Elevated Temperature Applications Research Articles

A Quantitative Phase Analysis by Neutron Diffraction of Conventional and Advanced Aluminum Alloys Thermally Conditioned for Elevated-Temperature Applications.

As the issue of climate change becomes more prevalent, engineers have focused on developing lightweight Al alloys capable of increasing the power density of powertrains. The characterization of these alloys has been focused on mechanical properties and less on the fundamental response of microstructures to achieve these properties. Therefore, this study assesses the quality of the microstructure of two high-temperature Al alloys (A356 + 3.5RE and Al-8Ce-10Mg), comparing them to T6 A356. These alloys underwent thermal conditioning at 250 and 300 °C for 200 h. Time-of-flight neutron diffraction experiments were performed before and after conditioning. The phase evolution was quantified using Rietveld refinement. It was found that the Si phase grows significantly (13-24%) in T6 A356, A356 + 3.5RE, and T6 A356 + 3.5RE alloys, which is typically correlated with a reduction in mechanical properties. Subjecting the A356 3.5RE alloy to a T6 heat treatment stabilizes the orthorhombic Al4Ce3Si6 and monoclinic β-Al5FeSi phases, making them resistant to thermal conditioning. These two phases are known for enhancing mechanical properties. Additionally, the T6 treatment reduced the vol.% of the cubic Al20CeTi2 and hexagonal ᴨ-Al9FeSi3Mg5 phases by 13% and 23%, respectively. These phases have detrimental mechanical properties. The Al-8Ce-10Mg alloy cubic β-Al3Mg2 phase showed significant growth (82-101%) in response to conditioning, while the orthorhombic Al11Ce3 phase remained stable. The growth of the beta phase is known to decrease the mechanical properties of this alloy. These efforts give valuable insight into how these alloys will perform and evolve in demanding high-temperature environments.

The impact of small Zr addition to Al–Ni cast alloy for elevated temperature applications

Most aluminium casting alloys are based on the eutectic system Al–Si, which has weak thermal properties. Alloys from the eutectic Al–Ni system on the other hand have higher thermal stability and good casting properties and are therefore promising for casting applications. Using casting simulations, a copper mold was designed to achieve cooling rates above 100 K/s with the aim of producing a Zr-rich supersaturated solid solution. Microstructural analysis revealed that the addition of Zr leads to notable changes in the microstructure characterised by the formation of primary Al3Zr and αAl dendrites. Subsequent heat treatment revealed that Zr-enriched alloys undergo significant age hardening, which showed an improvement in microhardness due to effective Al3Zr precipitation.

Improved elevated-temperature strength and thermal stability of additive manufactured Al–Ni–Sc–Zr alloys reinforced by cellular structures

Laser powder bed fusion (LPBF) processed Al–Ni alloys typically exhibit cellular structures, contributing to superior strength at ambient temperature as the cell walls can effectively impede dislocation motion during plastic deformation. However, it is still unclear whether cellular structures can lead to excellent elevated-temperature performance. In this study, we conducted a systematic investigation into the elevated-temperature mechanical properties and thermal stability of an LPBF Al–Ni–Sc–Zr alloy with cellular structures. The as-built alloy exhibits a yield strength of 368 MPa at 25℃ and 332 MPa at 250℃, with an exceptional strength retention rate of ∼90 % at 250℃. Moreover, the alloy maintains a hardness of ∼146 HV following exposure at 250℃ for 100 h and shows no apparent decrease despite increasing the exposure time to 500 h. The excellent elevated-temperature performance can be attributed to the cellular structures. The cell walls effectively confine dislocations at elevated temperatures, suppressing the dislocation annihilation and leading to exceptional strength retention. On the other hand, even if the cell walls decompose into nanoparticles after prolonged thermal exposure, the reduction in strength due to the decomposition can be compensated by the strengthening of the nanoparticles, resulting in excellent thermal stability. By studying the influence of the cellular structures on elevated-temperature performance, this study could provide valuable insights into developing high-performance Al alloys for elevated-temperature applications by additive manufacturing.

