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The green improvement of manufacturing high-temperature martensitic alloy steel using minimum quantity lubrication (MQL) involves an MQL device and a scientific method to assess the efficacy of the device application. This paper proposed a weight-variable machinability evaluation model based on multivariate heterogeneous data to compare the MQL process with the conventional machining lubrication processes. The proposed model comprises experimental-based intuitive evaluation and numerical machinability index (MI). The assessment model considers a multi-indicator and time-quality-cost-resource-environment (TQCRE) system. The MI is based on static-dynamic proximity, which is calculated according to indicator weights for subjective–objective combinations. The model was applied to a novel MQL system developed for manufacturing high-temperature martensitic alloys by performing milling experiments under four lubrication conditions. Experimental intuitive data indicated the superior feasibility of the MQL device, that is, the developed MQL method enhanced machining efficiency, ensured good machining quality, reduced tool wear by 17%, and cut forces by 7–14%. Moreover, the MQL process achieved the maximum machinability index regardless of the priority allocated to any indicator of machining quality, time, cost, resource loss, and environmental pollution. There was no degradation in machining via MQL under different environments, which validates the feasibility of the field application of the MQL method. The result is consistent with the experimental intuitive assessment, confirming the reasonableness and practical ability of the mathematical assessment model. This study may be considered as further validation of the multi-indicator machinability assessment for the green lubrication process. Future research on more cases might extend the explanations of the stability and hidden factors of the developed model.

Owing to their ultralow thermal conductivity and open pore structure 1 – 3 , silica aerogels are widely used in thermal insulation 4 , 5 , catalysis 6 , physics 7 , 8 , environmental remediation 6 , 9 , optical devices 10 and hypervelocity particle capture 11 . Thermal insulation is by far the largest market for silica aerogels, which are ideal materials when space is limited. One drawback of silica aerogels is their brittleness. Fibre reinforcement and binders can be used to overcome this for large-volume applications in building and industrial insulation 5 , 12 , but their poor machinability, combined with the difficulty of precisely casting small objects, limits the miniaturization potential of silica aerogels. Additive manufacturing provides an alternative route to miniaturization, but was “considered not feasible for silica aerogel” 13 . Here we present a direct ink writing protocol to create miniaturized silica aerogel objects from a slurry of silica aerogel powder in a dilute silica nanoparticle suspension (sol). The inks exhibit shear-thinning behaviour, owing to the high volume fraction of gel particles. As a result, they flow easily through the nozzle during printing, but their viscosity increases rapidly after printing, ensuring that the printed objects retain their shape. After printing, the silica sol is gelled in an ammonia atmosphere to enable subsequent processing into aerogels. The printed aerogel objects are pure silica and retain the high specific surface area (751 square metres per gram) and ultralow thermal conductivity (15.9 milliwatts per metre per kelvin) typical of silica aerogels. Furthermore, we demonstrate the ease with which functional nanoparticles can be incorporated. The printed silica aerogel objects can be used for thermal management, as miniaturized gas pumps and to degrade volatile organic compounds, illustrating the potential of our protocol. A direct ink writing protocol for silica aerogels enables 3D printing of lightweight, miniaturized objects with complex shapes, with the possibility to easily add functionality by incorporating nanoparticles.

Titanium alloys have emerged as the most successful metallic material to ever be applied in the field of biomedical engineering. This comprehensive review covers the history of titanium in medicine, the properties of titanium and its alloys, the production technologies used to produce biomedical implants, and the most common uses for titanium and its alloys, ranging from orthopedic implants to dental prosthetics and cardiovascular devices. At the core of this success lies the combination of machinability, mechanical strength, biocompatibility, and corrosion resistance. This unique combination of useful traits has positioned titanium alloys as an indispensable material for biomedical engineering applications, enabling safer, more durable, and more efficient treatments for patients affected by various kinds of pathologies. This review takes an in-depth journey into the inherent properties that define titanium alloys and which of them are advantageous for biomedical use. It explores their production techniques and the fabrication methodologies that are utilized to machine them into their final shape. The biomedical applications of titanium alloys are then categorized and described in detail, focusing on which specific advantages titanium alloys are present when compared to other materials. This review not only captures the current state of the art, but also explores the future possibilities and limitations of titanium alloys applied in the biomedical field.

