Heat Treatment Procedures Research Articles

Study on dislocation density, microstructure, and mechanical properties of P92 steel for different heat treatment conditions

AbstractThe impact of various heat treatment procedures on microstructure, dislocation density, hardness, tensile characteristics, and impact toughness of P92 steel was examined in the current experiment. The martensitic microstructure and average microhardness of 463 HV 0.2±8 HV 0.2 of the normalized steel were prevalent. A tempering procedure was carried out at 760 °C for a range of 2 hours to 6 hours. Additionally, an X‐ray diffraction examination was carried out, and the results were used to determine the dislocation density. The normalized sample was characterized by a high dislocation density. The dislocation density was decreased by tempering of normalized samples. With an increase in tempering time, the effect of the treatment coarsened the grains, precipitates, and decreased the area fraction of precipitates. After tempering, MX, M23C6, and M7C3 types precipitates were found to have precipitated, according to energy dispersive spectroscopy and x‐ray diffraction research. The ideal tempering period was determined to be 4 hours at a tempering temperature of 760 °C based on the microstructure and mechanical characteristics. Steel that was tempered at 760 °C for 4 hours had a yield strength of 472 MPa, an ultimate tensile strength of 668.02 MPa, and an elongation of 26.05 %, respectively.

Prediction of the mechanical properties of heat-treated fused filament fabrication thermoplastics using adaptive neuro-fuzzy inference system

The requirement for post-processing methods in 3D printing has increased due to its major limitations such as poor mechanical and surface properties. Thermal annealing, a heat-treatment procedure, has proven to be an excellent approach for increasing the mechanical strength of additive manufactured thermoplastics. The optimized thermal annealing parameters for maximum tensile strength are identified. The Adaptive Neuro-fuzzy Inference System (ANFIS) methodology is employed in this study to forecast the tensile strength of thermal annealed fused filament fabricated polylactic acid (PLA), carbon fiber filled polylactic acid (PLA-CF), and polycarbonate acrylonitrile butadiene styrene (PC-ABS). The root mean square error (RMSE) of the predicted tensile strength of PLA, PLA-CF, and PC-ABS are obtained as 1.012, 0.5, and 0.835 respectively. The coefficient of determination for the predicted model of thermoplastics PLA, PLA-CF, and PC-ABS is determined as 0.98, 0.99, and 0.89 respectively. The ANFIS model developed is successful in determining the tensile strength of annealed 3D printed thermoplastics at various annealing conditions of temperature and duration. Further, the study investigates the effect of heat treatment on the compressive, impact, and flexural properties of PLA prints.

Investigation of the Effect of Heat Treatment Time in Case of Recrystallization of Al99.5

In this study the effect of heat treatment time was investigated in case of recrystallization of Al99.5 material samples. Two different type were manufactured based on the previously applied cold forming. 12% and 24% cold forming was applied to the samples before the heat treatment procedure, which was always at 570 °C and cooled in water. Six different heat treatment time were investigated, namely 5, 10, 30, 60, 120 and 240 minutes. After the recrystallization procedure the microstructure and the mechanical properties were determined. It was found that in the case of the 12% cold formed samples after 30-minute-long heat treatment there were still signs of the original microstructure, however it does not affect the mechanical properties. The yield strength and the ultimate tensile strength were independent of the heat treatment time; they were only dependent on the grain size which was expected. A strong dependency can be discovered between the elongation at break and the heat treatment time. A tangent hyperbolic function was fitted on the measured data, which showed that the asymptote was ~29% for both type of samples. This is a 25% increase compared to the 5-minute-long heat treatment time samples, and this value was reached after ~120 minutes. Another result was that the elongation at break dependency on the grain size is decreasing with increasing heat treatment time.

Preparation and Characterization of Low Cost Cu-Al-Be Shape Memory Alloy for Aerospace Applications

Recently it has been found that a small addition of Beryllium (Be) widens the transformation temperature in Cu-Al based Shape Memory Alloys (SMA), that is particularly interesting in the industrial applications point of view. In this paper, the processing of Cu-Al-Be SMA by gravity die casting technology was described. The specially designed heat treatment procedure was designed to stabilize the SMA effect in this alloy. The DSC curve showed that this alloy has the transformation temperature in the range of 65°C to 120°C, and also exhibits the hysteresis behavior. Microstructure examinations confirmed the presence of lath martensite phases at room temperature. The bend test was used to prove the existence of the shape memory effect in this alloy.

