised of primarily aluminum oxide, with elevated levels of chlorine, sodium, potassium, and calcium. In several pits, cadmium was identified, consistent with spalled coating material from the adjacent snap ring. The fatigue crack and retaining ring groove were cross-sectioned, mounted, and polished for metallographic examination. Figure 6 shows a typical cross-section displaying cracking at the outboard corner(s). These cross-sections also revealed corrosion pits on other parts of the ring groove surfaces, including some with cracks. However, the largest cracks were consistently observed at the outboard groove corners. The chemical composition of the actuator barrel housing was inspected using EDS and x-ray fluorescence. In all instances, the composition was consistent with 7075 aluminum alloy. The hardness of the housing was examined per ASTM E18, and the electrical conductivity measurements were examined per ASTM E1004[1,2]. The hardness and conductivity results were always within those expected for a T6 peak hardened temper (30.5 to 36.0 %IACS and a hardness exceeding 84 HRB, per AMS 2658)[3]. ANALYSIS AND DISCUSSION For each accident, hydraulic fluid pressure was lost after the pressurized hydraulic actuator barrel ruptured following fatigue crack propagation. These cracks initiated at corrosion pits along the retaining ring groove that was machined into the housing inner surface. While additional pits were observed along all the surfaces of the retaining clip groove, those with the largest cracks had initiated at corrosion pits along the outboard corner, which had been rounded. Along this corner, the pits would act as additional stress concentration sites, increasing the probability of fatigue crack initiation during service of the actuator during each pressurization cycle[4]. The cracks would have propagated under the cyclic loading from the pressurization and depressurization of the hydraulic fluid inside the actuator. As there was a layer of aluminum oxide along the crack initiation sites, there may have been corrosion processes aiding the rate of propagation[5]. There were also cadmium remnants present at some of the initiation sites, consistent with material that had spalled from the adjacent cadmium- coated retainer ring. The remnants would most likely separate from the steel retainer ring due to wear and fretting from vibrations incurred[6]. While the cadmium-coated steel retainer ring was in contact with the aluminum housing along the groove, the pitting was likely due to chlorine ions (Cl-) as significant amounts of Cl were detected from EDS examination of the pitting[7,8]. The difference in electrochemical potentials of cadmium and 7075 aluminum alloys are small and produce little driving force for galvanic corrosion[9]. However, contact with a bare steel part inserted into an aluminum alloy could create such driving forces[10]. The spalling of the cadmium coating from the steel snap ring, creating direct contact with the corresponding groove in the aluminum housing may exacerbate local corrosion rates, which could be another factor decreasing mean time between failures. As of this writing, the NTSB Materials Laboratory has investigated at least five hydraulic actuator failures, with additional failures having been documented outside the agency’s purview. The features from all these accidents were identical, namely crack locations, sizes, and physical features. In the cases examined by the NTSB, the fatigue cracks had initiated from the ring groove on the interior of the actuator housing and propagated outward into the housing. When the cracks had grown large enough circumferentially, the housings fractured longitudinally, relieving hydraulic fluid pressure and causing the actuators to fail in service. The actuators from these investigations, manufactured by Electrol, were installed on the Cessna 210 Centurion from 1960 to 1964. As the Electrol actuators are no longer produced, when one must be replaced, an aircraft owner either must locate an airworthy Electrol actuator or install Fig. 5 — Backscattered electron (BE) micrograph of a corrosion pit and aluminum oxide layer at a fatigue crack initiation site on the retainer ring groove. Fig. 6 — Bright field optical micrograph of a cross-section through an intact portion of the retainer ring groove, showing a fatigue crack propagating from the lower left corner.
