APRIL 2021 | VOL 179 | NO 3 19 23 31 Near Net Shape Extrusion for Aerospace South American Historic Metals SMST NewsWire and iTSSe Newsletter Included in This Issue TITANIUMMICROTEXTURE PART I AEROSPACE MATERIALS AND TESTING P. 14
APRIL 2021 | VOL 179 | NO 3 19 23 31 Near Net Shape Extrusion for Aerospace South American Historic Metals SMST NewsWire and iTSSe Newsletter Included in This Issue TITANIUMMICROTEXTURE PART I AEROSPACE MATERIALS AND TESTING P. 14
63 ASM NEWS The latest news about ASM members, chapters, events, awards, conferences, affiliates, and other Society activities. TITANIUM MICROTEXTURE 101 — PART I Michelle Harr, Adam Pilchak, and Lee Semiatin Despite decades of research, fundamental questions still exist regarding the role of microtexture on the deformation, fatigue, and fracture behavior of titanium alloys. 14 A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 2 The Collins Aerospace integrated landing system for the A350-1000 features more than two dozen titanium components as part of the landing gear, wheels, and brakes. On the Cover: 72 3D PRINTSHOP Researchers are using light to modify printing direction and using 3D printing to finetune photonic crystal fibers. 27 EPA SAYS COPPER SURFACES HELP FIGHT COVID-19 Harold T. Michels The story behind the Environmental Protection Agency’s registration of copper surfaces against the virus that causes COVID-19.
4 Editorial 5 Research Tracks 6 Machine Learning 7 Process Technology 8 Metals/Polymers/Ceramics 10 Testing/Characterization 12 Emerging Technology 13 Nanotechnology 71 Editorial Preview 71 Special Advertising Section 71 Advertisers Index 72 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 wordwide by providing high-quality materials information, education and training, networking opportunities, and professional development resources in cost-effective 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. 179, No. 3, APRIL 2021. Copyright © 2021 by ASM International®. All rights reserved. Distributed at no charge to ASMmembers 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. Canada Post Publications Mail Agreement No. 40732105. Return undeliverable Canadian addresses to: 700 Dowd Ave., Elizabeth, NJ 07201. Printed by Publishers Press Inc., Shepherdsville, Ky. 19 ADVANCEMENTS IN NEAR NET SHAPE EXTRUSION FOR AEROSPACE APPLICATIONS Phani P. Gudipati and Michael B. Campbell The aerospace industry could benefit from recent progress in making near net shape titanium extrusions for applications beyond the long structural components of an aircraft. 23 AN EXPLORATION OF HISTORIC METALS IN SOUTH AMERICA Patricia Silvana Carrizo A study of metal artifacts from the Mendoza region of Argentina reveals the influences of native migration and European conquest. 31 iTSSe: Includes ITSC Virtual 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. 35 AEROMAT VIRTUAL SHOW PREVIEW AeroMat 2021 is pivoting to a 100% virtual conference and expo platform. FEATURES APRI L 2021 | VOL 179 | NO 3 A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 3 19 45 31 23 45 SMST NewsWire The official newsletter of the International Organization on Shape Memory and Superelastic Technologies (SMST). This biannual supplement covers shape memory and superelastic technologies for biomedical, actuator applications, and emerging markets, along with SMST news and initiatives.
4 A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 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 Jan Nejedlik, Layout and Design Kelly Sukol, Production Manager kelly.sukol@asminternational.org Press Release Editor magazines@asminternational.org EDITORIAL COMMITTEE Adam Farrow, Chair, Los Alamos National Lab John Shingledecker, Vice Chair, EPRI Somuri Prasad, Past Chair, Sandia National Lab Beth Armstrong, Oak Ridge National Lab Margaret Flury, Medtronic Surojit Gupta, University of North Dakota Nia Harrison, Ford Motor Company Michael Hoerner, KnightHawk Engineering Hideyuki Kanematsu, Suzuka National College of Technology Ibrahim Karaman, Texas A&M University Scott Olig, U.S. Naval Research Lab Amit Pandey, Lockheed Martin Space Satyam Sahay, John Deere Technology Center India Kumar Sridharan, University of Wisconsin Jean-Paul Vega, Siemens Energy Vasisht Venkatesh, Pratt & Whitney ASMBOARDOF TRUSTEES Diana Essock, President and Chair of the Board Judith A. Todd, Vice President Zi-Kui Liu, Immediate Past President John C. Kuli, Treasurer Burak Akyuz Elizabeth Ho man Diana Lados Navin Manjooran Toni Marechaux Jason Sebastian Larry Somrack Priti Wanjara Ji-Cheng Zhao Ron Aderhold, Secretary and Acting Managing Director STUDENT BOARDMEMBERS Ho Lun Chan, PayamEmadi, Casey Gilliams Individual readers of AdvancedMaterials & Processes may, without charge, make single copies of pages therefrom for personal or archival use, or may freelymake 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 fromarticles 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. GIVING LIFT TO AEROSPACE RECOVERY It’s been a yearlong, bumpy ride for the aerospace industry. But despite experiencing a pandemic-induced sharp descent, analysts forecast a recovery beginning this year (albeit quicker for the defense sector than commercial). And engineering will be key to that recovery. According to Deloitte, technological advancements and innovation could transform the industry and lead to long-term growth. Out on the horizon, areas of emerging technologies include advanced aerial mobility (AAM is being advanced by NASA and the Federal Aviation Administration), hypersonics (such as defense glide vehicles and cruise missiles), electric propulsion (e.g., Rolls-Royce’s hybrid version of the M250 gas turbine), and hydrogen-powered aircraft (e.g., a planned zero-emission aircraft from Airbus). While those innovations may sound too high in the clouds, in this issue we share some titanium advancements related to current aviation technology. First, “Titanium Microtexture 101”—Part I of a two-part series—explains this longstanding fatigue-related phenomenon in aerospace components. Second, we share how recent improvements to near net shape titanium extrusion make it a viable manufacturing option, not just for long structural components as it has been traditionally used, but for additional types of