Processing and properties of 3D woven SiC/SiC composites with hybrid matrix

3D woven SiC/SiC composites with Sylramic™-iBN SiC fibers have been fabricated by first partially infiltrating 3D woven fiber preforms with SiC by chemical vapor infiltration (CVI) and then by polymer infiltration and pyrolysis (PIP) of SiC-yielding polymer. The influence of fiber architecture on damage evolution and failure mechanisms during tensile loading, in-plane tensile properties, transverse thermal conductivity, and interlaminar tensile strength of the composites has been investigated. Wherever possible, the data are compared with those of 2D woven melt infiltrated (MI), CVI, and (CVI+PIP) hybrid SiC/SiC composites. The composites exhibit 300-hr creep durability at 1482 °C in air at stresses up to 138 MPa and show potential for elevated-temperature applications. Further improvements in composite properties are possible by optimizing composite constituents and fiber architecture.

Measurement of Diffusion Coefficients and Assessment of Atomic Mobilities in HCP Mg-Ag-Sn Alloys

Reliable thermodynamic and kinetic databases are essential for designing and developing novel magnesium (Mg) alloys for elevated-temperature applications in the automotive and aerospace industries. This study investigated diffusion behaviors of HCP Mg-Ag-Sn alloys by four sets of three diffusion couples annealed at 450, 500, and 550 °C, respectively. Interdiffusion and impurity diffusion coefficients at the three annealing temperatures were extracted using the forward-simulation method. The determined diffusion coefficients, combined with prior results in the literature, were then used to assess atomic mobilities for the HCP phase of the Mg-Ag-Sn system. This assessment was conducted using the DICTRA and the TCMG5 thermodynamic database within the Thermo-Calc software. Comprehensive comparisons between calculated and experimental diffusion coefficients yielded an excellent agreement. The atomic mobilities were also further validated by appropriate predictions of concentration profiles and diffusion paths observed in independent diffusion couple experiments performed at 525 °C for 18 hrs. It has been found that the addition of Sn and Ag both increase the diffusivity of Ag in HCP Mg and Sn in HCP Mg in the stable temperature range of HCP Mg, respectively. This improved understanding of the kinetics in the Mg-Ag-Sn ternary system is essential for controlling diffusion-dependent properties such as coarsening and, therefore, the mechanical properties of Mg-Ag-Sn alloys at elevated temperatures.

Compositional regulation in additive manufacturing of precipitation-hardening (CoCrNi)94Ti3Al3 medium-entropy superalloy: Cellular structure stabilization and strength enhancement

High or medium-entropy alloys that feature high thermal stability and excellent oxidation resistance are promising candidates for elevated temperature applications. The rapid softening of monolithic high or medium-entropy alloys with single face-centered cubic structure at elevated temperatures, however, is a main weakness. In this paper, we report new high strength γ′-hardened ((CoCrNi)94Ti3Al3)98Nb2 medium-entropy alloy through laser powder-bed fusion (L-PBF) followed by ageing. In particularly, the tensile strengths of the aged ((CoCrNi)94Ti3Al3)98Nb2 alloy at 20 °C and 700 °C can reach up to 1.93 GPa and 1.11 GPa, respectively, 112 % and 122 % stronger than the as-built CoCrNi alloy tested at the same condition. A new strengthening mechanism, i.e., elemental segregation induced the cellular structure stabilization, in tandem with other hierarchical microstructure features, including ultrafine γ′ precipitates, dense twin boundaries, and other types of crystallized defects, co-contribute to the superb tensile strength at room and elevated temperatures. Such a simple alloy design and processing strategy outlines a guideline for designing novel multicomponent alloys and/or composites with superior microstructural stability and mechanical response at room and elevated temperatures.

Nanoprecipitate strengthened, alumina forming austenitic stainless steels for elevated temperature applications

Low cost stainless steels (SS) with high performance, especially with good mechanical properties and oxidation resistance at high temperature, are continuous pursuit for manufacture industry. To achieve good combination of mechanical properties, oxidation resistance and cost, nanoprecipitate strengthened alumina forming austenitic (NSAFA) SS have been developed by removing expensive elements such as Nb and Ta, lowering Ni concentration in Fe–26Ni–15Cr-1.5Mo-(2.8–3.5)Al-(1–2.35)Ti (wt.%) alloys. Microstructure investigation demonstrates that NSAFA SS are strengthened by L12 structured (Ni, Fe)3(Al, Ti) γ′ nanoprecipitates with area fraction around 25%–40%. Oxidation experiments (750 °C/480 h) in air demonstrates that all the NSAFA steels have alumina forming ability. In addition, it is found that Al and Ti are all necessary for γ′ nanoprecipitates, but additional Al and Ti facilitate formation of the Ni2AlTi phase. To ensure high volume fraction of γ′ nanoprecipitates and reduce Ni2AlTi phase, 2.8–3.0 wt% Al and 1.8–2.35 wt% Ti are preferred. Benefit from the high volume fraction of γ′ nanoprecipitates, yield strength of NSAFA steels is much higher than that of Fe-base superalloy (e.g., A286) and can compare to some Ni-base superalloys (e.g., Hayners 282 & Inconel 740H).

