Lower Creep Rate Research Articles

Microstructures and High-Temperature Mechanical Properties of Inconel 718 Superalloy Fabricated via Laser Powder Bed Fusion.

The Inconel 718 superalloy demonstrates the potential to fabricate high-temperature components using additive manufacturing. However, additively manufactured Inconel 718 typically exhibits low strength, necessitating post-heat treatments for precipitate strengthening. This study investigated the microstructures and mechanical properties of the Inconel 718 superalloy fabricated via laser powder bed fusion. The room-temperature and high-temperature tensile properties of the Inconel 718 alloy samples following various post-heat treatments were evaluated. The results indicate that the as-built samples exhibited columnar grains with fine cell structures. Solution treatment resulted in δ phase formation and grain recrystallization. Subsequent double aging led to finely distributed nanoscale γ' and γ″ particles. These nanoscale particles provided high strength at both room and high temperatures, resulting in a balanced strength and ductility comparable to the wrought counterpart. High-temperature nanoindentation analyses revealed that the double-aging samples exhibited very high hardness and low creep rates at 650 °C.

Understanding post-irradiation creep behavior of M5Framatome zirconium alloy

After in reactor use, the nuclear fuel assembly of pressurized water reactors is stored in water and is eventually transported, in a dry cask, to a long-term storage facility or to a reprocessing plant. During transportation in dry environment the fuel rod temperature and internal pressure both increase. This leads to simultaneous creep deformation and annealing of the cladding tubes made of M5Framatome11M5 and M5Framatome are trademarks or registered trademarks of Framatome or its affiliates, in the USA or other countries. zirconium alloy. This study shows that post-irradiation creep, or heat treatment, leads to the recovery of the radiation induced hardening and also to the recovery of the uniform elongation because of <a>-loop annealing. On the other hand, it is shown that cladding tubes made of M5Framatome alloy exhibit low post-irradiation creep rates, especially at low applied stress. This strain rate is significantly lower than for the unirradiated material and similar to the as-irradiated material, despite the significant <a> loop annealing. The low creep rates are mainly attributed to the Nb-rich nano-precipitates that act as dispersed strengthening particles. These nano-precipitates appear under irradiation and are stable at temperatures up to 450 °C explaining their strengthening effect even after significant annealing.

Creep deformation behavior and microstructure of α-Mg/long-period stacking ordered (LPSO) duplex Mg-Y-Zn alloy prepared by hot extrusion and heat treatment

There exists a great demand for improving the creep resistance of α-Mg/long-period stacking ordered (LPSO) duplex alloys. In this study, microstructure control through hot extrusion and heat treatment was employed on Mg-Y-Zn duplex alloys with the aim of achieving superior creep resistance. The extruded Mg-Y-Zn alloy exhibited an enhancement in the creep resistance with increasing heat treatment temperature. Furthermore, the heat-treated samples demonstrated outstanding creep resistance even under high stress. Their creep behavior is characterized by a low minimum creep rate and a relatively small stress exponent (n ∼ 5) even at high stress. Microstructural observations revealed that heat treatment induces grain coarsening and an increase in solute concentration within the recrystallized grains. Additionally, during creep deformation, a plate-like LPSO phase and kink bands formed within the recrystallized grains. Therefore, it is affirmed that the exceptional creep resistance observed in the Mg-Y-Zn alloys in this study can be attributed to the microstructure evolution induced by heat treatment and creep deformation.