aircraft parts. Back on the ground, Patricia Silvana Carrizo—who prompted the formation of ASM’s Archaeometallurgy Community and has been leading its efforts—dug around in South America to bring us a review of copper artifacts found in her homeland of Argentina. Her study of these historic metals is fascinating as it traces their usage from before the 1500s through post-colonial times. Look for more archaeometallurgy articles later this year as outgrowths of this new ASM Connect community. In other copper news, we celebrate a recent announcement by the U.S. Environmental Protection Agency (EPA). Certain copper alloys have now been recognized by the EPA as having long-term efficacy against the virus that leads to COVID-19. In our Materials Science and Coronavirus series, Harold Michels shares his insights into what the announcement means for existing and future copper product registrations. In addition, the EPA statement provides further rationale for hospitals, extended care homes, and public transportation facilities to coat high-touch surfaces with copper alloys. We applaud the announcement! Likewise, the U.S Food and Drug Administration (FDA) recently released new guidance on the use of Nitinol in medical devices. We are honored to have authors from the FDA add context to the government document in their article in our SMST NewsWire supplement in this issue. And finally, circling back to aerospace, Mitchell Dorfman, FASM, TSS-HoF of Oerlikon Metco, will be viewed on computer screens around the globe as the joint keynote speaker at our co-located AeroMat and ITSC Virtual Events this May. Check out the show previews for both events included in this issue. Dorfman will describe how current challenges faced by the airlines and engine manufacturers—compounded by COVID-19—necessitate innovations in engine efficiency alongwith environmentally friendly advancements. He believes reliable and costeffective solutions will be required related to higher engine operating temperatures, new lighter weight components, andunique surface solutions for increased longevity of parts. As the aerospace industry makes its gradual ascent, technological innovations based on materials science will be more critical than ever. joanne.miller@asminternational.org
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 5 MACHINE LEARNING FOR AEROSPACE ALLOYS A new research initiative called Project MEDAL (Machine Learning for Additive Manufacturing Experimental Design) aims to accelerate the product development lifecycle of aerospace components by using a machine learning model to optimize additive manufacturing (AM) processing parameters for new metal alloys—and at a lower cost than current approaches. The project is being led by two U.K. entities, Intellegens and the University of Sheffield, along with Boeing, headquartered in Chicago. Intellegens is a University of Cambridge spin-off specializing in artificial intelligence. Project MEDAL’s research will concentrate on metal laser powder bed fusion—the most widely used industrial AM process—and will focus on the key parameter variables required to manufacture high density, high strength parts. The project is part of the U.K.’s National Aerospace Technology Exploitation Program. Intellegens will produce a software platform with an underlying machine learning algorithm based on one of its previous innovations. The project was conducted for a leading OEM and a new alloy was designed, RESEARCH TRACKS developed, and verified in 18 months instead of the typical 20-year timeline, saving about $10 million. While the new method is being developed with aerospace in mind, the team believes it will have applications in other sectors as well. “The opportunity for this project is to provide end users with a validated, economically viable method of developing their own powder and parameter combinations. Research findings from this project will have applications for other sectors including automotive, space, construction, oil and gas, offshore renewables, and agriculture,” says Ian Brooks, AM technical fellow at University of Sheffield North West. intellegens.ai. MORE EFFICIENT MATERIALS FOR ELECTROLUMINESCENCE New research from an international team of scientists offers insight into how electroluminescent materials could be designed to work more efficiently. Two years ago, theoretical chemist Andrew Rappe of the University of Pennsylvania (Penn) visited the lab of Tae-Woo Lee at Seoul National University (SNU) to see if they could develop a theory to explain some of their experimental results. The material being studied was formamidinium lead Machine learning will be used to make 3D printing of metallic alloys cheaper and faster for the aerospace industry. bromide, a type of metal-halide perovskite nanocrystal (PNC). Results collected by the Lee group indicated that green LEDs made of this material were working more efficiently than expected. PNCs like formamidinium lead bromide are used in photovoltaic devices, where they can store energy as electricity or convert electric current into light in LEDs. To make sense of the SNU results, the team developed a computational model of the material’s unexpected efficiency and designed follow-up experiments. Using their new model, researchers found that the PNCs were more efficient if the size of the quantum dots were smaller, although reducing the size also meant increasing the surface-to-volume ratio, creating more surface area prone to defects. The team found that replacing formamidinium with a larger organic cation called guanidiniummade the particles smaller while also preserving structural integrity. Building on this approach, the team found other strategies to improve efficiency, including the addition of longchain acids and amines to stabilize surface ions and adding defect-healing groups to repair any vacancies that might form. Besides Penn and SNU, other researchers came from the Korea Advanced Institute of Science and Technology, Ecole Polytechnique Fédérale de Lausanne, University of Tennessee, University of Cambridge, Universitat de Valencia, Harbin Institute of Technology, and University of Oxford. upenn.edu. A new study explores how a class of electroluminescent materials can be made to work more efficiently. Courtesy of Penn.
