High Temperature Structural Materials Research Articles

Integrated design of aluminum-enriched high-entropy refractory B2 alloys with synergy of high strength and ductility.

Refractory high-entropy alloys (RHEAs) are promising high-temperature structural materials. Their large compositional space poses great design challenges for phase control and high strength-ductility synergy. The present research pioneers using integrated high-throughput machine learning with Monte Carlo simulations supplemented by ab initio calculations to effectively navigate phase selection and mechanical property predictions, developing single-phase ordered B2 aluminum-enriched RHEAs (Al-RHEAs) demonstrating high strength and ductility. These Al-RHEAs achieve remarkable mechanical properties, including compressive yield strengths up to 1.7 gigapascals, fracture strains exceeding 50%, and notable high-temperature strength retention. They also demonstrate a tensile yield strength of 1.0 gigapascals with a ductility of 9%, albeit with B2 ordering. Furthermore, we identify valence electron count domains for alloy ductility and brittleness with the explanation from density functional theory and provide crucial insights into elemental influence on atomic ordering and mechanical performance. The work sets forth a strategic blueprint for high-throughput alloy design and reveals fundamental principles governing the mechanical properties of advanced structural alloys.

Evolution of residual stress of SiCf/Ti17 composites at high temperature evaluated by micro-Raman spectroscopy

SiCf/Ti17 composites are considered promising lightweight high-temperature structural materials for the aerospace field due to their excellent mechanical properties. However, during the manufacturing process, differences in the coefficients of thermal expansion between various material components inevitably generate thermal residual stresses at the interfaces. These thermal residual stresses can lead to stress concentration and other failure modes, thereby affecting the mechanical properties of SiCf/Ti17 composites. Therefore, it is crucial to systematically study the residual stresses in the interfacial C coating and the W/SiC interfacial regions, as well as the evolution of these stresses at high temperatures. In this study, samples were first subjected to vacuum heat treatment, followed by systematic micro-Raman experiments conducted radially on the fibers. Subsequently, the Raman spectra were subjected to peak deconvolution to obtain precise target peaks. By combining Raman peak shifts with Hooke's law, the evolution of high temperature residual stresses in the C coating and W/SiC interfacial regions were determined. Additionally, changes in the Raman spectral data at different temperatures were analyzed to investigate the variations in the micro-composition of different regions. The results showed that at 850°C, both the C coating and the W/SiC interfacial region exhibited good mechanical properties and strength retention. However, at 1050°C, the mechanical properties of both regions gradually deteriorated, with the W/SiC interfacial region showing a sharp increase in compressive stress. At this point, the SiCf/Ti17 composite material may face a risk of failure.

Temperature-dependent mechanical behavior in a novel hierarchical B2-strengthened high entropy alloy: Microscopic deformation mechanism and yield strength prediction

Integration of twinning and hierarchical microstructure into a face-centered cubic (FCC) matrix is a novel research approach for advancing high-temperature alloys, enhancing strength without the need for costly heavy elements. Here, a three-level B2 phase was incorporated into a NiCoCrFe high-entropy alloy (HEA) matrix, offering a high strengthening effect at room temperature and a good resistance to moderate-temperature softening while preserving the low stacking fault energy of the FCC matrix. The resulting NiCoCrFeAl0.3Si0.3 HEA exhibited stable yield strength, strain hardening, and deformation twinning over a broad temperature ranging from 77 to 973 K. By establishing a yield strength model based on the various strengthening mechanisms, the study highlighted the important role of the three-level B2 phase in the exceptional mechanical properties of the alloy across a wide temperature range. These findings present a promising avenue for the advancement of high-temperature structural materials.

Thermal Protection and Dielectric Properties of Borosilicate Coatings for SiCf/SiC Composites Under High-Temperature Oxidation

Currently, oxidation of SiCf/SiC composites in harsh environments such as high temperatures has become a key challenge for their application in high-temperature structural wave-absorbing materials. In this study, borosilicate glass (BSZ) coatings were prepared using the thermal nitrogen–oxygen process. The evolution of mechanical and coating microwave dielectric properties of the composites with and without BSZ coatings after oxidation at 1100 °C, 1200 °C, 1300 °C and 1400 °C was investigated. The results showed that the mechanical strength of the BSZ-coated SiCf/SiC specimens remains virtually unchanged, with a remarkable strength retention rate of 94%. The exceptional oxidation resistance of these coatings can be attributed to the formation of self-healing oxides and the reinforcing “pinning” effect of ZrSiO4. With an increase in oxidation temperature, the dielectric properties of the oxidized coatings are determined by the intrinsic properties of the generators and the porosity. Overall, these features highlight the potential of borosilicate coatings in the field of electromagnetic wave-absorbing composites, and the current work establishes a correlation between the oxidized microscopic properties of the coatings and the dielectric properties.