The aerospace community widely uses difficult-to-cut materials, such as titanium alloys, high-temperature alloys, metal/ceramic/polymer matrix composites, hard and brittle materials, and geometrically complex components, such as thin-walled structures, microchannels, and complex surfaces. Mechanical machining is the main material removal process for the vast majority of aerospace components. However, many problems exist, including severe and rapid tool wear, low machining efficiency, and poor surface integrity. Nontraditional energy-assisted mechanical machining is a hybrid process that uses nontraditional energies (vibration, laser, electricity, etc) to improve the machinability of local materials and decrease the burden of mechanical machining. This provides a feasible and promising method to improve the material removal rate and surface quality, reduce process forces, and prolong tool life. However, systematic reviews of this technology are lacking with respect to the current research status and development direction. This paper reviews the recent progress in the nontraditional energy-assisted mechanical machining of difficult-to-cut materials and components in the aerospace community. In addition, this paper focuses on the processing principles, material responses under nontraditional energy, resultant forces and temperatures, material removal mechanisms, and applications of these processes, including vibration-, laser-, electric-, magnetic-, chemical-, advanced coolant-, and hybrid nontraditional energy-assisted mechanical machining. Finally, a comprehensive summary of the principles, advantages, and limitations of each hybrid process is provided, and future perspectives on forward design, device development, and sustainability of nontraditional energy-assisted mechanical machining processes are discussed. A topical review of nontraditional energy-assisted mechanical machining is introduced. The advantages and limitations of each hybrid machining process are addressed. Perspectives on forward design, device development, and sustainability are discussed.

Load bearing/energy storage integrated devices (LEIDs) allow using structural parts to store energy, and thus become a promising solution to boost the overall energy density of mobile energy storage systems, such as electric cars and drones. Herein, with a new high-strength solid electrolyte, we prepare a practical high-performance load-bearing/energy storage integrated electrochemical capacitors with excellent mechanical strength (flexural modulus: 18.1 GPa, flexural strength: 160.0 MPa) and high energy storage ability (specific capacitance: 32.4 mF cm −2 , energy density: 0.13 Wh m −2 , maximum power density: 1.3 W m −2 ). We design and compare two basic types of multilayered structures for LEID, which significantly enhance the practical bearing ability and working flexibility of the device. Besides, we also demonstrate the excellent processability of the LEID, by forming them into curved shapes, and secondarily machining and assembling them into complex structures without affecting their energy storage ability. High-strength composite materials for electrochemical energy storage is attractive for mobile systems. Here the authors demonstrate high-performance load-bearing integrated electrochemical capacitors, which show high strength, large capacitance, and good machinability.

N -type polycrystalline SnSe is considered as a highly promising candidates for thermoelectric applications due to facile processing, machinability, and scalability. However, existing efforts do not enable a peak ZT value exceeding 2.0 in n -type polycrystalline SnSe. Here, we realized a significant ZT enhancement by leveraging the synergistic effects of divacancy defect and introducing resonance level into the conduction band. The resonance level and increased density of states resulting from tungsten boost the Seebeck coefficient. The combination of the enhanced electrical conductivity (achieved by increasing carrier concentration through WCl 6 doping and Se vacancies) and large Seebeck coefficient lead to a high power factor. Microstructural analyses reveal that the co-existence of divacancy defects (Se vacancies and Sn vacancies) and endotaxial W- and Cl-rich nanoprecipitates scatter phonons effectively, resulting in ultralow lattice conductivity. Ultimately, a record-high peak ZT of 2.2 at 773 K is achieved in n -type SnSe 0.92  + 0.03WCl 6 . N-type polycrystalline SnSe shows inferior ZT to p-type polycrystalline due to its high thermal conductivity and lower power factor. The authors overcome the problem via the synergy of divacancy defect and introducing resonance level into the conduction band.

