Temperature Time Research Articles

Annealing Time Dependence on Creation of SiV, GeV, and SnV in Diamond by Atmospheric Annealing at 1800 °C

The creation of SiV−, GeV−, and SnV− are presented by the atmospheric annealing in the argon flow. Compared to high‐pressure annealing, in which gas cannot flow, atmospheric annealing with an inert gas flow not only causes less degradation of the sample surface but also has the advantage of reducing equipment cost and preparation time. Excessive annealing time has been shown to reduce the amount of centers created. The optimal annealing time that maximizes formations depends on the type of diamond sample and the implanted ions. Furthermore, inspired by the split‐vacancy structure of the group IV–V centers, atmospheric pre‐annealing at 600 °C to increase the amount of di‐vacancy is demonstrated, followed by annealing at 1800 °C for 1 min. A shorter duration of high‐temperature annealing is expected to qualitatively reduce stress and deterioration of the crystallinity of the diamond sample.

Shear mechanical properties of AISI 316L stainless steel processed by unidirectional/cross rolling and annealing treatment

The effects of cold rolling routes followed by annealing on the mechanical properties of AISI 316L stainless steel were characterized. Both unidirectional and cross rolling methods were applied and the evolutions of shear mechanical properties by shear punch testing (SPT) and hardness during reversion/recrystallization annealing were systematically investigated. It was revealed that cross rolling promotes strain-induced martensitic transformation during rolling and also enhances grain refinement during annealing, leading to improved hardness and ultimate shear strength (USS). The variation of USS with annealing time was similar to that of Vickers hardness (HV), so that the simple and useful equation of USS = 0.196HV was derived. Moreover, by relating the USS to the ultimate tensile strength (UTS) via von Mises criterion, the finalized equation of HV = 2.95UTS was obtained, confirming the empirical formula of HV = 3UTS for steels. Accordingly, this work can shed light on the application of SPT for investigating the mechanical properties of austenitic stainless steels.

Fabrication and characterization of NiO nanoparticles deposited via reactive DC magnetron sputtering technique

Nickel oxide (NiO) nanostructure was successfully prepared via reactive DC magnetron sputtering on the soda-lima glass substrate, which can be used for various applications. Xray diffraction (XRD) investigations were used to evaluate NiO with two annealing durations. The results revealed that the deposited films had a cubic structure and polycrystalline nanoparticles. A significant polycrystalline structure could be seen in the sputtered films as a diffraction peak oriented toward NiO (200). Field-emission Scanning Electron Microscopy (FE-SEM) analysis identified the surface morphology of NiO nanoparticles prepared at two different annealing times with the two average sizes (24 and 32 nm) respectively. The samples' roughness was assessed using atomic force microscopy (AFM). Increased annealing time was shown to result in a decrease in grain size. The energy band gap (Eg) expanded with increasing annealing time, according to UV-visible spectroscopy (UV-Vis). FTIR spectroscopy was used to determine the functional groups of NiO nanoparticles and their bonding nature. The results indicate that optical characterizations are more sensitive to the annealing period.

Effect of microstructural inheritance window on the mechanical properties of an intercritically annealed Q&P steel

Different initial microstructures significantly influence the final microstructures and mechanical properties of the intercritically annealed quenching and partitioning steels. Previous studies have primarily focused on the mechanism for the inheritance of different initial microstructures into the final microstructures, which affects the phase fraction and mechanical properties. However, these studies have overlooked the existence of an inheritance window in the intercritical annealing process. In this study, we investigated the inheritance window and explored the impact of varying initial microstructures on the reverse transformation of austenite, final phase fraction, and mechanical properties. Our findings reveal that the varying initial microstructure exhibits minimal influence on the final microstructure and mechanical properties for short or long annealing times. However, for the intercritical annealing treatment for 60 s, the initial microstructure of martensite with more nucleation sites accelerated the austenite reverse transformation fraction, enhanced the reverse-transformed austenite content, increased the primary martensite content, and improved the yield strength. Conversely, the coil-cooled sample, with initial microstructures consisting of ferrite and pearlite without dissoluble Mn-rich cementites, reduced the austenite reverse transformation rate, decreased the reverse-transformed austenite content, enhanced the ferrite and RA content, and improved ductility.