ADVANCED MATERIALS & PROCESSES | APRIL 2025 1 7 an approved one from a different manufacturer. The geometry of the housing leaves a thin area of material that must withstand the internal hydraulic pressure, with the corners of the snap ring groove concentrating stress. Further, the housing and barrel are made from a wrought aluminum alloy, tempered to maximum strength and hardness, which can leave the material more susceptible to specific corrosion mechanisms[11]. Corrosion pitting, observed on interior surfaces of these parts, further reduces fatigue life[12]. To date, no significant injuries have been reported due to the failure of these actuators. However, loss of hydraulic fluid, which impairs a pilot’s control of the main landing gear, is a serious safety issue. Belly landings of aircraft, like the one that occurred in the Tacoma, Washington, accident, present a substantial risk to pilots and passengers of vehicles. Several service bulletins from the manufacturer, Cessna, have been issued concerning these hydraulic actuators since 1967. Service Letter 67-16 called for inspections of a specific series of the airplanes to look for and replace particular Electrol actuators with one from another manufacturer. Cessna later released service letters SE69-17 and SE75-21, eventually applying to all 210 airplanes manufactured between 1960 and 1964. In 1976, the Federal Aviation Administration (FAA) issued Airworthiness Directive (AD) 76-04-01 requiring compliance with SE75-21— this AD covers the part numbers listed in Table 1[13]. Cessna then updated the service manual in 2011 with Supplemental Inspection 32-10-01, calling for the actuator to be inspected after 6000 hours or 10 years, and then additionally every 1000 hours or three years. This inspection affects the airplanes in these investigations, as they were older than 10 years. This process can be a fluorescent penetrant inspection, a visual method looking for cracks[14]. A branch of the FAA is compiling information on the affected part numbers, and the NTSB is working in concert with them to ensure this problem can be remediated as soon as possible. For the airplane (N3607Y) that underwent this problem twice, it could not be determined if it had been maintained according to the AD or the supplemental inspections. It is imperative that older aircraft are inspected regularly at their required annual maintenance. The current annual inspection criteria specify operating the MLG repeatedly while checking the hydraulic system for leaks[15,16]. CONCLUSIONS The NTSB investigated multiple airplane accidents involving emergency landings where the pilots could not fully extend the main landing gear to a fully locked position. The agency determined that the probable cause was a loss of hydraulic fluid due to a fatigue failure of the main landing gear hydraulic actuator, which resulted in the pilot’s inability to fully extend the landing gear and inability to attain directional control during the landing roll. The fatigue cracking initiated along the retaining ring groove of the actuator at corrosion pitting present on the snap ring groove. Propagating outward circumferentially, once the fatigue crack grew to its terminal size, the remainder of the cross-section fractured from overstress. The design of the overhauled actuator and material, as well the high stress concentrations and corrosive ambient environments, all led to the premature failure of these actuators. Additionally, current inspection and overhaul procedures may not be robust enough to identify the fatigue in its early stages. ~AM&P Acknowledgments The authors would like to thank all the NTSB field investigators who have worked on these cases over the years, including Shaun Williams, Noreen Price, and John Brannen. The authors would also like to thank Henry Soderlund for his invaluable assistance in accessing historical information and service data. In accordance with Title 5 Code of Federal Regulations §2635.807(b)(2), the views expressed in this publication do not necessarily represent the views of the National Transportation Safety Board or the United States. For more information: Erik Mueller, materials research engineer, National Transportation Safety Board, 490 L’Enfant Plaza, SW, Washington, DC, 20594, erik.m.mueller@gmail.com, ntsb.gov. References 1. ASTM, ASTM E18 – Standard Test Methods for Rockwell Hardness of Metallic Materials, ASTM International, West Conshohocken, PA, 2017. 2. ASTM, ASTM E1004 – Standard Test Method for Determining Electrical Conductivity using the Electromagnetic (Eddy Current) Method, ASTM International, West Conshohocken, PA, 2017. 3. AMS D Nonferrous Alloys Committee, AMS 2658 ‑ Hardness and Conductivity Inspection of Wrought Aluminum Alloy Parts, SAE International, Warrendale, PA, 2016. 4. D.L. DuQuesnay, P.R. Underhill, and H.J. Britt, Fatigue Crack Growth from Corrosion Damage in 7075-T6511 Aluminium Alloy under Aircraft Loading, International Journal of Fatigue, 25(5), p 371-377, 2003, doi.org/10.1016/ S0142-1123(02)00168-8. 5. A.K. Vasudévan and S. Suresh, Influence of Corrosion Deposits on Near-threshold Fatigue Crack Growth Behavior in 2xxx and 7xxx Series Aluminum Alloys, Metallurgical and Materials Transactions A, 13, p 2271- 2280, 1982, doi.org/10.1007/BF02648397. 6. L. Lee, S. Descartes, and R.R. Chromik, Comparison of Fretting Behaviour of Electrodeposited Zn-Ni and Cd Coatings, Tribology International, 120, p 535-546, 2018, doi.org/10.1016/j. triboint.2018.01.021. 7. G. Chen, et al., Pitting Corrosion and Fatigue Crack Nucleation, Effects of the Environment on the Initiation of Crack Growth, Ed. W. Van Der Sluys, R. Piascik, and R. Zawierucha, West Conshohocken, PA, ASTM International, p 18-33, 1997, doi.org/10.1520/STP19951S. 8. P.S. Pao, C.R. Feng, and S.J. Gill, Corrosion Fatigue Crack Initiation in Aluminum Alloys 7075 and 7050,
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