Showing papers in "Advanced Engineering Materials in 2020"

Directional Freeze‐Casting: A Bioinspired Method to Assemble Multifunctional Aligned Porous Structures for Advanced Applications

Abstract: Herein, the potential of directional freeze-casting techniques as a very generic, green, and straightforward approach for the processing of various functional porous materials is introduced. These materials include 3D monoliths, films, fibers, and microspheres/beads, which are obtained by the assembly of network building blocks originated from cryoassembly of the various aqueous-based systems. The process simply relies on 1) directional freezing of the slurry through contact with a cold surface, 2) maintaining the slurry at the frozen state for a particular time with controlling the freezing parameters and directions, and 3) sublimation of the created ice crystal templates inside the developed structure to translate the ice growth pattern to final porous structure. The materials developed with such a cryogenic process contain a highly complex porous structure, e.g., a hierarchical and well-aligned microstructure in different levels, which renders a high control over the physicochemical and mechanical functionalities. Due to the versatility and controllability of this technique, the process can also be extended for the mimicking of the structures found in natural materials to the bulk materials to assemble bioinspired porous composites with many useful mechanical and physical features. The aim, herein, is to give a brief overview of the recent advances in developing anisotropic porous inorganic, organic, hybrid, and carbonaceous materials with a particular emphasis on materials with biomimicking microstructure using directional ice templating approach and to highlight their recent breakthrough for different high-performance applications. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Recent Development of TiNi-Based Shape Memory Alloys with High Cycle Stability and High Transformation Temperature

Abstract: In recent decades, shape memory alloys (SMAs) have attracted attention because of their combined functional properties of actuating and sensing, associated with the shape memory effect (SME), and their superelasticity. The unique SME and superelasticity realized in SMAs result from a thermoelastic martensitic transformation and its reverse transformation. The SME is a phenomenon in which a sample is deformed in a low-temperature phase (martensite) and subsequently regains its original shape upon heating above a certain temperature by the reverse martensitic transformation. Superelasticity, another important property of SMAs, occurs at a high-temperature range (in the parent phase). After the sample undergoes a nonlinear deformation, it can completely recover upon unloading because of the reverse stress-induced martensitic transformation. Among SMAs, TiNi-based SMAs are the most commercially successful materials because of their excellent functional properties (SME, superelasticity), corrosion resistance, and biocompatibility with the human body. As a result, various engineering and biomedical applications of TiNi alloys have been developed, such as couplings, actuators, orthodontic arches, stents, and bendable surgical tools. Very recently, TiNi-based SMAs have also been regarded as promising candidates for solid-state cooling applications because of the large elastocaloric effect originating from the stress-induced martensitic transformation. The adiabatic temperature change of TiNi-based SMAs can reach up to 10–30 C. From a practical application point of view, two key problems hinder the further applications of TiNi-based SMAs. One is functional fatigue and the other is the relatively low transformation temperature (TT). In recent years, some important progress has been achieved in TiNi-based SMAs to overcome these issues. In most cases, TiNi-based SMAs have to be exposed to thermal/stress cyclic conditions. Functional fatigue, also termed the cyclic instability of functional properties, which describes the degradation behavior of martensitic transformation, the SME, and superelasticity, inevitably occurs during these cyclic conditions. For TiNi alloys, the characteristic temperatures of martensitic transformation usually decrease with increasing thermal cycle number because of the introduction of dislocations, which compensate for the crystallographic compatibility between the martensite and parent phases. R-phase transformation and precipitation of the Ti3Ni4 phase are even induced by such thermal cycling. Deformation cycling also significantly influences superelastic behavior, as demonstrated by the change in the stress–strain curve. With increasing cycle number, the stress–strain curve of TiNi alloys is characterized by the following features: 1) reduced critical stress to induce martensitic transformation and stress hysteresis and 2) increased slope of the stress plateau and irreversible strain. These results indicate that the functional fatigue of TiNi alloys is unsatisfactory and hinders their use in applications requiring precise control or longduration operation, for example, elastocaloric cooling or artificial heart valves. To improve functional fatigue, long-term efforts have been made to tailor the microstructure or composition, Prof. Y. Tong, Dr. A. Shuitcev Institute of Materials Processing and Intelligent Manufacturing College of Materials Science and Chemical Engineering Harbin Engineering University Harbin 150001, China E-mail: tongyx@hrbeu.edu.cn Prof. Y. Zheng Department of Materials Science and Engineering College of Engineering Peking University Beijing 100871, China E-mail: yfzheng@pku.edu.cn