Metastability mediated grain size control in PH 17-4 stainless steel fabricated using Laser-Powder Bed Fusion (LPBF)

Varying the chemical composition and cooling rates during additive manufacturing (AM) can enable the formation and, in some cases, the retention of metastable phases affecting the solidification pathways. Altering the solidification pathways directly affects the microstructure and in turn the mechanical properties of the parts. In this study, we show that modifying the solidification pathway through the deliberate retention of metastable austenite in PH 17–4 stainless steel (SS) leads to significant grain refinement (one order of magnitude smaller grains) and improvement in tensile strength (30% higher ultimate tensile strength) of parts printed using Laser-Powder Bed Fusion (LPBF). Nitrogen (N2)-atomized feedstock powder containing higher concentrations of austenite-stabilizing elemental nitrogen was used to print parts with retained austenite. Parts absent of retained austenite printed using argon-atomized feedstock powder were used for comparison of microstructure and tensile properties. The grain refinement has been attributed to the “crowding effect” observed due to the simultaneous growth and coexistence of metastable austenitic phase with the stable ferrite. We also show that employing a three-step heat treatment procedure can eliminate the unwanted yield point behavior associated with the softer austenite while preserving the superior tensile properties in N2-atomized samples.

Magnetic nitrogen-doped carbon nanofibers containing homogeneously dispersed CoFe2O4 nanoparticles with lightweight and efficient microwave absorption performance

Homogeneously dispersed ultrafine CoFe2O4 nanoparticles embedded within N-doped carbon nanofibers (named as CFO@NCNFs) have been fabricated via electrospinning and following heat treatment procedures. The dielectric and magnetic parameters of CFO@NCNFs/paraffin wax composites are regulated through adjusting the concentration of CoFe2O4 to obtain good impedance matching and excellent microwave absorption (MA) properties. Benefiting from the unique structure involving CoFe2O4 @onion-like carbon nanospheres and 3D conductive NCNFs network, as well as the synergistic mechanism between ultrasmall magnetic CoFe2O4 nanoparticles and light mass dielectric NCNFs. The CFO@NCNFs-5 exhibit outstanding MA properties at only 20 wt% filler loading and minimum reflection loss (RL) achieves −47.9 dB (surpass 99.9% MA) at 9.2 GHz with a thin thickness of merely 1.7 mm, and the corresponding effective absorption bandwidth (RL < −10 dB) achieves 5.4 GHz (6.5–11.9 GHz). Moreover, the effective absorption bandwidth (EAB) can be obtained in multiband (3.9–18.0 GHz) by adjusting the thickness of sample layer. Our work indicates that the appropriate incorporation of ultrafine CoFe2O4 nanoparticles encapsulated in NCNFs is a versatile and high-efficiency strategy to integrate lightweight and excellent properties of magnetic carbon-based absorbers.

Taking inspiration from medieval architecture: Using catenary arches in place of straight beam as the building block into bending-dominated lattice structures

Regular bending-dominated lattice structures use straight strut elements as the building blocks in their unit cell which is easier to deform under compression. To improve their performance, replacing the straight elements with the curved members of catenary arch geometry is proposed. Two representative cases – body centered cubic and simple cubic are designed, manufactured using AlSi10Mg alloy and tested experimentally in this study with their struts replaced by catenary arches. Numerical simulations were also conducted at the unit cell level to understand the stress development and regions of high stress concentrations. The effect of different heat treatment procedures was also investigated for both test cases. It was observed that the use of catenary elements had opposing effects on the strength of the BCC and SCC lattice structures when compared to their straight element counterparts. The higher nodal connectivity adversely affected the strength and the lattice failure depended highly on the same. The residual stress release heat treatment improved the mechanical properties of the lattice structures while the solution treatment and aging reduced the strength and modulus but substantially increased the compressibility of the lattice structures.

Effect of Sm + Er and Heat Treatment on As-Cast Microstructure and Mechanical Properties of 7055 Aluminum Alloy.

