Outstanding Thermo-mechanical Properties Research Articles

Development of ultra-high temperature ceramic matrix composites for hypersonic applications via reactive melt infiltration and mechanical testing under high temperature

AbstractIn the ongoing development of hypersonic technologies, material advancements play a key role in meeting the ever-increasing thermomechanical demands of these applications. Ultra-High Temperature Ceramic Matrix Composites (UHTCMCs) offer a promising solution for components operating under such extreme conditions. Their outstanding thermomechanical properties, including high temperature and thermal shock resistance, excellent thermal conductivity and mechanical strength, position them as ideal candidates for applications in fields like leading edges or inlet ramps for ramjets and scramjets. Due to their remarkable material composition, UHTCMCs are capable of operating in temperature regimes that surpass 1700 °C during their operation times under oxidizing atmospheres. At the German Aerospace Center (DLR), a UHTCMC material based on carbon fibres and a zirconium diboride matrix is being developed utilizing Reactive Melt Infiltration (RMI). With RMI, the orientation of the reinforcement fibres can be tailored, to enable the material to fulfill the demanding load requirements. The reactive melt infiltration process comprises three stages: preform fabrication, pyrolysis, and the actual melt infiltration. The foundation for important material properties of the final ceramic, including the matrix composition, is established in the preform production, which is a crucial step in the process. A boron- and zirconium diboride-based slurry is infiltrated into pitch-based carbon fibre fabric. Subsequently, the preforms are consolidated, pyrolysed, and infiltrated with molten Zr2Cu to obtain the UHTC matrix by in situ reaction with the preform elements. Scanning Electron Microscopy (SEM) and Energy-dispersive X-Ray Spectroscopy (EDX) enable the examination of the microstructural features, including the arrangement and distribution of zirconium diboride within the matrix. Mechanical evaluation of the UHTCMCs is conducted via 3-point bending tests at both room temperature and at elevated temperature at 900 °C. It has been demonstrated that Ultra-High Temperature Ceramic Matrix Composites can be produced by means of reactive melt infiltration, and that they retain their strength even at elevated temperatures.

Thymol-Derived Trifunctional Epoxy Resin with Outstanding Thermomechanical Properties and Low Dielectric Constant: From High-Throughput Synthesis to High-Performance Thermoset

Thymol-Derived Trifunctional Epoxy Resin with Outstanding Thermomechanical Properties and Low Dielectric Constant: From High-Throughput Synthesis to High-Performance Thermoset

Constructing and characterizing various multi-component crosslinked epoxy resins based on molecular dynamics simulations with a curing reaction model

Epoxy resins are extensively used as the matrix for carbon-fiber-reinforced plastic (CFRP) in commercial airplanes due to their outstanding thermomechanical properties. Until now, few researchers have simulated multicomponent epoxy resins. In this work, the impact of stoichiometric variations in the base resins in the Di Glycidyl Ether of Bisphenol A (DGEBA)/Tetra Glycidyl Diamino Diphenyl Methane (TGDDM)/4,4′-Diamino Diphenyl Sulfone (4,4′-DDS) system on the curing process and thermomechanical properties is investigated. When the proportions of each component are comparable, the curing process is primarily determined initially by the component with a lower activation energy and subsequently by the component with a relatively greater quantity during the high conversion rate stage. Furthermore, a higher proportion of TGDDM in the DGEBA/TGDDM/4,4′-DDS system results in an increased number of ring structures, which in turn leads to enhanced thermomechanical properties. Our Python-LAMMPS algorithm can be further developed for designing new multi-component epoxy resin materials.