Biocompatible 3D Printed Microneedles for Transdermal, Intradermal, and Percutaneous Applications

Abstract: This work was funded and supported by King Abdullah University of Science and Technology (KAUST). The authors thank Dr. Simona Spinelli, Francesco Rottoli, and StefanoPietro Mandaglio from the Animal Research Core Lab (ARCL) at KAUST for their assistance with the mouse piercing experiment.

Controlling the Properties of Additively Manufactured Cellular Structures Using Machine Learning Approaches

Abstract: Cellular structures are lightweight-engineered materials that have gained much attention with the development of additive manufacturing technologies. This paper introduces a precise approach to predict the mechanical properties of additively manufactured lattice structures using deep learning approaches. Diamond shaped nodal lattice structures were designed by varying strut length, strut diameter and strut orientation angle. The samples were manufactured using laser powder bed fusion (LPBF) of Ti-64 alloy and subjected to compression testing to measure the ultimate strength, elastic modulus, and specific strength. Machine learning approaches such as shallow neural network (SNN), deep neural network (DNN), and deep learning neural network (DLNN) were developed and compared to the statistical design of experiment (DoE) approach. The trained DLNN model showed the highest performance when compared to DNN, DoE and SNN with a mean percentage error of 5.26%, 14.60%, and 9.39% for the ultimate strength, elastic modulus, and specific strength, respectively. The DLNN model was used to create process maps, and was further validated. The results showed that although deep learning is preferred for big data, the optimised DLNN model outperformed the statistical DoE approach and can be a favourable tool for lattice structure prediction with limited data.

Interfacial Nanostructure of 2D Ti3C2/Graphene Quantum Dots Hybrid Multicoating for Ultralow Wear

Abstract: National Natural Science Foundation of China 51905295 51975314 China Postdoctoral Science Foundation 2019M660619 Tsinghua University Initiative Scientific Research Program 20197050026 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 11180121 VID of the University of Chile

Grain Boundary Processes in Strengthening, Weakening and Superplasticity

Abstract: Grain boundaries provide strength to materials at low temperatures by impeding slip transfer and they weaken materials at high temperatures by intergranular creep processes such as grain boundary sliding (GBS) and diffusion creep. At very fine nanocrystalline grain sizes of 0.3 deform with a large GBS contribution to total strain of approximate to 40-80%. There are a limited number of studies showing superplasticity in fine-grained high-entropy alloys, involving GBS accommodated by dislocations.

Sandwiched Graphene Clad Laminate: A Binder‐Free Flexible Printed Circuit Board for 5G Antenna Application

Abstract: Printed circuit board (PCB), as the basic mechanically supports of electronic devices, is widely used in circuit, radio frequency (RF), and other fields. Copper is the most commonly used conductive material in the PCB structure due to its high electrical conductivity and matured manufacture techniques. Despite the advantages, with the increasing demand of electronic products, metal waste is becoming a severe problem, as it can cause significant environment pollutions. Metal materials also suffer from high prices (because of their limited reserves), relatively poor flexibility, large density, and easily oxidized. As communication technologies developing, copper and other traditional metals-based PCB are becoming difficult to meet the new requirements for 5G communication devices, such as of being lightweight, flexible, miniaturized, and chemically stable under certain severe conditions. Therefore, it is necessary to find a suitable material to realize metal substitution in the field of electronic products based on PCB. Many attempts have been made to find the right candidates for such substitution of copper so far. Recently, carbon-based allotropic materials, such as carbon nanotubes (CNTs), carbon fibers, graphene, and fullerenes, have been widely investigated in the fields of antennas, sensors, transistors, and other electronic fields, given that they are abundant in nature and their advanced properties of lightweight, corrosion resistant, and environmental friendly. For instance, CNTs not only have excellent mechanical properties, biocompatibility, and chemical stability, but also have the disadvantages of low conductivity, complex film-forming process, and high contact resistance. Fullerenes, such as the CNTs, also suffer from low conductivity and difficult film forming, which lead to the problems of high loss and unsatisfactory performance

