Advanced High-temperature Materials Research Articles

Overcoming intermediate-temperature brittleness via regulating trimodal γʹ structure in a novel multi-principal element alloy

Solving the intermediate-temperature brittleness (ITB) of traditional superalloys and multi-principal element alloys (MPEAs) is a serious challenge. In this paper, a novel MPEA with superior mechanical performance is prepared and successfully overcomes the ITB by simple heat treatment. The effects of different solution treatments on the microstructure and mechanical properties of the alloy are studied. This work shows that the dendrite structure with trimodal γʹ structure is preserved by the subsolvus heat treatment. The heterogeneously distributed trimodal γʹ structure with high volume fraction primary γʹ phases in the interdendritic region effectively prevents the localized slip and enhances the pinning effect of grain boundaries, which inhibits the generation of ITB. The yield strengths of the MPEA with trimodal γʹ structure are 802 ± 17 MPa at 973 K, 814 ± 20.7 MPa at 1023 K and 776 ± 9 MPa at 1073 K, respectively, which are superior than that of most cast superalloys and MPEAs. Moreover, the elongations of the MPEA at 973 K, 1023 K and 1073 K are 10.6 ± 1.3 %, 14.2 ± 1.4 % and 11.0 ± 1.5 %, respectively, which increase by 214.9 %, 510 % and 219.4 %, respectively, compared with the MPEA with uniformly distributed bimodal γʹ structure. Meanwhile, the MPEA shows the best intermediate temperature plasticity (14.2 ± 1.4 %) at 1023 K due to the microstwinning. The scheme of combining MPEAs with the trimodal γʹ structure and microtwinning opens up a new avenue for the development and manufacture of advanced high-temperature structural materials.

Preface

The International Conference on Frontier Materials (ICFM) is initiated and sponsored by International Union of Materials Research Societies (IUMRS) and Advanced Materials Alliance of CAST Members Societies (AMAC), and is co-organized by AMAC and Shanghai University. ICFM is intended to provide an open and exciting forum for researchers and students from materials science and interdisciplinary fields worldwide to present their new and exciting scientific discoveries and innovations in advanced materials. The conference is also designed to offer an international platform for researchers from industrial labs, academic institutes and business to discuss technology development and transfer as well as potential impact of frontier materials on commercial products and industrial applications.The first conference (ICMF2022) was held in May, 2022, by the hybridized approach of accepting both on-site participation and on-line presentation. The second one (ICFM2023) was held in Qingdao International Convention and Exhibition Center (Laoshan), Qingdao, China, Oct. 13-17.The ICMF2023 had 31 symposia which were grouped into seven topical clusters of Energy and Environmental Materials, Advanced Information Materials, Advanced Bio and Bio-Inspired Materials, Advanced Structural Materials, Advanced Functional Materials, Low-Dimensional Materials, and Design, Preparation and Evaluation for Materials. There were nearly 2000 participants attending ICFM2023, and more than 800 scientists and graduate students presented lectures at the parallel sessions of 31 symposia.Eight plenary lectures were presented by world-renowned materials scientists from Asia, Europe, North America and South America. Four specific forums as well as Exhibition on Analysis and Testing Equipment for Materials were held simultaneously. During the conference, the awards of IUMRS-FMA (Frontier Materials Awards) to scientists and students who have made outstanding contribution in the field of Frontier Materials was issued.The Conference papers have been published on four materials related journals and conference proceedings. This conference volume comprises of selected papers mainly in the field of advanced high-temperature structure materials and materials characterization as well as eco-materials.I would like to express my appreciation to the paper referees of Profs. Yongwang Kang, Jiangbo Sha, Jinxia Song, Wenlong Xiao, Xinqing Zhao and Chungen Zhou. Thanks also go to Mrs. Xiaomei Ma for the work of papers’ duplicate checking. And the special appreciation should be given to Mrs. Flora Han and Mr. Jianyun Lin for their miscellaneous work to correct the information about the papers as well as communicate with the authors.Prof. Yafang HanChair of academic Committee of ICFM2023Guest Editor of IOP ICFM2023 ProceedingsList of Organizing Committee is available in this pdf.