HighlightsThe current issues and recent advances in polymer/inorganic composite electrolytes are reviewed.The molecular interaction between different components in the composite environment is highlighted for designing high-performance polymer/inorganic composite electrolytes.Inorganic filler properties that affect polymer/inorganic composite electrolyte performance are pointed out.Future research directions for polymer/inorganic composite electrolytes compatible with high-voltage lithium metal batteries are outlined.Solid-state electrolytes (SSEs) are widely considered the essential components for upcoming rechargeable lithium-ion batteries owing to the potential for great safety and energy density. Among them, polymer solid-state electrolytes (PSEs) are competitive candidates for replacing commercial liquid electrolytes due to their flexibility, shape versatility and easy machinability. Despite the rapid development of PSEs, their practical application still faces obstacles including poor ionic conductivity, narrow electrochemical stable window and inferior mechanical strength. Polymer/inorganic composite electrolytes (PIEs) formed by adding ceramic fillers in PSEs merge the benefits of PSEs and inorganic solid-state electrolytes (ISEs), exhibiting appreciable comprehensive properties due to the abundant interfaces with unique characteristics. Some PIEs are highly compatible with high-voltage cathode and lithium metal anode, which offer desirable access to obtaining lithium metal batteries with high energy density. This review elucidates the current issues and recent advances in PIEs. The performance of PIEs was remarkably influenced by the characteristics of the fillers including type, content, morphology, arrangement and surface groups. We focus on the molecular interaction between different components in the composite environment for designing high-performance PIEs. Finally, the obstacles and opportunities for creating high-performance PIEs are outlined. This review aims to provide some theoretical guidance and direction for the development of PIEs.

The industry anticipates technological advancements for productivity improvement, and this can be accomplished by improving the machining performance in the areas where machinability challenges exist. The machinability and productivity of wire electric discharge machining (WEDM), which is a popular non-conventional cutting process, can be improved while having comparable surface integrity. Previously the non-conventional machining literature is focused on the machinability investigations of various industrial materials and process optimization. However, no extensive research on the study of flushing parameters optimization to improve machinability in non-conventional machining is known. In this research, WEDM of M42 HSS using controlled flushing is performed resulting in improved machinability in terms of material removal rate (MRR), surface roughness (Ra), and kerf width (KW). The findings indicate that the nozzle diameter (76.85%) has a substantial influence on total machining performance. Nozzle diameter, nozzle-workpiece distance, servo voltage, and flushing pressure all had a substantial influence on MRR, with percentage contributions of 34.50%, 26.02%, 22.94%, and 14.21%, respectively. Furthermore, multi-response optimization is also performed and depicts the possibility of achieving optimized values of MRR, Ra, and KW simultaneously. The flush-controlled machining improved work quality in terms of accurate production, increased productivity by lowering process time, and improved surface integrity of the machined piece thus can be a possible process advancement in the aerospace and automotive industries.

Implementing programmable actuation into materials and structures is a major topic in the field of smart materials. In particular the bilayer principle has been employed to develop actuators that respond to various kinds of stimuli. A multitude of small scale applications down to micrometer size have been developed, but up-scaling remains challenging due to either limitations in mechanical stiffness of the material or in the manufacturing processes. Here, we demonstrate the actuation of wooden bilayers in response to changes in relative humidity, making use of the high material stiffness and a good machinability to reach large scale actuation and application. Amplitude and response time of the actuation were measured and can be predicted and controlled by adapting the geometry and the constitution of the bilayers. Field tests in full weathering conditions revealed long-term stability of the actuation. The potential of the concept is shown by a first demonstrator. With the sensor and actuator intrinsically incorporated in the wooden bilayers, the daily change in relative humidity is exploited for an autonomous and solar powered movement of a tracker for solar modules.

Difficult-to-machine materials (DMMs) are extensively applied in critical fields such as aviation, semiconductor, biomedicine, and other key fields due to their excellent material properties. However, traditional machining technologies often struggle to achieve ultra-precision with DMMs resulting from poor surface quality and low processing efficiency. In recent years, field-assisted machining (FAM) technology has emerged as a new generation of machining technology based on innovative principles such as laser heating, tool vibration, magnetic magnetization, and plasma modification, providing a new solution for improving the machinability of DMMs. This technology not only addresses these limitations of traditional machining methods, but also has become a hot topic of research in the domain of ultra-precision machining of DMMs. Many new methods and principles have been introduced and investigated one after another, yet few studies have presented a comprehensive analysis and summarization. To fill this gap and understand the development trend of FAM, this study provides an important overview of FAM, covering different assisted machining methods, application effects, mechanism analysis, and equipment design. The current deficiencies and future challenges of FAM are summarized to lay the foundation for the further development of multi-field hybrid assisted and intelligent FAM technologies. The recent advancements of the field-assisted machining techniques are reviewed. Basic principles, equipment design, and typical applications of different field-assisted machining methods are summarized. The rational selection and effectiveness of energy field in field-assisted machining are presented. Challenges and prospects of field-assisted machining are orchestrated.