High-temperature Annealing Research Articles

Amine-releasable Mediator In situ Repair Perovskites for Efficient and Stable Perovskite Solar Cells.

Residual lead iodide (PbI2) is deemed to a double-edged sword in perovskite film as small amounts of PbI2 are beneficial to the photovoltaic performance, but excessive will cause degradation of photovoltaic performance and stability. Herein, an in situ repair strategy has been developed by introducing amine-releasable mediator (methylammonium pyridine-2-carboxylic, MAPyA) to eliminate over-residual PbI2 and regulate the crystal quality of perovskite film. Notably, MAPyA can be partially decomposed into methylamine (MA) gas and pyridine-2-carboxylic (PyA) during high temperature annealing. The released MA can locally form liquid intermediate phase, facilitating the reconstruction of perovskite microcrystals and residual PbI2. Moreover, the leftover PyA is confirmed to effectively passivate the uncoordinated lead ions in final perovskite film. Based upon this, superior perovskite film with optimized crystal structure and holistic negligible PbI2 is acquired. The assembled device realizes outstanding efficiency of 24.06 %, and exhibits a remarkable operational stability that maintaining 87 % of its origin efficiency after continuous illumination for 1480 h. And the unencapsulated MAPyA-treated devices present significant uplift in humidity stability (maintaining ~93 % of the initial efficiency over 1500 h, 50-60 % relative humidity). Furthermore, the further optimization of this strategy with nanoimprint technology proves its superiority in the amplificative preparation for perovskite films.

Amine‐releasable Mediator In situ Repair Perovskites for Efficient and Stable Perovskite Solar Cells

AbstractResidual lead iodide (PbI2) is deemed to a double‐edged sword in perovskite film as small amounts of PbI2 are beneficial to the photovoltaic performance, but excessive will cause degradation of photovoltaic performance and stability. Herein, an in situ repair strategy has been developed by introducing amine‐releasable mediator (methylammonium pyridine‐2‐carboxylic, MAPyA) to eliminate over‐residual PbI2 and regulate the crystal quality of perovskite film. Notably, MAPyA can be partially decomposed into methylamine (MA) gas and pyridine‐2‐carboxylic (PyA) during high temperature annealing. The released MA can locally form liquid intermediate phase, facilitating the reconstruction of perovskite microcrystals and residual PbI2. Moreover, the leftover PyA is confirmed to effectively passivate the uncoordinated lead ions in final perovskite film. Based upon this, superior perovskite film with optimized crystal structure and holistic negligible PbI2 is acquired. The assembled device realizes outstanding efficiency of 24.06 %, and exhibits a remarkable operational stability that maintaining 87 % of its origin efficiency after continuous illumination for 1480 h. And the unencapsulated MAPyA‐treated devices present significant uplift in humidity stability (maintaining ~93 % of the initial efficiency over 1500 h, 50–60 % relative humidity). Furthermore, the further optimization of this strategy with nanoimprint technology proves its superiority in the amplificative preparation for perovskite films.

Testing and characterization of high-temperature degradation performance of para-aramid fibres

Para-aramid fibres possess excellent properties, including high modulus, high strength, and high-temperature resistance, making them highly practical and cost-effective reinforcement materials. To further analyse the usage performance of para-aramid fibres under extreme conditions and explore their degradation behaviour and mechanisms at high temperatures, this paper investigates para-aramid fibres through high-temperature annealing. Various tests, including thermogravimetric analysis, infrared spectroscopy, X-ray diffraction, Ubbelohde viscometry, and universal material testing, were employed to analyse changes in the thermal degradation temperature, molecular structure, and mechanical properties of para-aramid fibres. Tests have shown that after high-temperature treatment of para-aramid fibres, different protruding particles and pits appear on the surface of the fibres, and the molecular structure gradually undergoes cleavage and cross-linking. This results in varying degrees of increase in the crystallinity, intrinsic viscosity, and apparent grain size of crystal planes in different directions of the para-aramid fibres with rising temperatures. On the other hand, the degree of orientation, the rate of the second type of lattice distortion, thermal performance, and mechanical properties show a declining trend. The thermal degradation conforms to the kinetics of a second-order reaction.