Temperature-Dependent Elastic Properties of B4C from First-Principles Calculations and Phonon Modeling

Boron carbide plays a crucial role in various extreme environment applications, including thermal barrier coatings, aerospace applications, and neutron absorbers, because of its high thermal and chemical stability. In this study, the temperature-dependent elastic stiffness constants, thermal expansion coefficient, Helmholtz free energy, entropy, and heat capacity at a constant volume (Cv) of rhombohedral B4C have been predicted using a quasi-harmonic approach. A combination of volume-dependent first-principles calculations (density functional theory) and first-principles phonon calculations in the supercell framework has been performed. Good agreement between the elastic constants and structural parameters from static calculations is observed. The calculated thermodynamic properties from phonon calculations show trends that align with the literature. As the temperature rises, the predicted free energy follows a decreasing trend, while entropy and Cv follow increasing trends with temperature. Comparisons between the predicted room temperature thermal expansion coefficient (TEC) (7.54×10−6 K−1) and bulk modulus (228 GPa) from the quasi-harmonic approach and literature results from experiments and models are performed, revealing that the calculated TEC and bulk modulus fall within the established range from the limited set of data from the literature (TEC = 5.73–9.50 ×10−6 K−1, B = 221–246 GPa). Temperature-dependent Cijs are predicted, enabling stress analysis at elevated temperatures. Overall, the outcomes of this study can be used when performing mechanical and thermal stress analysis (e.g., space shielding applications) and optimizing the design of boron carbide materials for elevated temperature applications.

Creep in a nanocrystalline VNbMoTaW refractory high-entropy alloy

Refractory high-entropy alloys (RHEAs) are considered to be a promising candidate for elevated temperature applications. Nanocrystalline (NC) RHEAs are supposed to exhibit many different high-temperature mechanical behaviors in comparison with their coarse-grained (CG) and ultrafine-grained (UFG) counterparts. However, the creep behaviors of NC RHEAs, which must be well evaluated for high-temperature applications, are largely unknown because it is difficult to produce bulk quantities of NC RHEAs for creep tests. In the present work, an equiatomic bulk NC VNbMoTaW RHEA with an average grain size of 67 ± 17 nm was synthesized by mechanical alloying (MA) and the subsequent high-pressure/high-temperature sintering. The creep tests were performed on bulk specimens by compression at high temperatures (973 and 1073 K) under different stresses (70–1100 MPa). The creep resistance of the bulk NC VNbMoTaW is slightly lower than that of the bulk CG VNbMoTaW, but much higher than that of previously reported CG and UFG HEAs. The derived activation volume, stress exponent, and activation energy of bulk NC VNbMoTaW indicate that the creep deformation is dominated by grain boundary diffusion. The creep deformation is controlled by the diffusion of Mo and Nb elements, which have the two slowest grain boundary diffusivities among the five alloying elements. The present work provides a fundamental understanding of the creep behavior and deformation mechanism of NC RHEAs, which should help design advanced creep-resistant RHEAs.

A refractory medium-entropy alloy with ultrahigh specific yield strengths for elevated-temperature applications

Refractory high- or medium-entropy alloys (RHEAs or RMEAs) with excellent high-temperature mechanical properties and softening resistance have been proven to be the potential candidates for advanced engineering applications. However, room temperature brittleness and high density have become an important challenge that needs to be addressed. In this work, the tensile mechanical behavior and the underlying deformation mechanisms of lightweight Ti40Zr20Nb13.33V26.67 RMEA at 298 and 873 K were investigated systematically. The results showed that the as-cast RMEA has a single body-centered cubic phase and low density (5.88 g/cm3) and exhibits excellent mechanical properties at 298 K, with yield strength of 1033.9 MPa, specific yield strength of 175.8 MPa·cm3/g, and tensile fracture strain of 5.3%. More importantly, it also exhibits ultrahigh strength and sufficient ductility at 873 K, with yield strength of 783.2 MPa, specific yield strength of 133.2 MPa·cm3/g, and tensile fracture strain of 5.7%. It showed that a large number of slip bands and dislocation bands are the main deformation products at 298 K, leading to excellent ductility. In comparison, high dislocation density was found between the slip bands in the samples deformed at 873 K, which can effectively hinder the motion of dislocations, resulting in strain hardening and the increase in strength. This work can provide a route for the design and fabrication of high-performance lightweight alloys, which would be beneficial for engineering applications.