Fabrication and characterization of NiO nanoparticles deposited via reactive DC magnetron sputtering technique

Nickel oxide (NiO) nanostructure was successfully prepared via reactive DC magnetron sputtering on the soda-lima glass substrate, which can be used for various applications. Xray diffraction (XRD) investigations were used to evaluate NiO with two annealing durations. The results revealed that the deposited films had a cubic structure and polycrystalline nanoparticles. A significant polycrystalline structure could be seen in the sputtered films as a diffraction peak oriented toward NiO (200). Field-emission Scanning Electron Microscopy (FE-SEM) analysis identified the surface morphology of NiO nanoparticles prepared at two different annealing times with the two average sizes (24 and 32 nm) respectively. The samples' roughness was assessed using atomic force microscopy (AFM). Increased annealing time was shown to result in a decrease in grain size. The energy band gap (Eg) expanded with increasing annealing time, according to UV-visible spectroscopy (UV-Vis). FTIR spectroscopy was used to determine the functional groups of NiO nanoparticles and their bonding nature. The results indicate that optical characterizations are more sensitive to the annealing period.

The influence of annealing process on the sagging resistance of AA3003 foil and laminated AA4343/AA3003/AA4343 composite foil materials

Upon 98% reduction cold-rolling, a single layer AA3003 foil material of 115 μm thick was intermediately annealed at 300–420 °C/1-8 h, and the preferred temperature and time of the intermediate annealing for the laminated AA4343/AA3003/AA4343 composite foil material were determined. All of these samples were cold rolled by 40% to 70 μm thick and finally annealed at a temperature in the range of 300–550 °C for 1–9 h. Their sagging resistance and microstructure were investigated using simulated brazing treatment, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For the single layer AA3003 foil, the sagging distance decreased first and then increased with increasing intermediate annealing temperature, and the lowest sagging distance corresponds to the coarsest grain in the recrystallized sample. After the final annealing for the single layer, the sagging distance decreased monotonously. For the laminated foil subjected to the final annealing, the sagging distance curves decreased first and then increased with increasing annealing temperature and time. The improvement of sagging resistance was attributed to the recovery of two types of materials during annealing process. The deterioration of the sagging resistance in the laminated foils was due to the corrosion in the brazing process, resulted from the Si diffusion from the cladding layer into the core layer. It is the coarse grains, few dislocations and minimal diffusion of Si that are crucial for improving the sagging resistance of the laminated foils.

Effects of diamond/Al interface structure evolution on interfacial thermal conductance during the carbonization of the Cr interlayer

The correlation between the interface structure evolution and the interfacial thermal conductance (ITC) in diamond particles reinforced Al matrix (diamond/Al) composites has been largely unclear. Herein, diamond/Cr/Al nanolayered structures with the interlayers in different carbonization stages were prepared via magnetron sputtering and annealing treatment to simulate the interfaces in diamond/Al composites. As the annealing time increases, the formed Cr3C2 phase progressively grows from discrete particles to a continuous layer at the diamond/Cr interface, during which the thickness of the carbide layer gradually increases. The formation of Cr3C2 phase improves the interface bonding and provides a more convenient channel for the heat exchange of hot carriers between the interfaces. Accordingly, the ITCs of the samples gradually increases with the annealing time and reaches the maximum value of 436.66 MW/(m2·K) at 120 min due to the formation of a thin and continues Cr3C2 layer. However, considering high interfacial thermal resistance was introduced at the interface when the Cr3C2 interlayer is too thick, the ITC of the sample decreased to 321 MW/(m2·K) as the annealing time extended to 240 min. In addition, Al8Cr5 phase is generated at the Al/Cr interface, but its impact on the ITC of the samples is negligible due to the small amount.

Effect of Carbon Content on the Phase Composition, Microstructure and Mechanical Properties of the TiC Layer Formed in Hot-Pressed Titanium-Steel Composites

During the hot pressing of pure titanium and different carbon steels in a temperature range of ϑ = 950–1050 °C, a compound layer up to dL≈10 μm thick is formed at the titanium–steel interface. With a higher carbon content of the used steel, the layer thickness increases. The carbon concentration within the layer is in the range of stoichiometry for TiC. Apart from TiC, no other phases can be detected by X-ray diffraction (XRD) measurements inside the formed layer. The calculation of the activation energy for the TiC layer formation is Q = 126.5–136.7 kJ mol−1 and is independent of the carbon content of the steel. The resulting microstructure has a grain size gradient, wherein the mechanical properties, such as hardness and Young‘s modulus, are almost constant. Statistical analysis using Response Surface Methodology (RSM) indicates that the carbon content of the steel has the most significant influence on layer thickness, followed by annealing temperature and annealing time. By selecting the appropriate carbon steel and the subsequent removal of the steel, it is possible to produce targeted TiC layers on titanium substrates, which holds enormous potential for this material in wear-intensive applications.