Highly oriented crystalline si on epitaxial Gd2O3/Si(111) substrate using low-cost Radio Frequency sputtering for Silicon on Insulator application

Silicon-on-Insulator (SOI) technology has been the center of attraction with the advancement in Radio Frequency (RF) technology and the advent of Internet-of-Things due to its low-power operation with reduced parasitic and short-channel effects. However, the state-of-the-art smart-cut method used for the SOI wafer is costly. Alternatively, the notion of using the Si channel layer on epitaxial rare-earth oxide has been proposed. In literature, the existing techniques used to achieve the same, such as Molecular beam Epitaxy or reduced-pressure chemical vapor deposition technique, are either costly or non-high-volume manufacturable. In this context, we propose a method to fabricate the highly oriented crystalline Si(111) channel layer (Top-Si) on an epitaxial Gd2O3/Si(111) virtual substrate (SOXI) utilizing the solid phase epitaxy using the high-volume manufacturing friendly (HVM), low-cost RF magnetron sputtering technique. First, we have shown the multicrystalline Si and epitaxial Gd2O3 layer grown on Si(111) substrate, as confirmed using high-resolution X-ray diffraction (HRXRD) and Transmission Electron Microscopy (TEM). Second, we investigated the impact of rapid thermal annealing at 850 °C on the heterostructure using HRXRD and TEM. It is observed that the high-temperature annealing transforms the Top-Si layer into the highly oriented crystalline Si(111) layer by fusing smaller grains towards larger grains. Hence, we demonstrate a low-cost, HVM-friendly technique for the fabrication of SOXI wafers.

Investigation of Contact Resistivities on APCVD (p) Poly-Si for Fired Passivating Contacts

We investigate the properties of boron doped polycrystalline Si (poly-Si) deposited by atmospheric pressure chemical vapor deposition (APCVD) applied to fired passivating contacts (FPC), where no high temperature annealing takes place apart from the contact firing step. X-ray diffraction measurements show that the APCVD poly-Si is already partially crystallized directly after deposition and the crystallite size further increases during firing. Without metallization an implied open circuit voltage of up to 719 mV is achieved. Screen-printing with an Ag paste yields minimal contact resistivities of down to 1 mΩcm² at high firing temperatures. Furthermore, thicker poly-Si layers, accomplished by driving the same wafer multiple times through the APCVD system, generally correspond to lower contact resistivities for the FPC. This can partly be explained by an increasing crystallinity and conductivity during deposition due to the higher thermal budget during deposition for thicker layers as well as by a larger contact area for thicker poly-Si layers. Scanning electron microscopy on sample cross-sections show that almost the entire poly-Si layer is covered with Ag crystallites at high firing temperatures. For lower temperatures a lower density of Ag crystallites in the poly-Si is visible. Both findings hold for planar and textured surfaces.

DIAMONDS OF THE PIONERSKAYA PIPE — MORPHOLOGY, SPECTROSCOPY, PROSPECTS

Diamonds of the Pioneer pipe, compared with the Arkhangelsk and Karpinsky-1 pipes, formed at higher temperatures, as well as were in such conditions for a longer time (experienced high-temperature annealing). Pionerskaya pipe has slightly lower productivity, but higher quality of diamonds, especially in large size classes, it also has a higher proportion of octahedra and highly transparent crystals that are not subject to accessory etching.