Achieving enhanced high-temperature strength in Ti-48Al-1Fe alloy sheets by direct hot pack-rolling of powder-sintered billets without cogging

The TiAl alloy is a novel lightweight high-temperature structural material that exhibits exceptional performance. The brittleness and mechanical properties of the material can be enhanced by improving the microstructure via rolling. The Ti-48Al-1Fe alloy with high density was produced using powder compaction and pressure-less sintering. Subsequently, the TiAl alloy sheet was formed via hot pack rolling. This study examined the sheet formability of PM Ti-48Al-1Fe alloy sheets at various temperatures, as well as the microstructure and mechanical properties at varied levels of rolling deformations. The microstructure of the powder metallurgy (PM) TiAl alloy sheet has a unique duplex structure, consisting of α2/γ lamellar colonies and a composite structure. The rolling deformation process generates spherical recrystallized grains, which effectively reduce stress concentration. The enhanced composite structure is mostly localized at the interfaces between grains, creating a robust obstacle for the movement of dislocations at high temperatures. This results in the desired outcome of reinforcing the mechanical properties of the material at high temperatures through grain boundary strengthening. This study demonstrates that the ultimate tensile strength (UTS) of PM TiAl sheet tensile specimens in the rolling direction at room temperature is 443 MPa with 1 % elongation, whereas at 800 °C, the UTS rises to 548 MPa with 2.5 % elongation. This study proposes a novel process for the efficient production of Ti48Al1Fe sheets with good high-temperature mechanical properties. This technique entails the hot rolling of high-density sintered powder metallurgy billets, offering an innovative approach for the economical and swift production of TiAl alloy sheets during practical manufacturing process.

Promoted room-temperature deformability and high-temperature strength synergy through zig-zag faceted interface design in TiNbTaWC0.7 eutectic refractory high-entropy alloy

With the development of aerospace technologies, there is an urgent demand for materials with better high-temperature performance. Despite the bottleneck of combining high-temperature strength and room-temperature deformability, refractory high-entropy alloys are potential candidates. Here, we report a novel alloy, TiNbTaWC0.7, with a good strength-ductility synergy by introducing the eutectic carbide phase. The alloy is composed of alternated BCC matrix phase and FCC carbide phase, forming a fully eutectic microstructure. With the introduction of the eutectic carbides, the alloy is robust at 1200 °C. The faceted phase interface together with the compositional complex carbides provides the alloy with good deformation ability at room temperature. The former promotes dislocation nucleation and transmission, and the latter generates stacking faults by partial dislocation movement. This strategy provides a new route to design promising high-temperature structural materials by combining the advantages of eutectic alloy, carbide strengthening, and refractory alloys utilizing the high entropy concept.

Plastic evolution and phase transition mechanisms in γ-TiAl nano polycrystal by a molecular dynamics simulation

γ-TiAl based alloys are widely regarded as one important high-temperature structural material, however the deformation behaviors are still not clearly clarified. The microscopic plastic deformation and phase transition of γ-TiAl nano polycrystals under compression are investigated by molecular dynamics simulations. The results show that the initial plasticity is dominated by slip of partial dislocations whose continuous formation and secondary slip on the same slip plane result in the generation and disappearance of intrinsic stacking faults (ISFs). At the strain of about 0.2, a continuous structure transformation of “ISF → ESF → TB” is observed, during which the interaction between different ISFs causes the atomic misalignment corresponding to the change in atomic stacking order near ISF. As the compressive strain exceeds 0.2, the FCC-to-BCC phase transition occurs within polycrystals due to the high Mises stress, the high stress level within grains facilitates the expansion of BCC phase from initial FCC phase, and the newly formed BCC phase maintains the atomic-arrangement orderliness of original phase. The interface between FCC and BCC phases obeys the low-energy Kurdjumov-Sachs orientation relationship. This work is helpful for better understanding the atomic-scale deformation behaviors and provides a theoretical guidance for designing high-performance alloy materials.

