Longer Heat Treatment Time Research Articles

Kinetic analysis of low-temperature MgAl2O4 formation from brucite with α-Al2O3 nanoparticles

This paper presents a detailed analysis of the synthesis of spinel MgAl2O4, a material with key industrial applications, through the calcination of brucite and alumina. The study reveals that a longer heat treatment time at 960°C favors the formation of spinel with spherical morphology and reduces the presence of MgO in irregular agglomerates. XRD analyses confirm the progressive phase transformation, while SEM-EDS provides evidence of chemical composition. These findings support the use of the Avrami equation to model spinel formation kinetics and highlight the importance of optimizing calcination parameters to improve material properties. The study concludes with an improved route for the efficient production of MgAl2O4, which could significantly influence its application in demanding environments.

RTV silicone rubbers cured by polyhedral oligomeric silsesquioxane and ladder-like polysilsesquioxane: Thermostability, long-term thermal properties, and pyrolysis mechanism

At present, silicone rubber has been widely used in the fields of aerospace and electronic materials, yet its long-term thermal performance still remains a challenge. In this investigation, polyhedral oligomeric silsesquioxane and ladder-like polysilsesquioxanes with multiple silicon-methoxy groups (MSPOSS, MSLPSQ) were synthesized successfully and used as cross-linkers to cure room temperature vulcanized silicone rubber (POSS-SR, LPSQ-SR). The results demonstrate that both MSPOSS and MSLPSQ can effectively improve thermostability, mechanical properties, and long-term thermal properties of RTV silicone rubber. The silicone rubber exhibits a remarkable preservation of strength and flexibility after long-time heat treatment at 400 °C. The silicone rubber demonstrates an impressive retention rate of 84.52% for tensile strength and 69.16% for elongation at break. An analysis of the pyrolysis process of the silicone rubber reveals that the 'back-biting' of polysiloxane chains were inhibited effectively by both MSPOSS and MSLPSQ. As a result of this inhibition, the silicone rubber's terminal chains are delayed from decomposing, resulting in retardation of initial thermal decomposition and significant improvement long-term thermal properties. This work may provide a new prospect for room temperature vulcanized silicone rubber for aerospace applications in extreme environments.

A rapid heat treatment for nanocrystallization of amorphous Fe75.1Cu1Nb1.5Si15.5B6.9 and Fe83Cu1Nb4B12 tape wound cores

A rapid annealing technique for soft magnetic Fe75.1Cu1Nb1.5Si15.5B6.9 and Fe83Cu1Nb4B12 tape wound cores is presented. Its effectiveness for creating a fine-grained nanocrystalline structure is demonstrated by measurements of the magnetic hysteresis loops as well as by structural investigations done by X-ray diffraction. The results show that the technique reduces the average crystallite sizes from about 27 nm to 17 nm for Fe75.1Cu1Nb1.5Si15.5B6.9, and from about 52 nm to 15 nm for Fe83Cu1Nb4B12. The coercivity after the rapid annealing is about three times lower for the Fe75.1Cu1Nb1.5Si15.5B6.9 alloy and up to one order of magnitude lower for the Fe83Cu1Nb4B12 alloy compared to the coercivity after the standardized long-time heat treatment. The improved heat treatment is outstanding in the way that it produces better soft magnetic properties in high-performance alloy cores within much shorter time than the standard core heat treatments.

Ultralow thermal conductivity of robust vermiculite aerogels fabricated by fast trivalent cation induced nanosheet gelation

Low thermal conductivities and high fire resistance are highly desired for the materials used in energy-efficient buildings with high-level safety. Traditional inorganic insulating materials are either fragile or have high thermal conductivities, while organic insulating materials or hybrids with inorganic ones are limited by poor fire resistance and significant volume shrinkage after heating. Herein we report mechanically robust vermiculite aerogels with a thermal conductivity as low as 0.033 W/(m·K), excellent fire resistance, and robust structural stability at high temperatures. The aerogels were assembled from delaminated two-dimensional vermiculite nanosheets via trivalent cations, such as Al3+, Fe3+, and La3+, induced fast gelation. The nanosheet concentration and ion cross-linking play critical roles in forming monolithic and robust aerogels. The vermiculite aerogels can resist a high-temperature flame without disintegration and show almost no volume shrinkage after long-time heat treatment at 700 °C. The excellent robustness and super-insulating performance (0.021 W/(m·K)) remain and even are improved after heating at 900 °C for 1 h. The as-made vermiculite aerogels show low-bulk density, high-porosity, super-insulating performance, excellent fire resistance, and environmental safety, endowing them with great potential as ideal thermal insulators for various applications, such as energy-efficient buildings.

