Controlled Heat Treatment Research Articles

In-situ Selective Laser Heat Treatment for microstructural control of additively manufactured Ti-6Al-4V

As-built Laser Powder Bed Fusion (LPBF) Ti-6Al-4V typically exhibits a fully acicular α′-martensite microstructure, and requires post-process heat treatment in order to decompose the martensite and achieve sufficient ductility. In the present study, we demonstrate a simple concept based on in-situ Selective Laser Heat Treatment (SLHT) that can effectively alter the microstructure and activate the decomposition of the α′-martensite into a lamellar α+β microstructure within a short time scale (~30s). SLHT consists of multiple rescanning of the printed part, with low energy density, triggering solid-state phase transformations. Operando X-ray diffraction has been performed on cuboid and thin wall geometries, and was augmented by thermal finite element simulations. Upon SLHT, a gradual formation of the β phase as well as an α/α′peak narrowing trend have been evidenced through X-ray diffraction, as an indication of the diffusional nature of α′-martensite decomposition. Moreover, through fine tuning of the process parameters at the final stage of SLHT, a controlled temperature evolution during cooling was achieved, leading to preservation of the β phase, a product of the decomposition, down to room temperature. Complementary microstructural characterizations via EBSD, SEM, and TEM confirm the presence of a lamellar α+β microstructure after SLHT. Our results evidence, for the first time, the fast kinetics of α′-martensite decomposition under in-situ SLHT. The approach is meant to be implemented at selected locations during the LPBF process, avoiding time-consuming post processing steps, and leading to composite-like, architected microstructures.

Effect of combined cold deformation and subsequent heat treatment on the microstructure, texture, mechanical properties and cementite spheroidization in AISI 1070 steel

In this study, the effects of thermomechanical heat treatments on two batches of commercial AISI 1070 steel were investigated. Both samples underwent cold rolling and annealing at 600 °C for 30 min, and their microstructure and crystallographic texture were analyzed using XRD, SEM observations, and EBSD measurements. Tensile testing was also conducted to evaluate the mechanical properties of the steels. The results showed that the lamella pearlitic microstructure of both samples was transformed into α-ferrite matrix with spheroidal cementite particles (Fe3C). Sample A exhibited a strong γ-fiber texture parallel to the rolling plane, with a typical cold-rolled texture and high anisotropic characterization dominated by (111)<uvw> orientation. Sample B, on the other hand, exhibited (111)[12¯1] and GOSS (110)<001> texture components with dominant (111) and (101) grain orientations along the rolling direction. While the yield stress and tensile strength were higher in sample A, sample B had better toughness and elongation properties, indicating that it was more ductile. These findings highlight the importance of controlling heat treatment processes to achieve desired microstructures and mechanical properties in steels and provide insights into the relationship between microstructure, crystallographic texture, and mechanical properties. The results of this research could be useful in optimizing the process and performance of steels in various industrial applications.

Full-spectrum and tunable white light emission of germanate glass-ceramic containing defective Zn2GeO4 and Mn2+ ions

The full-spectrum phosphors are key components for improving the light quality of phosphor-converted white light-emitting diodes (pc-WLEDs). In this work, a novel germanate glass-ceramic (GC) doped with Mn2+ was developed to achieve full-spectrum white light emission deriving from the defective Zn2GeO4 crystalline phase and Mn2+ with multisite occupancy. The defective Zn2GeO4 is crystallized in situ from the well-designed precursor germanate glass by a controllable heat treatment. The energy states of intrinsic defects, including oxygen and zinc vacancies and interstitial zinc and oxygen of Zn2GeO4 in GC, have been studied by first-principles calculations. The luminescence property and the energy transfer mechanism between the defect states and Mn2+ ions in the GC material was proposed. Under the UV excitation, the luminescence property can be tuned by adjusting the distribution of Mn2+ ions in between the glassy and crystalline phases. The correlated color temperature (CCT) and color rendering index (CRI) of the UV-excited full-spectrum white light emission can be tuned over a wide range. This combinatorial strategy of intrinsic defects and multisite ion doping for full-spectrum white light emission in GC, which overcomes the limitation of conventional discontinuous white light emitting materials that emit singly from doping ions, has shown good potential for application in pc-WLEDs.