Understanding machinability improvements and removal mechanism of ceramic matrix composites during laser-ablating assisted grinding

Ceramic matrix composites are advanced high-temperature materials for aerospace equipment, but they are also known as hard-to-machine materials. This study introduced laser-ablating assisted grinding (LAAG), and analyzed the complex physicochemical transformations of Cf/SiC composites during picosecond-laser ablating, then systematically explored the grinding characteristics, damage behavior, removal mechanism, and abrasive wear. It was revealed that Cf/SiC composites occurred sublimation and oxidation reactions during laser ablating, resulting in SiO2 ablation products with a loose microstructure. Grinding force, temperature and diamond wear remarkably decreased through LAAG. Besides, surface roughness was observably reduced, and the surface morphology of Cf/SiC composites was primarily shown as micro fracture and ductile removal. Furthermore, subsurface damages, including fiber pulling-out and interface debonding, were almost invisible after LAAG. More importantly, the graphite crystallites of carbon fibers near the ground surface became disordered, and an amorphous structure layer was first found on the micro-fractured carbon fibers. The grinding chips generated in LAAG were lamellar-fractured ablated materials rather than uncharacteristically-fractured fiber bundle, indicating the anisotropy removal behavior of Cf/SiC composites was decreased. The machinability improvements were especially significant when the laser scanning interval was small and the scanning direction was perpendicular to the grinding feed direction.

Fabricating physicochemical microstructures with super hydrophilicity on Cf/SiC composites surface via picosecond-laser induced ablation

Cf/SiC composites are advanced high-temperature materials for thermal protection and high-performance braking systems in the aerospace industry. Their surface wettability significantly affects the adhesion properties of the coatings. This study investigated the physical and chemical transformations of Cf/SiC composites during picosecond laser ablation and successfully fabricated micro-structured surfaces with super-hydrophilicity. The findings revealed that three-scale microstructures were formed on Cf/SiC composites after picosecond laser-ablating, which were orderly composed of regular convex plates (20–60 μm), agglomerate ablative products (1–5 μm), and nano particles (100–500 nm). The relative content of O on the laser-ablating surface was mostly>25%, both Si–O and Si–C bonds were found on the Si2p peak of the XPS spectrum. The primary content of the ablative products was crystalline and amorphous SiO2, resulting from the oxidation of the SiC matrix. The initial surface of the Cf/SiC composites was hydrophobic, and its contact angle was 92.7°. Conversely, the laser-ablating surfaces showed significant absorption of water droplets owing to the presence of the hydroxyl group in the amorphous SiO2, and the droplets quickly disappeared from the surface through the micro “tubular channels” caused by carbon fibers sublimating and oxidizing under the high laser temperature. Consequently, the superhydrophilic surfaces of the Cf/SiC composites were obtained via picosecond laser ablation, and the motion of the droplets was closely related to the laser power and scanning distance.

Investigation of Cr content, second phase, and sintering temperature on characteristics of WMoVTiCr refractory high entropy alloys

Refractory high-entropy alloys (RHEAs) are important candidate materials for the design of advanced high-temperature structural materials. In this work, WMoVTiCr RHEAs were synthesized by mechanical alloying. The effect of Cr variation, second phase formation, and sintering temperature on microstructural evolution and mechanical properties of the model alloys were investigated. The results demonstrate that the alloy mainly consists of BCC solid solution phase, Ti-rich oxides, and a trace of Cr-rich phases. The hardness and compressive strength increase significantly with increasing Cr content, which could be ascribed to the dispersion strengthening of second-phase particles and the effect of Cr on the solid solution strengthening. However, the presence of a high amount of Cr content can lead to the reduction of compressive strain due to an increase in the brittle Cr-rich phases. Moreover, a lower sintering temperature caused an incomplete solid solution, thereby reducing material performance.

