A metal/UHMWPE/SiC multi-layered composite armor against ballistic impact of flat-nosed projectile

A novel multi-layered composite armor system is proposed for ballistic protection in the present study. The composite armor is composed of a ductile metal front, followed by a ceramic/UHMWPE laminate composite as the intermediate layer, and a ductile metal back layer. The ballistic performance of the composite armor against flat-nosed projectile was investigated experimentally and numerically. Experimental results show that the proposed composite armor exhibited several failure modes, including ductile hole enlargement of metallic face sheets, fragmentations and cracks of the ceramic layer, delamination, fiber fracture and bulge deformation of UHMWPE laminates. Three-dimensional numerical model was established to analyze the evolution of the whole ballistic response, and to discuss the effect of the ceramic layer placement and the mass allocation between the ceramic layer and UHMWPE laminate layer on the ballistic performance. Simulation results reveal the evident reduction in residual velocity that results from the optimal placement of the ceramic layer. Good balance among the contributions of the target components can be achieved to maximize the total energy absorption of composite armor by optimizing the ceramic placement strategy. The projectile residual velocity and the total energy absorption are insensitive to the mass ratio of ceramic layer to UHMWPE laminate layer within a certain range. Under the condition of a higher mass ratio, the specific energy absorption of UHMWPE layer can be significantly improved due to the full development of its bulging deformation. Consequently, it would benefit the energy absorption capability of the composite armor.     

Alumina ceramic tool material with enhanced properties through the addition of bionic prepared nano SiC@graphene

Graphene-coated SiC nanoparticles containing graphene floating bands (SiC@G) were prepared by a liquid-phase laser irradiation technique, and SiC@G nanoparticles with high dispersivity were incorporated into an Al₂O₃ matrix. An Al₂O₃-based composite ceramic tool was prepared by spark plasma sintering (SPS), and the effects of SiC@G nanoparticles on the mechanical and cutting properties and microstructure of the materials were further investigated. Analysis of the cross-sectional morphology shows that SiC@G nanoparticles containing graphene floating bands were homogeneously dispersed in the composite, which resulted in tighter bonds between the Al₂O₃ particles. This particular core-shell structure increased the contact area between the graphene and the matrix due to the formation of a graphene 3D mesh by extrusion, which enhanced the difficulty of relative sliding of graphene. Second, this special core-shell structure also made the crack propagation path more tortuous, further increasing the energy consumed in the fracture process, which is conducive to improving the mechanical properties of ceramic tools. The addition of SiC@G nanoparticles improves the mechanical properties of Al₂O₃-based composite ceramic tools. The fracture toughness (7.2 Mpa·m^1/2) and flexural strength (709 MPa) increased by 75.6% and 28.7%, respectively. Cutting experiments with Al₂O₃/SiC/G composite ceramic tool and Al₂O₃/SiC@G composite ceramic tools on 40Cr hardened steel were performed. The results prove that the addition of SiC@G nanoparticles improves the cutting life by 18.1% and reduces the cutting force and friction coefficient by 6.3% and 14.8%, respectively.     

Mechanical properties of Al2O3 and Al2O3/Al with Gyroid structure obtained by stereolithographic additive manufacturing and melt infiltration

To obtain both plasticity and toughness of the material at the same time, various manufacturing techniques of ceramic-metal composites and structures have been studied. In this work, a bio-inspired Al₂O₃ ceramic scaffold with Gyroid structure was designed and prepared by stereolithographic (SL) additive manufacturing, then the Al₂O₃/Al ceramic-metal hybrid structure was prepared by infiltrating molten Al into the Al₂O₃ ceramic structure. The performances of the Al₂O₃ ceramic scaffold and the Al₂O₃/Al ceramic-metal hybrid structure were compared and analyzed by a quasi-static compression experiment. The quasi-static compressive strength of the pristine Al₂O₃ scaffold was 14.36 MPa, while that of the Al₂O₃/Al ceramic-metal hybrid structure was up to 89.06 MPa. Moreover, the plasticity of the Al₂O₃/Al ceramic-metal hybrid structure was much higher than that of the Al₂O₃ scaffold. During compression, the Al₂O₃/Al ceramic-metal hybrid structure had excellent energy absorption, reaching up to 2569.16 KJ/m³, 15 times that of the Al₂O₃ scaffold. Therefore, this method can obtain materials with excellent ductility and toughness.     