In-situ monitoring of changes in ultrastructure and mechanical properties of flax cell walls during controlled heat treatment

Plant fibres are increasingly used as reinforcements, especially in thermoplastic composites. Understanding the impact of temperature on the properties of these fibres is an important issue for the manufacturing of high-performance materials with minimal defects. In this work, the structural evolution and mechanical behaviour of flax fibre cell walls were dynamically monitored by temperature-controlled X-ray diffraction and nanoindentation from 25 to 230 °C; detailed biochemical analysis was also conducted on fibre samples after each heating step. With increasing temperature up to 230 °C, a decrease in the local mechanical performance of the flax cell walls, of about −72 % for the indentation modulus and −35 % for the hardness, was measured. This was associated with a decrease in the packing of the cellulose crystal lattice (increase in d-spacing d200), as well as significant mass losses measured by thermogravimetric analysis and changes in the biochemical composition, i.e. non-cellulosic polysaccharides attributed to the middle lamellae but also to the cell walls. This work, which proposes for the first time an in-situ investigation of the dynamic temperature evolution of the flax cell wall properties, highlights the reversible behaviour of their crystalline structure (i.e. cellulose) and local mechanical properties after cooling to room temperature, even after exposure to high temperatures.

Vapor heat treatment for quarantine control of the oriental fruit fly (Diptera: Tephritidae) in papaya fruit from Thailand

A two-stage vapor heat treatment (VHT) is used commercially for disinfestation of the oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) in various tropical fruits exported from Thailand to international markets. In the present study, VHT was tested against B. dorsalis in papayas to confirm a high level of quarantine security. The first instar larva of B. dorsalis was the most heat tolerant life stage. The VHT consists of heating papaya fruits with hot air at 50–80 % RH from ambient temperature to a fruit center temperature of 43 °C (dry pre-heating period), then heating with saturated hot air to 47 °C (wet heating period) with a 20-min hold at 47°. In large-scale confirmatory tests of this VHT treatment schedule, none of the treated 78,405 first instar larvae survived. Papayas at the color break maturity stage treated by VHT and held under simulated commercial export conditions showed no differences in fruit quality compared with non-treated controls. VHT showed high efficacy in disinfestation of papayas of B. dorsalis while maintaining fruit quality and could be used as a standard quarantine treatment for papaya exported from Thailand.

Ti3C2Tx MXene integrated hollow carbon nanofibers with polypyrrole layers for MOF-derived freestanding electrodes of flexible asymmetric supercapacitors

Effective customization of Ti3C2Tx MXenes by electrospinning technique is crucial for the preparation of freestanding/flexible electrodes exhibiting enhanced performance in supercapacitors. Herein, we prepared MXenes containing hollow carbon nanofibers (MXHCNF) by co-axial electrospinning, and the inside-out of MXHCNF is decorated with polypyrrole layers (PPy@MXHCNF), which is sufficiently flexible, conductive, and highly functionalized with a unique trilayer morphology. Using the self-designed electroactive PPy@MXHCNF, a ZnCoMOF is homogeneously grown. The as-prepared bimetallic MOF on PPy@MXHCNF is used as a common precursor with which to fabricate the positive (ZCO@PPy@MXHCNF) and negative (NPC@MXHCNF) electrodes by a controlled heat treatment process using a “two from one” strategy. The freestanding positive and negative electrodes provide specific capacitances of 1567.5 F g−1 and 477.2 F g−1 at 1 A g−1, respectively, with high capacitance retention, cyclic stability, and coulombic efficiency. A flexible asymmetric device (ZCO@PPy@MXHCNF//NPC@MXHCNF) is assembled, and it exhibits an energy density of 61.3 Wh kg−1 at a power density of 796.8 W kg−1 and 92.8% capacitance retention after 10,000 GCD cycles. This work provides a unique approach involving MXene modification, polypyrrole decorated electrospun MXHCNFs as efficient substrates for freestanding electrodes, and the use of bimetallic MOF as a common strategic route for both positive and negative electrodes in flexible asymmetric supercapacitors.