Improving mechanical properties and isotropy of laser DED 17-4 PH stainless steel by combining ultrasonic vibration

Nanoscale Cu-rich precipitates (CRPs) are important to achieve high strength for the extensively applicated 17-4 precipitation hardening (PH) stainless steel (SS). Traditionally, the precipitation of CRPs requires high-temperature and long-time heat treatments. In this work, ultrasonic vibration (UV) was introduced into the laser direct energy deposition (L-DED) process to fabricate 17-4 PH deposits, a large density of nanoscale CRPs was directly and uniformly precipitated during depositing, the microstructure was also improved. Consequently, the mechanical properties of the deposit, both at the vertical and horizontal directions, were enhanced remarkably compared with those of the deposit manufactured by normal DED. Especially, the elongation was improved significantly, reached to around 20%. Moreover, the isotropy of mechanical property was improved, all the counterpart mechanical properties of the UV-DED sample were nearly close. This investigation supplied a potential method to mitigate the post heat treatments during fabricating 17-4 PH with L-DED.

Affable thermal treatment process to overcome the trade-off relation via interface engineering in an Fe-based amorphous film

As pre-eminent soft magnetic materials, Fe-based amorphous alloys have been extensively studied due to adjustable composition, low cost, and low iron core loss. The soft magnetic properties could be further improved after thermal annealing, which achieve a low coercive force (Hc) due to the low magnetic anisotropy and a high saturation magnetic flux density (Bs) on account of the precipitation of soft magnetic nanocrystalline phases. However, it is a key difficulty to control the nucleation and growth procedures of nanocrystals during annealing, resulting in rapid deterioration of Hc. Here, a soft magnetic Fe76Si8B13Nb3 film with ultra-fine amorphous/crystalline (a/c) core–shell structure is achieved from an amorphous precursor with the nanoscale phase separation. The pre-existing nanoscale phase separation provides vast nucleation sites and interphase boundaries, which could generate high concentration of nanocrystals and depresses the subsequent coarsening behavior even for long-time heat treatment. In consequence, the a/c core–shell soft magnetic film breaks the general trade-off relation in the soft magnetic material family with the highest Bs and lowest Hc simultaneously. This work provides a new perspective to design a/c alloys by amorphous precursor with dual phase structure, and importantly, it supplies effortless thermal treatment requirement to conveniently regulate the microstructures and soft magnetic properties of metallic glasses.

Microstructure and high-temperature sintering properties of APS coatings prepared from spherical thin-walled hollow-shell powders

High-performance thermal barrier coatings (TBCs) made of 4 mol.% Y2O3–stabilized ZrO2 (4YSZ) powder with a spherical thin-walled hollow-shell (STHS) structure exhibited a special microstructure different from the conventional lamellar structure of air plasma-sprayed (APS) coatings. The as-sprayed STHS APS coatings had a completely tetragonal prime (t′) structure and non-lamellated closed-cell structure with high porosity, which resulted in relatively low thermal conductivity (∼1.0 W m−1 K−1) and high Vicker's hardness (∼6 GPa). The influences of high-temperature aging on the microstructure stability, phase stability, and sintering capability were investigated after long-time heat treatment at different temperatures. The characterization results indicated that the pore content was basically constant, and it was less than 0.5% for sintered linear shrinkage of the STHS coatings after heat treatment at 1500 °C for 100 h. Furthermore, no spalling appeared in the STHS APS coating with the t′ phase structure after 101 thermal cycles of the water-quenching method at 1050 °C, and no monoclinic ZrO2 (m-ZrO2) phase was present in all of the STHS coatings after aging at 1200 °C for 1–1100 h. The excellent anti-sintering properties and phase stability of the STHS coatings are attributed to the closed-pore microstructure and the highly pure t′ phase composition with uniform distribution of ions, respectively. The results suggested that the non-lamellated closed-cell microstructure is beneficial for improving the coating properties, and the results also provide guidelines for microstructure design of TBCs using a feedstock powder.

