Low-temperature Annealing Research Articles

High-energy storage performance achieved in PbZrO3 thin films via Li+ doping and low-temperature annealing

High-energy storage performance achieved in PbZrO3 thin films via Li+ doping and low-temperature annealing

Dually-refined grain and precipitate microstructure of ATF-FeCrAl alloy by a two-step annealing process to separate the recrystallization from precipitation

The service of ATF-FeCrAl cladding requires excellent mechanical properties, creep resistance and radiation resistance, which can be improved by microstructure refinement. Traditional thermomechanical process is difficult to refine the matrix and precipitates simultaneously due to the interaction between the precipitation and recrystallization. Here by separating the recrystallization from the precipitation process, we proposed a two-step annealing strategy to obtain both refined grain and precipitate microstructure. A warm-rolled FeCrAl alloy was firstly annealed at a high temperature for a short time to obtain an extended recovery or recrystallized microstructure without significant precipitation. Then low-temperature annealing was applied to obtain homogenous and dense nano-sized precipitates without changing the grain size. Compared to the conventional one-step annealing processes, the alloy processed by the two-step process exhibited excellent radiation-induced hardening resistance, ultrahigh tensile strength (1064.9 MPa) at room temperature with an appreciable elongation (11.7%) and best resistance to degradation in tensile properties during exposure at 800 °C. The “dually-refined” microstructure obtained by the two-step annealing exhibits good stability under ion irradiation at 320 °C. The two-step annealing strategy can provide a promising pathway to achieve microstructure refinement for other alloy systems.

High-performance blue TADF OLED using two-step heat plasma-treated MoTe2 as a hole-injection layer

In the pursuit to overcome the limitations posed by traditional hole injection layers (HILs), such as PEDOT: PSS, researchers are focusing on innovative strategies to modify electrode/organic interfaces to facilitate charge-carrier injection and reduce the turn-on voltage, particularly in the context of high-efficiency organic light-emitting diodes (OLEDs). Two-dimensional materials show great potential in addressing the energy barrier challenges at electrode/organic interfaces owing to their exceptional optoelectronic properties and robust chemical stability. However, their implementation in OLEDs has been hindered by complex fabrication processes and work function (WF) mismatches. This study presents a novel approach by introducing a magnetron-sputtered MoTe2 as HIL via two-step O2 doping. This strategy enhances the crystallinity of MoTe2 at a relatively low annealing temperature (350 °C), combined with a plasma-treated anode possessing high WF (approximately 5.05 eV), high transmittance (93 % at 478 nm), and low sheet resistance (33 Ω/sq). Consequently, compared with the conventional blue thermally activated delayed-fluorescence OLED using MoO3 as a HIL, the external quantum efficiency of the manufactured device using MoTe2 as a HIL was improved by 57 % and turn-on voltage was reduced to 2.6 V. This study provides a new pathway for overcoming the limitations of conventional solution-based HILs and chemical vapor deposition techniques to industrialize the large-scale manufacturing and commercialization of OLEDs.

The influence of the volume concentration of hydrogen on the fine structure of the IR absorption spectra and conductivity features in congruent LiTaO3 crystals

A new method for changing the volume concentration of hydrogen in congruent LiTaO3 (lithium tantalate, LT) crystals has been studied. It has been established that pre-treatment of the sample in adipic acid significantly increases the volumetric concentration of hydrogen in the sample during subsequent annealing in a humid atmosphere at a relatively low annealing temperature. First of all, this preserves the LT single crystal in a single-domain state. In contrast to known methods for increasing the volumetric concentration of hydrogen, the proposed method affects the absorption coefficient of the sample in the optical range less than for a congruent LiNbO3 crystal. It has been shown that the type of IR absorption spectrum of OH− groups and the defect structure of the LT crystal significantly depend on the volume concentration of hydrogen in the sample. The study also analyzed the reasons for this effect. The temperature dependences of the electrical conductivity of LT samples with different hydrogen concentrations have been studied. It has been shown that the type of electronic conductivity of LT samples changes when the concentration of OH groups in the crystal increases significantly.