Gallium and cerium‐doped phosphate glasses with antibacterial properties for medical applications

Abstract: Phosphate glasses (PGs) are promising materials for medical applications due to their controllable solubility in aqueousmedia. In particular, their ability to continually dissolve can be exploited to release biologically active ions in a controlled, linearmanner in applications requiring a biodegradable material in contact with bone and soft tissues. PGs have lower melting temperatures compared with silicate glasses, and themost studied compositions (in the system: P2O5–Na2O–CaO) [1,3–5] comprise elements naturally occurring in the human body. PGs are soluble and their degradation rate can vary from hours to weeks depending on the composition. The solubility of PGs make them an interesting baseline for controlled delivery of therapeutic or antibacterial ions such as Ag, Cu, or Ga. Moreover, high PG solubility opens up their potential use in soft tissue repair applications (e.g., in contact with skin, muscle, and nerve tissues) or as temporary implants dissolving gradually, whilst the healing process takes place. The composition of PG strongly influences their potential, in particular the structural, chemical, and biological behavior. For example, an increase in calcium oxide content decreases glass degradation, whereas an increase in P2O5 encourages high dissolution rates due to the presence of P─O─P bonds, which lack resistance to hydrolytic attack. One of the interesting features of PGs is their ability to release ions known to be antibacterial at controllable rates. The growing problem of antibacterial resistance to antibiotics has pushed scientists to look for alternative solutions. Each year, the USA spends $20 billion in treating infections caused by antibiotic-resistant bacteria. Among the many antibacterial ions available, gallium and cerium show interesting properties. The antibacterial effect provided by gallium is called “the Trojan horse strategy” as gallium is introduced easily into bacteria due to similarities with iron (Fe). This approach is

Additively Manufactured Polyetheretherketone (PEEK) with Carbon Nanostructure Reinforcement for Biomedical Structural Applications

Abstract: The study is focused on carbon nanostructure (CNS), including both carbon nanotubes (CNTs) and graphene nanoplatelets (GNP), reinforcement of medical‐grade polyetheretherketone (PEEK) and in‐vitro bioactivity for biomedical structural applications. CNS/PEEK scaffolds and bulk specimens, realized via fused filament fabrication (FFF) additive manufacturing are assessed primarily in the low‐strain linear‐elastic mechanical regime. 3D printed PEEK nanocomposites are found to have enhanced mechanical properties in all cases while maintaining the desired degree of crystallinity in the range of 30‐33%. A synergetic effect of the CNS and sulfonation towards bioactivity is observed– apatite growth in simulated body fluid increased by 57 and 77%, for CNT and GNP reinforcement, respectively, doubling the effect of sulfonation and exhibiting a fully‐grown mushroom‐like apatite morphology. Further, CNT‐ and GNP‐reinforced sulfonated PEEK recovers much of the mechanical losses in modulus and strength due to sulfonation, in one case (GNP reinforcement) increasing the yield and ultimate strengths beyond the (non‐sulfonated) printed PEEK. Additive manufacturing of PEEK with CNS reinforcement demonstrated here opens up many design opportunities for structural and biomedical applications, including personalized bioactivated surfaces for bone scaffolds, with further potential arising from the electrically‐conductive nanoengineered PEEK material towards smart and multifunctional structures.