Two optimized post-heat treatments to achieve high-performance 90W–7Ni–3Fe alloys fabricated by laser-directed energy deposition

Preparing tungsten heavy alloys with high strength and toughness by laser-directed energy deposition (LDED) is challenging. Here, we obtained high-performance LDED-fabricated 90W–7Ni–3Fe (90W) alloys through two optimized post-heat treatments. The results show that the 90W sample achieves a superior combination of the ultimate tensile strength (UTS: 821 ± 26 MPa) and ductility (17.46 ± 2.93%) after the high-temperature and long-time heat treatment, which are comparable to or even better than those of 90W alloys processed by powder metallurgy methods. The superior ductility is attributed to the improvement of the matrix-phase coordinated deformability, the enhancement of the W-M interfacial bonding strength, and the involvement of W particles in the coordinated deformation during tensile testing. In addition, the cycle-short-time heat treatment can simultaneously improve the UTS and elongation of the as-fabricated sample. The significant improvements in UTS (834 MPa → 870 MPa) and elongation (3.44% → 6.96%) are mainly related to the increase of W particles cleavage, the improvement of W-M interfacial bonding strength, and the reduction of porosity in the microstructure. This work provides a theoretical guide for improving the mechanical properties of tungsten alloys manufactured by additive manufacturing (AM) technology, which can be beneficial for expanding the application of AM technology in the field of tungsten alloys.

Changes in the microstructure and mechanical properties of Al2O3/YSZ directionally solidified eutectic ceramics during long-time heat treatment

Al2O3/YSZ directionally solidified eutectic ceramics (DSECs) were prepared using the induction heating zone melting (IHZM) method. The microstructures of the DSECs formed with various crucible pulling rates (2.5–300 mm/h) changed from the discontinuous lamellar into the colony structure, finally into the cell structure. The intracolony had better microstructural stability than the intercolony during heat treatment due to two factors: the size effect and the t-m transformation effect. The hardness changes were mainly related to the release and generation of residual stress caused by repeated heating and cooling. The quantity of cracks in DSECs increased with the heat treatment time, leading to a gradual decrease in the fracture toughness, 300 mm/h DSEC had the lowest reduction in fracture toughness after 500 h heat treatment due to fine microstructure, the fracture toughness was 7.15 MPa·m1/2, which was 76 % of that before the heat treatment (9.39 MPa·m1/2).

Simulation of Grain Coarsening Process in Copper Wiring by Phase Field Method

We simulated heat treatment of the fine copper wiring containing impurities by the phase field method. We evaluated effects of the initial grain size and the impurity concentration on the final average grain size and confirmed qualitative agreement between simulation and previous experimental results. Our claim was supported that the increase in interfacial driving force (due to grain refinement) and the effect of grain boundary pinning (due to impurities) are the main factors in grain coarsening in ultra-fine wiring. We clarified that the refinement of the initial grain size has a particularly strong effect on the growth rate at the initial stage of the heat treatment (i.e., 0–60 s), and has a slight effect on the subsequent growth stage (60–600 s). On the other hand, the impurity concentration affects the entire heat treatment process. This indicates that it is difficult to obtain coarse crystal grains by long-time heat treatment (about 30 min as in a conventional process) without lowering the impurity concentration, and that the high-purity plating process gives coarse grains by short-time heat treatment (about 3 min in rapid thermal annealing).

Effect of heat treatment on structure of nickel-based catalysts

Nickel-based catalyst is the general-purpose catalyst with a wide application and good performance. Widely used in fine chemicals, petrochemicals and other industries, it has received continuous attention from researchers. Taking silica gel (SiO2) and HZSM-5 molecular sieves as carriers, and Ni(NO3)2 · 6H2O and Cu(NO3)2 · 3H2O as precursors, in the work we prepared a series of NiO/SiO2, NiO/HZSM-5 and NiCu/HZSM-5 catalysts by impregnation method. Focused on the effects of heat treatment (baking) temperature and time on the structure of the catalysts, the structure of the catalysts was characterized by X-ray diffraction (XRD) spectroscopy. The results showed that in terms of carriers, HZSM-5 had stronger interaction with active metal particles than that SiO2 presented. It could better prevent the sintering agglomeration of catalytic particles during heat treatment, which is beneficial to preparing catalytic particles with smaller particle size. SiO2 exhibited better thermal stability for higher heat treatment temperatures and longer heat treatment time. At the same time, the heat treatment at the high temperature for a long time was liable to cause sintering growth of the active metal particles of the catalysts. The selection of suitable heat treatment process conditions was critical to obtaining the highly active nickel-based catalysts. The work briefly discussed the effect of heat treatment temperature and time on the structure of the catalysts, expecting to provide the useful reference for the preparation technology of supported nickel-based catalysts.