Enhancing strength and γ’-coarsening resistance through micro-alloying additions to an oxidation resistant Al-Co-Cr-Fe-Ni-Ti compositionally complex alloy

The effect of alloying additions of Mo and Ta (0.4 at% each) on the microstructure, mechanical properties, oxidation resistance and coarsening resistance of the L12-strengthened (γ’) Al-rich Ni51Co18Fe5Cr10Al12Ti4 alloy was determined. The micro-alloyed composition exhibited improved yield strength (from room temperature to 1000 °C) and coarsening resistance (enhanced by 33 % at 800 °C) compared to the base Ni51Co18Fe5Cr10Al12Ti4 alloy. The present Al-rich alloy compositions (both the micro-alloyed and reference compositions) exhibited superior oxidation resistance (800–1000 °C) compared to a Ti-rich Ni51Co18Fe5Cr10Al8Ti8 alloy (with similar precipitate volume fraction and (Al+Ti)-content) and commercial Inconel 718. The present work highlights the promise of Al-rich γ’-strengthened Al-Co-Cr-Fe-Ni-Ti alloys as candidates for high-performance, high-temperature structural materials, characterised by an attractive blend of strength, resistance to coarsening, and resilience against oxidation.

Unveiling exotic multi-scale microstructure transformation and crack formation mechanisms in eutectic ceramic composite by laser powder bed fusion

Laser powder bed fusion (LPBF) represents an advanced and versatile technology. Exploiting its distinctive advantages for direct and rapid fabrication of complex-structured melt-grown oxide eutectic ceramic composite represents a pioneering yet challenging endeavor. In this work, LPBF is creatively employed to fabricate turbine blade-shaped, in-situ ternary eutectic ceramic composite. Through the integration of experimental procedures, Finite element method (FEM) simulations, and numerical analyses, an innovative design and manufacturing of oxide eutectic ceramic composites have been successfully established. Comprehensive FEM simulations, with detailed interface characteristic analysis, have revealed macro-scale cracks induced by intense maximum principal stress, and micro-cracks stemming from significant interfacial energy disparities among the three constituent phases. The applications of rapid solidification and nucleation theories have facilitated profound insights into the formation mechanisms of multi-scale exotic microstructures, including top-layer coarse dendrites, rosette-like spherical internally grown eutectic colony within layers, and columnar eutectic colonies with ultra-fine lamellar eutectic structures. Micro-mechanical property testing reveals enhanced performance in the inter-layer ultra-fine lamellar eutectic structure, which is attributed to a refined eutectic spacing of approximately 61 nm, coupled with distinct and robust bonding interfaces. These groundbreaking achievements, focusing on the processing-microstructure-property relationship in the fabrication of gas turbine blade-shaped solidified eutectic ceramic composite using LPBF, provide invaluable theoretical insights and data. This knowledge is crucial for the LPBF production of high-temperature structural materials, highlighting its significant potential applications in fields of aerospace and mechanical engineering.

Self-generated B-MAX phase composites: The effect of sintering temperature on surface morphology and phase composition

The use of metal-based MAX phase composites is widespread in the production of high-temperature structural materials, anticorrosive materials and electrode materials. Herein, novel B-Ti3AlC2 and B-Ti4AlN3 composites were prepared using the hot-pressing method at varying sintering temperatures ranging from 950 °C to 1325 °C. This study also explores the effect of sintering temperature on the surface morphology and phase composition of both B-MAX phase composites. The morphological and crystal phase composition of MAX phase composites were investigated through SEM coupled with EDS, FE-SEM, AFM, and XRD test analysis. The results revealed that higher sintering temperatures increase the clear formation of MAX phases and composites as compared to lower temperatures. The findings also expose that the in-situ formation of B-MAX composites significantly changes the structure, contributing to transforming the overall performance and making it suitable for high-stress applications like electronics, aerospace, and cutting tools.

Internal damage evolution of C/SiC composites in air at 1650 °C studied by in-situ synchrotron X-ray imaging