Perpendicular magnetic anisotropy in multilayers arising from the interplay of thermal strains and diffusion-driven plastic deformation

Magnetic films with perpendicular magnetic anisotropy (PMA) are the basis for efficient memory-storage and future spintronic devices. PMA predominantly stems from surface effects, e.g., symmetry reduction, at the magnetic-layer interface and quickly decays with increasing layer thickness. Strong PMA is thus typically observed in sub-nanometer multilayers with alternating magnetic and noble metals. Using in-situ temperature-dependent measurements of ferromagnetic resonance it is demonstrated that strong PMA can be achieved in Si/Ni multilayers with individual layer as thick as 16 nm. Here, PMA is imposed by thermal strains acting via magnetoelastic coupling and directly depends on the annealing temperature and time, which regulate the diffusion-driven plastic deformation. This opens a way to PMA-film fabrication that avoids complex and resource-intensive production of atomically thin multilayers.

Thermal stability and coarsening of eutectic and near-eutectic Ni–Ce alloys

Ni–Ce alloys are currently being studied as a castable alternative to conventional Ni-based superalloys. To understand the evolution of microstructure and mechanical behavior at elevated temperatures, this study investigates the mechanism of coarsening behavior in eutectic and near eutectic Ni–Ce at 900 °C. The as-cast eutectic Ni–Ce consists of a combination of fine lamellar and rod eutectic colonies with coarser boundary regions. Upon annealing, continuous coarsening, via process of globularization, initiates at colony boundaries or primary dendrites where faults (termination and branches) in the lamellar structure are plentiful. Coarsening then proceeds by a combination of fault migration mechanism and lamellar boundary splitting, growing toward the center of the eutectic colonies with increasing annealing time. Coarsening near the center of a colony is extremely slow, indicating the eutectic microstructure itself is very stable. The near-eutectic alloys containing primary dendrites coarsen and stabilize faster compared to the fully eutectic alloy. Moreover, an anomaly is observed in the hardness of the fully eutectic alloy after long exposure at elevated temperature compared to the near-eutectic alloys.

Synergistic optimization of microstructure and mechanical properties of AISI 430 ferritic stainless steel via dual-phase zone annealing process

This study systematically evaluated the impact of dual-phase zone annealing on the microstructure and mechanical properties of cold-rolled 430 Ferritic Stainless Steel (FSS), focusing on the phase transformation process from ferrite to austenite and the dissolution and precipitation behavior of the M23C6 phase. The annealing process significantly affects the microstructural characteristics of ferrite and martensite, including grain size, the distribution of grains of various sizes, aspect ratio, and phase content. The amount of martensite first increased and then decreased with rising annealing temperatures. The sample annealed at 1050 °C exhibited the highest martensite content of 29.5%. The variation in martensite content reflects the complex interplay between phase transformation kinetics and thermodynamic equilibrium. As the annealing time increased or temperature rose, the M23C6 phase at ferrite grain boundaries gradually dissolved and re-precipitated at higher temperatures. At lower temperatures, the M23C6 phase precipitated within martensite, but as the temperature increased, the precipitated phase diminished until it disappeared. Temperature changes affect the solubility of precipitates, atomic diffusion rates, and the uniform distribution of atoms across different phases. Appropriately increasing annealing temperature or extending annealing duration enhances the strength and hardness of 430 FSS. However, excessively high annealing temperatures lead to a decline in mechanical properties. The sample annealed at 1000 °C demonstrated the best mechanical properties, achieving a tensile strength of 783 MPa and an elongation of 16.0%. Furthermore, the analysis of fracture morphology and yield behavior in stress-strain curves further elucidated the macroscopic mechanical performance of the material.

Unveiling Thermal and Athermal Effects in Strain Hardening Removal of A6061 Aluminum Alloy

AbstractThis study explored the application of a high-density pulsed electric current (HDPEC) to mitigate strain hardening in a cold-rolled A6061 aluminum alloy while examining the simultaneous application of HDPEC with furnace heating to reveal the contributions of thermal and athermal effects. The results showed that significant strain-hardening relief was achieved through the HDPEC treatment, particularly at 300 A/mm² for 260 ms, resulting in a 23% reduction in strength and an 86% increase in ductility. Microstructural analysis revealed a shift to fine and equiaxed grains with reduced dislocation density, which was primarily attributed to thermal effects. HDPEC annealing exhibits superior efficiency compared to the conventional annealing treatment, offering cost and time advantages. In addition, this study validated the synergistic impact of HDPEC and furnace heating, with furnace heating supplementing energy requirements, facilitating practical HDPEC implementation. These findings suggest that the HDPEC method and the combined method with conventional heating are promising alternatives for strain-hardening alleviation in A6061 aluminum alloy manufacturing, supporting the development of an eco-friendly and efficient process. Graphical Abstract

Crystal Lattice Recovery and Optical Activation of Yb Implanted into β-Ga2O3.