Effect of matrix crystallinity of carbon fiber reinforced polyamide 6 on static bending properties

Recently, carbon fiber reinforced thermoplastics (CFRTP) have been widely used for various applications instead of carbon fiber reinforced thermosetting plastics (CFRP). Some matrix resins of CFRTP are crystalline polymers such as polyamide (PA), polyetheretherketone (PEEK), and polyimide. In this study, carbon fiber reinforced polyamide 6 was used, and the effect of crystal state of PA6 on the mechanical properties of CFRTP was investigated. To understand the crystal state of PA6, Differential scanning calorimetry (DSC) analysis was carried out, and an increase in the heat treatment time increased the crystallinity of PA6. The results of bending tests showed that there was a relationship between bending strength and crystallinity, however, longer heat treatment time decreased Young’s modulus. The results of acoustic emission (AE) analysis and fractography showed that 30-h heat treatment made the matrix resin of CFRTP more brittle. To investigate the reason for this behavior, the DSC analysis of CFRTP was carried out. After the 30-h heat treatment, the crystal state was different compared to that of other materials. Therefore, bending properties are affected by the crystal state. Consequently, the crystal state must be considered to create CFRTP with desired properties.

Microstructure and mechanical properties of maraging 18Ni-300 steel obtained by powder bed based selective laser melting process

PurposeThe purpose of this paper is to maraging 18Ni-300 steel fabricate by powder bed based selective laser melting (SLM) process. Microstructure and mechanical properties of the maraging steel part before and after heat treatment at a slow cooling rate were investigated.Design/methodology/approachThe microstructure of the printed part was observed by optical microscopy and scanning electron microscopy. The phases were determined by X-ray diffraction. The surface roughness of the part was recorded by a profilometer. The tensile properties and microhardness of the parts before and after heat treatment were characterized by an electronic universal tensile testing machine and a Vickers hardness tester, respectively.FindingsMaraging 18Ni-300 steel part comprised of the martensitic phase and a small fraction of austenite phase. After heat treatment, the volume fraction of austenite slightly increased. The surface roughness of the part was about 96 µm. The printed part was dense, but irregular pores were present. The yield strength, ultimate tensile strength (UTS), elongation and Young’s modulus of as-fabricated parts were 554.7 MPa, 1173.1 MPa, 10.9% and 128.9 GPa, respectively. The yield strength, UTS, elongation and Young’s modulus of as-treated parts were 2065 MPa, 2225 MPa, 4.2% and 142.5 GPa, respectively. The microhardness values of surface and cross-section of the as-fabricated part were 407.1 HV and 443.0 HV, respectively. After short-time heat treatment, the microhardness values of the surface and cross-section of the part were 542.7 HV and 567.3 HV, respectively. After long-time heat treatment, the microhardness values of the surface and cross-section of the part were 524.4 HV and 454.8 HV, respectively. The microhardness and tensile strength increased significantly with decreasing elongation due to the changes in phases and microstructure of the parts after heat treatment.Originality/valueThis work studied the effect of heat treatment at 550°C combined with a subsequent slow cooling rate on microstructure and mechanical properties of maraging 18Ni-300 steel obtained by the powder bed based SLM process.

Zn-Doped Calcium Copper Titanate Synthesized via Rapid Laser Sintering of Sol-Gel Derived Precursors.