Two–dimensional metal–organic framework nanosheets: An efficient two–electron oxygen reduction reaction electrocatalyst for boosting cathodic luminol electrochemiluminescence

Exploration of electrocatalytic–luminol systems is still in the developmental stages because of the weak electrochemiluminescence (ECL) of cathodic luminol, and it is still a challenge to establish a conformational relationship between electrocatalytic materials and ECL performance. Herein, functionalized two–dimensional NiZn metal–organic framework (MOF) nanosheets were synthesized using controlled heat treatment and were successfully applied to the two-electron (2e−) oxygen reduction reaction (ORR) to produce H2O2. Interestingly, it was found that both the intermediates and products of the ORR significantly affected the ECL emission of luminol. It is worth noting that extending NiM MOF (M = Fe, Co, and Zn) to 2e− ORR reaction and achieving efficient luminol emission is undoubtedly beneficial for constructing cathodic luminol systems. This work demonstrates the relationship between the electrocatalytic materials and luminol ECL performance, thereby, broadening the applications of ECL reactions. Finally, the proposed biosensor was successfully used for the sensitive detection of alpha-fetoprotein (AFP).

The comparative studies on the physicochemical properties of mung bean protein isolate–polysaccharide conjugates prepared by ultrasonic or controlled heating treatment

Protein isolate was obtained with maximum yield from mung bean and conjugated with different polysaccharides. Production of mung bean protein isolate was optimized with the Design Expert Program, Response Surface Methodology (RSM), Central Composite Design. The optimum extraction conditions were found to be 40.78 min at 38.20 °C, the solution/solid ratio was 24.79 mL/g and the pH value was 8.23. Mung beans contain 86.18 ± 0.1 (g/100 gDM) protein, of which 69.44 ± 2.62% was extracted under optimum conditions. The conjugation process with polysaccharides was continued with the Maillard reaction. Two different treatment effects were determined over conjugation: controlled heating (60 °C, 5 days, 79% RH) and ultrasound (200 W, 80 °C, 40 min). FT-IR analysis, sodium-dodecyl-sulphate polyacrylamide (SDS-PAGE) gel electrophoresis, solubility measurement, analysis of emulsifying properties and measurement of conjugation degree analyzes were performed on the conjugates. Compared to mung bean protein isolates, the solubility of the conjugates increased by 30.22% and their emulsifying properties increased by 46.77%.

Layered Structure Regulation for Zinc‐Ion Batteries: Rate Capability and Cyclability Enhancement by Rotatable Pillars

AbstractRegulating the interlayer spacing of vanadium oxides by various pillars has commonly been used for improving zinc‐ion storage performance. However, most of the reported pillars are large and rigid, which sacrifices interlayer free volume, increases the steric hindrance, and results in large volume change. Herein, a layered vanadium oxide with –OH pillars by controllable heat treatment of layered vanadium oxide with rigid NH4+ pillars is prepared. Although the –OH pillars are small‐sized, they can firmly support the interlayers through the covalent bond. In addition, the rotatable –OH pillars can promote Zn‐ion diffusion and accommodate lattice deformation. Compared to the layered vanadium oxide with rigid pillars, the one with rotatable pillars shows a higher rate capability (321 mAh g−1 at 0.5 A g−1 and 83 mAh g−1 at 20 A g−1) and a better cyclability (93% capacity retention over 2000 cycles at 5 A g−1). Further mechanism studies demonstrate that the rotatable pillars show low‐hindrance and high‐stability to regulate the interlayer structure. It is emphasized that the interlayer microenvironment can not be neglected, but is crucial for advanced electrodes of aqueous zinc‐ion batteries, rather than pursuing larger interlayer spacing.

Al/CuO@CNFs Conductive Flexible Energetic Films with High Electrical Safety.