β-Ga2O3 is an ultra-wide bandgap semiconductor (Eg~4.8 eV) of interest for many applications, including optoelectronics. Undoped Ga2O3 emits light in the UV range that can be tuned to the visible region of the spectrum by rare earth dopants. In this work, we investigate the crystal lattice recovery of (2¯01)-oriented β-Ga2O3 crystals implanted with Yb ions to the fluence of 1 ×1014 at/cm2. Post-implantation annealing at a range of temperature and different atmospheres was used to investigate the β-Ga2O3 crystal structure recovery and optical activation of Yb ions. Ion implantation is a renowned technique used for material doping, but in spite of its many advantages such as the controlled introduction of dopants in concentrations exceeding the solubility limits, it also causes damage to the crystal lattice, which strongly influences the optical response from the material. In this work, post-implantation defects in β-Ga2O3:Yb crystals, their transformation, and the recovery of the crystal lattice after thermal treatment have been investigated by channeling Rutherford backscattering spectrometry (RBS/c) supported by McChasy simulations, and the optical response was tested. It has been shown that post-implantation annealing at temperatures of 700-900 °C results in partial crystal lattice recovery, but it is accompanied by the out-diffusion of Yb ions toward the surface if the annealing temperature and time exceed 800 °C and 10 min, respectively. High-temperature implantation at 500-900 °C strongly limits post-implantation damage to the crystal lattice, but it does not cause the intense luminescence of Yb ions. This suggests that the recovery of the crystal lattice is not a sufficient condition for strong rare-earth photoluminescence at room temperature and that oxygen annealing is beneficial for intense infrared luminescence compared to other tested environments.

Lithography-Free Metaplasmonic Sensors Developed by TWD/GLAD Technique

Nowadays, plasmonic sensors are the most widely used and commercialized label-free optical biosensors and have become a widespread tool for studying chemical/biochemical interactions. Label-free, real-time, and direct measurements are the major benefits of the plasmonic sensors, including high-throughput surface bio-functionalization strategies without amplification or pretreatment of the sample [1]. The working principle of plasmonic sensing has been extensively described and reviewed over the decades [2], however, the possibility to develop cheap, effective, and clinically-accepted biosensors has recently become available due to the development of nanotechnology. Briefly, these nanostructures can be localized or can be arranged on 2D arrays of plasmonic metasurfaces, and can be fabricated by single-layer metallic films and a combination of metallic and dielectric films. The most popular plasmonic metals are gold and silver due to their high conductivity and low dielectric losses. Generally, top-down nanofabrication methods based on laser/e-beam lithography have been used, including nanostencil lithography based on shadow-masked nano-pattering and nanoimprint lithography [3]. Although such technologies have a high potential to achieve scalable and cost-effective nanofabrication at the wafer scale, these processes maintain the following main challenge: a master nano-mold/pattern is required to transfer metasurfaces with an associated high cost. Therefore, other technologies are the subject of research that overcomes this limitation and still offer an outstanding quality of metallic films, such as TDW (thermal dewetting) and GLAD (glancing angle deposition) (Fig.1). These techniques do not require master nano-mold/patterns; consequently, they can achieve lithography-free large-scale plasmonic metasurfaces [4]. TDW and GLAD usually generate quasi-ordered plasmonic metasurfaces compared to conventional lithographic methods.In this paper, the experimental results of the optical sensing properties of the sensors developed by the utilization of the combination of these two technologies in a single system are presented. The TWD/GLAD magnetron sputtering system has been designed and manufactured based on the Kurt J. Lesker MAG-Torus magnetrons, supplied with DC/RF power sources and an ECR manipulator that enables deposition at various angles with maximal 20 rpm rotation speed and heating option up to 850oC. The system is controlled by the software that enables deposition of the samples with the same parameters which pave the way for fabrication of the sensors on the industrial scale. The optical-sensing system was built based on an ST-VIS-50 spectrometer (Ocean Optics) and Tungsten Halogen Source (360-2000 nm, 2800 K, Ocean Optics) and optical table from Thorlabs. The obtained reflectance measurement has shown that the utilization of the GLAD technique decreases the reflectance peak in comparison with samples deposited without GLAD (flat samples). At the same time, angles in the range of 82-86oC seem to be preferable for nanostructure fabrication.Additionally, the utilization of the TWD technique, i.e. deposition at lower temperatures in the range of 60-100oC (depending on the substrate) and then annealed at higher temperatures such as 250oC and 300oC in a vacuum and under argon flow in the deposition chamber led to increased normalized response. However, the experiments have shown that the optimal annealing time is between 30-45 min depending on the SPR multi-structure, for example for Ag (6nm), Ti (2nm), and Au (2nm) the 30min at 250oC seems to be the best set. For such compositions, the surface sensitivity (nm/nm) and bulk sensitivity (nm/RIU) are more or less the same - 0.9 and 300, respectively. The obtained results are very promising for developing cheap, rapid, and very effective biosensors for various applications. Therefore, the obtained results seem to be very interesting for the ECS conference audience, for example, the developed Ag/Ti/Au multi-structures can be applied in novel organ-on-a-chip platforms for LADMET (liberations, absorption, distribution, metabolism, excretion, and toxicology) analysis [5].Fig. 1. Schematic diagram representation of lithography free methods for developing quasi-ordered metamaterials from left to right: Thermal dewetting and glancing angle deposition. The insert shows the chiral plasmonic nanospirals fabrication by glanced angle deposition [4].