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 6 MACHINE LEARNING | AI AI IMPROVES CHEMICAL SEPARATION Led by researchers at the University of Toronto (U of T) and Northwestern University, Evanston, Ill., a new study is using machine learning and artificial intelligence (AI) to create the best building blocks in the pool of materials used for a specific application, such as improving chemical separation in industrial processes. “We built an automated materialsdiscoveryplatformthatgenerates the design of various molecular frameworks, significantly reducing the time required to identify the optimal ma- terials for use in this particular process,” says U of T researcher Zhenpeng Yao. The team focused on development of metal-organic frameworks (MOFs) that are considered the ideal absorbing material for removing CO2 from flue gas and other combustion processes. “The new approach uses machine learning algorithms to learn from the data as it explores the space of materials and actually suggests new materials that were not originally imagined,” explains professor Randall Snurr of Northwestern. www.utoronto.ca. MACHINE LEARNING SUPPORTS AEROSPACE Using machine learning, researchers from the National Institute for Materials Science (NIMS), Japan, determined the optimum parameters for manufacturing high quality, Ni-Co-based superalloy powders at high yields—a promising development for aircraft engine materials. The team then demonstrated that these parameters led to low-cost manufacturing of powders suitable for high-pressure turbine disk production. Because metal 3D printing has been rapidly adopted in aerospace engine production, there is growing demand for the alloy powders these printing techniques require. When the materials are used to produce high-pressure turbine disks, they must be heat resistant, highly plastic, and homogeneous superalloy powders that can be processed into spheres. They also must be produced at high yields to reduce costs. Super- alloy powders are commonly produced for this purpose using large gas atomizers. The team used machine learning in an attempt to optimize gas atomization processes for the manufacturing of Ni-Co-based superalloy powders without relying on the knowledge of experts. As a result, the team succeeded in manufacturing fine-grained powders that can be processed into spheres. In addition, use of the parameters dramatically increased production yields from the conventional 10-30% to approximately 78% after performing experiments only six times without using previously collected data. The powder manufactured in this research was approximately 72% cheaper than commercially available powders when the prices of the rawmaterials were compared. The prediction accuracy of machine learning models increases as they receive more training data, and superalloy powder manufacturers possess largely unexploitedmanufacturing process data. Integrating this data may further improve the ability to predict optimum parameters, leading to even higher quality powders at lower cost. www.nims.go.jp/eng. Optimization of superalloy powder manufacturing processes using machine learning. Courtesy of NIMS. AI enables autonomous design of nanoporous materials. Courtesy of University of Toronto. Researchers at UCLA developed a new image autofocusing technique to digitally bring a given microscopy image into focus without the need for special equipment during the image acquisition phase. The approach is based on deep learning, where an artificial neural network is trained to take a single defocused image as its input to rapidly create an in-focus image of the same sample. ucla.edu. BRIEF
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 7 PROCESS TECHNOLOGY ONE-STEP METAMATERIALS PROCESS While studying a thin-film material called strontium stannate (SrSnO3), researchers at the University of Minnesota Twin Cities, Minneapolis, discovered a groundbreaking one-step process for creating metamaterials. They demonstrated the realistic possibility of designing similar self-assembled structures with the potential of creating built-to-order nanostructures with wide applications in electronics and optical devices. In the new work, researchers studied a thin-film material called strontium stannate. During their research, they noticed the surprising formation of checkerboard patterns at the nanoscale similar to the metamaterial structures fabricated in the costly, multistep process. “At first we thought this must be a mistake, but soon realized that the periodic pattern is a mixture of two phases of the same material with different crystal structures,” says researcher Bharat Jalan. The material had spontaneously organized into an ordered structure as it changed from one phase to another. During a first-order structural phase transition process, the material moved into a mixed-phase in which some parts of the system completed the transition and others did not. The team then demonstrated a process for the first-ever self- assembled, tunable nanostructure to create metamaterials in just one step. They were able to tune the ability to store electrical charge property within a single film using temperature and laser wavelength, effectively creating a variable photonic crystal material with 99% efficiency. Using high-resolution electron microscopes, the researchers confirmed the unique structure of the material. They are now looking to future applications for their discovery in optical and electronic devices. twin-cities.umn.edu. GRAPHENE FUNCTIONALIZATION An international research team has demonstrated a new pro- cess to modify the structure and properties of graphene. This chem- ical reaction, photocycloaddition, modifies the bonds between atoms using ultraviolet light. Although graphene has outstanding physical, optical, and mechanical properties, it currently has limited use in electronics. “No other material has properties similar to graphene, yet unlike semiconductors used in electronics, it lacks a band gap. In electronics, this gap is a space in which there are no energy levels that can be occupied by electrons. Yet it is essential for interacting with light,” says Professor Federico Rosei of the Institut National de la Recherche Scientifique’s (INRS) Énergie Matériaux Télécommunications Research Centre in Quebec City, Canada. The multidisciplinary group of researchers from Canada, China, Denmark, France, and the U.K. succeeded in modifying graphene so as to create a band gap. According to Rosei, current research is rather fundamental but could have repercussions over the next few years in optoelectronics, such as in the fabrication of photodetectors or in the field of solar energy. “These include the manufacture of high-performance photovoltaic cells for converting solar energy into electricity, or the field of nanoelectronics, for the extreme miniaturization of devices,” he added. www. inrs.ca/en. Checkerboard patterns surprisingly formed at the nano scale of thin films, similar to structures fabricated in costly, multistep processes. Courtesy of Jalan Group/University of Minnesota. Researchers from Kanazawa University, Japan, report a major improvement in recovering silver and palladium ions from aqueous acidic waste. Recovery of the metals in elemental, metallic form is straightforward—simply burn the extraction material and collect the remaining metal after further heating. www.kanazawa-u.ac.jp. BRIEF Magnified experimental and simulated scanning tunneling microscopy images of the molecule network on graphene. Courtesy of INRS.