Yield stress anomaly and creep of single crystal Ni-base superalloys – Role of particle size

In the present work we subject the single crystal Ni-base superalloy ERBO1 (CMSX 4 type) to constant strain rate (CSR) and creep testing at temperatures between 1023 and 1223 K. Three material states are considered which have similar particle volume fractions >60% but differ in γ′-particle sizes (material states S, M and L of particle sizes: 240, 390 and 540 nm). In constant strain rate testing, a yield stress anomaly is observed for all three material states, with a yield stress maximum at 1073 K. This increase of strength with increasing temperature is not observed during creep testing at significantly lower deformation rates in this low temperature high stress creep regime, where different elementary deformation mechanisms govern CSR and creep behavior. In contrast, in the low stress high temperature creep regime, stress/strain rate data pairs from CSR creep tests both show decreasing strength with increasing temperature. It is found that in both types of tests the material state M shows the highest strength (highest yield stress and lowest creep rate). This can be rationalized based on a scenario where both, γ-channel and γ′-particle dislocation activities are important. Diffraction contrast transmission electron microscopy is used to study the relevant elementary deformation processes. Details of dislocation arrangements are discussed with a special focus on the role of Kear Wilsdorf (KW) locks, γ′-particle shearing by superlattice stacking faults (extrinsic and intrinsic) and dislocation climb.

Shear creep characteristics and creep constitutive model of bolted rock joints

The shear creep behavior of bolted rock joints is closely related to the long-term stability of bolt-reinforced high slopes and underground caverns. To investigate the controlling effect of bolts on rock joint shear creep, limestone samples from the Wudongde dam site area in southwest China were collected and processed, and multistep shear creep tests were conducted on both bolted an unbolted rock joints. The results show that the shear creep of bolted rock joints includes the instantaneous strain stage, transient creep stage and steady-state creep stage, yet the accelerating creep typically occurs instantaneously and is unobservable. By comparing the shear creep process of bolted and unbolted rock joints, it is observed that the presence of bolts decelerates the deterioration of joint surfaces, resulting in a shorter duration of transient creep and lower creep rate. Furthermore, the bolt alters the creep failure mode of the rock joint from brittle failure to plastic failure. Based on experimental results, the reinforcement effect of the bolt through joint creep is analyzed, and the stress evolution during creep is divided into three stages, i.e., the stress-compatibility stage, the stress-compensation stage, and the stress-limitation stage. We summarize how the bolt compensates for stress loss caused by joint surface deterioration through increased shear and axial forces, thereby reducing the creep rate and creep deformation of the rock joint. Based on the stress compensation mechanism of the bolt, a B-Q-N (Burgers-shear force Qo-axial force No) creep constitutive model for bolted rock joints is proposed. When the creep behavior of the unbolted rock joint and the anchorage parameters are known, the B-Q-N model can describe the shear creep behavior of bolted rock joints without experimental data for parameter identification, as well verified by our tests.

High‐Temperature Creep Behavior of Selective‐Laser‐Melting‐Fabricated Lattice Structures Inspired from Euplectella Aspergillum

In this study, the lattice‐like arrangement of Euplectella aspergillum is used to derive bionic grid‐stiffened structures in the form of thin tubes. The bionic tubes are 3D printed with AlSi10Mg alloy using a selective laser melting process. High‐temperature creep behavior at 250 °C and stress (0.3–0.7) times yield strength of the tubes is studied under uniaxial constant compressive load. The effect of the stress level, temperature, and tube design on the creep performance and deformation behavior is studied. The creep performance of bioinspired tubes is compared with honeycomb lattice tubes. In the results, the dependence of creep life and creep rate on the design of the bionic tubes is shown. E. aspergillum–based thin tubes show higher creep life and lower creep rate as compared to honeycomb‐based tubes at all stress levels. Also, the creep curves of lattice structures based thin tubes are different than the solid material, especially in the primary and tertiary regions. The fractography analysis shows higher creep life in E. aspergillum–inspired thin tubes is due to the improvement in ductility at high temperature. The stress exponent value in the Mukherjee–Bird–Dorn equation shows that the mechanism of creep is diffusion. Herein, in the results, it is shown that the bioinspiration and additive manufacturing provide an opportunity to design and fabricate advanced iso‐grids structures.