Behavior and properties of helium cavities in ductile-phase-toughened tungsten irradiated with He+ ions at an elevated temperature

Ductile-phase toughened tungsten (DPT W) composites have demonstrated a great potential for plasma-facing components in fusion power systems. These materials can retain the outstanding thermomechanical properties of W while significantly enhancing the fracture toughness. The DPT W composite in this study consists of W particles (88 wt.%) embedded in a ductile NiFeW (12 wt.%) solution matrix. Irradiation of the composite was performed with 90 keV He+ ions to 1.0 × 1017 He+/cm2 at 973 K. The He cavities formed in both W and NiFeW phases are examined using convergent-beam scanning transmission electron microscopy (CB-STEM) at an atomic-level resolution. Full-range depth profiles of the He cavity diameters and number densities are analyzed. The results show that the average cavity diameter in NiFeW is ∼2.7 times that in W, while the number density is an order of magnitude lower. A quantitative analysis of the He density and pressure in the cavities is also achieved using STEM electron energy loss spectroscopy (STEM-EELS) mapping. The He atoms in the cavities in NiFeW are found to be under-pressurized, while those in similar-sized cavities in W are not detectable. The He energy-loss shift exhibits a linear relationship with the He density in cavities in NiFeW, with the slope comparable to that for martensitic steel.

Design of Nacre-Inspired 2D-MoS2 Nanosheets Assembled with Mesoporous Covalent Organic Frameworks (COFs) for Smart Coatings.

High loading capacity and smart release of inhibitors are the first and foremost characteristics of nanocontainers, which play a pivotal role in metal active corrosion protection. The present work explores the development of novel protective nanocontainers based on recently emerged covalent organic frameworks (COFs). These highly porous frameworks with large surface area, outstanding thermomechanical properties, low density, and ease of functionalization are used as nanocontainers. On the other hand, molybdenum disulfide (MoS2), a state-of-the-art 2D layered compound with a sheetlike structure, was utilized thanks to its excellent barrier properties. However, these lamellar structures suffer a high agglomeration tendency in polymeric matrices. Therefore, we developed a novel hybrid nanocontainer, inspired by natural nacre, by an in situ growth of COF on MoS2 to improve the stability and provide a high inhibitor loading capacity. The porous and nitrogen-rich structure of COF made it a good carrier to adsorb europium cations as inorganic inhibitors and release them on demand by pH changes to suppress the electrochemical reactions. The as-synthesized nanoplatforms were used as pH-responsive fillers in the epoxy resin. The nanocomposite coatings showed almost 50 kΩ cm2 total resistance and high impedance values (1011 Ω cm2) even after 77 days of immersion. Moreover, salt spray analysis depicted the smallest amount of rust and corrosion product after 31 days in the filled nanocomposite coating. Cathodic delamination and pull-off outcomes denoted that the filled coatings with the as-synthesized nanofiller showed the smallest cathodic delamination radius (3.41 mm) and lowest adhesion loss (24%) compared to the neat epoxy (7.55 mm and 46.7%). As such, the highly porous modified MoS2 nanosheets are considered promising alternatives in a wide range of applications with anticorrosion properties.

Curing reaction and properties of a kind of fluorinated phthalonitrile containing benzoxazine

• Fluorinated phthalonitrile containing benzoxazine exhibited good processability. • Generated structures of nitrile groups were obviously influenced by curing procedures. • Reducing polarity of matrix resin was more efficient to decrease dielectric constant. • Cured BPAF-ph matrix resins exhibited outstanding thermomechanical properties. Introducing of fluorinated substituents into molecular chains was an efficient way to prepare materials with decreased dielectric constant and loss. In this work, a kind of fluorinated phthalonitrile containing benzoxazine (BPAF-ph) was synthesized. Curing reactions and processability were investigated by DSC and dynamic rheological analysis (DRA). Non-isothermal curing kinetics analysis was applied to calculate the activation energy of BPAF-ph. Results showed that BPAF-ph exhibited obvious double-stage curing reaction behaviors and good processability. Based on the results of DSC and DRA, cured BPAF-ph was firstly fabricated at 200 °C. Then, BPAF-ph matrix resin was treated with different post heat-treatment procedures. Generated structures and properties of BPAF-ph matrix resins with different post curing procedures were investigated. Results showed that generated structures could be obviously influenced by the curing procedures. Relative low dielectric constants and loss of cured BPAF-ph was obtained and could be decreased with increasing of curing degree. BPAF-ph matrix resins also possessed good thermomechanical properties (50–250 °C: CTE ~ 41.1 ppm/ o C; T g ~ 327 °C) and thermal stability ( T 5% > 450 °C). Additionally, glass fiber reinforced BPAF-ph composites were prepared and their properties were investigated.