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 8 METALS | POLYMERS | CERAMICS generators. But the researchers think the process could easily be scaled up to make superhard metal coatings or larger industrial components. The key to the process, scientists say, is the chemical treatment given to the nanoparticle building blocks. Metal nanoparticles are typically covered with ligands, which generally prevent the formation of metal-metal bonds between particles. The team found a way to strip those ligands away chemically, allowing the clusters to fuse together with just a bit of pressure. In theory, the technique could be used to make any kind of metal and even metallic glass. The team has patented the technique and foresees widespread potential in both industry and the scientific research community. brown.edu. Various types of plate-lattices were designed and built by engineers in Glasgow, in the pursuit of lightweight engineering. Courtesy of University of Glasgow. This gold “coin” was made from nanoparticle building blocks. Courtesy of Chen Lab/Brown University. TOUGHER THAN ALUMINUM METAMATERIAL A team led by University of Glasgow, U.K., engineers developed a new plate-lattice cellular metamaterial capable of impressive resistance to impacts. Scientists say their new 3D-printed material, made by combining commonly used plastics with carbon nanotubes, is tougher and lighter than similar forms of aluminum. The material could lead to the development of safer structures for use in the aerospace, automotive, renewables, and marine industries. The composite uses mixtures of polypropylene, polyethylene, and multiwall carbon nanotubes. The researchers used their nanoengineered filament composite as the feedstock in a 3D printer that fused the filaments together to build a series of plate-lattice designs. Those designs were then subjected to a series of impact tests. The hybrid design, which amalgamated elements of all three typical plate-lattice designs, proved to be the most effective in absorbing impacts, with the polypropylene version showing the greatest impact resistance. Using specific energy absorption as a measure, the team found that the polypropylene hybrid plate-lattice could withstand 19.9 joules per gram—a superior performance over similarly designed microarchitected metamaterials based on aluminum. www.gla.ac.uk. MAKING SUPERHARD METALS Researchers from Brown University, Providence, R.I., created a new method to customize metallic grain structures by smashing individual metal nanoclusters together to form solid macroscale hunks of solid metal. Mechanical testing of the metals manufactured using the technique showed that they were up to four times harder than naturally occurring metal structures. The researchers made centimeter-scale coins using nanoparticles of gold, silver, palladium, and other metals. Items of this size could be useful for making high-performance coating materials, electrodes, or thermoelectric Researchers from the University of California’s San Diego and Berkeley campuses, Carnegie Mellon University, and the University of Oxford produced islands of amorphous, noncrystalline material inside high-entropy alloys. Potential applications include landing gear, pipelines, and automobiles, with the new material able to make these structures lighter, safer, and more energy efficient, according to the team. ucsd.edu. BRIEF IMPROVING CERAMIC FUEL CELL PERFORMANCE Researchers at the Korea Advanced Institute of Science and Technology (KAIST) developed a new technology
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 9 that suppresses the deterioration brought on by the reduction-oxidation cycle, a major cause of ceramic fuel cell degradation, by significantly reducing the quantity and size of the nickel catalyst in the anode using a thin-film technology. Ceramic fuel cells generally operate at high temperatures—800°C or higher. Therefore, inexpensive catalysts, such as nickel, can be used in these cells, as opposed to low-temperature polymer electrolyte fuel cells, which use expensive platinumcatalysts. Nickel usually comprises approximately 40% of the anode volume of a ceramic fuel cell. However, since nickel agglomerates at high temperatures, when the ceramic fuel cell is exposed to the oxidation and reduction processes that accompany stop-restart cycles, uncontrollable expansion occurs. This results in the destruction of the entire ceramic fuel cell structure. This fatal drawback has prevented the generation of power by ceramic fuel cells from applications that require frequent start-ups. To overcome this challenge, the team developed a new concept for an anode that contains significantly less nickel, just 1/20 of a conventional ceramic fuel cell. This enables the nickel particles in the anode to remain isolated fromoneanother. Tocompensate for the reduced amount of the nickel catalyst, the nickel’s surface area is drastically increased through the realization of an anode structure where nickel nanoparticles are evenly distributed throughout the ceramic matrix using a thin-film deposition process. In ceramic fuel cells using this novel anode, no deterioration or performance degradation of the ceramic fuel cells was observed, even after more than 100 reduction- oxidation cycles, in comparison with conventional ceramic fuel cells, which failed after fewer than 20 cycles. Moreover, the power output of the novel anode ceramic fuel cells was improved by 1.5 times compared to conven- tional cells, despite the substantial reduction of the nickel content. www. kaist.ac.kr/en/. Conceptual diagram of the oxidation-reduction cycle of ceramic fuel cells and new concept vs. deterioration rate of conventional fuel plates. Courtesy of Korea Institute of Science and Technology.