Zn-doped calcium copper titanate (CCTO) was successfully synthesized by rapid laser sintering of sol-gel derived precursors without the conventional long-time heat treatment. The structural, morphological, and crystalline properties were characterized, and the performances of dielectrics and impedance were measured and discussed. The X-ray diffractometer results show that Zn-doped CCTO is polycrystalline in a cubic structure, according to the doping ratio of Ca(Cu2Zn)Ti4O12. Electron microscopy showed that Zn-doped CCTO has a denser microstructure with better uniformness with shrunken interplanar spacing of 2.598 nm for the plane (220). Comparing with undoped CCTO, the permittivity almost remains unchanged in the range of 102–106 Hz, demonstrating good stability on frequency. The electrical mechanism was investigated and is discussed through the impedance spectroscopy analysis. The resistance of grain and grain boundary decreases with rising temperature. Activation energies for the grain boundaries for Zn- doped CCTO were calculated from the slope for the relationship of ln versus 1/T and were found to be 0.605 eV, smaller than undoped CCTO. This synthesis route may be an efficient and convenient approach to limit excessive waste of resources.

Exfoliated vermiculite nanosheets supporting tetraethylenepentamine for CO2 capture

CO2 capture is a critical process to reduce CO2 emission into the atmosphere. Here we report a novel and inexpensive composite adsorbent for capturing CO2. The composite was prepared by supporting tetraethylenepentamine (TEPA) onto exfoliated vermiculite (E-VER) nanosheets using wet-impregnation and freeze-drying methods. Vermiculite, as a cheap and natural abundant clay, was delaminated into ultrathin nanosheets via liquid-phase exfoliation. The negatively charged E-VER has exposed surfaces and a large surface area, which is ideal for supporting TEPA with the desired loading. It was found out that the TEPA loading has a crucial impact on the pore structures, surface areas, and the CO2 adsorption capacities. E-VER-TEPA-2% with a TEPA loading of 2% demonstrates the optimal performance for CO2 capture, showing a CO2 adsorption capacity of 29.5 ​mmol/g at 45 ​bar and 25 ​°C and 22.6 ​mmol/g at 40 ​bar and 75 ​°C. The E-VER/TEPA composites are compressible, a volumetric capacity of 29.93 ​mmol/cm3 was obtained for E-VER-TEPA-2% at 45 ​bar and 25 ​°C after being compressed at 20 ​MPa. Furthermore, E-VER/TEPA composites exhibited excellent cyclic stability over six cycles and long-time heat-treatment.

Heat-treated bean (Phaseolus vulgaris) residue meal as an alternative protein source in pelleted diets for Nile tilapia fingerlings: growth, body composition, and physical characteristics of diets.

The study aimed to evaluate heat-treated bean residue meal (Phaseolus vulgaris)-BRM-as an alternative protein source in diets for Nile tilapia fish. A completely randomized design was used, totaling four (n = 4) dietary treatments: diet without BRM (CON), raw BRM (RBRM) and heat-treated BRM at 100°C for 15min (BRM15), and 30min (BRM30) before inclusion in diets. Nile tilapia fingerlings (1.3g initial weight) were hand-fed the experimental diets for 66days, divided equally into three meals per day. Performance parameters, body composition, nutrient retention, and physical characteristics of diets were evaluated. Growth and feed conversion were lower (P <0.05) in fish fed BRM. Protein productive value was higher (P <0.05) in fish fed CON diet than in fish receiving BRM. However, 30min heat treatment of BRM increased (P <0.05) protein retention in fish. Fish fed BRM30 also had higher protein content (P <0.05) and reduced body lipid content (P <0.05) than those fed CON diet. The physical characteristics (durability, dry matter leaching, waterproof time, and water stability time) were significantly improved (P <0.05) in the BRM30 diet compared with other dietary treatments. The dietary inclusion of BRM at the level of 15% is not recommended for tilapia due to low growth performance and feed efficiency, regardless of preheating treatment. However, research on longer heat treatment time is needed due to the improvements observed in nutrient retention and physical characteristics of diets.