Cu-Containing Metal-Organic Framework Electrocatalyst for Efficient Production of C2+ Compounds via CO2 Reduction Reaction

The electrochemical reduction of CO2 (CO2RR) is a promising strategy to yield valuable carbon-containing products and mitigate current environmental and energy issues. Cu-based MOF electrocatalysts have great potential for the selectivity of C2+ products due to their unique property. However, the rational design of active sites in Cu-based MOFs needs to be further studied. In this work, we propose a strategy to evolve abundant partially oxidized Cu species by applying a negative potential prior to CO2RR on Cu-MOFs, which results in high faradaic efficiency of 78% and partial current density of −46 mA cm−2 at −0.95 VRHE towards multi-carbon products. The electrochemical activation of Cu-MOFs can lead to the shift of superficial chemical state from Cu2+ to Cu+. Interestingly, the conversion rate is varied by different thermal annealing times on the pre-catalysts. Thereby, the relative concentration of Cu+ species can be quantitatively compared before and after activation to reveal the dependence on those FEC2+. The insights gained from this study can provide valuable guidance for the design and development of efficient Cu-MOF catalysts for the production of C2+ products.

Investigations of the adsorbed layer of polysulfone: Influence of the thickness of the adsorbed layer on the glass transition of thin films.

This work studies the influence of the adsorbed layer on the glass transition of thin films of polysulfone. Therefore, the growth kinetics of the irreversibly adsorbed layer of polysulfone on silicon substrates was first investigated using the solvent leaching approach, and the thickness of the remaining layer was measured with atomic force microscopy. Annealing conditions before leaching were varied in temperature and time (0-336h). The growth kinetics showed three distinct regions: a pre-growth step where it was assumed that phenyl rings align parallel to the substrate at the shortest annealing times, a linear growth region, and a crossover from linear to logarithmic growth observed at higher temperatures for the longest annealing times. No signs of desorption were observed, pointing to the formation of a strongly adsorbed layer. Second, the glass transition of thin polysulfone films was studied in dependence on the film thickness using spectroscopic ellipsometry. Three annealing conditions were compared: two with only a tightly bound layer formed in the linear growth regime and one with both tightly bound and loosely adsorbed layers formed in the logarithmic growth regime. The onset thickness and increase in the glass transition temperature increases with annealing time and temperature. These differences were attributed to the distinct conformations of the formed adsorbed layers.

The effect of tempering time and cooling environment on the corrosion behavior of AA5083‐H111 alloy

AbstractThe tempering process can increase the mechanical properties of the material, such as hardness and impact strength, as well as enhance the corrosion resistance. Therefore, the selection of appropriate tempering time and cooling environment is crucial. This study aims to investigate changes in properties such as hardness, tensile strength, corrosion resistance, and microstructure of AA5083‐H111 alloy after a brief tempering process (30 minutes, 45 minutes and 60 minutes) at 320 °C, followed by cooling in air and water environments. The study found that tempering time and cooling environment significantly affect the mechanical properties and corrosion rate. The results show that samples labeled as S30 and S60 have the highest hardness and impact strength, but the best corrosion resistance is achieved in the S60 sample. This study demonstrates that even after a limited‐term tempering process, the mechanical properties and corrosion resistance of AA5083‐H111 alloy can be improved. This information is crucial data for use in the production and application of alloys. The findings of this study could have important implications for the production and application of AA5083‐H111 alloy in industries such as aerospace, automotive, and marine engineering.