Heat of Decomposition and Fire Retardant Behavior of Polyimide-Graphene Nanocomposites

Polyimide is a high-performance engineering polymer with outstanding thermomechanical properties. Because of its inherent fire-retardant properties, polyimide nanocomposite is an excellent material for packaging electronic devices, and it is an attractive electrode material for batteries and supercapacitors. The fire-retardant behavior of polyimide can be remarkably improved when polyimide is reinforced with multilayered graphene sheets. Differential scanning calorimetry and thermogravimetric analysis were used to study the heat of decomposition and gravimetric decomposition rate, respectively, of polyimide-graphene nanocomposites. Polyimide/graphene nanocomposites containing 10, 20, 30, 40, and 50 wt.% of multilayered graphene sheets were heated at a rate of 10 and 30 °C/min in air and in nitrogen atmosphere, respectively. The rate of mass loss was found to remarkably decrease by up to 198% for nanocomposites containing 50 wt.% of graphene. The enthalpy change resulting from the decomposition of the imide ring was found to decrease by 1166% in nitrogen atmosphere, indicating the outstanding heat-shielding properties of multilayered graphene sheets due to their high thermal conductivity. Graphene sheets are believed to form a continuous carbonaceous char layer that protects the imide ring against decomposition, hence decreasing initial mass loss. The enthalpy changes due to combustion, obtained from differential scanning calorimetry, were used to calculate the theoretical heat release rates, a major parameter in the determination of flammability of polymers. The heat release rate decreased by 62% for composites containing 10 wt.% of graphene compared to the neat polyimide matrix. Polyimide has a relatively lower heat of combustion as compared with graphene. However, graphene significantly decreases the mass loss rates of polyimide. The combined interaction of graphene and polyimide led to an overall decrease in the heat release rate. It is noted that both mass loss rate and heat of combustion are important factors that contribute to the rate of heat released.

Behavior of Silicon Carbide Materials under Dry to Hydrothermal Conditions.

Silicon carbide materials are excellent candidates for high-performance applications due to their outstanding thermomechanical properties and their strong corrosion resistance. SiC materials can be processed in various forms, from nanomaterials to continuous fibers. Common applications of SiC materials include the aerospace and nuclear fields, where the material is used in severely oxidative environments. Therefore, it is important to understand the kinetics of SiC oxidation and the parameters influencing them. The first part of this review focuses on the oxidation of SiC in dry air according to the Deal and Grove model showing that the oxidation behavior of SiC depends on the temperature and the time of oxidation. The oxidation rate can also be accelerated with the presence of H2O in the system due to its diffusion through the oxide scales. Therefore, wet oxidation is studied in the second part. The third part details the effect of hydrothermal media on the SiC materials that has been explained by different models, namely Yoshimura (1986), Hirayama (1989) and Allongue (1992). The last part of this review focuses on the hydrothermal corrosion of SiC materials from an application point of view and determine whether it is beneficial (manufacturing of materials) or detrimental (use of SiC in latest nuclear reactors).

Experimental observation of thermally-driven frictional instabilities on C/C materials

The outstanding thermo-mechanical and tribological properties of C/C materials make them suitable in a wide range of industrial applications, where high performance at harsh temperature conditions are required. The great interest for their frictional properties points out the need to comprehend and characterize the dynamical phenomena occurring during frictional contact. Within this framework, this work offers an overview of their prevailing frictional and dynamic contact response taking place under different temperatures. The tests reveal a strong relationship between the C/C frictional response, the material propensity to destabilize the system dynamics and the working temperature, providing a glimpse into the occurrence of thermally-driven instabilities for C/C materials and offering information in terms of dynamical response in a broad range of temperature.

Hot‐Lithography SLA‐3D Printing of Epoxy Resin

AbstractThe hot‐lithography stereolithography 3D printing technology is used to print epoxy resins with high reactivity in order to achieve 3D printed structures. Different hydroxyl containing compounds are investigated as chain transfer agents and the viscoelastic properties of UV‐cured materials are fully characterized. The most promising formulations are studied at a high temperature, the 3D printing process parameters are defined and the printed object is fully characterized. By combining the suitable precursor materials in the photocurable formulation with the advanced hot‐lithography process, it is possible to produce 3D printed structures that are characterized by outstanding thermomechanical properties and good printability precision.