Carbon fibre reinforced silicon carbide (C/SiC) ceramic matrix composites have attracted considerable attention due to their exceptional properties and extensive potential applications as high-temperature structural materials. However, due to their complex structure and manufacturing defects, C/SiC composites exhibit intricate mechanical behaviour under thermal-mechanical-oxidative coupling environments. To date, systematic studies on the internal damage evolution and failure mechanisms of C/SiC composites under high-temperature oxidative environments are lacking. In this study, a combination of synchrotron X-ray micro-computed tomography (SR-μCT) and in-situ experiments under thermal-mechanical-oxidative coupling environments at room temperature and 1650 °C in air was used to characterize the internal microstructures and damage evolution processes of C/SiC composites at different loading levels. Additionally, the 3D strain fields during in-situ loading were quantitatively analysed using the Digital Volume Correlation (DVC) method. The findings underscore the substantial impact of oxidative damage on the mechanical response of C/SiC composites, particularly concerning tensile properties and fracture modes. At room temperature, severe delamination, fibre bundle pull-out and interfacial debonding occurred internally. Whereas, under high-temperature atmospheric conditions, severe fibre oxidation reactions occurred at the specimen edges, resulting in rapid porosity escalation. Crack initiation from surface defects followed by rapid inward propagation is observed. Moreover, while the strain distribution remains relatively uniform until fracture, a pronounced concentration of strain is evident near the fracture zones at room temperature, with an even greater concentration observed at 1650 °C. Notably, the region of concentrated strain within the 3D deformation field corresponds closely to the final fracture location, as revealed by quantitative DVC analysis.

Full-scale insight into high-entropy ceramics from basic concepts, synthesis technologies, structural characteristics, and properties to application prospects

High-entropy ceramics (HECs) are an emerging material system that has gained significant attention and become a focal point of research due to their unique structure and outstanding performance. This paper provides a comprehensive examination of the basic concepts, synthesis methods, structural characteristics, unique properties, and application prospects of HECs. It begins with an overview of the basic concepts and historical context, followed by a detailed comparison of synthesis techniques, including both traditional and innovative approaches. The paper then analyzes the structural characteristics and phase compositions of HECs, particularly focusing on oxide, carbide, boride, and other non-oxide ceramics. In addition, it delves into the mechanical, thermal, electrical, and magnetic properties of HECs. The article also reviews the applications of HECs in high-temperature structural materials, functional materials, high-performance coatings, and biomedical implants. Finally, it discusses the future challenges and development pathways for HECs. By highlighting new applications and transformative possibilities, this study not only sheds light on cutting-edge research but also emphasizes the significant impact of HECs on sustainable material development. The integration of machine learning and artificial intelligence can further unlock the unique structural capabilities of HECs, offering substantial potential for advancements in emerging fields like new energy and biomedicine.

Development of Ti3SiC2 MAX phase tubular structures for solar receiver applications

Solar receiver tubes are key components of concentrating solar-thermal power (CSP) systems that harvest solar energy. For better efficiency, the Gen3 CSP receivers, which collect heat into a heat transfer fluid, require a temperature exceeding 700 °C during operation and need to perform under extreme conditions of high temperature and high thermal stress. Operators are seeking CSP designs using new high-temperature structural materials with high thermal conductivity and high creep resistance to achieve a design life of 30 years and thus help recover the plant capital cost sooner. MAX phase materials, which consist of an early transition metal element, an A-group element, and carbon or nitrogen, are expected to exhibit high creep resistance as well as high fracture toughness. In this paper, we describe fabricating both (1) dense Ti3SiC2 MAX phase disks and (2) short-length tubes using field-assisted sintering technology (FAST). First, the disk samples that we fabricated are fully dense and contain ≈90 % Ti3SiC2 MAX phase materials and ≈10 % TiC phase materials. We determined a flexure strength of 519 ± 32 MPa by conducting a four-point bending test at room temperature with rectangular bar samples of ≈100 % density. The thermal conductivity of the Ti3SiC2 MAX phase samples, measured by light-flashing analysis, decreases linearly from a value of 41 W·m−1·K−1 at room temperature to a value of 36 W·m−1·K−1 at 650 °C. A solar reflectance measurement of the Ti3SiC2 MAX phase revealed that, temperature increases from 400 to 1400 °C, thermal emittance increases from 0.39 to 0.49, while selectivity decreases from 1.8 to 1.4, respectively. Whereas the surface oxidized MAX phase samples after 100 h exposure to air at 1000 °C exhibit that of SiC.Next, we discuss fabrication of the crack-free Ti3SiC2 MAX phase tubular structures accomplished by using FAST processing in graphite bedding. A Ti3SiC2 MAX phase content of > 95 % with traceable ≈3% remaining TiC phase and ≈15 % porosity were demonstrated after high-temperature annealing. An average fracture strength of ≈250 MPa was determined with Ti3SiC2 MAX phase tubes of ≈85 % density by diametral compression testing at room temperature. Our work demonstrated that using FAST processing to produce Ti3SiC2 MAX phase tubular structures for CSP receiver applications is a viable approach.