1 0 A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 fibers is key to enabling progress in numerous photonic applications. Most notably, these would improve Internet performance, which heavily relies on optical fibers for data transmission and where current technology is starting to reach its limits. Backscattering in optical fibers is often highly undesirable as it causes attenuation of signals propagating down the optical fiber and limits the performance of many fiber-based devices, such as fiber optic gyroscopes that navigate airliners, submarines, and spacecrafts. However, the ability to measure backscattering reliably and accurately can be beneficial in other instances, such as the characterization of installed fiber cables where the backscatter is used tomonitor the condition of a cable and identify the location of any breaks along its length. The latest generation of hollow-core nested antiresonant nodeless fibers (NANFs) exhibit backscattering that is so low that up until this point it remained unmeasurable. The researchers developed an instrument that enables them to reliably measure the extremely weak signals back-scattered in their latest hollow-core fibers—confirming that scattering is over four orders of magnitude lower than in standard fibers, in line with theoretical expectations. www.southampton.ac.uk, www.ulaval.ca/en. TESTING | CHARACTERIZATION NANOMAPPING WITH ULTRASOUND Researchers at Delft University of Technology and ASML, both in the Netherlands, recently developed a new imaging technique based on ultrasound that can explore materials at the nanoscale. “Existing nondestructive imaging techniques for nanoelectronics, such as optical and electron microscopy, are not accurate enough or applicable to deeper structures,” explains Delft researcher Gerard Verbiest. “A well-known 3D technique on a macroscale is ultrasound. But resolution is typically determined by the wavelength of the sound used. “To improve this, ultrasound has already been integrated into an atomic force microscope (AFM),” Verbiest continues. “The advantage here is that it isn’t the wavelength, but the size of the tip of the AFM, that determines the resolution. But at the initial frequencies, the AFM response was unclear. So the team increased the frequency of the sound used even further. Increasing the frequency is something that has only become possible recently, Verbiest explains. They achieved this through photoacoustics and integrated the technique into an AFM. The new method is particularly interesting for nanoelectronics, but the researchers say there are potential applications outside of electronics as well. It could be used to make detailed images of single living cells and also aid heat transport research in materials science. www.tudelft.nl/en, www.asml. com/en. IMPROVING OPTICAL FIBERS For the first time, researchers from the University of Southampton, U.K., and Université Laval, Canada, successfully measured back reflection in cutting-edge hollow-core fibers that is around 10,000 times lower than conventional optical fibers. This discovery highlights yet another optical property in which hollow-core fibers are capable of outperforming standard optical fibers. Improving optical Triangular holes make this material more likely to crack from left to right. Courtesy of N.R. Brodnik et al./Phys. Rev. Lett. Engineers at Iowa State University, Ames, developed technology capable of recovering precious metals from electronic waste. Using controlled applications of oxygen and relatively low temperatures, the team says they can dealloy a metal by slowly moving the most reactive components to the surface where they form spikes of metal oxides. iastate.edu. BRIEF Researchers Gerard Verbiest, Ruben Guis, and Martin Robin. Courtesy of Delft University of Technology. A new dealloying method brings the most reactive components to the surface, forming stalagmite-like spikes (left), while leaving the least reactive components in the core surrounded by metal-oxide spikes (right).
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 1 DETECTING ULTRA-TRACE ELEMENTS Chemists at the DOE’s Pacific Northwest National Laboratory (PNNL), Richland, Wash., developed a simple and reliable method that holds promise for transforming how ultra-trace elements are separated and detected. Low levels of naturally occurring radioactive elements like uranium and thorium atoms are often embedded in valuable metals like gold and copper. It has been extraordinarily difficult, impractical, or sometimes even impossible to tease out how much is found in samples of ore mined across the globe. Yet sourcing materials with very low levels of natural radiation is essential for certain types of sensitive instruments and detectors, like those searching for evidence of currently undetected particles that many PNNL scientists Khadouja Harouaka (seated), and Isaac Arnquist, prepare samples in an ultra-clean laboratory, which is necessary to ensure accurate mass spectrometry measurements. Courtesy of Andrea Starr/PNNL. physicists believe comprise most of the universe. Scientists locate extraordinarily rare atoms from the huge field of ordinary atoms by sending their samples through a series of isolation chambers. These chambers first filter and then collide the rare atoms with simple oxygen, creating a “tagged” molecule of a unique weight that can then be separated by its size and charge. In this case, the sophisticated counter is a mass spectrometer. The central innovation is the collision cell chamber, where charged atoms of thorium and uranium react with oxygen, increasing their molecular weight and allowing them to sepa- rate from other overlapping signals that can disguise their presence. Among other uses, the innovation may allow chemists to further hone the chemistry that produces the world’s purest electroformed copper. The copper forms a key component of sensitive physics detectors, including those used for in- ternational nuclear treaty verification. pnnl.gov.