The 7055 aluminum alloy is an ultra-high strength aluminum alloy, which is widely used in the aerospace field and new energy automobile manufacturing industry. As it retains high strength, its plastic deformation ability needs to be improved, which limits its application in plastic processing. In this study, the cast grains of the 7055 aluminum alloy were refined by adding Sm + Er, and the proper heat treatment procedure was utilized to further precipitate the rare earth phase in order to increase the alloy's strength and toughness. The grain size, microstructure and phase were characterized by optical microscopes (OMs), scanning electron microscopy-energy spectrum (SEM-EDS) and a XRD diffractometer (XRD). The macroscopic hardness, yield strength and tensile strength of alloy materials were measured by a hardness meter and universal electronic tensile machine. The results showed that the as-cast sample and the heat treatment sample all contained Al10Cu7Sm2 and Al8Cu4Er rare earth phases. But, after heat treatment, the volume percentage of the rare earth phase dramatically increased and the dispersion was more unified. When 0.3 wt.%Sm and 0.1 wt.%Er were added, the grain size could be refined to 53 μm. With the increase in the total content of rare earth elements, the refining effect first increased and then decreased. Under 410 °C solid solution for 2 h + 150 °C and aging for 12 h, the macroscopic hardness, yield strength, tensile strength and elongation of 0.3 wt.%Sm + 0.1 wt.%Er + 7055 as-cast samples were 155.8 HV, 620.5 MPa, 658.1 MPa and 11.90%, respectively. After the addition of Sm and Er elements and heat treatment, the grain refinement effect of 7055 aluminum alloy was obvious and the plastic property was greatly improved under the premise of maintaining its high-strength advantage.

A study on micro‐mechanical deformation behaviour of heat‐treated 20MnMoNi55 steel

AbstractSeveral heat treatment procedures are designed considering critical temperatures of phase transformation evaluated through dilatometric testing of 20MnMoNi55 steel to transform low carbon bainitic as‐received material into ferrite‐martensite dual‐phase steels consisting of varied martensite fractions. A thorough metallographic study correlated with the micro‐hardness of constituent phases ensures morphological characteristics along with its fractional variations in as‐received and dual‐phase steels. The impact of fractional variation in constituent phases on the uniaxial monotonic deformation characteristics of dual‐phase steels has been observed with a correlation study between experimental tensile and finite element simulated results. Therefore, a physical‐based model with a 2‐dimensional representative volume element has been established, addressing actual morphological characteristics obtained from metallographic studies. Moreover, the constitutive flow behaviours of ferrite and martensite are also derived from the dislocation‐based hardening model to address the actual deformation phenomenon. Finally, an inhomogeneous deformation behaviour among constituent phases and localization of plastic strain in ferrite matrix has been observed with von‐Mises stress, and equivalent plastic strain distribution through finite element simulated results. This phenomenon is again confirmed with kernel average misorientation mapping and geometrically necessary dislocation density evaluation through electron backscattered diffraction of tensile samples subjected to different degrees of plastic strain.

Utilization of ANOVA analysis in identifying the effects of various parameters on the corrosion behaviour of 7021 Al alloys in simulated RED SEA conditions

In the statistical examination of experimental results, the analysis of variance, or ANOVA, is one of the most important tools to use when the number of results is quite high. The investigation of the effects of various parameters such as concentrations of electrolyte, types of electrolytes, heat treatment procedures including solution treatments and artificial aging, and pre-treatment conditions on the corrosion behaviour of engineering materials is one of the many steps involved in corrosion behaviour analysis. The result of a one-way ANOVA shows the effect that one parameter has on the other, but the results of a two-way or three-way ANOVA determine the synergistic effect that one, two, or more parameters have on the outcome variable. This study is focused on determining the effect that various parameters, such as the type of heat treatment in relation to the temperature of treatment, modes of cooling procedures, and variations in hardness, have on the corrosion behaviour of the 7021 Al alloy in environments that are modelled in terms of the red sea conditions. It has been discovered that subjecting the alloy to an artificial aging process has a significant impact on the way it behaves in terms of corrosion.

Lithium ion conductivity, crystallization tendency, and microstructural evolution of LiZrxTi2-x(PO4)3 NASICON glass-ceramics (x = 0 - 0.4)

In this research, NASICON type (LiZrXTi2-X(PO4)3) glass-ceramics were fabricated (x = 0.1, 0.2, 0.3, 0.4). Lithium-ion conductivity along with the crystallization tendency and microstructural features were examined in this regard. Parent glasses obtained through melt quenching were converted to the glass-ceramic specimens after one-step heat treatment procedure. The resultant glass-ceramics were deeply explored by means of different techniques including scanning electron microscope, differential thermal analysis, X-ray diffractometry, and ionic conductivity measurements. According to the obtained results, presence of Zr4+ ions in the glass network and its gradual increase caused the enhanced crystallization temperature as well as declined crystallinity and microstructure coarsening. In all studied glass-ceramics, LiT2(PO4)3 solid solution was the dominant crystalline phase and Zr4+ ions partly substituted in the structure of this crystalline phase. Moreover, presence of Zr4+ ions in the glass composition resulted in diminished lithium-ion conductivity of corresponded glass-ceramics at ambient temperature. Consequently, total conductivity of specimen with the highest level of ZrO2 (x = 0.4) was measured to be 0.78 x 10-5 Scm-1, being considerably less than ionic conductivity of the base (x = 0) glass-ceramic (3.04 x 10-5 Scm-1). It seems that less crystallinity of ZrO2 containing glass-ceramics decreases required connectivity between the lithium-ion free paths and is responsible for the diminished ionic conductivity of these specimens.