L12-strengthened heterostructure high-entropy alloys with ultra-high strength over a wide temperature range

The L12-strengthened heterostructure Co40Cr20Ni30Mo2Al4Ti4 (at%) high-entropy alloys (HEAs) exhibit excellent tensile mechanical properties over a wide temperature range. In particular, the yield strength of this alloy reaches up to about 1400 MPa from room temperature to 600 °C, which is much higher than that of most alloys. The reasons for the different mechanical behaviors of this alloy above and below the transformation temperature are discussed. Unique super-lattice stacking faults appear in the high-temperature deformed alloys, which may be attributed to the decrease of super-lattice stacking fault energy when the temperature increases. In the present work, the deformation mechanisms of precipitation-strengthened HEAs at high temperatures are preliminarily explored, which has guiding significance for the development of advanced high-temperature structural materials.

Microstructure Investigation of Mechanically Alloyed 316L-6Al-0.5Y2O3 Oxide Dispersion Strengthened Austenitic Steel Powder

Development of accident-tolerant fuel cladding (ATFC) materials for LWRs (Light Water Reactors) is being intensively carried out in many research centers in the world as the lesson-learned from the Fukushima Daiichi nuclear reactor power plant accident. One of the advanced high temperature materials which is intensively developed is Oxide Dispersion Strengthened (ODS) steel. The strengthened mechanism is generated by homogeneous dispersion of nano-meter sized ceramic oxide particles in the matrix of the steel which is done by mechanical alloying technique so called mechanosynthesis. Synthesis of an austenitic ODS steel powder of 316L with additional element of 6 wt.% aluminum and dispersion of nano-particles of 0.5 wt.% yttrium oxide (yttria: Y2O3) has been done. The aim of the research is to achieve a better performance of 316L austenitic steel as the proven material for power plant at elevated temperature by modified to become ODS austenitic steel with additional of aluminum. Mechanosynthesis was done using High Energy ball Milling (HEM) for 30 hours with BPR (Ball to Powder Ratio) of 10:1. Afterward, the sample was characterized using Scanning Electron Microscope-Energy Dispersive Spectroscope (SEM-EDS) and X-ray Diffraction (XRD) to analyze the microstructure characteristics. The results showed that the alloying between 316L and aluminum powders was formed. Furthermore, crystal grains and the particles of 316L-6Al-0.5Y2O3 steel powder was much smaller than as received 316L austenitic steel and aluminium powders. The particles size and element composition was homogeneously distributed. The results showed that the parameters of mechanical alloying for development of 316L-6Al-0.5Y2O3 ODS austenitic steel powder have reached the optimum condition.

Development of an Oxide Dispersion Strengthened Austenitic Steel Powder with 4% Aluminum Addition

Development of accident-tolerant fuel (ATF) cladding materials for LWR (Light Water Reactors) is being intensively carried out in many research centers in the world as the lesson-learned from the Fukushima Daiichi nuclear reactor power plant accident. One of the advanced high temperature materials which is intensively developed is Oxide Dispersion strengthened (ODS) steel. The strengthened mechanism is generated by homogeneous dispersion of nanometer sized ceramic oxide particles in the matrix of the steel which is done by mechanical alloying technique so called mechanosynthesis. Synthesis of an austenitic ODS steel powder of SS316L with additional element of 4% aluminum and dispersion of nanoparticles of 0.5% yttrium oxide (yttria: Y2O3) has been done. The aim of the research is to achieve a better performance of SS316L steel as the established material for power plant at elevated temperature. Mechanosynthesis was done using High Energy ball Milling (HEM) for 30 hours with BPR (Ball to Powder Ratio) of 10:1. Afterward, the sample was characterized using Scanning Electron Microscope-Energy Dispersive Spectroscope (SEM-EDS) and X-ray diffraction (XRD) to analyze the microstructure characteristics. The results showed that the alloying between SS316L and aluminum powders was formed. Furthermore, crystal grains and the particles of SS316L-4Al-0.5Y2O3 powder was smaller than as received SS316L and aluminum powders.