Annealing effect on deuterium retention in W-Cr-Y alloy

Deuterium (D) trapping in the W-11.4Cr-0.6Y alloy manufactured by field assisted sintering technology (FAST) and pre-annealed at temperatures of 1050, 1250, 1473 K was studied by in-situ thermal desorption spectroscopy (TDS). D incorporation in W-11.4Cr-0.6Y alloy was carried out by irradiation with deuterium ions (670 eV/D+) to a fluence of 5 × 1019 D/m2. The change in Cr concentration in the bulk of the W-Cr-Y alloy was studied using energy dispersive spectroscopy (EDS). The elemental composition on the surface of alloy samples before and after annealing was investigated using low energy ion scattering spectroscopy (LEIS). The Cr concentration increases on the surface of alloy sample during annealing at 1000 and 1050 K due to intensive Cr segregation, while it decreases at temperatures of 1250 K and above by dominant Cr sublimation. Pre-annealing of W-Cr-Y alloy at 1050 K leads to a decrease in the D trapping in the alloy which is connected with an increase in the Cr concentration on the surface. At high annealing temperatures of 1250 K and above, the appearance of new phases and decomposition-induced grain refinement leads to new types of defects with high binding energy for D.

On the effect of high-temperature annealing on the microstructure and mechanical properties of a hot-rolled 90W7Ni3Fe tungsten heavy alloy

We previously reported on commercial 90W7Ni3Fe (90W, wt. %) tungsten heavy alloy (WHA) plates, which were hot-rolled (HR) at 900 °C to thickness reductions of 62 %, 74 % and 87 % (62R, 74R and 87R), and an as-sintered (AS) 90W plate. In contrast to 62R and 74R, the 87R WHA was given a final processing heat treatment (HT) at 1400 °C/3 h (87RHT). HR deforms the WHA microstructure into an anisotropic brick (W) and mortar (NiWFe ductile phase) composite architecture. Fracture toughness tests showed that after the processing HT, the 87RHT plate experienced stable crack growth, with an average elastic-plastic fracture toughness of KJm ≈ 116 ± 20 MPa√m, somewhat higher than the AS KJm ≈ 97 ± 18 MPa√m. This compares to elastic fracture toughness of KIm ≈ 35 ± 2 MPa√m in the 62R and 74R conditions, absent a final HT. Here, we report on the microstructures and mechanical properties of four new WHA conditions following an additional recovery anneal at 1300 °C/24 h. The recovery anneal results in similar average elastic-plastic toughness of KJm ≈ 125 ± 12 MPa√m in all four processing conditions, which is slightly higher than for the AS and 87RHT WHA, and much higher than for the 62R and 74R WHA, without the processing HT. Scanning electron microscopy and electron backscatter diffraction showed that the final 1300 °C/24 h anneal recovers the hardening microstructures in the 62R and 74R WHA. The lower strength promotes crack tip microcracking dilatational shielding, which increases the WHA fracture toughness. The implications of these results to the design of WHA are briefly discussed.

Light-emitting diodes with Ge(Si) nanoislands embedded in photonic crystals

Room temperature lateral p+–i–n+ light-emitting diodes (LEDs) with photonic crystals embedded in the i-region were fabricated on structures with Ge(Si) self-assembled islands and their optical properties were investigated. The use of preliminary amorphization and solid phase epitaxy of the implanted p+ and n+ contact regions made it possible to reduce the impurity activation temperature from 800 °С–1100 °С to 600 °С, which corresponds to the growth temperature of Ge(Si) islands. This resulted in a significant reduction of the detrimental effect of the high-temperature annealing used for diode formation on the intensity and spectral position of the luminescence signal from the islands. It was shown that significant enhancement (more than an order of magnitude) of room temperature electroluminescence of Ge(Si) islands in the spectral range of 1.3–1.55 μm can be achieved due to their interaction with different modes of the photonic crystals. The measured radiation power of the obtained diodes in the spectral range of 1.3–1.55 μm exceeds 50 pW at a pump current of 8 mA, which is an order of magnitude higher than the previously achieved values for micro-LEDs with Ge(Si) nanoislands. The obtained results open up new possibilities for the realization of silicon-based light emitting devices operating at telecommunication wavelengths.