Mechanical and dielectric properties of short carbon fiber reinforced Al2O3 composites with MgO additive

A series of short-carbon-fiber/Al₂O₃ composites with MgO as sintering additive were fabricated by pressureless sintering process. The effects of short carbon fiber (C_sf) content on the mechanical, dielectric and microwave absorbing properties of the composite were investigated. The results show that the addition of MgO enhances the density, hardness and the flexural strength of the alumina ceramic. However, these mechanical properties of the C_sf/Al₂O₃–MgO composite decrease with increasing C_sf content. Both the real and imaginary parts of the complex permittivity increase with increasing C_sf content in the frequency range of 8.2–12.4 GHz, which is attributed to the increasing electron polarization and associated polarization relaxation, respectively. When the C_sf content is 0.3 wt%, the reflection loss less than −10 dB and the minimum value of −27 dB are obtained with the coating thickness being 1.4 mm. The results indicate that the C_sf/Al₂O₃ with MgO is an excellent candidate for microwave absorbing material with favorable mechanical property.     

Investigation of the solidification behavior of Al2O3/YAG/YSZ ceramic in situ composite with off-eutectic composition

Directionally solidified Al₂O₃/YAG/YSZ ceramic in situ composite is an interesting candidate for the manufacture of turbine blade because of its excellent mechanical property. In the present study, two directionally solidified hypoeutectic and hypereutectic Al₂O₃/YAG/YSZ ceramic in situ composites are prepared by laser zone remelting, aiming to investigate the solidification behavior of the ternary composite with off-eutectic composition under high-temperature gradient. The results show that the composition and laser scanning rate significantly influence the solidification microstructure. The ternary in situ composite presents ultra-fine microstructure, and the eutectic interspacing is refined with the increase of the scanning rate. The Al₂O₃/YAG/YSZ hypoeutectic ceramic displays an irregular hypoeutectic network structure consisting of a primary Al₂O₃/YAG binary eutectic and fine Al₂O₃/YAG/YSZ ternary eutectic. Only at low scanning rate, homogeneous ternary eutectic-like microstructures are obtained in the hypoeutectic composition. Meanwhile, the Al₂O₃/YAG/YSZ hypereutectic ceramic shows homogeneous eutectic-like microstructure in most cases and the eutectic interspacing is finer than the ternary eutectic. Furthermore, the formation and evolution mechanism of the off-eutectic microstructure of the ternary composite are discussed.     

New insights into the damage assessment and energy dissipation weight mechanisms of ceramic/fiber laminated composites under ballistic impact

Ceramics/composite laminated armor structures have become the mainstream in the design of bulletproof materials. To obtain systematic improvements in composite targets, it is essential to design the structure of each ceramic/fiber to ensure synergistic energy matching between them. However, the challenges of heavy workload and high-costs limit the experimental testing of these composites. In this report, B₄C ceramics/ultra-high molecular weight polyethylene (UHMWPE) composite targets are studied and the impact of ceramic splicing size, impact position and size on the anti-elastic performance is predicted. Finite element analysis is used to comprehensively analyze critical obstacles of the failure damage, energy dissipation weight and ballistic mechanism of each material. Prediction results indicate that ceramics damage, fiber damage, and fiber delamination account for about 65%, 21%, and 14% of the total energy consumption, respectively. Square splicing and large size ceramics/fiber composites are found to have the best anti-elastic properties when the center position is impacted. This is ascribed to the transversal rapid stress wave propagation on the ceramic surface and the beneficial energy dissipation of the composite-backing arising from the longitudinal stress wave transfer of homogeneous panels. The results provide insights for identifying viable design methods for each structure, optimizing the matching of panels and backplanes, which reduces the number of experimental tests need to validate a given structure.     