The development of energetic materials with both high energy and high safety has always been the focus of the field of energetic materials. In this paper, a low-current-sensitivity flexible energetic film composed of carbon nanofibers (CNFs)-coated Al/CuO metastable intermolecular composites (MICs) was prepared by a blow-spinning combined with controlled heat treatment technique. Hotspots can hardly generate in this kind of energetic film due to the increased electrical and thermal conductivity, leading to low sensitivity of MICs. It evenly stays at a high voltage (60 V) for 24 h without raising the temperature significantly. The energetic films keep the high energy release of MICs due to the additional violent reactions between CuO and CNFs as well as the light weight of CNFs, showing the heat release of 2864 J/g. In addition, the obtained films exhibit good mechanical properties and can maintain the structural integrity after 1000 cycles of repeated bending to a 6 mm curvature radius. The above characteristics reveal that energetic films presented in this paper have certain safety, high energy, and flexibility and have potential applications in transient electronics with flexible requirements such as micro-electromechanical system.

Performance evaluation for Ag and Au nanoparticle containing K 2 O‐MgO‐B 2 O 3 ‐Al 2 O 3 ‐SiO 2 ‐F glass sealants for SOFC application

Performance evaluation for Ag and Au nanoparticle containing K ₂ O‐MgO‐B ₂ O ₃ ‐Al ₂ O ₃ ‐SiO ₂ ‐F glass sealants for SOFC application

Breaking strength-ductility trade-off in laser-powder bed fused Fe–Cr–Ni–Al maraging stainless steel: Controlled precipitation and preserved dislocations

In the current study, cylindrical rods of Fe–Cr–Ni–Al maraging steel (with the brand name CX) are fabricated using the laser-powder bed fusion (L-PBF) technique. The material is analyzed using the differential scanning calorimetry (DSC) technique under continuous heating at different heating rates. The DSC results are employed to identify the heat flow peaks associated with the precipitation and austenite reversion phase transformations. The peaks are then analyzed and processed to determine the onset, peak, and end temperatures associated with each phase transformation. These results are used to calculate the degree of phase transformation under non-isothermal conditions and to evaluate the activation energy of transformation through the Kissinger method. In the next step, the modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model is employed to model the kinetics of phase transformations during non-isothermal heating. The validated model is then used to predict the kinetics of precipitation and austenite reversion phase transformations under isothermal aging heat treatments. The isothermal modeling results are employed to design a direct aging heat treatment to promote the evolution of nanometric β-NiAl precipitates and meanwhile preserve the pre-existing dislocation networks. Such a heat treatment results in the enhancement of both yield and tensile strengths from 929 MPa and 1032 MPa in the as-built condition to 1659 MPa and 1738 MPa after heat treatment. Meanwhile, ductility slightly changes from 15.3% in the as-built condition to 14.7% after heat treatment. Such an achievement in breaking the strength-ductility trade-off is due to a controlled heat treatment process that preserves the dislocation networks.

Er-doped zinc-silicate glass-ceramics with enhanced emission in the near-infrared region

Erbium-doped lasers and amplifiers exhibit emission around 1.5 μm, which makes them perspective in various applications, such as telecommunications, material processing or defence. The conventionally used silica glass suffers from various drawbacks, such as low solubility of erbium ions or high phonon energy of the silica lattice, which limit the luminescence properties. The zinc-silicate glass-ceramics containing ZnO or Zn2SiO4 nanocrystals represent a suitable alternative. The incorporation of erbium ions into the nanocrystals should result in the enhancement of luminescence properties. In this work, we prepared a zinc-silicate glass-ceramic material containing Zn2SiO4 nanocrystals by the controlled heat treatment of a precursor glass. The luminescence properties of the 1.5 μm emission were measured and the influence of the crystallization on the near-infrared emission was evaluated.

Modified BiFeO3/rGO nanocomposite by controlled synthesis to enhance adsorption and visible-light photocatalytic activity