Recrystallization effect on surface passivation of Hastelloy X alloy fabricated by laser powder bed fusion

Post-heat treatment is generally adopted in the additive manufacturing field due to its alleviation of high residual stress and modification of rapid-solidified multilevel heterogeneous microstructure, and the related performance of the heat-treated counterparts calls for a systemic investigation to build a criterion of the heat treatment procedure. In this work, we focus on the heat treatment effects on the recrystallization of the Hastelloy X alloy produced by the laser powder bed fusion (LPBF) method, and the related surface passivation of the heat-treated counterparts is meticulously assessed as well. Results show that the multilevel heterostructure for LPBF Hastelloy X alloy consists of sub-micro dislocation cell substructures with Cr/Mo elemental segregation, fine columnar grains, and periodically-distributed molten pools. After heat treatment, partially and fully recrystallized structures for LPBF Hastelloy X alloys were achieved at 1100 and 1200 °C for 1 h, respectively. Furthermore, the as-built LPBF Hastelloy X alloy shows superior corrosion resistance while the heat-treated one (1100 °C) exhibits the worst in the borate buffer solution. The growth of passive film exhibited a highly linear correlation with the nucleation process controlled by diffusion, and high dislocation density and low angle grain boundary decreased the diffusion coefficient of cation vacancies, augmenting the nucleation sites of the passive film and enhancing its growth rate. Moreover, the micro-galvanic effect resulting from the partially recrystallized microstructure actively facilitated the formation of inhomogeneous porous passive films, leading to the worst corrosion resistance.

Semi-supervised deep transfer learning for the microstructure recognition in the high-throughput characterization of nickel-based superalloys

Nickel-based superalloys, owing to their superior resistance against mechanical and chemical degradation, have been widely applied in the aerospace, turbine engine, nuclear reactor, and chemical industries. The microstructure recognition plays a key role in the characterization and design of new superalloys. Although deep learning techniques have achieved satisfactory performance in the microstructure recognition, these methods usually suffer from generalization when the alloy composition or process changed, especially in the high-throughput experiments. In this paper, we propose a semi-supervised deep transfer learning framework for the microstructure recognition of nickel-based superalloys with different compositions and heat treatment procedures. To be specific, we achieve the knowledge transfer of recognition models from one condition (source domain) to another (target domain) by feature distribution alignment (FDA). To avoid the over-fitting, we design a dynamic alignment strategy to achieve the feature alignment based on the label guidance. Additionally, we effectively utilize the unlabeled samples in the target domain and achieve the distribution alignment between the two domains by adversarial training. The experimental results show that our method is superior to the commonly used deep transfer learning methods. In spite of few labeled samples, it can also approach the satisfactory accuracy. Codes are available at: https://github.com/yangchuanwu/FDA.

Chromaticity-Tunable All-Inorganic Color Converters Fabricated by 3D Printing for Modular Plant Growth Lighting Devices

In photopolymerization-induced 3D printing of glass and ceramics, the demand for a slurry that has high photosensitivity, low viscosity, and high solid content leads to a limited selection of suspended particles. To this end, ultraviolet-assisted direct ink writing (UV-DIW) is proposed as a new 3D printing compatible approach. A curable UV ink is synthesized, which overcomes the material limitation. Benefiting from the advantage of the UV-DIW process, CaAlSiN3:Eu2+/BaMgAl10O17:Eu2+ phosphors in glass (CASN/BAM-PiG) as chromaticity-tunable specially shaped all-inorganic color converters are prepared for plant growth lighting using an optimized heat treatment procedure. Size compatible dome-type and flat-type CaAlSiN3:Eu2+ phosphors in glass (CASN-PiG) are constructed in batches. The manufactured dome-type PiG-based light-emitting diodes (LEDs) exhibit better heat dissipation capacity and a larger divergence angle. The advantage of CASN/BAM-PiG in plant growth lighting is confirmed by the high degree of resemblance between the emission spectra of CASN/BAM-PiG and the absorption spectra of carotenoid and chlorophyll. A series of dome-type CASN/BAM-PiG based LEDs with selective region doping are constructed, which can weaken reabsorption effects and scientifically match the requirements of different plants. The excellent color-tunable ability and high degree of spectral resemblance indicate the superiority of the proposed UV-DIW process in all-inorganic CASN/BAM-PiG color converters for intelligent agricultural lighting.