Enhancement of the Silicon Nanocrystals’ Electronic Structure within a Silicon Carbide Matrix

Using plasma-enhanced chemical vapor deposition (PECVD), a mixed gas of silane (SiH4) and methane (CH4) was diluted with hydrogen (H2) to produce thin films of silicon nanocrystals embedded in a silicon carbide (SiC) matrix. This method prevents the co-deposition of SiH and SiC from high-temperature annealing procedures. This study experimentally explores the improvement of the electronic structure by adjusting two processing parameters according to classical nucleation theory (ratio of SiH4 to CH4 and working gas pressure). The deposited films were examined using ellipsometry spectroscopy, X-ray diffraction, scanning electron microscopy, atomic force microscopy, and photoluminescence to determine grain size, crystal volume fraction, topography, and bond configurations. The results show that increasing the working gas pressure can increase the density of SiC, while increasing the ratio of SiH4 to CH4 can only produce larger grain sizes. This is consistent with how SiC works and grows. Without using a high-temperature annealing procedure, this technique can improve the electrical structure of SiC contained in the SiC matrix formed by PECVD.

High‐Temperature Annealing of Si‐Doped AlGaN

This study explores the impact of Si doping on the material properties of high‐temperature annealed (HTA) Al0.71Ga0.29N layers, which are grown on AlN/sapphire templates. The AlGaN layers are doped with Si by applying different IV/III ratios during epitaxial growth and compared to undoped Al0.71Ga0.29N. Before HTA, the threading dislocation density (TDD) for all samples is about 6.0 × 109 cm−2. After HTA, the Si‐doped AlGaN grown with the highest IV/III ratio of 3.6 × 104shows the lowest TDD of 1.2 × 109 cm−2. Secondary ion mass spectrometry depth profiles reveal an accelerated Ga diffusion from the doped AlGaN into the AlN buffer layer compared to undoped AlGaN. This suggests that the Ga diffusion process is mediated by Si diffusion. Consequently, the Ga diffusion leads to a decrease in the Ga mole fraction of annealed Si‐doped AlGaN. Furthermore, strain relaxation is higher for the Si‐doped AlGaN than for the undoped AlGaN, before and after HTA. The results from this study suggest that Si doping can be a new promising approach in enhancing the quality of HTA‐AlGaN as a useful template for the growth of UV LED heterostructures.

Microstructural and Textural Evolution of Cold-Drawn Mg-Gd Wires during Annealing Treatment.

In addition to cold drawing, the process of annealing is also essential in the preparation of Mg-4.7 wt%Gd (G4.7) alloy wires. The effect of annealing treatment on the recrystallized microstructure and texture of cold-drawn G4.7 wires was investigated. The results demonstrate that the uniformity and regularity of the recrystallized grains, as well as the annealing texture, impact the follow-up cold drawing performance. When the as-drawn G4.7 wires were annealed at 375 °C, the recrystallized grains were refined, accompanied by uniformity and regularity. Accordingly, the G4.7 wire had a good subsequent drawing deformability, with a maximum accumulative true strain (ATS) of 144%. Additionally, the evolution of the microstructure was consistent with the evolution of the texture. While annealing at a lower temperature (325 °C), the {0002} basal texture of the G4.7 wire was weak, forming the main texture component <101¯0>//DD (the drawing direction). With the increase in temperature, the basal texture was gradually strengthened and the texture component transformed from <101¯0>//DD to a recrystallized texture based on <112¯0>//DD. Even under high-temperature annealing, the G4.7 wire was still affected by the cold-drawn deformation texture and could not fully recover to the as-extruded texture, thus causing a decrease in the subsequent drawing performance.