A novel approach for the fabrication of carbon nanofibre/ceramic porous structures

This paper describes the fabrication of hybrid ceramic/carbon scaffolds in which carbon nanofibres and multi-walled carbon nanotubes fully cover the internal walls of a microporous ceramic structure that provides mechanical stability. Freeze casting is used to fabricate a porous, lamellar ceramic (Al₂O₃) structure with aligned pores whose width can be controlled between 10 and 90 μm. Subsequently, a two step chemical vapour deposition process that uses iron as a catalyst is used to grow the carbon nanostructures inside the scaffold. This catalyst remains in the scaffold after the growth process. The formation of the alumina scaffold and the influence of its structure on the growth of nanofibres and tubes are investigated. A set of growth conditions is determined to produce a dense covering of the internal walls of the porous ceramic with the carbon nanostructures. The limiting pore size for this process is located around 25 μm.     

An advanced self-lubricating ceramic composite with the addition of core-shell structured CaF2@Al2O3 powders

Aiming to improve the performance of self-lubricating ceramic tools, an advanced self-lubricating ceramic composite was developed. Core-shell structure CaF₂@Al₂O₃ powders were synthesized by liquid-phase non-uniform nucleation method. Al₂O₃/Ti(C,N)/CaF₂@Al₂O₃ composite made by adding CaF₂@Al₂O₃ powders exhibited notable improvements in microstructure and mechanical properties as compared with Al₂O₃/Ti(C,N)/CaF₂ composite made by adding uncoated CaF₂ powders. The core-shell coated self-lubricating ceramic tool with different content of CaF₂@Al₂O₃ was designed and prepared by hot pressing sintering process. The results show that when the content of CaF₂@Al₂O₃ is 10 vol%, The composite has the best mechanical properties, the flexural strength, and the fracture toughness and the hardness is 680 MPa, 6.50 MPa·m^1/2, and 17.29 GPa. Compared with the tool material with only CaF₂ solid lubricant added, the above performances were increased by 8.91%, 29.48%, and 14.50% respectively. The influence of different CaF₂@Al₂O₃ content on the physical and mechanical properties and microstructure of the tool material was analyzed.     

Design of a New Zirconia–Alumina–Ta Micro‐Nanocomposite with Unique Mechanical Properties

2Y‐TZP/Al₂O₃ hybrid nanoparticles prepared by CO₂ laser covaporization (CoLAVA) were wet mixed with biocompatible lamellar Ta metal particles (20 vol%) and consolidated by spark plasma sintering. The microstructure and mechanical properties of this novel ceramic–metal composite have been studied. The achieved results demonstrate that both the homogeneity of the 2Y‐TZP/Al₂O₃ nanocomposite matrix and the reinforcement with a micrometer‐sized ductile phase are prerequisites for the successful design and fabrication of ceramic–metal composites with high strength (1300 MPa), enhanced fracture toughness (16 MPa·m^1/2), and improved low‐temperature degradation resistance.     

Flexible and robust YAG-Al2O3 composite nanofibrous membranes enabled by a hybrid nanocrystalline-amorphous structure

A flexible and robust YAG-Al₂O₃ composite nanofibrous membrane was fabricated by a combination of sol-gel and electrospinning methods, then a sintering at 900 °C. The effects of Al₂O₃ on the microstructure and mechanical performance of YAG nanofibrous membranes were investigated. The YAG nanofibrous membrane is brittle but the composite membranes exhibit a brittle-to-flexible transformation as the Al₂O₃ content reaches 30 wt.%, which can be attributed to an optimized dense hybrid microstructure consisting of finer YAG grain size surrounded by amorphous Al₂O₃. The YAG-30 wt.% Al₂O₃ nanofibrous membrane sintered at 900 °C shows a tensile strength of 3.52±0.31 MPa, three times of that of pure Al₂O₃ sintered at the same temperature. The membrane still presents a decent flexibility with a tensile strength of 0.75±0.25 MPa after sintering at 1000 °C, which is at least 100 °C higher than the sintering temperature of most reported ceramic nanofibrous membranes.     