Influence of low temperature annealing time on CdS thin films

In this work, a low temperature annealing process is shown to improve the photoresponse time of CdS thin films. The films were deposited on glass substrates by chemical bath deposition. The samples were annealed in air for different times (0, 2, 4 and 6 h) at 200 °C. The morphology, optical and electrical properties of the CdS thin film was studied. The films were characterized by scanning electron microscope, X-ray diffraction, spectroscopic ellipsometry, 3D optical profilometry and UV–vis spectroscopy. The CdS thin films presented a compact structure with a grain size of approximately 80–100 nm. The average thickness of the films was 200 nm. All films exhibited a cubic CdS phase with preferred orientation along the (111) direction. The average value of the crystallite size was 30 nm. The refractive index varied from 2.40 to 2.64 as the annealing time increased. The optical bandgap for the samples showed a decreasing trend as the annealing time increased from 2.36 eV to 2.24 eV while the Urbach's energy had an inverse behavior from 0.160 eV to 0.270 eV. The annealing time was studied in the photoresponse of CdS films under ultraviolet and blue light. The fastest rise and fall times were 190 ms and 90 ms respectively for the 4 h annealing under blue light. We show that a low annealing temperature is possible to improve the photoresponse by 2 orders of magnitude.

Synthesis of ultra-small Co3O4-C core-shell nanoparticles with improved thermal stability and microwave absorption properties

Ultra-small Co3O4-C nanoparticles were synthesized with an average core size of 8.2 nm by annealing CoC nanoparticles in air at a relative low temperature. The formation mechanism of these nanoparticles can be attributed to the presence of defective C shells, the high chemical activity of ultra-small Co nanoparticles, and the gradual oxidation of the C shell during the low-temperature annealing process. The Co3O4-C nanoparticles demonstrated remarkable thermal stability at temperatures of up to 360 °C in air. Moreover, he Co3O4-C nanoparticles exhibited excellent microwave absorption performances, with an optimal reflection loss of −64.2 dB and an effective bandwidth of 6.08 GHz at a single thickness of 2.2 mm. These impressive microwave absorption properties can be attributed to the small size effects, the core-shell nanostructure, and the presence of defective C shells in the nanoparticles. Overall, the as-synthesized Co3O4-C nanoparticles show great potential for future applications as microwave absorbers, thanks to their large bandwidth, strong microwave absorption, and high thermal stability in air.

Conversion of chitosan and biomass fiber into recyclable superhydrophobic aerogel for efficient oil/water separation through a facile and green approach

Developing high performance and recyclable sorbent through a facile, low-cost, and eco-friendly way is quite important for oily wastewater treatment. Among the various fabrication approaches developed so far, the one using biomass waste as starting materials is particularly attractive in view of the cost and environmental benignity. Herein, a magnetic chitosan/typha orientalis fibers aerogel (MCS/TOFs) with excellent elasticity and superhydrophobicity was facilely prepared through freeze-drying and subsequent low-temperature annealing of biomass fibers (typha orientalis fibers, TOFs), chitosan (CS), and Fe3O4 nanoparticles. Benefiting from the 3D interconnected porous structure, superhydrophobic-lipophilic surface, and capillary effect of TOFs, the MCS/TOFs aerogel exhibited excellent sorption performance including fast sorption speed (few second to achieve saturation), high sorption capacity (up to 88.4 g/g), large flux (2.2 × 104 L m−2 h−1), and high separation efficiency (98.4%). Additionally, the MCS/TOFs aerogel can be facilely separated from the solution phase by a magnet at the end of the sorption process. After removal of the adsorbate by extrusion, the recovered MCS/TOFs can be used for next separation cycle, delivering high sorption capacity retention (> 91% of the initial capacity) after ten sorption-extrusion cycles. This work provides a facile biomass-based approach to high-performance and recyclable sorbent for oily wastewater treatment, exhibiting great potential in practical applications.