The recovery of microstructure and mechanical properties of directionally solidified Ni-based superalloy DZ411 after long-term thermal exposure at different temperatures

Directionally solidified (DS) Ni-based superalloys are widely used in gas turbine blades due to excellent mechanical properties for elevated temperature applications. In harsh service environments, the microstructure degrades and mechanical properties deteriorate. In order to extend the service life of gas turbine blades, rejuvenation heat treatment (RHT) is applied. Considering the existence of temperature gradient in a real gas turbine blade during service, the effects of RHT on the different degraded microstructure at different temperatures are necessary to be investigated. However, few investigations concentrated on it. In this study, to simulate the existence of temperature gradient in a real gas turbine blade during service, DS Ni-based superalloy DZ411 was carried out with long-term thermal exposure at different temperatures. The impact of RHT on the different degrees of degraded microstructure and mechanical properties after thermal exposure at different temperatures was explored. Furthermore, the evolution of dislocations after RHT is studied, which has been rarely investigated. It was found that the degenerated microstructure at different aging temperatures can be significantly restored by RHT, including dissolution and reprecipitation of γ′ and M23C6 carbides and annihilation and rearrangement of dislocations. In addition, creep and low cycle fatigue (LCF) properties could also be effectively recovered by RHT. After RHT, the steady-state creep rate is decreased and creep rupture life has been prolonged. The LCF life and the shape of the stabilized hysteresis loop are restored. However, the creep properties are not completely restored, due to the unrecovered microstructure including the undissolved γ′ in interdendritic regions, the residual dislocations, and irreversible decomposition.

Constitutive equation and microstructural evolution of one distinctive Al–based hybrid composite reinforced by nano–AlN and micro–TiC particles during hot compression

In this study, an (8.2AlN + 4TiC)/Al–0.3Fe–0.1Mn composite was successfully fabricated for elevated– temperature applications by the liquid–solid reaction method, and the high–temperature performance (hot workability) of the composite was evaluated by unidirectional hot deformation experimentation. The tested temperatures and strain rates were 350–500 °C and 0.001–1 s−1, respectively. The results indicated that the peak stress of the composite was as high as 226 MPa at 350 °C and 1.0 s−1, which was significantly higher than the reported strength values of commercial deformed aluminum alloys or other particle–reinforced Al matrix composites under the same experimental conditions. Although the flow stress of the composite decreased with the increase of deformation temperature and the decrease of strain rate, the peak stress remained at 82 MPa under the experimental conditions of 500 °C and 0.001 s−1. This reflected the excellent high–temperature synergistic strengthening effect of the in–situ nanosized AlN and submicron TiC particles. Based on the true stress–true strain curve, the hot deformation constitutive equation of the composite was established and fitted. The relative microstructural evolution of the composite during hot deformation was characterized by electron backscattering diffraction (EBSD) and transmission electron microscopy (TEM). It was found that the Orowan strengthening and load–transfer strengthening effect of the nanosized AlN and submicron TiC particles were the main reasons for their high–temperature strengthening, and the softening effect of the composite could be attributed to dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), accompanied by partial discontinuous dynamic recrystallization (DDRX). This study provided a new strategy for the design of heat–resistant Al alloys and their high–temperature strengthening and softening mechanism. This study may provide new insights for designing and achieving good workability in Al–based composites for elevated temperature applications.

Determination of the Rate Dependence of Damage Formation in Metallic‐Intermetallic Mg–Al–Ca Composites at Elevated Temperature using Panoramic Image Analysis

A cast Mg‐4.65Al‐2.82Ca alloy with a microstructure containing an α‐Mg matrix is studied, which is reinforced with a C36 Laves phase skeleton. Such ternary alloys are targeted for elevated temperature applications in automotive engines, since they possess excellent creep properties. However, in application, the alloy may be subjected to a wide range of strain rates, and thus accelerated testing is often essential. It is, therefore, crucial to understand the effect of such rate variations. Herein, their impact on damage formation is focused. The analysis is based on high‐resolution panoramic imaging using scanning electron microscopy, combined with automated damage analysis using deep learning for object detection and classification (YOLOv5). It is found that with decreasing strain rate the dominant damage mechanism for a given strain level changes: at a strain rate of 5 × 10−4 s−1, the evolution of microcracks in the C36 Laves phase dominates damage formation. However, when the strain rate is decreased to 5 × 10−6 s−1, interface decohesion, becomes equally important. A change in crack orientation is also observed, indicating an increasing influence of plastic codeformation of the α‐Mg matrix and Laves phase. This transition is attributed to the leading damage mechanism to thermally activated processes at the interface.