A multiscale methodology quantifying the sintering temperature‐dependent mechanical properties of oxide matrix composites

A novel methodology combining multiscale mechanical testing and finite element modeling is proposed to quantify the sintering temperature‐dependent mechanical properties of oxide matrix composites, like aluminosilicate (AS) fiber reinforced Al₂O₃ matrix (AS_f/Al₂O₃) composite in this work. The results showed a high‐temperature sensitivity in the modulus/strength of AS fiber and Al₂O₃ matrix due to their phase transitions at 1200°C, as revealed by instrumented nanoindentation technique. The interfacial strength, as measured by a novel fiber push‐in technique, was also temperature‐dependent. Specially at 1200°C, an interfacial phase reaction was observed, which bonded the interface tightly, as a result, the interfacial shear strength was up to ≈450 MPa. Employing the measured micro‐mechanical parameters of the composite constituents enabled the prediction of deformation mechanism of the composite in microscale, which suggested a dominant role of interface on the ductile/brittle behavior of the composite in tension and shear. Accordingly, the AS_f/Al₂O₃ composite exhibited a ductile‐to‐brittle transition as the sintering temperature increased from 800 to 1200°C, due to the prohibition of interfacial debonding at higher temperatures, in good agreement with numerical predictions. The proposed multiscale methodology provides a powerful tool to study the mechanical properties of oxide matrix composites qualitatively and quantitatively.     

Influence of a heterolayered Al2O3–ZrO2/Al2O3 ceramic protective overcoat on the high temperature performance of PdCr thin film strain gauges

The application of PdCr thin film strain gauges on gas turbine engines requires protective overcoats to prevent the oxidation of the PdCr sensitive element. In this work, a heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic film, which was fabricated by electron beam evaporation, is utilized as a protective overcoat over the PdCr sensitive thin film. The morphology and microstructure of the prepared films indicate that the composite Al₂O₃–ZrO₂ film is smooth and compact, and the interface between the composite Al₂O₃–ZrO₂ film and Al₂O₃ film is crack-free, which contributes to improving the protective performance of the heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic protective overcoat at high temperature. Moreover, the PdCr thin film strain gauge with heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic film as protective overcoat displays a minimum drift rate of less than 0.09%/h at 800 °C, and excellent cyclic repeatability such that the eight cyclic curves of the relative grid resistance are almost overlapped from room temperature to 800 °C, indicating the excellent protecting performance of the heterolayered Al₂O₃–ZrO₂/Al₂O₃ ceramic overcoat. It also reveals the smallest temperature coefficient of resistance of 155.3 ppm/°C compared to the monolayer Al₂O₃ overcoat and composite Al₂O₃–ZrO₂ overcoat.     

Design and fabrication of Al2O3f/SiCN composite with excellent microwave absorbing and mechanical properties

A new kind of structural and functional integration ceramic matrix composite material was prepared from high-performance alumina (Al₂O₃) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al₂O₃ fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al₂O₃ fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al₂O_3f/SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter-bundles of Al₂O₃ fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al₂O_3f/SiCN composite were determined to be 9.4 ± 0.5 MPa m^1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al₂O_3f/SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X-band. In conclusion, Al₂O_3f/SiCN composite can serve as a high-temperature structural material with excellent microwave absorption properties for aerospace applications.     