White emitting aluminosilicate glass phosphors derived from Dy3+, Ag+ co-exchanged LTA zeolite

White emitting glass phosphors were derived from the Dy3+, Ag+ co-exchanged LTA zeolite by heat treatment. Attributed to the porous structure and low Si:Al ratio of LTA, an aluminosilicate glass phosphor with outstanding thermomechanical and optical properties was obtained at a relatively low melting temperature. Due to the energy transfer from the Ag+ ions to the Dy3+ ions, the emission intensity of the Dy3+, Ag+ co-doped sample (λex = 250 nm) was improved by 4 times compared with the Dy3+ singly doped sample (λex = 388 nm). And the chromaticity coordinates moved from the yellow region to the white region. All the results suggested a facile method to fabricate glass phosphors for white light source applications.

Outstanding thermo-mechanical properties of graphene-like B3C3 and C3N3

Experimentally fabricated two-dimensional (2D) carbon-based nanomaterials have received significant attention because of their ultra-high physical properties, in recent years. In this manuscript, the thermal conductivity (TC) and mechanical response of 2D B3C3 and C3N3 structures are studied in detail, using molecular dynamics (MD) simulations. Their superior mechanical properties (Young’s modulus, ultimate tensile strength and failure strain) and TC make an excellent candidate for various applications of nanodevices. The mechanical properties of these 2D structures are also examined at five various temperatures up to 900 K along with the different loading directions and various strain rates from 107 to 109 s−1. MD results demonstrate that the mechanical properties of these 2D structures gradually decrease as temperature increases, due to the weakening effect of high temprerature. Additionally, when the strain rate increases, it is revealed that the mechanical properties show an increasing trend. Furthermore, at 300 K, the failure processes of these 2D structures are studied. MD simulations results demonstrate that these structures show brittle failure mechanism. On the other hand, various types of structural defects occurs during the production process and so these defects affect the physical properties of these structures adversely. Accordingly, the effects of various atom types, such as, N, B and C, vacancy defects on the mechanical properties and TC of these structures were investigated. The existence of vacancy defects in these structures reduces the TC and mechanical properties significantly by increasing the concentrations of defects. Finally, non-equilibrium MD simulations results indicate exceptionally high TC values of these structures.

X-ray tomography applied to the void/defect measurement of hybrid CFRC/SiC composites

Carbon fiber reinforced carbon composites (CFRC) and carbon fiber reinforced silicon carbide composites (CFRC/SiC) are materials of wide interest in the aerospace industry due mainly to their outstanding thermo-mechanical properties at high temperature. The control of the process of obtaining these composites, carried out non-destructive processes, such as x-ray tomography, are of great interest to the industry, since they are able to present not only information concerning density and porosity, but also 3D vision with identification of closed and open pores, as well as a precise location of these defects in the sample. In this study a CFRC/SiC hybrid matrix composite obtained by employing carbon-silicon reaction by direct impregnation of silicon powder and phenolic resin, followed by heat treatment at 1600 °C under inert atmosphere is monitored step by step, in its preparation stages, using x-ray computed tomography techniques compared with optical microscopy techniques to detect voids in its microstructure. The three methods presented were satisfactory for structural analysis of the steps of obtaining the CFRC/SiC composite, considering the resolution and sample preparation restrictions applied to each of them, under the working conditions described in this study.