Experimental study on the influence of cracks on tunnel vibration under subway train load

The impact of train vibration on the tunnel lining is a popular research topic. Under long-term train operation, the tunnel lining may incur damage, mainly longitudinal cracks, which will further increase the vibration caused by running trains, impacting the lining and the surrounding soil and eventually endangering the safety of train operation. To understand the influence of cracks on tunnel vibration under train load, we performed a model test of a shield tunnel with and without typical cracks based on a line of Hangzhou metro prototype to characterize its dynamic responses under train vibration loads. To simulate the tunnel lining material, the tunnel segment was lined up with polymer cast nylon with low creep rate and high strength. An inverted shaker simulated the train vibration load, and an accelerometer was used to measure the dynamic response of the tunnel structure and the surrounding soil. The results show that the dynamic response of the cracked section is significantly larger than that of the intact section, and due to the propagation characteristics of vibration, the expansion effect inside the tunnel is significantly greater than that of the surrounding soil. When the frequency spectrum results of the tunnel structure and the surrounding soil are compared, it is found that the vibration level of the surrounding soil due to cracks is mainly concentrated at around 100 Hz, while that of the tunnel structure at around 315 Hz, indicating that the cracks have a targeted effect on the expansion of the dynamic response. Meanwhile, the excessive vibration of intact segments is –2 or –1 dB, and the existing vibration reduction measures can meet the damping requirements. However, the excessive vibration caused by typical cracks can go up to 12 dB. Therefore, corresponding vibration reduction measures should be taken according to specifications. Finally, this paper proposes some vibration reduction suggestions and crack repair measures.

Tensile creep of textured Ti2AlC in the 1000–1150°C temperature range

Alumina forming, oxidation and thermal shock resistant MAX phases are of high interest for high temperature applications. Herein we report on the fabrication of a highly textured Ti2AlC MAX phase and its creep behavior. Creep rates were measured in the temperature range of 1000–1150 °C under a tensile stress range of 15–50 MPa. The minimum creep rate is given by a power law, with stress exponent of 2.5 ± 0.1 and an apparent activation energy of 320 ± 20 kJ/mol. The textured Ti2AlC samples has significantly lower creep rates than their untextured counterparts, and their times to failure are longer. These enhancements can be partially attributed to the ability of the textured grains, whose basal planes were parallel to the applied load, to form crack bridges. Transmission electron microscopy indicated the defect density before creep was higher than after creep and that the vast majority of grains were defect-free. And while this observation cannot be explained in a dislocation framework, it can in a ripplocation one. We carried out molecular dynamics calculations on graphite showing that ripplocations near a free surface can readily escape, even at 10 K, in principle, solving the mystery.

Modifying Microstructure and Mechanical Properties of Mo-Nb Single Crystals via Thermal Annealing

Molybdenum-Niobium (Mo-Nb) single crystals possess excellent mechanical properties, such as high strength and low creep rate at high temperatures, which leads to Mo-Nb single crystals’ potential application in the irradiated and aerospace environment. Mechanical properties at high temperatures are closely related to structural defects, including the density of dislocation and low-angle grain boundaries in a single-crystal Mo alloy. It is well known that the density of defects is mainly contributed to by processing and annealing. To clarify the microstructural evolution of Mo-Nb single-crystal alloys, thermal annealing tests with temperatures varying from 1100 °C to 1700 °C were conducted. Two Nb contents (3 at.% and 6 at.%) were chosen to investigate the effect of Nb content on the thermal stability (≤1700 °C) of single-crystal Mo-Nb alloys. Samples with high Nb content (6 at.%) soften after annealing, while ductility at room temperature obviously enhances In the low Nb content (3 at.%) sample, however, hardening and softening occur after low (1100 °C) and high temperature annealing, respectively. The evolution of mechanical properties could be mainly attributed to the change of density in the low-angle grain boundary. Furthermore, the changing Nb element and dislocation density during annealing are still important to the strength and ductility of Mo-Nb single crystals.