A novel Al-Si-Ni-Fe near-eutectic alloy for elevated temperature applications

A novel near-eutectic Al-15.0Si-4.1Ni-1.9Fe (wt%) alloy with a ternary eutectic reaction of Liquid→α-Al+Si+(Al,Si)5(Fe,Ni) was investigated. Eutectic Si and (Al,Si)5(Fe,Ni) phases exhibit short nanoscale fibrous morphologies with volume fractions of 14.3 ± 1.6% and 15.1 ± 1.9%, respectively. The (Al,Si)5(Fe,Ni) phase has a tetragonal Al2.7FeSi2.3-type crystal structure with excellent thermal stability, which contributes to high mechanical properties at room and elevated temperatures. First-principles density-functional theory (DFT) calculations reveal its chemical composition of tetragonal (Al4.75Si0.25)(Fe0.5Ni0.5) having Si solution at the Al sites with two Fe neighbours contributes to the lowest solution energy. The newly developed alloy has superior mechanical properties at room and elevated temperatures compared with other typical heat-resistant aluminium alloys, which has great potential for industrial applications.

PLATech overview -radiation-heat tailored VOC-free, bio-renewable polylactic acid polymer formulations & methods for multiple industrial adhesion applications

This paper presents an overview of research and results about tailoring crystalline and amorphous form polylactic acid (PLA) polymer resin for use as an adhesive for joining a range of substrates, production of wood-based composites plywood and particle wood-based composites, and, for potential use for elevated temperature applications as for wood structures when subject to fires. The range of substrates successfully joined (with and without bio-plasticizer) ranges from metals, woods, glasses, ceramics, stones, and bricks to synthetic fluoro-polymers. Tensile bond strength for steel-to-steel bonding ranged towards 40+ MPa; superior (over 100%) bonding strength was obtained compared with EVA and other standard adhesives for wood and metal surfaces. Three successful industrial product arenas are described: 3-ply composite plywood panels meeting water soak and shear strength industry metrics; particle boards meeting-exceeding rupture strength, elasticity, and water resistance metrics similar to those expected from urea-formaldehyde based adhesive but without VOC release limitation, PVC-free luxury flooring tiles which meet strict requirements for wear cycles, distortion-free adhesion peel strength; and, production of renewable particle boards with elastic modulus and internal bond strengths comparable with boards made with urea formaldehyde. Thermal and gamma ionizing radiation research results are discussed to tailor key adhesive-relation properties: adhesion strength, viscosity, flow rate, molecular weight, hardness, flexibility, and friability. Scoping studies on radiation-based tailoring with a cross-linking agent were found to permit up to 30% improvements in bond strength as well as for enabling application as an adhesive for elevated (100 °C+) temperature applications with ∼30–50% higher operating temperatures compared with commonly used adhesives. A discussion is included about the remaining challenges and recommendations for further research.

A comparative study on characteristics of composite (Cr3C2-NiCr) clad developed through diode laser and microwave energy

A typical ferrite/martensitic heat-resistant steel (T91) is widely used in reheaters, superheaters and power stations. Cr3C2-NiCr-based composite coatings are known for wear-resistant coatings at elevated temperature applications. The current work compares the microstructural studies of 75 wt% Cr3C2- 25 wt% NiCr-based composite clads developed through laser and microwave energy on a T91 steel substrate. The developed clads of both processes were characterized through a field emission scanning electron microscope (FE-SEM) attached with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and assessment of Vickers microhardness. The Cr3C2-NiCr based clads of both processes revealed better metallurgical bonding with the chosen substrate. The microstructure of the developed laser clad shows a distinctive dense solidified structure, with a rich Ni phase occupying interdendritic spaces. In the case of microwave clad, the hard chromium carbide particles consistently dispersed within the soft nickel matrix. EDS study evidenced that the cell boundaries are lined with chromium where Fe and Ni were found inside the cells. The X-ray phase analysis of both the processes evidenced the common presence of phases like chromium carbides (Cr7C3, Cr3C2, Cr23C6), Iron Nickel (FeNi3) and chromium-nickel (Cr3Ni2, CrNi), despite these phases iron carbides (Fe7C3) are observed in the developed microwave clads. The homogeneous distributions of such carbides in the developed clad structure of both processes indicated higher hardness. The typical microhardness of the laser-clad (1142 ± 65HV) was about 22% higher than the microwave clad (940 ± 42 HV). Using a ball-on-plate test, the study analyzed microwave and laser-clad samples' wear behavior. Laser-cladding samples showed superior wear resistance due to hard carbide elements. At the same time, microwave-clad samples experienced more surface damage and material loss due to micro-cutting, loosening, and fatigue-induced fracture.