Design and Characterization of Al-Cr-Nb-Ti-V-Zr High-Entropy Alloys for High-Temperature Applications

High-entropy alloys (HEAs) are a new class of metallic alloys without a principal component. These materials are attractive because of their unique structures and properties, including mechanical ones. Some of HEAs based on refractory metals are considered as advanced high-temperature materials. However, the development of new applicable compositions is complicated by poor understanding of relationships between the chemical and phase composition of HEAs and their effect on mechanical performance. Here we report the results of comprehensive studies of Al-Cr-Nb-Ti-V-Zr high-entropy alloys, particularly AlCrxNbTiVZry (х = 0.00, 0.25, 0.50, 1.00, 1.50 at y = 0 and y = 0.0, 0.25, 0.50, 1.00, 1.50 at x = 0). The strength and ductility of such alloys are shown to have a complex relationship with the composition and order of the parent B2 phase, and the amount and nature of secondary phases (C14 Laves phase and zirconium aluminides). Some of the investigated alloys demonstrate high specific strength at T ≤ 800°C. AlNbTiVZr0.25 alloy also has a stable microstructure and higher creep resistance at 600°C compared to existing creep-resistant alloys. Based on calculations of equilibrium and nonequilibrium phase diagrams by the CALPHAD method, we propose new Al-Cr-Nb-Ti-Zr alloy compositions with unique lamellar eutectic structure composed of the B2 and C14 Laves phases and with enhanced strength properties. The structure/property relationships and high-temperature deformation mechanisms of refractory HEAs with eutectic microstructure are analyzed.

Ultrahigh Temperature Copper-Ceramic Flexible Hybrid Electronics.

Advanced high-temperature materials, metals and ceramics, have been widely sought after for printed flexible electronics under extreme conditions. However, the thermal stability and electronic performance of these materials generally diminish under extreme environments. Additionally, printable electronics typically utilize nanoscale materials, which further exacerbate the problems with oxidation and corrosion at those extreme conditions. Here we report superior thermal and electronic stability of printed copper-flexible ceramic electronics by means of integral hybridization and passivation strategies. High electric conductivity (5.6 MS/m) and thermal stability above 400 °C are achieved in the printed graphene-passivated copper platelet features, while thermal management and stability above 1000 °C of printed electronics can be achieved by using either ultrathin alumina or flexible alumina aerogel sheets. The findings shown here provide a pathway toward printed, extreme electronic applications for harsh service conditions.

Accelerating the discovery of novel γ/γ' Co-based superalloys by probing temperature and alloying effects on the γ' precipitates

The discovery of γ/γ’ Co-based alloys has set off a great wave of searching advanced high-temperature materials. However, finding appropriate compositions to acquire the γ’ phase is a challenge in metallurgical experiments. We first perform a systematic investigation of temperature-induced entropy contributions to the stability of a series of γ’ Co3(Al, TM) (TM = W, Ti, Mo, V, Nb, Ta, Re, Cr) phases. The results suggest that the finite-temperature induced entropy terms govern the thermodynamic stability of Co3(Al, TM). The scale of individual entropy contribution is obviously different for each Co3(Al, TM). The metastability of Co3(Al, TM) is drawn as: W > V > Cr > Nb > Ta > Re > Ti > Mo. We elucidate the foregoing observations and extend to identify one potential γ/γ’ Co-Al-Nb system. Probing into the further quad-alloying effect on stability, it is confirmed that the experimental observed γ’-Co3(Al, Nb, Mo) originates from the stabilization of >4 at.% Mo which weakens the engagement of Nb in electronic hybridizations. Moreover, both >1.5 at.% Ta and > 3.0 at.% Ni promote the stability of Co3(Al, Nb) phase. A further result of mechanical properties shows that Ta enhances the strength of Co3(Al, Nb) while Ni deteriorates it. The disparate impact can be traceable from the electronic hybridization surrounding the nucleus of the solute atom.