Secondary dispersion of BaTiO3 for the enhanced mechanical properties of the Poly (arylene ether nitrile)-based composite laminates

Secondary dispersion of the nano barium titanate (BaTiO3) was performed to obtain the fiber-reinforced polyarylene ether nitrile-based (PEN) composite laminates with improved mechanical properties. BaTiO3/PEN composite films were prepared via casting with ultrasonic dispersion, and then the glass fiber-reinforced (GF) composite laminates were obtained by the hot-melting method, which were favored to realize the secondary dispersion of the BaTiO3 nanoparticles. The fracture surface of the BaTiO3/PEN films and BaTiO3/PEN/GF composite laminates investigated by SEM showed that the BaTiO3 dispersed homogenously both in the PEN matrix and the gaps between the fibers. The mechanical and thermo-mechanical properties of the laminates were characterized and results indicated that the nano-BaTiO3 particles and fibers show enhanced synergistic effects. That is, with increasing the BaTiO3 content, the flexural strength and modulus of the composite laminates increased correspondingly, as well as the glass transition temperatures. Additionally, with the introduction of nano-BaTiO3 particles, the dielectric constants (>5.5 at 1 kHz) of the composite laminates were improved obviously and the low dielectric loss (˂0.02 at 1 kHz) was maintained. The temperatures at weight loss 5% (T5%) of all the composite laminates with various content of BaTiO3 were over 490 °C both in N2 and air atomosphere. Good dielectric properties and outstanding thermo-mechanical properties would enable the PEN-based fiber-reinforced composite laminates as the candidates in the material fields of structure-functional integrations.

Recent advances in modeling of interfaces and mechanical behavior of multilayer metallic/ceramic composites

Since the introduction of the term “nanolaminate” in the mid-1990s, considerable research activities on metallic/ceramic nanolaminates (MCN) have been conducted. Incorporating ceramics with high hardness and high melting point together with high ductile metals can improve their thermomechanical behavior in corrosive environments. A great number of researchers have reported that MCNs exhibit outstanding thermomechanical properties compared with the constituent layers and bulk material, which is attributed to the atomic structure and high density of the interfaces. This article provides a review of recent advances in modeling of the mechanical behavior of MCN composites, with focus on Nb/NbC and Ti/TiN multilayer composites. The main strengthening mechanisms of MCNs, based on the layer thickness, the interface structure, and the interaction of threading dislocations with the interface as well as dislocations nucleation from the interface, are reviewed, and recently, obtained results from molecular dynamics simulations, along with these findings, are presented. Moreover, MD-based flow surfaces for use in large-scale continuum models are reviewed in connection with results from MD of MCNs under various mechanical loading conditions, including uniaxial and biaxial loadings.

Cerium doping of Ti-Al-N coatings for excellent thermal stability and oxidation resistance

Ti–Al–N thin films are well established due to their outstanding thermo-mechanical properties. Nevertheless, this system is still a subject of many research activities to further enhance their oxidation resistance and thermal stability. The addition of reactive elements, such as Cerium, can significantly improve especially the oxidation resistance of various materials. Therefore, we study in detail the impact of Ce (2 at.% alloyed to powder metallurgically prepared Ti0.50Al0.50 targets) on growth processes, structure, mechanical properties, thermal stability, and oxidation resistance of magnetron sputtered Ti1−x−yAlxCeyN coatings prepared with DC bias potentials of Ubias=−25, −50, −75, and −100V. The deposition rate is significantly increased by a factor of ~1.75 (Ubias=−25V) to 1.45 (Ubias=−100V) when using Ti0.49Al0.49Ce0.02 instead of Ti0.50Al0.50 targets. Furthermore, also the hardness of the resulting single phase face centered cubic Ti0.43Al0.55Ce0.02N is with ~35GPa above that of Ti0.42Al0.58N with ~34GPa, for coatings on polycrystalline Al2O3 and Ubias=−50V.All temperature dependent characteristics of Ti0.42Al0.58N are improved significantly by the addition of Cerium. Wurtzite-structured AlN formation within Ti0.43Al0.55Ce0.02N can only be detected at Ta=1100°C, about 200°C higher as for Ti0.42Al0.58N. Their peak-hardness, due to spinodal decomposition of the supersaturated cubic phase is ~37.0GPa with Ta=900°C, as compared to 34.6GPa with Ta=800°C for Ti0.42Al0.58N. Additionally, even after exposure to ambient air at 950°C for 3h, still >50% of the Ti0.43Al0.55Ce0.02N coating is intact (below the ~1.2μm thin oxide scale), whereas Ti0.42Al0.58N is already fully oxidized.Based on our results we can conclude, that Ce-doping improves the deposition characteristics and mechanical properties as well as thermal stabilities (incl. oxidation resistance) of Ti–Al–N, to be used as protective coatings for a wide range of high-demanding applications.