Achieving 2.7 GPa tensile strength in ultrastrong high-carbon steel through prolonged low-temperature tempering

The mechanical properties of high‑carbon martensitic steel are improved by low-temperature tempering. This is due to carbon diffusion and carbide precipitation, which depend on temperature and time. To further improve mechanical properties and develop optimum tempering conditions of the conventional high‑carbon martensitic steel, long-term tempering was carried out at approximately 175 °C and 250 °C. Excellent mechanical properties, which had not been achieved before, were obtained after tempering samples at 175 °C for over 40 d, resulting in tensile strength of 2.7 GPa, yield strength of 2.3 GPa and total strain of 2.6%. Similarly, yield strength values exceeding 2.4 GPa were observed in samples tempered at 250 °C for 5 d. To understand the remarkable outcomes achieved, a detailed investigation into the tempering stages, with the use of Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD) analyses, was essential. The microstructure contained the typical tempered martensite matrix embedded by ultrafine carbides and retained austenite which decomposed slowly with increasing tempering time at 175 °C, contributing to a noticeable increase in strength. Conversely, no pronounced effect of retained austenite was observed on the strength evolution of tempered specimens at 250 °C. At the initial stage of long-term tempering, the primary strengthening mechanism was carbon solid solution strengthening with a value exceeding 1000 MPa. The solid solution strengthening weakened with tempering time, while precipitation strengthening increased with the growth and increasing volume fraction of carbides. The interplay of their effects and the softening of retained austenite led to a trend in which the total yield strength increased, followed by a decrease with increasing holding time. The resulting nuanced mechanical properties and microstructure obtained from long-term tempering offer strategies for synergistic strengthening and ductility of high‑carbon steels, thereby facilitating the expansion of their potential applications.

Revealing the effect of annealing at Tg on the crystal growth in Au49Ag5.5Pd2.3Cu26.9Si16.3 metallic glass via nanocalorimetry

In this study, Au49Ag5.5Pd2.3Cu26.9Si16.3 metallic glass is annealed at Tg and its impact on crystal growth is demonstrated with nanocalorimetry. With annealing following the rapid quenching, an amorphous phase free of nuclei, a relaxed amorphous phase, an amorphous phase with nuclei, and an amorphous phase with crystals are sequentially produced. With the reheating at rates ranging from 100 to 50,000 K/s, these four stages are quantitatively distinguished. Additionally, crystal growth behaviors of these four stages are demonstrated by the Kissinger and Mauro-Yue-Ellison-Gupta-Allan model. For the quenched and relaxed amorphous phases, the apparent crystallization activation energy (Ea) decreases with increasing heating rate, with a noticeable upward deviation at ultrahigh heating rates. When nuclei and crystals form in the amorphous phase, Ea keeps decreasing with the heating rate. As the annealing time increases, the maximum growth rate (umax) exhibits a monotonic increase while the temperature corresponding to umax displays a maximum.

Thermo-oxidative crosslinking of carbon fiber reinforced PEEK (Polyetheretherketone) for additive manufactured ceramic matrix composites

Carbon fiber reinforced polyetheretherketone (CF-PEEK) samples were fabricated using material extrusion. These additive manufactured green bodies are later processed to their final application as ceramic matrix composites (CMC) by the liquid silicon infiltration (LSI) route. Past studies showed that the application of material extrusion for the fabrication of CMC requires an additional stabilization-step after 3D-printing in order to prevent the remelting of CF-PEEK during the high temperature process of pyrolysis. The thermally induced crosslinking of the CF-PEEK parts ensured shape accuracy and avoided remelting during the pyrolysis afterwards but is limited by the melting temperature of PEEK (T m ∼ 343 °C). The study revealed a correlation between the annealing conditions time and temperature and the degree of crosslinking. Based on the analytical results from differential scanning calorimetry (DSC), a kinetic model was calculated, allowing predictions in dependence of the annealing temperature and time. Rheological and shape stability investigations of thermally annealed specimens verified the analytic results. The main findings of the study highlight an increasing degree of crosslinking with increasing annealing temperature and time.