Oxidation and Corrosion properties of a Novel Al15Ti30Si30Mo15Ni10 High Entropy Alloy fabricated by Spark Plasma Sintering Technology

The need for new advanced high temperature materials is in high demand. High Entropy Alloy (HEAs) has been described to possess excellent mechanical oxidation and good corrosion resistance properties even far above the ambient temperature. Attempts are made in this research to study the corrosion, oxidation, microhardness and densification properties of Al15Ti30Si30Mo15Ni10 HEA produced by spark plasma sintering (SPS) for high temperature applications. In addition, the effects of SPS temperature (800, 900 and 1000°C) on the microstructure and phase formation of the developed HEA were reported. The microstructural modification and phases present were examined using the scanning electron microscope (SEM) equipped with the energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD) respectively. Ordered FCC and BCC systems were identified along with clearly defined crystal lattice along with Mo, Ti and Si rich regions were observed. No pores or cracks were observed from the microstructures. Densification of 98.8% accompanied with microhardness of 1445.29HV was achieved for both HEA at 1000°C. The Al15Ti30Si30Mo15Ni10 HEA fabricated at 1000°C displayed a higher polarization value of 3477 Ω.

Tungsten-based bcc-superalloys

Applications from nuclear energy to rockets and jet engines are underpinned by advanced high temperature materials. Whilst state of the art, the performance of current nickel-based superalloys is fundamentally limited to Ni’s melting point, Tm=1455∘C. Here, we develop an analogous superalloy concept but with superior high temperature capability by transitioning to a bcc tungsten base, Tm=3422∘C. This strategy involves reinforcing bcc β-W by β′ TiFe intermetallic compound, which results in impressive high temperature compressive strengths of 500 MPa at 1000∘C. This bcc-superalloy design approach has wider applicability to other bcc alloy bases, including Mo, Ta, and Nb, as well as to refractory-metal high entropy alloys (RHEAs). By investigation of the underlying phase equilibria, thermodynamic modelling, characterisation and mechanical properties, we demonstrate the capability of ternary W-Ti-Fe tungsten-based bcc-superalloys as a new class of high temperature materials.

Advanced High-Temperature Structural Materials for Aerospace and Power Sectors: A Critical Review

Advanced high-temperature structural materials are expected to play an important role in realizing the aspirations related to the next-generation aerospace propulsion devices, thermal protection system of reusable launch vehicles and thermal/nuclear power reactors. Despite considerable amount of research conducted for developing new and more efficient high-temperature structural materials, the advancement is inadequate and warrants continued efforts to address several unresolved issues concerning synthesis and processing of new materials, related characterization and testing to evaluate and ensure desired performance, durability, reproducibility and reliability in simulated experiments and real-life condition and finally, upscaling the operation for large-scale commercially viable production. In this article, an attempt has been made to review the latest status and trend in developing high-temperature structural materials for aerospace and thermal/nuclear sectors and highlight the challenges associated with development and processing of such advanced structural materials.

Review KEMS 2012 till 2017

Review on the main results on high temperature behavior of inorganic systems and materials obtained by the Knudsen effusion mass spectrometry (KEMS) during last five years is presented. The available information on vaporization processes and thermodynamic properties of these systems found recently is discussed with the indication of its great importance for the developing of advanced high temperature materials that may be used in the various fields of modern technologies such as space, nuclear and optical industries.

Finite Elements Approach to Predicting Impedance Response of Geometrically Convoluted Samples

Capacitance and resistance are extensive variables that depend on the geometry of a sample. Therefore, to obtained a normalized value, attributable to the material and not the sample shape and dimension, the geometry has to be taken into account. While with certain geometric forms simple division of multiplication, based on length and cross-section can be applied, with more convoluted forms this is not as straightforward. Ideal measurement will be done on samples geometrically simple. However, with awkward shapes or irregular electrode placements, measurements are still done and the geometry effect can be corrected after the fact. As an example is a ceramic disc with grain and boundary resistance and capacitance, that could be encountered in studies of advanced high temperature materials, e.g., for sensors of high-temperature fuel cells. The disks prepared by various methods of synthesis are contacted on their flat sides to the impedance analyzer circuitry. Our study correlates the (simulated) measured data to data that would be expected if perfectly symmetrical all-covering contacts were used.