Functionalized MWCNTs, an efficient reinforcement for the preparation of eugenol based high performance PBz/BMI/CNT nanocomposites exhibiting outstanding thermo-mechanical properties

This work contemplates the stabilization of eugenol-based benzoxazine networks with the addition of BMI and amine functionalized multiwalled carbon nanotubes.

Investigating thermal, mechanical and rheological properties of novel antibacterial hybrid nanocomposites based on PLLA/triclosan/nano-hydroxyapatite

In this study, the encapsulated triclosan in low molecular weight PLLA containing 30% triclosan (LATC30), mixed with nano hydroxyapatite (nHA), were dispersed within the PLLA matrix with higher molecular weight via melt blending. Thermal, mechanical and rheological properties of the obtained nanocomposites were thoroughly investigated. The mechanical properties including modulus, impact strength and hardness were all improved upon addition of nHA as compared to the composites only comprised of LATC30 and neat PLLA; however, the elongation at break and tensile strength showed an increase once the nHA content was increased to 5%. The activation enthalpy of relaxation was also increased upon addition of nHA, and the nanocomposites exhibited a fragile behavior; however, the fragility index was decreased as a result of adding nHA in the presence of LATC30. The thermal studies showed that the presence of nHA caused an increase in the crystallinity while the Tm remained nearly unchanged. The thermal stability of nanocomposites was drastically decreased at first but it was counterbalanced by adding a higher level of nHA due to the improved interaction between PLLA and nHA. Moreover, degradation behavior of the composites was described by the kinetic analysis via Flynn–Wall–Ozawa (FWO) method. It was found that with increasing the nHA content up to 5%, the activation energy of degradation was increased. Upon addition of nHA, all the rheological parameters were increased, however no G′ and G″ intersection was detected in the lower frequencies. The aforementioned hybrid nanocomposite with 5% nHA and 5% LATC30 is recommended as a suitable antibacterial candidate for bone tissue engineering and medical fixations due to its outstanding thermomechanical properties.

Ablation behavior and mechanism analysis of C/SiC composites

Ablation is an erosive phenomenon with removal of material by a combination of thermo-mechanical, thermo-chemical, and thermo-physical factors with high temperature, pressure, and velocity of combustion flame. Materials with outstanding thermo-mechanical and thermo-chemical properties are required for future high-temperature components. C/SiC is a kind of great potential high-temperature structural material in aeronautics and astronautics with low specific weight, high specific strength, good thermal stability, oxidation resistance and excellent resistance to ablation. In this paper, the ablation phenomenon and mechanisms were summarized adequately. The ablated surface of C/SiC composites could be divided into three regions from center to external. In general, the higher the density, the lower the ablation rate; the lower the ablation temperature and less time, the lower the ablation rate, and the preparation methods also had a great influence on the ablation property. Thermo-physical and thermo-mechanical attacks were the main ablation behavior in the center region; oxidation was the main ablation behavior in the transition region and the border oxidation region.

In search of zero thermal expansion anisotropy in Mo5Si3 by strategic alloying

Reducing the thermal expansion anisotropy (TEA) of alloy compounds is one of the most important issues for their potential applications in high temperature environment. The Mo5Si3 (T1 phase) is known to be an important intermetallic compound with high melting temperature. Unfortunately, its large TEA renders it unsuitable for high temperature structural/coating applications. Many attempts have been made in the past to reduce TEA by substituting Mo by other transition metal ions such as V with little success and some unexpected observations. Here we use accurate ab initio molecular dynamics (AIMD) simulations to obtain the TEA from thermal expansion coefficients for two T1 phase alloy systems (Mo,V)5Si3 and Mo5(Si,Al)3. We demonstrate that strategic alloying with Al substituting Si can achieve zero TEA for T1 phase. The microscopic origin of this outstanding thermomechanical properties in this alloy is explained by the calculation of higher order elastic constants in conjunction with atom and direction-resolved phonon density of states.