A strong and ductile ferrite-based lightweight steel manufactured via high-temperature warm rolling process

A trade-off between strength and ductility is unavoidable in ferrite-based lightweight steels due to the presence of δ-ferrite, and improving the properties of such steels requires precise control of the retained austenite and the complete mobilization of multiple strengthening mechanisms. In this study, we obtain a ferrite-based lightweight steel with the chemical composition Fe-0.3C-2.8Mn-3.5Al-0.5Cr-0.2V by adopting a higher temperature warm rolling process, endowing the best comprehensive properties. The results demonstrate that multi-scale heterogeneous microstructures are built without additional recrystallization annealing under the higher temperature (>700 °C) warm rolling process. Meanwhile, a large amount of retained austenite, higher dislocation density and strain-induced vanadium carbide precipitation were obtained through the warm rolling process. As warm rolling refines austenite grains, Mn and Cr are further diffused and enriched, enhancing the chemical stability of the retained austenite. After low-temperature tempering, this warm-rolled steel shows excellent comprehensive properties, including a tensile strength of 1140 MPa and elongation of 30%. The enhanced strength-ductility is attributed to the higher stability of retained austenite, stable maintenance of dislocation density and the pinning effect of precipitation relative to dislocation lines. Furthermore, a stronger discontinuous yielding behavior of the warm-rolled and tempered steel was obtained, enhancing the overall strain.

Sensitivity of reduction rate on the mechanical response of boron-doped Fe50Mn30Co10Cr10 high entropy alloy

Phase transformation induced plasticity (TRIP) effect is an effective technical solution to enhance the strength and ductility of alloys, represented by Fe50Mn30Co10Cr10 high entropy alloy (HEA). Introducing heterostructures into alloys is also an effective synergistic method for enhancing the strength and ductility of alloys. Combining element doping, heterostructures, and the TRIP effect of the alloy itself can enable the alloy to achieve both high strength and high ductility. In this work, the boron doped Fe50Mn30Co10Cr10 HEA were prepared by cold rolling with different reduction rates followed by recrystallization annealing processes. Different reduction rates result in different heterogeneous structures. The large rolling reduction weakens the advantage of heterogeneous structure for introducing large stress concentration, resulting in the low ductility of the alloy. The sample with small rolling reduction shows excellent strength and ductility, which comes from the synergistic effect of large-small grains matching and TRIP effect. In summary, the TRIP effect combined with the appropriate amount of reduction and low recrystallization temperature annealing induced heterostructure is an effective solution to overcome the strength ductility trade-off.

Tempering behavior of an ultra-high-strength steel with 1.6 wt% Si at low to medium temperatures

Tempering behavior of a 0.53%C-1.6%Si-0.9%Mn-0.76%Cr-0.14%V-0.05%Nb steel was examined. Water quenching produced lath martensite structure with a 10.5% volume fraction of retained austenite (RA) with film-like shape. Low temperature tempering (LTT) leads to precipitation of transition carbides and carbon partitioning between martensite and RA. The following precipitation sequence was found: martensite →non-stoichiometric η-carbide→stoichiometric η-carbide→Fe3C. Highest density of non-stoichiometric Fe2C η−carbides was found after isochronal tempering at 280 °C that provided attractive combination of high yield stress (YS) (1890 MPa) with a ductility of ∼6% and a Charpy V-notch (CVN) impact energy of ∼10 J/cm2. At 400 °C, the replacement of non-stoichiometric η-carbide by the stoichiometric one decreases strength and increases ductility due to 30% decrease in its volume fraction. No tempered martensite embrittlement was found due to the fact that Si effectively suppresses the precipitation of cementite at T ≤ 400 °C. The replacement of transition η-carbide by boundary cementite after isochronal tempering at 500 °C leads to considerably decrease in YS down to 1360 MPa, while elongation to failure increases up to 9.3%. Effect of decomposition of RA on strength, ductility and fracture toughness is insignificant.

Effect of surfactant-assisted low-temperature annealing on the refinement of particle size and enhancement of magnetic properties of SrFe12O19 ferrite

The fabrication of SrFe12O19 ferrite powders with good magnetic properties is a key process in the industrial production of permanent magnets. Remanence and coercivity of the powders was seriously decreased due to the generation of surface lattice defects produced during the crushing of pre-sintered ferrite powders. And the traditionally applied high-temperature annealing above 800 °C can only partially restore the magnetic properties. In this work, the effects of types, adding mode and contents of surfactant (hexadecyl trimethyl ammonium bromide, triethanolamine) on the magnetic properties of crushed powders of the pre-sintered SrFe12O19 ferrite under a low-temperature annealing of 400 °C process were systematically explored. The results showed that surfactants are beneficial to restore or even enhance the magnetic properties of the crushed powders compared with the pre-sintered ferrite due to the refinement of the particles and repairing the surface defects. The surfactant-assisted low-temperature annealing process proposed in this work will promote the commercial production of high performance ferrite powders and ferrite magnets, which can also effectively reduce the production energy consumption.