Strong and tough laminated ceramics prepared from ceramic foams

Here, we present a novel strategy to prepare laminated ceramics by combining the ceramic foams and hot-pressing sintering. Al₂O₃ and ZrO₂ ceramic foams prepared by the particle-stabilized foaming method was cut into thin slices and then directly laminated and hot-pressing sintered. Al₂O₃/ZrO₂ laminated ceramics with various structures were prepared. Compared with the slices prepared by conventional process, ceramic foams can easily regulate the thickness of laminate to resemble the nacre-like structure. In addition, the grain in the ceramic foams have lower activity and shrinkage rate, thereby weakening the residual tensile internal stress caused by grain coarsening and differences in coefficient of thermal expansion. The effects of layer number and thickness ratio on residual stress and the structure-activity relationship between mechanical properties and microstructure were investigated. The fracture toughness, flexural strength, and work of fracture of the optimal Al₂O₃/ZrO₂ laminated ceramics are 8.2 ± 1.3 MPa·m^1/2, 356 ± 59 MPa, and 216 J·m^?2, respectively.     

Significantly enhanced electromagnetic interference shielding in Al2O3 ceramic composites incorporated with highly aligned non-woven carbon fibers

Macroscopic parallel aligned non-woven carbon fibers were incorporated into Al₂O₃ composites in this study to evaluate the contribution of multiple reflections to the total electric magnetic interference (EMI) shielding. Results indicate that parallel aligned non-woven carbon fiber layers contribute significantly to the total EMI shielding effectiveness (SE_T) of Al₂O₃ composites by largely enhancing the EMI absorption, and seven parallel aligned thin non-woven carbon fiber layers finally make the almost microwave-transparent Al₂O₃ an excellent EMI shielding material with an EMI SE_T as high as 29–32 dB in the X-band frequency range. The volume fraction of carbon fibers in Al₂O₃ composites with seven carbon fiber layers is calculated to be only 0.5%, and therefore the EMI SE enhancement efficiency by parallel aligned large non-woven carbon fiber layers is much higher than other highly conducting nano fillers. It validates the significance of multiple reflections in achieving high EMI shielding properties in ceramic composites and provides an instructive approach to design efficient EMI shielding ceramic composites.     

Multi-contact hybrid thermal conductive filler Al2O3@AgNPs optimized three-dimensional thermal network for flexible thermal interface materials

In this work, a multi-contact Al₂O₃@AgNPs hybrid thermal conductive filler was synthesized by in-situ growth method to fill high thermal conductivity polydimethylsiloxane (PDMS)-based composites to prepare TIMs. And the thermal conductivity, electrical conductivity, and mechanical properties of the composite materials were studied. During the synthesis process of the multi-contact hybrid filler, different concentrations of silver ions were reduced to generate silver nanoparticles and attached to the surface of Al₂O₃. Al₂O₃@AgNPs/PDMS thermally conductive composites were prepared by changing the filler addition. Using SEM, XPS, and XRD is used to characterize the morphology and chemical composition of Al₂O₃@AgNPs hybrid filler. The thermal conductivity of PDMS-based composites with different AgNPs content under 70 wt% filler loading was studied. The results show that the thermal conductivity of PDMS-based composites filled with 7owt%Al₂O₃@3AgNPs/PDMS multi-contact hybrid filler is 0.67 W/m·K, which is 3.72 times that of pure PDMS, and is higher than that of unmodified Al₂O₃ with the same addition amount. /PDMS composite material has a high thermal conductivity of 24%. This work provides a new idea for the design and manufacture of high thermal conductivity hybrid fillers for TIMs.     

Alumina ceramics toughened by a piezoelectric secondary phase

A process for ceramic toughening is developed, where a selected piezoelectric or ferroelectric secondary phase is incorporated and dispersed in a ceramic matrix as reinforcement. The toughening effect of Nd₂Ti₂O₇ secondary phase on Al₂O₃ ceramic is determined together with the microstructures and phase constitution of the composite ceramics. Dense composite ceramics can be formed with the secondary phase and the Al₂O₃ matrix. Compared to single phase Al₂O₃ ceramics, the Nd₂Ti₂O₇/Al₂O₃ composite ceramic shows a significant increase in fracture toughness, and K_IC reaches 6.7 MPa m^1/2 for a composition of 0.03 Nd₂Ti₂O₇/0.97Al₂O₃.     