THE EFFECT OF QUENCHING TREATMENT BY VARIATION OF COOLING MEDIA (WATER, USED OIL, COOKING OIL) ON EGREK HARDNESS

Oil palm is harvested using the egrek agricultural implement. Using water for gilding, the blacksmith's egrek is toughened. The egrek that blacksmiths manufacture frequently is tarnished and worn out. Oil palm growers are consequently forced to swap them out for new ones.The product's economic value decreases as a result. Because of incorrect heat treatment, the cause of egrek is easily destroyed. The goal of this research was to ascertain how the heat treatment procedure affected how hard the quenched egrek was. Rockwell hardness test results. The hardness of the quenched egrek can be affected by changes in the water chilling medium, utilized oil, or cooking oil, according to statistical data processing using ANOVA and supported by the use of design expert software. Having an average carbon content of 0.379%, the raw material is made up of medium carbon steel. According to the results of the hardness test, the cooking oil cooling medium quenching process, which occurs at an average temperature of 800°C and a hardness value of 50.1 HRC, produces the average minimum hardness value, while the water cooling medium, which has an average hardness value of 60.4 HRC, produces the average maximum hardness value. The percentage contribution calculation reveals that used oil and cooking oil are the cooling media that have the greatest impact on the hardness level, with used oil contributing 96.37% and cooking oil contributing 96.61%, respectively, while water cooling media contribute 88.41%.

High-Temperature Behaviour of Zn-Based Galvannealed Coatings on Steel.

The potential of using a Zn-based, hot-dip coating to limit steel scale formation was investigated. The phase evolution within a pure Zn and a Zn0.1Al coating on a medium-carbon (0.5 wt.% C, 0.25 wt.% Si) steel sheet during a series of heat treatment steps was investigated. Such Zn-based coatings react with the steel substrate depending on the actual heat treatment condition. A series of expected intermetallic phases was observed via SEM/EDX and XRD techniques, such as ζ, δ and Γ phases along the η(Zn) phase. The η(Zn) phase was transformed to mainly δ and Γ phases during galvannealing (500 °C). The rapid quenching from 850 °C enabled the formation of the supersaturated α-(Fe) solid solution with increased Zn content. A continuous, intact, ~20 µm thick coating was observed after the final step of the heat treatment procedure, while signs of liquid metal embrittlement (LME) were not observed near the coating/steel interface. This will ensure reliable protection against heavy scale formation on heat-treated steel parts.

Mixed-Phase Fe2O3 Derived from Natural Hematite Ores/C3N4 Z-Scheme Photocatalyst for Ofloxacin Removal

Abatement of pharmaceutical pollutants from aquatic systems is crucial but remains a challenge. Semiconductor photocatalysis has emerged as an eco-friendly technique that utilizes renewable solar energy to address environmental issues. Naturally occurring and earth abundant hematite (Fe2O3) ores can be incorporated as a suitable component of a photocatalyst. Herein, Brazilian hematite was partially phase transformed into heterophase (consisting of α/γ-Fe2O3) by a simple single-stage heat treatment procedure. The method of synthesis was simple and economical, requiring neither solvents nor concentrated acids. The existence of α/γ-phases in the produced Fe2O3 (FO) was confirmed by X-ray diffraction analysis. After the phase transformation process, the local structure surrounding the Fe atoms was varied as evidenced from X-ray absorption spectroscopy. Given its low toxicity, narrow bandgap, and chemical stability, FO was further combined with g-C3N4 (CN) to form composites. The optical properties of the synthesized CNFO composites confirmed that the visible light harvesting ability of CN was enhanced after combining with FO. The CN sheets were grown uniformly over the surface of FO as evidenced from scanning electron microscopy. The prepared composites could degrade an aqueous solution of ofloxacin (OFX, 10 ppm) under visible light with remarkable efficacy. The performance of CNFO-5% was 4.8 times higher when compared to pure CN. The initial rate constant value for the photocatalytic degradation of OFX by CNFO-5% was 0.1271 min−1. The catalyst was stable even after five repeated cycles of photodegradation. The photoluminescence spectra and electrochemical measurements confirmed the efficient separation and transfer of the photogenerated charges across their interface. The investigations on different scavengers demonstrated that superoxide anion radicals and holes played a significant role in the degradation of OFX. The mechanism for the charge transfer was proposed to be a Z-scheme heterojunction. These results point to the potential of using inexpensive, abundant, and recyclable natural hematite ores as state-of-the-art photocatalysts for the elimination of pharmaceuticals in wastewater.