A Review of Molecular Dynamics Simulation of Different Ti-Al-Based Alloys

Ti-Al-based alloys, particularly two-phase TiAl and Ti3Al alloys, have garnered significant attention as potential replacements for various high-temperature structural materials due to their exceptional properties, including low density, oxidation resistance, and high strength at elevated temperatures. Despite these advantages, experimental studies on the microstructure evolution of Ti-Al-based alloys under complex conditions remain challenging to observe and characterize. This review article examines the current research on molecular dynamics (MD) simulations of Ti-Al-based alloys, focusing on two-phase Ti-Al alloys, Ti-Al amorphous alloys, Ti-Al composite materials, and the welding and multi-layer/film applications of Ti-Al alloys. This review highlights the unique capabilities of MD simulations in predicting the behavior of Ti-Al-based alloys and addresses existing scientific challenges. Furthermore, this article discusses future research directions and development prospects in this field.

A single-phase Nb25Ti35V5Zr35 refractory high-entropy alloy with excellent strength-ductility synergy

Refractory high entropy alloys (RHEAs) are promising candidates for high-temperature structural materials due to their excellent high-temperature performance. However, the room-temperature brittleness of most alloys results in poor plastic formability, thereby limiting their engineering applications. In this study, Nb25Ti35V5Zr35 alloy with cold-rollability was developed, and its phase stability, tensile mechanical properties, elastic properties, strengthening mechanism, and deformation mechanism were investigated by combining experiments, CALPHAD, DFT and molecular statics (MS) methods. The results demonstrate that Nb25Ti35V5Zr35 alloy possesses good phase stability, with both the as-cast and annealed states maintaining a single-phase BCC structure without undergoing phase transformation. The tensile yield strength of the alloy reaches its peak at 1152 MPa in the cold-rolled condition, while its annealed state exhibits an optimal balance of strength and plasticity, with a yield strength of 836 MPa and an elongation of 22.45 %, respectively. Solid solution strengthening is the primary source of its high strength, with V and Zr playing key roles in this strengthening mechanism. Dislocation slip plays a dominant role in plastic deformation. Additionally, compared to traditional BCC alloys, the significance of edge dislocations in the deformation process is notably enhanced, with the {112} plane serving as the preferred slip plane for dislocations. DFT results indicate that the alloy exhibits significant anisotropy in both Young's modulus and shear modulus. This work contributes to understanding the material properties of the Nb25Ti35V5Zr35 alloy and provides a reference for the design of new ductile RHEAs.

Carbon whiskers reinforced porous glassy carbon composites by synchronous growth

A crystalline and non-crystalline composite of pure carbon was proposed, which is a carbon whiskers reinforced porous glassy carbon composite, where crystalline carbon whiskers support the microscopic pores of non-crystalline glassy carbon matrix. Two allotropes of carbon were produced simultaneously and compounded together in a single high temperature treatment of thermosetting phenolic resin, with aluminum oxide (Al2O3) as a catalyst. A synchronous growth theory was proposed to explain the growth mechanism. In the pyrolysis process of phenolic resin to generate porous glassy carbon, hydrocarbon gas was produced and trapped in the generated pores. By the same time, the hydrocarbon gas in pores was decomposed and grew carbon whiskers by catalysis of Al2O3. With linear thermal expansion coefficient from 2.0∙10−6 to 3.8∙10−6 K−1, thermal conductivity from 1.763 to 2.518 W∙m−1 K−1, specific heat capacity from 0.396 to 0.752 J∙g−1 K−1, thermal diffusivity from 6.115 to 4.598 mm2 s−1, between room temperature (RT) and 500 °C, the Vickers hardness is at 65 MPa, and the fracture toughness is at 0.329 Mpa∙m1/2 in RT. The carbon whiskers reinforced porous glassy carbon composite keeps a balance between thermophysical and mechanical properties, showing its application value in thermal insulation materials and high temperature structure materials.