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 2 MAGNETOCURING ADHESIVE Scientists at Nanyang Technological University, Singapore, invented glue that is activated by a magnetic field. Their “magnetocuring” glue has applications in environmental conditions where current adhesives do not work well. When the adhesive is sandwiched between insulating material like rubber or wood, traditional activators like heat, light, and air cannot easily reach it. The new adhesive is made by combining a commercially available epoxy adhesive with specially tailored magnetic nanoparticles made by the scientists. It does not need to be mixed with any hardener or accelerator, unlike two-component adhesives, making it easy to manufacture and apply. The adhesive bonds the materials when it is activated by passing through a magnetic field, which is easily generated by a small electromagnetic device. This eliminates the need for large industrial ovens to cure the glue, resulting in a smaller manufacturing footprint and less energy consumption. Potential applica- tions include high-end sports equipment, auto- motive products, electronics, energy, aero- space, andmedical manufacturing processes. Laboratory tests have shown that the new adhesive has a strength up to seven megapascals, on par with many of the epoxy adhesives on the market. Moving forward, the team hopes to engage adhesive manufacturers to collaborate on commercializing their technology. They have filed a patent through NTUitive, the university’s innovation and enterprise company. www.ntu.edu.sg. MORE DURABLE TOUCHSCREENS Using a new theoretical model, scientists at the University of Tsukuba, Japan, gained a better understanding of vibrational spread through disordered materials such as glass. They found that as the degree of disorder increased, sound waves traveled less and less like ballistic particles, and instead began diffusing incoherently. This work may lead to new heat- and shatter-resistant glass for smartphones and tablets. Understanding the possible vibrational modes in a material is important for EMERGING TECHNOLOGY The DOE’s Critical Materials Institute, Ames, Iowa, developed a low-cost, high-performance permanent magnet by drawing inspiration from ironnickel alloys found in meteorites. The new magnet rivals widely used alnico magnets in magnetic strength and has the potential to fill a strong demand for magnets that are rare-earth free and cobalt free. ameslab.gov/cmi. BRIEF controlling its optical, thermal, and mechanical properties. The propagation of vibrations in the form of sound of a single frequency through amorphous materials can occur in a unified way, as if it were a particle. However, this approximation can break down if thematerial is too disordered, which limits the ability to predict the strength of glass under a wide range of circumstances. Now, researchers have developed a new theoretical framework that explains the observed vibrations in glass with better agreement with experimental data. They demonstrate that thinking about vibrations as individual phonons is only justified in the limit of long wavelengths. On shorter length scales, disorder leads to increased scattering and the sound waves lose coherence. The equations for low frequencies start looking like those for hydrodynamics, which describe the behavior of fluids. The researchers compared the predictions of the model with data obtained from soda lime glass and showed that they proved a better fit compared with previously accepted equations. “Our research supports the view that this phenomenon is not unique to acoustic phonons, but rather represents a general phenomenon that can occur with other kinds of excitations within disordered materials,” the researchers say. Future work may involve utilizing the effects of disorder to improve the durability of glass for smart devices. www.tsukuba.ac.jp/en. Iron-nickel permanent magnets. Courtesy of DOE Ames Laboratory. From left: NTU faculty, Terry Steele, Raju V. Ramanujan, and Richa Chaudhary holding up various soft and hard materials bonded by their newmagnetocuring glue. Courtesy of NTU Singapore.