Function of microelement Hf in powder metallurgy nickel-based superalloys

(1) High Temperature Material Institute, Central Iron and Steel Research Institute, Beijing, China; (2) Beijing Key Laboratory of Advanced High Temperature Materials, Central Iron and Steel Research Institute, Beijing, China; (3) School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, China

Finite Elements Approach to Predicting Impedance Response of Geometrically Convoluted Samples

The geometry of a sample is of utmost importance in interpretation of impedance measurements and correlating them to the properties of the studied material. The first, always considered, issue is inclusion of the geometrical dimensions, so that capacitance and resistance of a sample can be interpreted and reported for proper comparison based on values per unit dimensions. In ideal measurements the samples prepared are a prioriprepared in simple geometries, allowing proper electric contact connections so that the calculations are simplified and measurements in a single laboratory, even without data interpretation, lend themselves to quick visual side-by-side comparison. However, such arrangement is not always possible and therefore we investigated, by method of computer simulation, dependence of impedance results on geometry of a sample and location of electrode connection. As an example is a ceramic disc with grain and boundary resistance and capacitance, that could be encountered in studies of advanced high temperature materials, e.g.,for sensors of high-temperature fuel cells. The disks prepared by various methods of synthesis are contacted on their flat sides to the impedance analyzer circuitry. Our study correlates the (simulated) measured data to data that would be expected if perfectly symmetrical all-covering contacts were used. While in part the correlation reveals that a simple multiplication factor can be used in some cases to correct for the geometry of the electrode placement, under conditions of more extreme electrode placements the response is such, that equivalent modeling of the obtained impedance data is not adequately described only by RC circuits. Instead, a constant phase element has to be introduced. The simulation for this work was done using the ANSYS software package. The figure shows the geometric layout used for simulation. In this case a sample disk of a 30-mm diameter, thickness 7 mm is connected to the measurement circuit by two symmetrical, centrally placed metal circular electrodes of diameter 14 mm. In the process of simulations the size of the electrodes and their placement vs. the centerr of the sample was varied. For the data fitting to the suitable equivalent circuits was used the ZView package from Scribner Associates. This work was supported by the project “CEITEC - Central European Institute of Technology” (CZ.1.05/1.1.00/02.0068) from European Regional Development Fund. Figure 1

Crystal structures and magnetic performance of nanocrystalline Sm-Co compounds

A variety of intermetallic compounds in the binary Sm-Co system were reviewed, and the contents were focused on the crystal structures, magnetic properties and the nanoscale effects. The representative nanocrystalline Sm-Co compounds were introduced in details, the diagrams for their lattice structures and the atomic sites and occupancies were provided. Moreover, the magnetic properties of the nanocrystalline Sm-Co compounds were compared with those of the conventional polycrystalline counterparts. It showed that the nanocrystalline Sm-Co compounds exhibit special phase stability and remarkably enhanced magnetic performance, which are promising candidates for the matrix phases to develop permanent magnets, particularly the advanced high-temperature magnetic materials.

Plasma spouted/fluidized bed for materials processing

Plasma when coupled with spout/fluidized bed reactor for gas-solid reaction brings in several advantages such as high rate of heat and mass transfer, generation of high bulk temperature using a thin jet of plasma itself as a heat source. The science and technology of plasma and fluidization or spouted bed are well established except of these two put together for high temperature application. Plasma heating of fluid/ spouted bed can bring down the size of the equipment and increase the productivity. However the theory and practice of the hybrid technology has not been tested in a variety of applications that involves high temperature synthesis of materials, TRISO particle coating for nuclear fuel particle, thermal decomposition of refractory type ore, halogenations of minerals, particulate processes and synthesis of advanced materials. This paper gives an account of the use and exploitation of plasma coupled with spouted/ fluidized bed especially for material processing and also addresses the issues for adapting the same in the era of developing advanced high temperature materials.