Evaluation of graphene microstructural and optical properties affected by high-temperature annealing and rapid cooling in a nitrogen-rich environment

Annealing at high temperatures holds the possibility of concentrating defects in the graphene. Moreover, a significant increase in annealing temperature destroys the surface properties. In this work, the reduced graphene oxide (RGO) was prepared by an electrochemical technique with a high voltage ([Formula: see text][Formula: see text]V, [Formula: see text][Formula: see text]A). Then, the potential effects of impact on thermal treatment in a temperature range of 800–1000∘C in nitrogen-rich environment on the microstructure and surface morphology, thermal stability, phase and crystallinity, structural disorder, absorption properties, and optical properties of RGO for optoelectronic applications were investigated. In addition, a link was established between the estimated crystallite sizes determined by X-ray diffraction (XRD) and Raman data. The microstructural data indicate that the annealing temperature has a significant effect on the microstructure and carbon–oxygen (C/O) ratio. The C/O ratio increases as a function of annealing temperature. Atomic force microscope (AFM) analysis revealed that the root mean square (RMS) roughness of annealed RGO increases with increasing annealing temperature indicating an increase in crystallite size during annealing. Since most organic compounds were removed from the surface of the annealed RGO, oxygen functionalities appear to have minimal effect on the thermal stability of RGO. The size of graphene crystallites increases with annealing temperature, as shown by XRD observations. The crystalline structure was restored by annealing. The Raman results show that in the “low” defect density zone, the [Formula: see text] values increase because a larger defect density causes a stronger elastic scattering. UV–Vis spectroscopy shows that the absorption of RGO is not affected by annealing temperatures between 800∘C and 900∘C. The optical bandgap of annealed RGOs decreases from 4.08 to 3.72[Formula: see text]eV upon annealing in the temperature range of 800–1000∘C.

Effect of Gradient Heat Conduction on Secondary Recrystallization of Grain-Oriented Silicon Steel

The grain-oriented silicon steels were subjected to gradient heat conduction during high-temperature annealing by using thermal insulation cotton. The macrostructures of samples subjected to circumferential gradient heat conduction showed a “petal-like” morphology with peripheral columnar grains and central equiaxed grains, while samples subjected to transverse gradient heat conduction showed a morphology with approximately 50% columnar grains and 50% equiaxed grains. The grain orientations, magnetic domains as well as magnetic properties in different regions were detected. Results showed that the magnetic induction intensity of cylindrical grains was better than that of equiaxed grains while the iron loss was worse, which indicated that a fast heating rate during high-temperature annealing was conducive to the accuracy of Goss grains. The magnetic domains in columnar grains were wider than the equiaxed grains, which resulted in poorer iron loss. A theory of the competitive growth among secondary Goss grains was proposed. Under the condition of gradient heat conduction, once the Goss grains with the fastest heat conduction grew up abnormally, they would compete with other Goss grains which were supposed to survive in traditional processes and swallow up them until adjacent to the secondary equiaxed grains which were later developed.

Realization of tunable-performance in atomic layer deposited Hf-doped In2O3 thin film transistor via oxygen vacancy modulation.

Due to the limitation of inherent ultra-high electron concentration, the electrical properties of In2O3 resemble those of conductors rather than semiconductors prior to special treatment. In this study, the effect of various annealing treatments on the microstructure, optical properties, and oxygen vacancies of the films and transistors is systematically investigated. Our finding reveals a progressive crystallization trend in the films with increasing annealing temperature. In addition, a higher annealing temperature is also associated with the reduction in the concentration of oxygen vacancies, as well as an elevation in both optical transmittance and optical bandgap. Furthermore, with the implementation of annealing process, the devices gradually transform from no pronounced gate control to exhibit with excellent gate control and electrical performances. The atomic layer deposited Hf-doped In2O3 thin film transistor annealed at 250 °C exhibits optimal electrical properties, with a field-effect mobility of 18.65cm2V-1s-1, a subthreshold swing of 0.18 V/dec, and an Ion/Ioff ratio of 2.76 × 106. The results indicate that the impact of varying annealing temperatures can be attributed to the modulation of oxygen vacancies within the films. This work serves as a complementary study for the existing post-treatment of oxide films and provides a reliable reference for utilization of the annealing process in practical applications.