Experimental Investigation of Application Taguchi Method to Optimize Heat Treatment Parameters Using Nanofluids of AISI 52100 Steel

The present work describes a heat treatment procedure using nanofluids as quenchants for (AISI 52100 Steel) via the Taguchi method to optimize process parameters. The nanofluids have been prepared from nanoparticles (SiO2, SiC and Fe2O3) and base media consist of distilled water, toluene and ethylene glycol of volume concentrations of 0.02, 0.04 and 0.06 %. The present investigation considers hardness and wear rate as optimization criteria. The experimental variables that were selected for this study are: (austenitizing and tempering temperature), (type and volume fraction of nanoparticles) and (base media). They represent significant factors that influence on these optimization criteria. (AL18 orthogonal array), (analysis of variances (ANOVA)) and (signal/noise ratio (S/N)) were applied by means of (Minitab 18) software to examine the performance characteristics of the process parameters. The analysis of (S/N) ratio shows that the most significant parameters that give the optimum heat treatment conditions for hardness of the examined steel (AISI 52100) are: (austenitizing temperature of 800°C), (distilled water as a type of base media) and (tempering temperature of 180°C), in addition to (Fe2O3 as a nanoparticles type) and finally (nanoparticles volume fraction of 0.06%). In contrast, for the wear rate, they were: (austenitizing temperature of 800°C), type of base media (distilled water), tempering temperature of (180°C), and volume fraction of nanoparticles (0.06%) tempering. Finally, nanoparticles type (Fe2O3) is the most significant parameter for hardness and wear rate. ANOVA, exhibited that the austenitizing temperature has major effect on producing high values of hardness and wear rate for the AISI 52100 Steel.

Flexible, breathable, and reinforced ultra-thin Cu/PLLA porous-fibrous membranes for thermal management and electromagnetic interference shielding

Electromagnetic interference shielding and thermal management by wearable devices show great potential in emerging digital healthcare. Conventional metal films implementing the functions must sacrifice either flexibility or permeability, which is far from optimal in practical applications. In this work, an ultra-thin (15 µm), flexible, and porous Cu/PLLA fibrous membrane is developed by depositing copper particles on the polymer substrate. With novel acetone & heat treatment procedure, the membrane is considerably stronger while maintaining the porous fibre structure. Its fantastic breathability and super high electrical conductivity (9471.8130 S/cm) enable the composites to have fast electrical heating characteristics and excellent thermal conductivity for effective thermal management. Meanwhile, the porous polymer substrate structure greatly enhances the diffusion of conductive substances and increases the electromagnetic interference shielding effectiveness of the membranes (7797.98 dB cm2/g at the H band and 8072.73 dB cm2/g at the Ku band respectively). The composites present high flexibility, breathability, and strength with the functions of thermal management and electromagnetic shielding, showing great potential for future portable electronic devices and wearable integrated garments.

Superior thermal stability and strength of additively manufactured CoCrFeMnNi high-entropy alloy via NbC decorated sub-micro dislocation cells

Additively manufactured metallic alloys often exhibit mesoscale chemical-structural heterogeneity due to the inherent melting and solidification processes. The resulting metastable microstructural constituents, ranging from dislocation cells to non-equilibrium precipitates, significantly impact either the thermal stability in the subsequent heat treatment procedure or the load-bearing performance at elevated temperatures for the additively manufactured alloys. This study focuses on NbC-added CoCrFeMnNi high-entropy alloys (NbC-HEAs) that were prepared using laser beam powder bed fusion (PBF-LB) with ball-milled mixed powders (5 wt.% NbC nanoparticles). The results showed that PBF-LB HEAs contain sub-micro Mn/Ni-decorated dislocation cells, and the addition of NbC leads to additional Nb segregation at cellular boundaries. After an 800 °C heat treatment, the dislocation density gradually decreased, the cell size increased, and Mn/Ni segregation was reduced for PBF-LB HEAs. In contrast, PBF-LB NbC-HEAs demonstrated superior thermal stability due to the formation of NbC precipitates at cellular boundaries, resulting in exceptional yield strength.