Morphology and anti-ablation properties of composites nozzles under the Ф100mm H2O2- polyethylene hybrid rocket motor test

Environmentally friendly commercial applications spurred us to screen a suitable ablative throat material for the hybrid rocket, while preserving its cost-effective advantages as a special chemical motor. In this research, two types of carbon fiber reinforced composites, i.e. carbon/carbon (C/C) composite and C_f/C–SiC–ZrC composite utilized in high temperature environment, were employed to make the hybrid rocket nozzle. By comparison with the high-density graphite, the anti-ablation properties under the firing environment of Ф100mm H₂O₂-polyethylene hybrid rocket motor were characterized. We used whole felt preform to make C/C composite, whose matrix carbon was coming from chemical vapor infiltration of propylene; and the C_f/C–SiC–ZrC composite, which employs the same whole felt preform to make the low-density C/C billet, by infiltrated with Si and Zr organic precursors and pyrolysis at elevated temperatures repeatedly to make the advanced ceramic matrix composite. The firing test lasted 40s for all the candidate materials and the result indicated that the C_f/C–SiC–ZrC composite, whose average linear ablation rate was only 0.003 mm/s, was the most stable one in the firing environment. The SEM images gave detailed morphologies of those nozzle throat materials and proved that the fiber architecture, together with the glassy ceramic oxide, helped the nozzle to withstand the hybrid motor firing environment.     

High-performance Al2O3‒YAG:Ce composite ceramic phosphors for miniaturization of high-brightness white light-emitting diodes

The miniaturization of high-brightness white light-emitting diodes (WLEDs) is limited by the low thermal performance of phosphors. In this study, the microstructure, optical properties, and thermal performance of Al₂O₃–Y₃Al₅O₁₂:Ce³⁺ (Al₂O₃–YAG:Ce) composite ceramics fabricated by hot pressing were investigated. By promoting the growth of Al₂O₃ grains while maintaining a high composite density, thermal performance of the composite ceramics was significantly increased. The thermal conductivity of a Al₂O₃–40-vol% YAG:Ce ceramic reached 21.8 W/m/K, which is close to the theoretical value. In addition, this composite ceramic exhibited the highest energy efficiency. After packaging with a high-power LED chip with dimensions of 1 mm × 1 mm, a high luminous flux of 639 lm was generated, while the reduction in output power at 250 °C was as low as 6%. This indicated excellent high-temperature stability and potential for applications in solid-state lighting.     

Enhancement in ballistic performance of composite hard armor through carbon nanotubes

The use of carbon nanotubes in composite hard armor is discussed in this study. The processing techniques to make various armor composite panels consisting of Kevlar^®29 woven fabric in an epoxy matrix and the subsequent V50 test results for both 44 caliber soft-point rounds and 30 caliber FSP (fragment simulated projectile) threats are presented. A 6.5% improvement in the V50 test results was found for a combination of 1.65 wt% loading of carbon nanotubes and 1.65 wt% loading of milled fibers. The failure mechanism of carbon nanotubes during the ballistic event is discussed through scanning electron microscope images of the panels after the failure. Raman Spectroscopy was also utilized to evaluate the residual strain in the Kevlar^®29 fibers post shoot. The Raman Spectroscopy shows a Raman shift of 25 cm^?1 for the Kevlar^®29 fiber utilized in the composite panel that had an enhancement in the V50 performance by using milled fiber and multi-walled carbon nanotubes. Evaluating both scenarios where an improvement was made and other panels without any improvement allows for understanding of how loading levels and synergistic effects between carbon nanotubes and milled fibers can further enhance ballistic performance.