Magnetic properties and magnetocaloric effect of DyCo9Si4

Polycrystalline samples of DyCo9Si4 with the tetragonal LaFe9Si4-type structure have been synthesized by arc melting and high-temperature annealing. Results of the magnetization M and specific heat Cp measurements show the existence of two magnetic anomalies at TC = 40 K and Tm = 20 K. The transition at TC = 40 K is attributed to the ferromagnetic transition of the Co sublattice. The magnetic moments of Dy3+ appear to align gradually below TC, and almost fixed below Tm, at which a broad maximum in Cp has been observed. Field-dependent M at T = 2 K up to H = 7 T suggested that the magnetic moment of Dy3+ is coupled antiferromagnetically with those of Co, forming a ferrimagnetic structure. Magnetization measurements up to 50 T at low temperatures using a pulse magnet demonstrated a spin-flip transition around H = 20 T, above which the magnetic moments of Co and Dy are in parallel. The spin-flip transition becomes broad with increasing temperature but still remains at TC = 40 K, indicating a strong antiparallel coupling between Co and Dy moments even in the paramagnetic state. The magnetocaloric effect was evaluated from Cp and M, and also from the sample-temperature variation in the quasi-adiabatic process with the pulsed magnetic field. The maximum entropy change for the field change from 5 to 0 T was observed at around T = Tm with the value ΔS = 5 J/kg K. The maximum temperature of ΔS shifts to higher temperatures in high magnetic fields, resulting in the large value of ΔS = 24 J/kg K at T ∼ TC by the field change from 50 to 0 T. The present results demonstrate that the pulsed-field measurement is a powerful method to evaluate the magnetocaloric effect of materials.

Site-selective sulfur anchoring produces sintering-resistant intermetallic ORR electrocatalysts for membrane electrode assemblies

Intermetallic compounds are emerging as promising oxygen reduction reaction (ORR) catalysts for fuel cells due to their typically higher activity and durability compared to disordered alloys. However, the preparation of intermetallic catalysts often requires high-temperature annealing, which unfortunately leads to adverse sintering of the metal nanoparticles. Herein, we develop a scalable site-selective sulfur anchoring strategy that effectively suppresses alloy sintering, ensuring the formation of efficient intermetallic electrocatalysts with small sizes and high ordering degrees. The alloy-support interactions are precisely modulated by selectively modifying the alloy-support interfaces with oxidized sulfur species, thus simultaneously blocking both the nanoparticle migration and Oswald ripening pathways for sintering. Using this strategy, sub-5 nm PtCo intermetallic electrocatalysts enclosed by two atomic layers of Pt shells have been successfully prepared even at a metal loading higher than 30 wt%. The intermetallic catalysts exhibit excellent ORR performances in both rotating disk electrode and membrane electrode assembly conditions with a mass activity of 1.28 A mgPt−1 at 0.9 V (vs. RHE) and a power density of 1.0 W cm−2 at a current density of 1.5 A cm−2. The improved performances result from the enhanced Pt-Co electronic interactions and compressive surface strain generated by the highly ordering structure, while the atomic Pt shells prevent the dissolution of Co under highly acidic conditions. This work provides new insights to inhibit the sintering of nanoalloys and would promote the scalable synthesis and applications of platinum-based intermetallic catalysts.

Optical activation of implanted lanthanoid ions in aluminum nitride semiconductors by high temperature annealing

Lanthanoid (Ln)-doped aluminum nitride (AlN) semiconductors are one candidate for optoelectric devices and single photon sources, although their optical properties are less understood. We clarify the room temperature optical properties of Ln ion implanted single crystal AlN semiconductors and their changes upon thermal annealing by up to 1700 °C. Photoluminescence (PL), cathodoluminescence (CL), and time-resolved PL for praseodymium (Pr), europium (Eu), and neodymium (Nd) ion implanted AlN are analyzed. Recovery of implantation induced damages and thermal diffusion of implanted Ln ions by thermal annealing are also investigated. Our systematic studies reveal that there is a trade-off between optical activation of implanted Ln ions due to recovery of implantation damage and deactivation (quenching) due to complex formation and aggregation of Ln ions. The PL intensity of implanted Pr ions increases with increasing annealing temperature in the case of high-dose implantation (above 1020 cm-3), whereas it rather decreases in the case of low-dose implantation (below 4 × 1019 cm-3). However, the PL intensity is significantly reduced after annealing at 1700 °C in both cases, indicating that the quenching factor is dominant in this temperature range.

