It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm. Traditional polishing methods are disabled to polish the component, meanwhile keeping the structure intact. To overcome this challenge, small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer. A novel approach to multi-phase jet (MPJ) polishing is proposed, utilizing a self-developed polisher that incorporates solid, liquid, and gas phases. In contrast, abrasive air jet (AAJ) polishing is recommended, employing a customized polisher that combines solid and gas phases. After jet polishing, surface roughness (Sa) on the interior surface of grooves decreases from pristine 8.596 μm to 0.701 μm and 0.336 μm via AAJ polishing and MPJ polishing, respectively, and Sa reduces 92% and 96%, correspondingly. Furthermore, a formula defining the relationship between linear energy density and unit defect volume has been developed. The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm⁻¹ to 0.22 J mm⁻¹. The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones. Computational fluid dynamics simulation results reveal that material is removed by shear stress, and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove, resulting in uniform material removal. This is in good agreement with the experimental results. The novel proposed setups, approach, and findings provide new insights into manufacturing complex-structured components, polishing the small-grooved structure, and keeping it unbroken.

High-performance devices usually have curved surfaces, requiring high accuracy of shape and low surface roughness. It is a challenge to achieve high accuracies for form and position on a device with low surface roughness. However, due to the unique nonlinear rheology, magnetorheological fluids with hard abrasives are widely applied in ultra-precision surface finishing. Compared with conventional mechanical finishing, magnetorheological finishing displays obviously advantages, such as high precision shape of machined surface, low surface roughness and subsurface damage, and easy control for finishing processes. However, finishing performance depends on various factors, e.g. volume fraction and distribution of magnetic particles, types of hard abrasives and additives, strength of magnetic field, finishing forms. Therefore, a comprehensive review on related works is essential to understand the state-of-the-art of magnetorheological finishing and beneficial to inspire researchers to develop lower cost, higher machining accuracy and efficient approaches and setups, which demonstrates a significant guidance for development of high-performance parts in fields of aerospace, navigation and clinical medicine etc. This review starts from the rheological property of magnetorheological fluids, summarizing dynamically nonlinear rheological properties and stable finishing approaches. Then, the effect of components in magnetorheological fluids is discussed on finishing performance, consisting of magnetic particles, carrier fluid, additives and abrasives. Reasonable configuration of magnetorheological fluids, and different magnetorheological finishing methods are presented for variously curved surfaces. In addition, the current finishing forms and future directions are also addressed in this review.

Refractory high/medium entropy nitrides (HENs/MENs) exhibit comprehensive application prospects as protective films on mechanical parts, particularly those subjected to sliding contacts at elevated temperatures. In this study, a new MEN system TiNbWN, forming a single fcc solution, is designed and its wear performance at temperatures ranging from 25 to 750 °C is explored. The wear mechanisms can be rationalized by examining the subsurface microstructural evolutions using the transmission electron microscopy as well as calculating the phase diagrams and interfacial adhesion behavior employing calculation of phase diagram (CALPHAD) and density functional theory (DFT). To be specific, increased wear losses occur in a temperature range of 25–600 °C, being predominantly caused by the thermally-induced hardness degradation; whereas at the ultimate temperature (750 °C), the wear loss is refrained due to the formation of nanocrystalline oxides (W_nO_3n−2, TiO₂, and γTiO_x), as synergistically revealed by microscopy and CALPHAD, which not only enhance the mechanical properties of the pristine nitride film, but also act as solid lubricants, reducing the interfacial adhesion. Thus, our work delineates the role of the in situ formed nanocrystalline oxides in the wear mechanism transition of TiNbWN thin films, which could shed light on the high-temperature wear behavior of refractory HEN/MEN films.

The self-attraction of nanowires (NWs) would lead to NWs bunching up together when fabricated in high density and the short circuit of NW-based devices during service. However, the underlying mechanism of the self-attraction of NWs remains debatable due to the lack of in situ characterization of the attraction. In this study, a versatile method of in situ investigating the self-attraction of NWs was developed. The attractive force between two NWs and their distance can be determined quantitatively in the process of attraction under an optical microscope, eliminating the influence of electron beam in electron microscopes. With this approach, the self-attraction of SiC NWs was investigated and a two-stage mechanism for the self-attraction was proposed. The electrostatic force between two individual SiC NWs increased as their distance decreased, and acted as the initial driving force for the attraction of NWs. SiC NWs remained in contact under van der Waals force until they separated when external force exceeded van der Waals force. The charge density and the Hamaker constant of SiC NWs were determined to be 1.9 × 10⁻⁴ C·m⁻² and 1.56 × 10⁻¹⁹ J, which played an important role in the attraction of NWs. The results shed light on the mechanism of self-attraction among NWs and provide new insights into fabricating high-quality NWs and developing high-performance NW-based devices.

The random distribution of graphene in epoxy matrix hinders the further applications of graphene-epoxy composites in the field of tribology. Hence, in order to fully utilize the anisotropic properties of graphene, highly aligned graphene-epoxy composites (AGEC) with horizontally oriented structure have been fabricated via an improved vacuum filtration freeze-drying method. The frictional tests results indicated that the wear rate of AGEC slowly increased from 5.19×10^-6 mm³/(N·m) to 2.87×10^-5 mm³/(N·m) with the increasing of the normal load from 2 to 10 N, whereas the friction coefficient (COF) remained a constant of 0.109. Compared to the neat epoxy and random graphene-epoxy composites (RGEC), the COF of AGEC was reduced by 87.5% and 71.2%, and the reduction of wear rate was 86.6% and 85.4% at most, respectively. Scanning electron microscope (SEM) observations illustrated that a compact graphene self-lubricant film was formed on the worn surface of AGEC, which enables AGEC to possess excellent tribological performance. Finally, in light of the excellent tribological properties of AGEC, this study highlights a pathway to expand the tribological applications of graphene-epoxy composites.

As a widely used engineering polymer, epoxy resin has been successfully employed in high-performance components and setups. However, the poor thermal and friction properties of traditional epoxy resin greatly limit its application in many extreme environments. In this work, a new kind of epoxy-Ti₃C₂ with three-dimensional nanosheets (3DNS) composite which was designed by freeze-drying method showed up excellent thermal and friction properties. As a result, the coefficient of thermal expansion (CTE) of epoxy-Ti₃C₂ 3DNS 3.0 composites was 41.9 ppm/K at 40 ℃, which was lower than that of the traditional epoxy resin (46.7 ppm/K), and the thermal conductivity (TC) was also improved from 0.176 to 0.262 W/(m·K). Meanwhile, epoxy-Ti₃C₂ 3DNS 1.0 composites showed up the best friction property, with wear rate 76.3% lower than that of epoxy resin. This work is significant for the research of high-performance composite materials.