January_2021_AMP_Digital

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 | J A N U A R Y 2 0 2 1 1 2 PROCESS TECHNOLOGY IMPROVING ALUMINUM ALLOY FATIGUE LIFE Engineers fromMonash University, Australia, determined that weak links, called precipitate free zones (PFZs), are the cause of poor fatigue performance of high-strength aluminum alloys. They demonstrated improvements in fatigue life of high-strength alloys by 25 times that of current state-of-the-art alloys. The work has significant implications for the transport manufacturing indus- try. The team created aluminum al- loy microstructures that can heal PFZs while in operation using the mechani- cal energy imparted into the materials during the early cycles of fatigue. This delays the localization of plasticity and the initiation of fatigue cracks while en- hancing fatigue life and strength. “Our research has demonstrat- ed a conceptual change in the micro- structural design of aluminum alloys for dynamic loading applications,” the team says. “The structure is trained and the training schedule is used to heal the PFZs that would otherwise repre- sent the weak points. The approach is general and could be applied to other precipitate hardened alloys containing PFZs for which fatigue performance is an important consideration.” monash.edu. OPTICAL FIBERS UNDER PRESSURE An international team of research- ers from Hokkaido University, Japan, and Penn State University, State Col- lege, produced silica glass fibers under high pressure to significantly improve optical fiber data transmission. Using computer simulations, the researchers and their industry collaborators theo- retically show that signal loss from sil- ica glass fibers can be reduced by more than 50%, which could dramatically ex- tend the distance data can be transmit- ted without the need for amplification. Optical fibers have revolutionized high-bandwidth, long-distance com- munication, globally. The cables carry- ing the data are primarily made of fine threads of silica glass, slightly thick- er than a human hair. The material is strong, flexible, and very good at trans- mitting information, in the formof light, at low cost. But the data signal peters out before reaching its final destination due to light being scattered. Amplifiers and other tools are used to contain and relay the infor- mation before it scatters, en- suring it is de- livered success- fully. Scientists are seeking to re- duce light scat- ter, called Rayleigh scattering, to help accelerate data transmission and move closer toward quantum communication. The team used multiple computa- tional methods to predict what hap- pens to the atomic structure of sili- ca glass under high temperature and high pressure. They discovered large voids between silica atoms form when the glass is heated up and then cooled down under low pressure. But when this process occurs under 4 gigapas- cals, most of the large voids disappear and the glass takes on a much more uniform lattice structure. Specifical- ly, the models show that the glass un- dergoes a physical transformation, and smaller rings of atoms are eliminated or “pruned,” allowing larger rings to join more closely together. This helps to re- duce the number of large voids and the average size of voids, which cause light scattering, and decrease signal loss by more than 50%. The researchers suspect even greater improvements can be achieved using a slower cooling rate at high- er pressure. The process could also be explored for other types of inorganic glass with similar structures. psu.edu , www.global.hokudai.ac.jp . Rolled aluminum. Courtesy of Pixabay. The voids in silica glass (yellow) become much smaller when the glass is quenched at higher pressures. Courtesy of Yongjian Yang, et al. Scientists at the National University of Science and Technology MISIS, Moscow, developed a unique method to process bulk metallic glasses, significantly improving mechanical properties and eliminating brittleness. In future work, the team plans to use the new technology to produce titanium and other high-quality bulk metallic glasses. www.en.misis.ru . BRIEF Metallic glass sample. Courtesy of NUST MISIS.