Production of a Reinforced Refractory Multielement Alloy via High-Energy Ball Milling and Spark Plasma Sintering

Refractory high entropy alloys have shown potential to be developed as structural materials for elevated temperature applications. In the present research, the multielement alloy Fe2TiVZrW0.5 was produced by high-energy ball milling of elemental powders in the air to promote the formation of reinforcing oxide and nitride particles followed by spark plasma sintering consolidation. The sintering temperature was optimized to achieve a full-density material that was characterized from the microstructural and mechanical points of view. Hardness and KIC were measured in the as-sintered condition as well as after thermal treatment at 1100 °C. TEM observations showed the presence of a fine distribution of ZrO2 and Ti(V)-N in the microstructure mainly constituted by the bcc Fe-V and Fe-V-W phases. The fine distribution of ceramic particles in a metallic multielement matrix is responsible for the consistent hardness and thermal stability of this alloy.

Microstructure and mechanical properties of novel Al–Cu–Mg–Zn lightweight entropy alloys for elevated-temperature applications

Microstructure and mechanical properties of novel Al–Cu–Mg–Zn lightweight entropy alloys for elevated-temperature applications

Effect of Mo and V additions on the coarsening kinetics and high-temperature strength in γ′ precipitation-strengthened high-entropy alloys

High-entropy alloys (HEAs) containing well-stabilized nano-precipitates have a huge advantage in elevated temperature applications. This study investigated the effects of Mo and V additions on the morphological evolution, the coarsening kinetics of multi-component γ′ precipitates, and the high-temperature tensile strength of HEAs. HEAs with the additions of Mo and V have significantly lower lattice misfit values and exhibit a smaller coarsening rate of γ′ nanoparticles compared to Ni and Co-based superalloys. Moreover, the precipitate morphology related to the lattice misfit exhibits completely different effects attributed to Mo and V addition. Remarkably, Mo2.5V2.5 HEA has a yield strength of 496 MPa at 800 °C, which shows great potential for high-temperature applications.

Intermediate-temperature creep behaviors of an equiatomic VNbMoTaW refractory high-entropy alloy

As one of refractory high-entropy alloys (RHEAs), VNbMoTaW is considered to be a promising candidate for elevated-temperature application. However, its creep behavior is rarely reported. In the present work, the compressive creep behaviors of an equiatomic VNbMoTaW RHEA with a grain size of 138 ± 36 μm were well studied over an intermediate temperature range (973–1173 K) and under high applied stress (130–520 MPa). The stress exponent of the alloy is found to remain stable (∼1) at relatively low temperatures (973–1073 K), whereas a stress-dependent transition behavior occurs at high temperatures (1123–1173 K), i.e., the stress exponent of the alloy changes from ∼1 in the low stress region (130–390 MPa) to ∼ 4 in the high stress region (390–520 MPa). Meanwhile, the creep activation energy increases from 139 to 156 kJ mol−1 at low temperatures to 307–373 kJ mol−1 at high temperatures. The low stress exponent and low activation energy at low temperatures suggest that the creep is controlled by dislocation pipe diffusion. The low stress exponent and relatively high activation energy in the high-temperature low-stress region suggest that the creep is controlled by lattice diffusion. In the high-temperature high-stress region, the prevalent dislocations detected by the post-mortem microstructural observation, the high stress exponent, and high activation energy suggest that the creep deformation is controlled by a lattice diffusion mediated dislocation climb process. These findings provide a fundamental understanding of the creep behavior and deformation mechanism of VNbMoTaW, which can be applied to design advanced creep-resistant RHEAs.