Enhancing Performance and Stability of Sn-Pb Perovskite Solar Cells with Oriented Phenyl-C61-Butyric Acid Methyl Ester Layer via High-Temperature Annealing.

Phenyl-C61-butyric acid methyl ester (PCBM) can be used as a passivation material in perovskite solar cells (PeSCs) in order to reduce the trap site of the perovskite. Here, we show that a thick PCBM layer can form a smoother surface on the SnO2 substrate, improving the grain size and reducing the microstrain of the perovskite. High-temperature annealing treatment of PCBM layer not only increases its solvent resistance to perovskite precursor or antisolvent, but also enhances its molecular alignment, resulting in improved conductivity as an electron transport layer. High-temperature annealed PCBM (HT-PCBM) effectively minimizes trap-assisted nonradiative recombination by reducing trap density in perovskite and improving the electrical properties at the interface between SnO2 and perovskite layers. This HT-PCBM process significantly enhances the performance of the PeSCs, including the open-circuit voltage (VOC) from 0.39 to 0.77 V, fill factor from 52% to 65%, and power conversion efficiency (PCE) from 6.03% to 15.50%, representing substantial improvements compared to devices without PCBM. This PCE is the highest efficiency among conventional (n-i-p) Sn-Pb PeSCs reported to date. Moreover, passivating the trap sites of SnO2 and separating the interface between the Sn-containing perovskite and the substrate effectively have improved the stability of the Sn-Pb perovskite in the n-i-p structure. The optimized best device with HT-PCBM has maintained an efficiency of over 90% for more than 300 h at 85 °C and 5000 h at room temperature in a glovebox atmosphere.

Study on Microstructure and High Temperature Stability of WTaVTiZrx Refractory High Entropy Alloy Prepared by Laser Cladding.

The extremely harsh environment of the high temperature plasma imposes strict requirements on the construction materials of the first wall in a fusion reactor. In this work, a refractory alloy system, WTaVTiZrx, with low activation and high entropy, was theoretically designed based on semi-empirical formula and produced using a laser cladding method. The effects of Zr proportions on the metallographic microstructure, phase composition, and alloy chemistry of a high-entropy alloy cladding layer were investigated using a metallographic microscope, XRD (X-ray diffraction), SEM (scanning electron microscope), and EDS (energy dispersive spectrometer), respectively. The high-entropy alloys have a single-phase BCC structure, and the cladding layers exhibit a typical dendritic microstructure feature. The evolution of microstructure and mechanical properties of the high-entropy alloys, with respect to annealing temperature, was studied to reveal the performance stability of the alloy at a high temperature. The microstructure of the annealed samples at 900 °C for 5-10 h did not show significant changes compared to the as-cast samples, and the microhardness increased to 988.52 HV, which was higher than that of the as-cast samples (725.08 HV). When annealed at 1100 °C for 5 h, the microstructure remained unchanged, and the microhardness increased. However, after annealing for 10 h, black substances appeared in the microstructure, and the microhardness decreased, but it was still higher than the matrix. When annealed at 1200 °C for 5-10 h, the microhardness did not increase significantly compared to the as-cast samples, and after annealing for 10 h, the microhardness was even lower than that of the as-cast samples. The phase of the high entropy alloy did not change significantly after high-temperature annealing, indicating good phase stability at high temperatures. After annealing for 10 h, the microhardness was lower than that of the as-cast samples. The phase of the high entropy alloy remained unchanged after high-temperature annealing, demonstrating good phase stability at high temperatures.