Anomalous increase of fracture toughness of TiAl-based alloys at high temperature

The anomalous increase of mechanical property of TiAl-based alloys at high temperature caters to the property requirements as the high-temperature structural materials, which is thus important and worth studying. However, people currently are not clear whether the fracture toughness of TiAl-based alloys has an anomalous increase at high temperature, and if so, how much it increases, and why it increases. In order to answer these questions, the forged Ti-44Al-8Nb model alloy with fine and uniform microstructure was used. The fracture toughness of the alloy at different temperatures was tested. The results indicated that the alloy did show an anomalous increase of fracture toughness at 700 °C–800 °C. The main crack deflected a large angle at 700 °C, and terminated at the upper part at 750 °C and 800 °C. The fracture morphology was fine, and the cleavage plane became smaller and less at high temperature. These characteristics corresponded to the anomalous increase of fracture toughness at high temperature. Through reverse thinking, we found that the high dislocation density was the root causing the anomalous increase of fracture toughness at high temperature. The forging-induced texture, such as B2 〈100〉//RD and γ-TiAl 〈011]//RD could also promote the dislocations slip on the main slip surfaces during the high temperature fracture toughness test, contributing to the final high dislocation density. The critical crack size at 700 °C–800 °C was about 4 times that of room temperature, corresponding to the higher fracture toughness of the alloy at high temperature.

The effect of TiSi2 healing improver in self-healing ability of ceramics

A method to enhance the temperature range in which continuous self-healing fiber-reinforced ceramics (shFRCs) can self-heal is proposed to obtain a new high-temperature structural material. The effect of TiSi2 oxidation on self-healing was investigated using SiC, a typical self-healing agent, and TiSi2, which oxidizes at a lower temperature than SiC. Mixtures of SiC and TiSi2 powders were prepared by wet-mixing, and changes in their high-temperature oxidation behavior were investigated using thermogravimetry/differential thermal analysis. The oxidation of TiSi2 at 1000 °C enhanced the oxidation rate of SiC by 2–3 times. A shFRC consisting of an Al2O3 matrix, an interface layer of SiC and TiSi2, and Al2O3 fiber bundles was fabricated by slurrying and filament-winding. The strength recovery of the shFRC following three-point bending was investigated, and results indicated that the prepared material recovered 50 times faster than conventional shFRCs at 1000 °C. The self-healing improver described in this study can promote the oxidation of self-healing agents via its reaction heat. Thus, this improver may be applied as a practical component of self-healing materials.

Multiscale oxide dispersion strengthened refractory high entropy alloys with superior mechanical properties

Refractory high-entropy alloy (RHEA) is one of the most promising materials for high-temperature applications. However, their application is inhibited by insufficient strength at elevated temperatures and brittleness at ambient temperatures. Herein, we proposed a multiscale oxide dispersion strengthened (ODS) NbTaTiV RHEA with an excellent combination of strength and plasticity at both room and elevated temperatures. The multilevel microstructures are composed of a fine-grained BCC phase matrix (∼1.2 μm), submicron Ti-(O, N) particles (∼330 nm), and nanoscale Y2Ti2O7 particles (∼18 nm). Owing to the strengthening of combinatorial multilevel microstructures, the yield strength of the RHEA was found as high as 1626 MPa, which exhibits a significant improvement (∼46%) in comparison with the NbTaTiV RHEA, without significant loss of ductility. The ODS NbTaTiV RHEA also shows superior thermal-softening resistance, with yield strengths of 945 MPa at 700 °C and 482 MPa at 1000 °C. The enhanced strength is mainly attributed to the multilevel microstructures that mediate the collaborative strengthening mechanism among dispersed strengthening, precipitation strengthening, and grain boundary strengthening. This work presents a new insight to develop multiscale microstructures in RHEAs for high-temperature structural materials.

Experimental determination and thermodynamic optimization of Nb-Al-Y ternary system

Niobium-aluminide-based alloys show excellent application potential as high-temperature structural materials. In the present work, the isothermal sections of the Nb-Al-Y system at 800 and 1050°C are constructed based on X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscopy (TEM). Two new ternary compounds, designated as τ-phase (Nb8Al80Y12) and ρ-phase (Nb26Al58Y16), are identified and their homogeneity ranges and crystal structures have been described. The ρ-phase can exist at temperatures within the isothermal sections of 800 and 1050°C, while the τ-phase exists at 800°C and disappears as the temperature rises to 1050°C. In addition, the primary solidification phases were also identified, and five different primary solidification phases were found. Based on the experimental data, the thermodynamic optimization of the Nb-Al-Y ternary system is carried out using the thermo-calc method. The calculated results are in good agreement with the experimental results, and a set of reasonable and self-consistent thermodynamic parameters is obtained. The results provide a basis for the design of Nb-Al-Y-based alloys and enrich the database of Nb-based alloys.