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 3 DIVERSE NANOPARTICLES Scientists from University of Illinois Chicago (UIC) and the DOE’s Argonne National Laboratory, Lemont, Ill., recently discovered that certain types of alloy nanoparticles display exceptionally high stability and durability during a chemical reaction that often quickly degrades catalytic materials. The nanoparticles could have many applications, including water-splitting to generate hydrogen in fuel cells, reduction of carbon dioxide by capturing and converting it into useful materials like methanol, more efficient reactions in biosensors to detect substances in the body, and solar cells that produce heat, electricity, and fuel more effectively. The team of researchers focused on high-entropy alloy nanoparticles and used Argonne’s Center for Nanoscale Materials (CNM) to characterize the particles’ compositions during oxidation. Using flow transmission electron microscopy (TEM) allowed them to capture the entire oxidation process in real time and at high resolution. They found that the high-entropy alloy nano-particles NANOTECHNOLOGY Depiction of the movement of different molecules during the oxidation of high-entropy alloy nanoparticles. Courtesy of University of Illinois Chicago. are able to resist oxidation much better than general metal particles. To perform the TEM, scientists embedded the nanoparticles into a silicon nitride membrane and flowed different types of gas through a channel over the particles. A beam of electrons probed the reactions between the particles and the gas, revealing the low rate of oxidation and the migration of certain metals—iron, cobalt, nickel, and copper—to the particles’ surfaces during the process. The researchers say their discoveries could benefit energy storage and conversion technologies, such as fuel cells, lithium-air batteries, supercapacitors, and catalyst materials. anl.gov. Scientists from the University of Manchester in the U.K. achieved a Guinness World Record for weaving threads of individual molecules together to create the world’s finest fabric. The team produced a 2D-molecularly woven fabric with a thread count of 40-60 million, overtaking the finest Egyptian linen with a thread count of roughly 1500. manchester.ac.uk. BRIEF
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 4 TITANIUM MICROTEXTURE 101— PART I Michelle Harr,* Adam Pilchak,* and Lee Semiatin, FASM* Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio University of Dayton Research Institute, Ohio Despite decades of research, fundamental questions still exist regarding the role of microtexture on the deformation, fatigue, and fracture behavior of titanium alloys. *Memberof ASMInternational 1 4 T I T A N I U M F O R A E O S P A C E
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 5 Fig. 1 — Length scale of salient microstructural features in α/β titanium alloys. Microtexture is a feature of titaniumalloymicrostructures that has received considerable renewed attention in the past several years as it impacts materials processing, properties, and inspectability of titanium alloys. This article describes the microstructural evolution processes that result in microtexture formation, while Part II of this series will further elaborate on the effects of microtexture on deformation behavior. Titanium alloys feature an excellent blend of high strength, low density, and good corrosion resistance. It is the fatigue performance, however, that helped titanium find its way into fracture-critical rotating hardware in gas turbine engines. Following the 1989 crash of a DC-10 in Sioux City, Iowa, due to the presence of a melt-related anomaly known as “hard α,” the titanium industry set out to refine melt practices and improve nondestructive inspection methods in order to prevent such an event from occurring again. Fast forward nearly three decades and we can say with confidence that those involved significantly advanced the state of the art in titanium melt practices. Following the event, the Federal Aviation Administration (FAA) convened the Jet Engine Titanium Quality Committee (JETQC), which still exists today. This group is responsible for ensuring that the premium quality titanium that finds its way into gas turbine take equiaxed or elongated morphology, and secondary α or “transformed β,” which can take on either basketweave or colony morphology. As discussed in this article, the mechanism by which MTRs develop results in crystallographically aligned primary α particles, so the solution heat treatment temperature is often selected to be high enough in the α/β phase field that the primary α particles are isolated from one another and separated by the transformed β. While this strategy is generally effective, under certain conditions the secondary α can adopt a similar orientation to its adjacent primary α[3-5]. The causes and implications of such an event are also discussed. The goal of this article series is to bring awareness to this microstructural feature and highlight what the community currently knows about microtexture, draw attention to some gaps in understanding, and highlight opportunities for future research. MICROTEXTURE EVOLUTION The evolution of microtextured regions in near-α and α/β titanium alloys such as Ti-6242 and Ti-6Al-4V is related to industrial thermomechanical processes used to convert large cast ingots (~800-1000 mm in diameter) into semi-finished mill products such as billets, slabs, and plates. Typically, ingots are synthesized via techniques such engines is safe and free from melt-related anomalies. The entire industry shares its experience with such anomalies in the interest of aviation safety. In fact, the industry has cleaned up titanium so much that it is rare to find hard α during the now-routine ultrasonic inspections performed on billets and forgings. With no other hard second phases, inclusions, or pores (when properly processed), fatigue cracks tend to initiate at microstructural weak links. In the case of titanium alloys, these are known as microtextured regions (MTRs) or macrozones. These terms are used interchangeably to describe a feature of the microstructure that is actually an aggregation of the lower length scale microstructural features, specifically when those features share a common crystallographic orientation. These features have long been known to cause issues related to dwell fatigue of near-α alloys[1]. However, it has only recently come to light that the industry workhorse Ti-6Al-4V alloy may also be susceptible under certain combinations of stress, temperature, microstructure, and composition[2]. The salient microstructural features, which span about seven orders of magnitude, are depicted in Fig. 1. Titanium alloys used for rotating components are most often used in the so-called bimodal condition, which consists of a mixture of primary α particles that may