Measurement and Analysis of Magnetic Properties of YBa2Cu3O7-y Bulk Superconductor

YBa2Cu3O7-y single crystal bulk high-temperature superconductor has high critical current density with large magnetic levitation and trapping magnetic forces. Despite its distinctive electromagnetic properties, the longtime heat treatment process of oxide high-temperature superconductor, a ceramic material, is widely considered as a factor that can degrade industrial applicability of superconductors seriously. For applications in power systems, metal-ceramic composites need to be fabricated to enhance magnetic performance. In this study, CeO2 was utilized as an additive to control Y211 particles and improve superconducting magnetic properties. The study achieved meaningful outcomes, given that it reduced the processing time by half (1/2) with the interior seeding technique, realized the effect of top seeding by positioning one additional seed layer on the top surface, and obtained a magnetic levitation force of 67.015 N. In order to improve the physical properties of superconducting materials, interior seeding technique was applied, and the effect of top seeding was obtained by placing one seed layer on the top surface. Therefore, when two seed layers were used to fabricate a specimen, it could improve physical properties of superconductors to the extent that both the top and bottom pellets could be used.

Direct formation of La(Fe,Si)13 phase with enhanced mechanical property of off-stoichiometric La1.7Fe11.6Si1.4 alloys by directional solidification

The off-stoichiometric La1.7Fe11.6Si1.4 alloys fabricated by directionally solidification using zone melting liquid metal cooling is systematically studied in terms of morphology, microstructure, magnetocaloric effect, phase transition and mechanical property. Different from the conventional casting in which the La(Fe,Si)13 phase can only be obtained after a long-time heat treatment, a large volume fraction (over ∼80%) of La(Fe,Si)13 phase is formed directly during solidification. The Curie temperature is increased and the magnetic entropy change under applied fields of 2T attains 9.1 J kg−1 K−1. The activation energy of the magnetic phase transition is calculated using the Johnson-Mehl-Avarmi-Kolmogorov equation and the Arrhenius relation for the first time, showing a higher value than that of NiMn-based alloys. Compared with the Fe-rich alloys, the directionally solidified off-stoichiometric La1.7Fe11.6Si1.4 alloys show higher bending strength, which is due to the existence of the preferential growth α(Fe,Si) phase. Furthermore, the α(Fe,Si) phase plane interface and periodic morphology are detected along the crystal growth direction, and the corresponding formation mechanism is discussed.

Microstructure and properties of Cu-Cr-Nb alloy powder prepared by argon gas atomization

The Cu-2Cr-1Nb (at%) alloy powder was prepared by close-coupled argon gas atomization. The morphology, microstructure and phase were characterized by SEM, TEM, HRTEM, SAED and XRD. The effects of heat treatment on the microstructure and microhardness of the powder were investigated. The alloy matrix had equiaxed crystal structure, and the second phase was Cr2Nb intermetallic compound in sub-micron and nano-scale. Compared with large powder, the second phase of small powder is finer, and its distribution in the matrix is more uniform, the microhardness of the small powder is higher. After heat treatment at 773 K for 1 h, Cr and Nb precipitated and formed a large number of small precipitates, age hardening and peak aging phenomena occurred, and the peak hardness of the powder reached 130 HV. With the increase of heat treatment temperature, the second phase was coarsened. When the heat treatment temperature was 973 K, the short-time heat treatment hardening and long-time heat treatment softening were shown. However, after the heat treatment at 1223 K, only softening phenomenon was observed. This method can be used to prepare the excellent powder for Cu-Cr-Nb alloy, which can be used as a potential structural material for aerospace.

Post heat treatment time induced distinguished superconducting features of JR Nb3Al wires rapidly heated around the Tc peak condition

This work investigated the effect of post heat treat time on the structure and superconducting properties of Nb3Al wires prepared around the current condition of getting Tc peak. Properties of Nb3Al wires rapidly heated at much lower current of 76 A were also studied for comparison. M-T results show that prolongation of post-heat treatment time can elevate the Tc value of all Nb3Al wires because of the stoichiometry improvement of Nb3Al phase. The best Jc of post heat treated Nb3Al wires rapidly heated at 76 A and 272 A were obtained after post heat treated for 2 h at 800 °C, compared to that of 10 h for the 276 A samples. The different optimism post heat treatment time to get best Jc of the wires might attribute to the disorder degree difference of the Nb(Al)ss phase fabricated under different rapid heating current. The main pinning mechanism of Nb3Al superconducting wires was grain boundary pinning, as deduced from the fitting of pinning curve. Gradually degrade of Jc of the Nb3Al wire performed at longer heat treatment time was attributed to the coarse of Nb3Al grain that attenuated grain boundary pinning.