Synchronous surface reconstruction and grain boundary healing toward efficient and stable inverted CsPbI3 perovskite solar cells

Cesium lead iodide (CsPbI3) perovskite has gained considerable attentions due to its unique photoelectric properties. However, numerous defects are inevitably existed on the surface and grain boundaries (GBs) of CsPbI3 resulting from the rapid crystallization and growth progress. Herein, different from the traditional ammonium salt treatment mechanism, we propose a facile strategy to synchronously achieve surface reconstruction and grain boundary healing by using 1,3-propylene diamine (PDA) post-treatment on CsPbI3 film. It is discovered that the PDA with suitable concentration can preferentially invade the defect sites of surface and GBs of CsPbI3 film, thereby break the soft perovskite structure in the shallow surface. With further low temperature annealing treatment, the broken CsPbI3 surface would undergo rapid secondary crystal growth to acquire smoother and blurred morphology with reduced GBs and pinholes, primarily derived from the strong interaction between the highly active amino groups of liquid PDA and Pb of perovskite. Meanwhile, the residual PDA molecules mainly anchor at the surface and GBs, and thus connect neighboring perovskite grains, coordinate uncoordinated sites to effectively passivate defects, and also resist the external invasions. Consequently, the inverted PDA-based CsPbI3 device yields a champion PCE of 20.02% with significantly improved long-term storage stability and operational stability.

Controlling Nucleation and Crystallization of CsPbI3 Perovskites for Efficient Inverted Solar Cells.

The unfavorable morphology and high crystallization temperature (Tc) of inorganic perovskites pose a significant challenge to their widespread application in photovoltaics. In this study, an effective approach is proposed to enhance the morphology of cesium lead triiodide (CsPbI3) while lowering its Tc. By introducing dimethylammonium acetate into the perovskite precursor solution, a rapid nucleation stage is facilitated, and significantly enhances the crystal growth of the intermediate phase at low annealing temperatures, followed by a slow crystal growth stage at higher annealing temperatures. This results in a uniform and dense morphology in CsPbI3 perovskite films with enhanced crystallinity, simultaneously reducing the Tc from 200 to 150°C. Applying this approach in positive-intrinsic-negative (p-i-n) inverted cells yields a high power conversion efficiency of 19.23%. Importantly, these cells exhibit significantly enhanced stability, even under stress at 85°C.

Effect of low-temperature annealing on electric resistivity and mechanical anisotropy of Al-Si binary alloy fabricated by laser-powder bed fusion

Al-12mass%Si binary alloy was fabricated by laser-powder bed fusion (L-PBF). The effect of low temperature annealing (LTA) less than 573 K on electrical and mechanical properties, microstructure, and residual stress of L-PBF Al-12mass%Si was investigated. Due to LTA, electrical resistivity at 77 K and 293 K changed from 34 nΩm down to 10 nΩm and from 68 nΩm down to 45 nΩm, respectively. The lattice constant of α-Al phase increased around 0.0005 nm by LTA according to X-ray diffraction. The change was associated with the decrease in the concentration of solid-solution Si of around 3.4 mass% by electrical resistivity measurement and 3 mass% by X-ray diffraction, when the annealing temperature was 473 K. Whereas, Vickers hardness increases around 145 HV compared with that for the as-built value of 141 HV, and then, decreases down to 126 HV and saturates. TEM/EDS observations confirmed the precipitation of fine Si within the α-Al phase. The decrease in annealing temperature increases the time to reach the Vickers hardness peak. 0.2% proof stress obtained by compression tests shows anisotropy, which can be attributed to the anisotropy on residual stress, which still exists after LTA.

Research on corrosion behavior of safety valve spring in liquid chlorine tank

The corrosion behavior of the safety valve spring in the liquid chlorine tank is investigated in this study. The chemical composition, metallographic structure and hardness of the spring are also analyzed. The higher hardness of spring steel is caused by lower tempering temperatures. The corrosion product is grey with many cracks, spalling and pitting is also found. The phenomenon that where there is higher chloride, there is higher carbon is observed. Chloride ion is adsorbed by carbides and then pitting preferentially nucleate at carbides.