In this study, a sol-gel process is used to synthesize a bismuth ferrite (BiFeO3, or BFO for short)/reduced graphene oxide (rGO) nanocomposite (BGO). The structural, morphological, and optical characteristics of the BiFeO3 nanopowder are modified by controlling heat treatment parameters and rGO contents. The semi-spherical BFO nanoparticles possess rhombohedral distorted perovskite crystal structure and are grafted on rGO nanosheets of various sizes which are attributed to the existence of rGO content during the sol-gel process. The observed interface between rGO nanosheets and BFO nanoparticles assists in the efficient charge separation and transfer of photogenerated BFO charge carriers through rGO nanosheets. Compared to BFO, BGO has a narrower band gap energy of 1.8 eV, a lower rate of charge carrier recombination, and stronger magnetic characteristics. The adsorption performance and photocatalytic activity mechanisms have been thoroughly examined. By adding rGO, the adsorption isotherm of methylene blue (MB) on the BFO photocatalyst changed from the Freundlich to the Langmuir. Also, the adsorption kinetics were investigated using a pseudo-second-order model. Furthermore, the degradation of MB is used to evaluate the visible light photocatalytic activity whereby 98% degradation was reached after 300 min. The Mott-Schottky test and the active species scavenger experiment are used to assess the potential mechanisms of MB photodegradation. The findings showed that the primary active species in photodegradation were hydroxyl radicals. Also, the nanocomposite was reasonably stable, and it could be magnetically removed from aqueous environments and utilized again for subsequent usage.

"Electron Complementation"-Induced Molybdenum Nitride/Co-Anchored Graphitic Carbon Nitride Porous Nanoparticles for Efficient Overall Water Splitting.

Maximizing the usable space of electrocatalysts and fine-tuning the interface geometry as well as the electronic structure to facilitate hydrogen and oxygen evolution reactions (HER and OER) have always been the focus of research. Herein, a homogeneous porous nanoparticle construction strategy was proposed, in which molybdenum nitride (Mo2N) particles were prepared by controlled heat treatment of the precursor nanoparticle induced by polyethylene glycol, and the Mo2N/Co-C3N4 heterostructure with a pore size of about 1.13 nm was obtained by compounding Co-anchored graphitic carbon nitride. In particular, exploring the change of charge distribution at the interface based on the principle of "electron complementation" shows that under the regulation of nitrogen with high electronegativity, the affinity of active site Co to oxygenated species in the OER process and the adsorption as well as cleavage ability of HER reactants in the active site were effectively optimized. Thus, Mo2N/Co-C3N4 not only inherits the functions of each component, but also provides an ideal heterogeneous interface for exhibiting impressive bifunctional activity, which only needs 100 and 210 mV to deliver 10 mA cm-2 for the HER and OER, respectively. In addition, the Mo2N/Co-C3N4 catalyst also demonstrates high overall water splitting stability with a slight current decrease after 95 h. Manipulating the electronic structure of multiple sites by constructing electronically complementary interfaces may provide another avenue to develop highly active catalysts for overall water splitting and other applications.

The Effect of Femtosecond Laser Irradiation and Plasmon Field on the Degree of Conversion of a UDMA-TEGDMA Copolymer Nanocomposite Doped with Gold Nanorods.

In this work, the effects of femtosecond laser irradiation and doping with plasmonic gold nanorods on the degree of conversion (DC) of a urethane dimethacrylate (UDMA)-triethylene glycol dimethacrylate (TEGDMA) nanocomposite were investigated. The UDMA-TEGDMA photopolymer was prepared in a 3:1 weight ratio and doped with dodecanethiol- (DDT) capped gold nanorods of 25 × 75 or 25 × 85 nm nominal diameter and length. It was found that the presence of the gold nanorods alone (without direct plasmonic excitation) can increase the DC of the photopolymer by 6-15%. This increase was found to be similar to what could be achieved with a control heat treatment of 30 min at 180 °C. It was also shown that femtosecond laser impulses (795 nm, 5 mJ pulse energy, 50 fs pulse length, 2.83 Jcm-2 fluence), applied after the photopolymerization under a standard dental curing lamp, can cause a 2-7% increase in the DC of undoped samples, even after thermal pre-treatment. The best DC values (12-15% increase) were obtained with combined nanorod doping and subsequent laser irradiation close to the plasmon resonance peak of the nanorods (760-800 nm), which proves that the excited plasmon field can directly facilitate double bond breakage (without thermoplasmonic effects due to the short pulse length) and increase the crosslink density independently from the initial photopolymerization process.

The Influence of Heat Treatment on Corrosion Resistance and Microhardness of Hot-Dip Zinc Coating Deposited on Steel Bolts.

