Yayun Liu

Ultrasonic elliptical vibration was applied to the machining of green ZrO₂ ceramics to investigate its effects on surface damage and tool wear. The experimental results were validated using discrete element simulations. Compared with conventional cutting, ultrasonic elliptical vibration-assisted cutting (UEVC) reduces surface roughness. The maximum reduction reaches 23.20% at a depth of cut of 0.8 mm and 25.39% at a cutting speed of 300 m/min. In addition, it reduces the average flank wear width by 11.5%. A substantial decrease in tangential force is observed at a depth of cut of 0.8 mm, an ultrasonic amplitude of 4 µm, and higher cutting speeds. Although the thickness of the surface compaction layer increases with cutting depth, UEVC reduces it by up to 59.33% at a depth of 0.8 mm. The PFC2D simulations predict lower subsurface residual stress magnitudes under UEVC than under CT. The chips generated during machining change from block-shaped chips under conventional cutting to powder-shaped chips under UEVC. This transformation facilitates chip removal. In addition, UEVC suppresses abrasive wear by minimizing scratching of the tool flank face from hard particles.

Zirconia ceramics are promising materials for restoration and are widely used in the field of artificial teeth. However, wear resistance affects the longevity of artificial teeth. In this study, peacock tail feather micro-textures and groove micro-textures are prepared on the surfaces of zirconia ceramics via the laser ablation technique to improve their tribological properties. The effects of micro-textures on the surface wettability and tribological properties of zirconia ceramics are studied. The micro-textures improve the surface wettability and tribological properties of zirconia ceramics. The average coefficient of friction of peacock tail feather micro-textured samples decreases by 53% compared to that of the samples without micro-textures. Different operating conditions affect the friction properties of zirconia ceramics. The samples have the best friction performance when the rotational speed, load, and acid/alkaline environment are 200 r/min, 15 N, and weakly alkaline, respectively. Furthermore, the mechanism by which surface micro-textures reduce frictional wear is as follows: the textured grooves store debris, and the bottom edge of the textured groove acts as a cutting tool to cut debris, preventing debris from scratching the surface. The micro-textures store lubricant and form a liquid film on the ceramic surface to reduce wear.

Continuous fibers with outstanding mechanical performance due to the continuous enhancement effect, show wide application in aerospace, automobile, and construction. There has been great success in developing continuous synthetic fiber-reinforced composites, such as carbon fibers or glass fibers; however, most of which are nonrenewable, have a high processing cost, and energy consumption. Bio-sourced materials with high reinforced effects are attractive alternatives to achieve a low-carbon footprint. In this study, continuous bamboo fiber-reinforced polyethylene (CBF/PE) composites were prepared via a facile two-step method featuring alkali treatment followed by 3D printing. Alkali treatment as a key processing step increases surface area and surface wetting, which promote the formation of mechanical riveting among bamboo fibers and matrix. The obtained treated CBF (T-CBF) also shows improved mechanical properties, which enables a superior reinforcement effect. 3D printing, as a fast and local heating method, could melt the outer layer PE tube and impregnate molten plastics into fibers under pressure and heating. The resulting T-CBF/PE composite fibers can achieve a tensile strength of up to 15.6 MPa, while the matrix PE itself has a tensile strength of around 7.7 MPa. Additionally, the fracture morphology of printed bulks from composite fibers shows the alkali-treated fibers–PE interface is denser and could transfer more load. The printed bulks using T-CBF/PE shows increased tensile strength and Young’s modulus, with 77%- and 1.76-times improvement compared to pure PE. Finally, the effect of printing paraments on mechanical properties were analyzed. Therefore, this research presents a potential avenue for fabricating continuous natural fiber-reinforced composites.

ZrO₂ ceramics, known for their high strength and wear resistance, are ideal for artificial joints. This study enhanced the friction performance of these joints by fabricating textured structures (50 μm width and 20–25 μm depth) on the ceramic surface. Friction tests, conducted at 200 r/min for 30 min with a 5–20 N load and lubricant concentration of 15–60 mg/mL using PEEK balls, showed that textured joints outperformed untextured ones. The symmetrical triangular structure had the lowest coefficient of friction and the best hydrophilicity, with a 53.0% reduction in the coefficient of friction and a 57.4% reduction in the contact angle compared to the untextured structure. The textures effectively store the PEEK residue and facilitate the smooth movement of the worn ball. Concurrently, the textured structure stores some of the lubricant, which reduces the static pressure during fluid flow by 12.6%. Overall, the friction performance of ZrO₂ ceramic artificial joints was significantly improved by the textured structures.

The processing of green ceramics aims to obtain parts with complex shapes and good surface quality. This paper prepared tools with micro/nano‐textured flank face by femtosecond laser to improve the cutting performance in processing of Al ₂ O ₃ green ceramics. The wear resistance of cutting tools and characteristics of machined compacts are analyzed. Results shows that textures can improve the wear resistance of cutting tools and surface quality of green ceramics. Micro/nano‐textured tools own the best cutting performance, the improvement rate of wear resistance and surface roughness can reach 28.5% and 25% respectively. The reasonable mechanisms are explained by the storage of powder chips and the derivative‐cutting phenomenon by textures. The derivative‐cutting behavior can prevent cutting tool from severe abrasive wear by hard phase particles. The storage function prevents the powder chips from scratching the unworn surface of cutting tools, and the additional scratching of the machined surface by the hard phase particles is reduced. The two functions contribute to the improvement of cutting performance of micro/nano‐textured tools.

Al₂O₃‐based green ceramics are prepared by isostatic cold pressing technology. The prepared green ceramics are pre‐sintered at the temperature from room temperature to 1100°C, and then Al₂O₃ ceramics are prepared by laser sintering. The effects of pre‐sintering temperatures and laser parameters on mechanical properties and the sintering quality are analyzed. The results show that good crystallinity of Al₂O₃ particles is obtained at a higher pre‐sintering temperature. The flexural strength and density of green ceramics increase with the temperature of heat treatment. The flexural strength decreases slightly at ∼200°C due to the paraffin binder disintegration. The pre‐sintering temperature and laser processing parameters have a significant influence on the sintering quality. With the increase of laser power and laser frequency, dynamic grain growth occurs, and then grains are refined. The majority of plate‐like grains are transformed into long cylindrical‐like grains in the severe densification process. However, porous flocculation microstructures are generated on the samples pre‐sintered at 1100°C after laser sintering, which is due to the material gasification in atmospheric environment during sintering by infrared laser. More uniform microstructure and better sintering quality of samples pre‐sintered at 500°C can be achieved after laser sintering with a relatively narrower grain size distribution.