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 6 (a) be inhomogeneous due to the presence of neighboring hard colonies, the shape of the lamellae per se, and other such factors. Thus, it is quite common to see microstructural features such as kinked lamellae, lamellae that have rotated to Fig. 2 — Microstructure evolution during thermomechanical processing of α/β titanium alloys: (a) as-cast ingot; (b) after recrystallization; and (c) after spheroidization of the lamellar αmicrostructure via α/β hot working[6]. (b) (c) as vacuum arc or electroslag melting/ remelting, electron beam melting, or plasma cold hearth melting to control interstitial content and remove high-density/low-density inclusions. However, slow cooling following solidification leads to coarse, columnar grains that are multiple millimeters in length and diameter (Fig. 2a)[6]. A number of hot working and heat treatment steps are subsequently performed (principally in the high temperature, single phase bcc β field) to obtain billet or slab with recrystallized, equiaxed β grains, typically with a size of ~2-3 mm in diameter (Fig. 2b). Following β recrystallization, the relatively slow cooling associated with the thermal inertia of large-section workpieces results in the decomposition of each β grain into a microstructure comprising a number of ~0.5-to-1.5-mm- diameter colonies of hcp α lamellae (Fig. 2b), each of which has its own crystallographic orientation relative to a specified set of reference coordinates such as the radial and axial directions of the cylindrical billet. Due to a Burgers orientation relationship (BOR) between the high temperature β phase and low temperature α phase, the number of possible orientations of the α colonies (also called α variants) within a given β grain cannot exceed 12, and typically lies in the range of 3-10. Each colony of α lamellae formed during cooling from the β field can be thought of as a nascent MTR, or a region in which all of the α phase has the same (or nearly the same within a specified tolerance limit) crystallographic orientation. The objective of subsequent hot working steps performed in the α/β phase field is therefore twofold: (1) break down each colony to develop a uniform, fine, equiaxed structure of globular α particles within the β matrix (Fig. 2c), and (2) randomize the orientation of each α particle relative to its neighbors to minimize (or eliminate) the extent of MTRs. Accomplishing these objectives can be quite difficult due the plastic anisotropy of the hcp α phase. The anisotropy translates to a sizeable difference (of the order of three times) between the material flow stress when deformation is imposed along the c-axis (i.e., the normal to the closepacked planes of the hcp Ti crystal) versus perpendicular to it, and this results in very inhomogeneous deformation. “Soft” colonies (having c-axes oblique to the forging direction) undergo large deformation, and “hard” colonies (with c-axes parallel or nearly parallel to the forging direction) suffer relatively small strains (Fig. 3)[7]. Depending on the hot working tem- perature, the difference in local stresses and strains may lead to generation of deleterious cavities between the harder and softer colonies (Fig. 4)[8-12]. Equally important, the hard oriented, less deformed colonies may retain their nature as relatively equiaxed microtextured features. By contrast, deformation within the softer colonies can be relatively large overall, but it tends to Fig. 3 — EBSD compression axis, inverse pole figure map for a region in a Ti-6Al-4V pancake forging illustrating the variation in deformation among colonies with hard orientations (red) and soft orientations (other colors). Courtesy of T.R. Bieler.
A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 7 that have rotated to lie along the primary metal flow direction with little or no spheroidization or orientation randomization may form especially long and deleterious MTRs (Fig. 5)[13]. HEAT TREATMENT CONSIDERATIONS During static heat treatment following hot working, remnant stored work (dislocation substructure) may promote static spheroidization without additional changes in the misorient- ation of the α particles in a prior colony and thus result in little mitigation of MTR characteristics. The severity of MTRs associated with spheroidized (but not randomized) α particles can be exacerbated by the tendency of surrounding secondary α plates with a similar orientation to form in the β matrix during cooling following hot working or final heat treatment[3-5]. Such a tendency can be mitigated somewhat by imposing a high cooling rate following hot working or heat treatment to develop multiple α variants within the β grains surrounding each α particle[14]. A second heat treatment step at a lower temperature may then be applied to coarsen the secondary α produced in the first step[15]. It is worth noting that such a condition can only occur if the β phase does not recrystallize dynamically during deformation or subsequent static heat treatment and hence retains a long range common orientation (denoted as “β microtexture” in Fig. 1). Begley et al.[16] hypothesized that this could occur under two conditions: (1) α and β phases co-rotate during deformation such that the orientation relationship is preserved, or (2) where very little deformation occurs such that there is insufficient strain to cause recrystallization. Moreover, extended recovery processes that occur during near but sub-transus annealing can result in substantial changes to the β phase texture[17]. A great need exists for additional research in this area because β microtexture is believed to be a key contributor to dwell fatigue, and it has also been implicated in abnormal grain growth in β annealed structural titanium forgings. lie along the direction of primarily metal flow, and regions of very high strain near β grain boundaries. High local strains within the soft colonies lead to the development of dislocation walls within individual α lamellae, which promote spheroidization during deformation (i.e., dynamically), especially if a multiplicity of slip systems has been activated. Further, the combination of high local strains, evolution of high angle boundaries (associated with dislocation walls), and strain gradients may serve to rotate individual portions of long lamellae to different degrees and thus result in both spheroidization and randomization of the orientation of the resulting α particles, thereby eliminating MTRlike features, at least locally. On the other hand, lamellae within a given prior colony (or several adjacent colonies) Fig. 4 — EBSD inverse pole figure maps for Ti-6Al-4V samples with an initial colony—a microstructure in which cavities developed during hot deformation at 1089 K (815°C) via (a) uniaxial tension[9], (b) pancake forging[10], or (c) torsion testing[11]. Hexagons indicate the orientations of hard and soft colonies adjacent to some of the cavities. Fig. 5 — EBSD radial direction, inverse pole figure maps illustrating (red) microtextured regions in a 209-mm-diameter Ti-6242 billet at various radial locations[13]. (a) (b) (c)
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