The analyzed topic refers to the corrosion resistance and changes in microhardness of the heat-treated (HT) hot-dip zinc coating deposited on bolts. The research aimed to evaluate the influence of the HT on the increase of the coating hardness and changes in anticorrosion properties. Hot-dip zinc coating was deposited in industrial conditions (acc. EN ISO 10684) on chosen bolts (M12x60). The achieved results were assessed based on corrosion resistance tests in neutral salt spray (salt chamber) and microhardness measurements. Tests were conducted in accordance with the adopted fractional plan, generated in the DOE module of the Statistica software. Using the conjugate gradient method optimal parameters of HT were determined. The conducted tests proved that the controlled heat treatment may increase the hardness of the hot-dip zinc coating without a significant deterioration in its basic protective function (corrosion resistance). The observed changes in the hardness and corrosion resistance of the zinc coating are a consequence of changes in its structure.

Recent Advances and Remaining Challenges in Manufacturing of Amorphous and Nanocrystalline Alloys

A review of advanced Fe-based amorphous and nanocrystalline soft magnetic alloys that are currently being used in the market and their primary industrial applications is discussed as well as emerging trends. The high-efficiency distribution transformer market continues to be the largest segment by volume for Fe-based amorphous foil. The industry has been shifting toward higher induction levels (1.63 T) with increased stacking factor (>90%) to minimize the transformer size and reduce costs. New magnetic domain refined grades of amorphous foil are now commercially available which show a reduction of ~25% in core losses compared to the standard amorphous material. Nanocrystalline soft magnetic alloys have become the standard material for many applications including low-loss electrical components, magnetic shielding, electronic filtering, medium frequency transformer cores, and a variety of others. The nanocrystalline alloys are commonly cast fully amorphous and devitrified through controlled heat treatments. New nanocrystalline alloy compositions and processing methods have enhanced both the mechanical and magnetic performance of the final properties. Amorphous and nanocrystalline alloys show promise for use in electric motors but fabrication challenges for limited their commercial adoption.

Structure and corrosion behavior of Cu-26Zn-5Al alloy processed by accumulative roll bonding and heat treatment

Cu-26Zn-5Al shape memory alloy (SMA) was produced by accumulative roll bonding (ARB) and subsequent heat treatment. In this regard, different austenitization cycles and cooling conditions, including furnace, air, cold-water, and boiling-water cooling were experimented. The heat-treated specimens were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The corrosion behavior of the specimens was also studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl solution. The results revealed that only by cooling in the boiling- and ice-water environments, a fully martensitic microstructure showing the shape memory effect is obtained. In contrast, by using the other cooling conditions, different phases like α-phase (Cu-saturated solid solution) are formed as well as martensite. From the corrosion testing results, it was found that the SMA specimens with the fully martensitic microstructure have the highest corrosion resistance, where cooling in boiling water was recognized to be optimal. In conclusion, Cu-26Zn-5Al SMA with an improved corrosion resistance can be produced by ARB followed by controlled heat treatment.

Functional enhancement of whey protein concentrate and egg by partial denaturation and co-processing

This study investigated functional enhancement strategies for whole egg (WE), egg yolk (EY) and whey protein concentrate (WPC) with a view to reducing their required concentrations in formulations and the resulting environmental footprint. WE and EY underwent a combined phospholipase PLA2 and controlled heat treatment (WE2 and EY2) while WPC was partially-denatured via controlled heating (pdWPC). WE2 and EY2 samples were mixed with pdWPC and were also control-heated (h) with WPC. WE2-WPC(h) foams proved more stable than their untreated controls. WE2, EY2 and EY2-pdWPC showed higher emulsifying properties than their untreated controls. pdWPC, EY2 and EY2-WPC(h) hydrogels proved more viscoelastic than their untreated controls. EY2 and EY2-WPC(h) displayed an additional 45 kDa protein band, which could correspond to surface-active apoproteins released from lipoproteins. This work highlighted the potential to enhance WE, EY and WPC functionality via combined partial denaturation treatments and via synergy between WPC and WE or EY when co-processed.