Effects of Retained Austenite upon Softening during Low-temperature Tempering in Martensitic Carbon Steels

Effects of Retained Austenite upon Softening during Low-temperature Tempering in Martensitic Carbon Steels

Multi-aspect Characterization of Low-temperature Tempering Behaviors in High-carbon Martensite

Multi-aspect Characterization of Low-temperature Tempering Behaviors in High-carbon Martensite

Evolution of surface microstructure of Re‐Al‐Ni‐Au based ohmic contacts on n‐type GaN

AbstractRecently, rhenium (Re) based ohmic contacts to GaN have been studied for their low resistivity, smooth surface morphology, and sharp edge acuity at low annealing temperatures. In this work, we discuss the evolution of surface microstructures for Re‐Al‐Ni‐Au ohmic contacts on n‐GaN as a function of Re layer thickness and annealing temperature. For all Re thicknesses, the Al and Ni segregate into agglomerates that increase in size with increasing annealing temperature. These agglomerates are surrounded by Al‐Au films. Along with the underlying Re layer, they form different crystallographic phases of Re‐Al‐Ni, Al6Re, AlAu2, and Al2Au5. This, along with the formation of Re‐N phases at the metal‐semiconductor interface leads to low resistivity ohmic contacts on n‐GaN. Investigating the evolution of the contact microstructure is an important step in understanding the behavior of the Re‐based ohmic contact system.

Influence of Thermal Annealing on Mechanical and Optical Property of SiO2 Film Produced by ALD.

The application range of fused silica optical components can be expanded and the cost of fused silica components can be reduced by depositing the same material film on fused silica substrate. However, due to the different manufacturing process, the performance of ALD SiO2 film is lower than that of fused silica substrate, which also limits the use of this process. In this paper, ALD SiO2 film with different thicknesses were deposited, and then the structure and properties were tested. Finally, the ALD SiO2 film was treated via the annealing process. Transmission electron microscopy (TEM) showed that the ALD SiO2 film had good compactness and substrate adhesion. The Raman spectra showed that the ALD SiO2 film and substrate had the same structure, with only slight differences. The XRD pattern showed that ALD-fused silica did not crystallize before or after annealing. The infrared spectra showed that there was an obvious Si-OH defect in the ALD SiO2 film. The laser damage showed that the ALD SiO2 film had a much lower damage threshold than the fused silica substrate. The nanoindentation showed that the mechanical properties of the ALD SiO2 film were much lower than those of the fused silica substrate. After a low-temperature annealing treatment, the ALD SiO2 film Si-OH defect was reduced, the ALD SiO2 film four-member ring content was increased, the elastic modulus of the ALD SiO2 film was increased from 45.025 GPa to 68.025 GPa, the hardness was increased from 5.240 GPa to 9.528 GPa, and the ALD SiO2 film damage threshold was decreased from 5.5 J/cm2 to 1.3 J/cm2.

Microstructure-mechanical properties evolution of hot-rolled medium Mn steel: Effects of short-time holding and low-temperature tempering following ultrafast heating

In this work, the mechanical properties of hot-rolled 7Mn steel are significantly sensitive to the short-time isothermal holding after ultrafast heating (UFH). These samples also exhibited significant disparities in sensitivity of mechanical properties to subsequent low-temperature tempering. Through a combination of multi-scale experimental characterization, calculations of yield strength, and numerical simulations of elemental diffusion, we discussed the sensitivities described above. The results indicate that mechanical properties of the samples subjected to ultra-fast heating is not sensitive to subsequent low-temperature tempering. This due to the preferential segregation of C atoms at dislocation sites during the ultra-fast heating, leading to less noticeable C atoms segregation during low-temperature tempering. Short-time isothermal holding after ultrafast heating results in the precipitation of numerous nanoscale carbides within the martensite, thereby reducing solid solution strengthening and significantly decreasing the yield strength. Simultaneously, the low-temperature tempering process induces the segregation of C atoms towards dislocations, grain boundaries, or phase interfaces. This significantly mitigates the Portevin-Le Chatelier (PLC) effect in the sample, increasing the elongation rate of the steel from about 10% to 19%. Additionally, the combined effects of strengthening induced by Cottrell atmosphere and phase boundary segregation contribute to an elevation in yield strength.