Compressive creep behavior and microstructural evolution of sand-cast and peak-aged Mg–12Gd–0.4Zr alloy at 250 °C

Magnesium (Mg) alloys with high concentrations of Gd additions are known to exhibit high strength and good creep resistance at elevated temperatures. However, the main mechanisms including microstructural evolution and dislocation configurations for clarifying the low creep rates of Mg–Gd–Zr alloys are still controversial. The present work investigates the compressive creep behavior of both the sand-cast and peak-aged Mg–12Gd–0.4Zr (wt.%) alloys at a fixed temperature of 250 °C under the applied stress range of 60–100 and 80–120 MPa, respectively. It is revealed that β' and β'F precipitates distribute alternately forming precipitate chains in Mg–Gd–Zr alloys. Furthermore, β'+β'F precipitate chains led to the honeycomb-like structure in the sand-cast alloy during the creep process, improving its creep resistance to some extent. Nevertheless, weakly strengthening β1 precipitates occurred and detrimental β phases coarsened, which weakened the creep performance of the sand-cast alloy. However, the slight improvement of creep resistance in the peak-aged Mg–12Gd–0.4Zr alloy can be mainly attributed to the formation of precipitate-free zones (PFZs) and also the premature coarsening of β'+β'F precipitate chains. During creep, the cross slip of basal and prismatic <a> dislocations become the dominant creep mechanism for the sand-cast alloys. By contrast, the cross-slip of basal <a> dislocations and pyramidal <c + a> dislocations is the dominant creep mechanism for the peak-aged alloys, which was arrested by precipitates then strengthening the creep resistance of peak-aged alloys.

Unexpected creep behavior in a rejuvenated metallic glass

Rejuvenation, bringing metallic glasses (MGs) to the younger and higher energy states, provides an alternative avenue to explore the interplay between the property and microstructures of MGs. In this study, the creep behavior of the Zr69.5Cu12Ni11Al7.5 MGs was experimentally examined by controlling the energy state in terms of structural rejuvenation and thermal annealing. It is found that compared to the as-cast counterpart, the annealed MG at a lower energy state exhibits a higher hardness, a smaller displacement, and a lower creep rate due to the decreased free volume and the inhibited activation of the shear transformation zone. Conversely, the rejuvenated MG at a high energy state displays lower hardness and increased free volume content, yet it demonstrates superior creep resistance compared to its as-cast counterpart, which deviates from conventional understanding. This unexpected phenomenon occurs as the initial high-content free volume annihilates during creep, and strain hardening takes precedence over strain softening as the prevailing process during creep deformation, leading to a superior creep performance in extremely rejuvenated MGs.

Prediction of nanoindentation creep behavior of tungsten-containing high entropy alloys using artificial neural network trained with Levenberg–Marquardt algorithm

This paper describes the synthesis of tungsten-containing high-entropy alloys (HEAs). The synthesis method involves a powder metallurgy process, and spark plasma sintering (SPS) is used to compact the powder. XRD and SEM analyses of synthesized HEAs showed that the main phases formed were body-centered and face-centered cubic phases, and a sigma phase was also observed after sintering at 900 ℃. Furthermore, nanoindentation showed that the introduction of tungsten in HEA resulted in high hardness and elastic modulus, which ranged from 8.31 to 13.57 GPa and 197.21–209.43 GPa respectively. The indentation creep behavior was ascertained at room temperature. The HEAs exhibited a significant benchmark after the addition of a specific amount of W for further investigation because of their lower creep rate. Experimental creep displacement data were used for modeling by artificial neural networks (ANNs) in which the training has been performed by the Levenberg–Marquardt algorithm. The experimental creep displacement data and the ANN model predictions have an excellent agreement. The ANN model is reliable and can accurately forecast the room temperature creep behavior of HEAs. HEAs are promising candidates for use in elevated and wear-resistance applications, owing to their unique combination of high hardness and high creep resistance.

Effect of Ru on Deformation Mechanism and Microstructure Evolution of Single-Crystal Superalloys under Medium-Temperature and High-Stress Creep

In this work, the effect of the Ru element on the γ'-phase evolution and deformation mechanism in the fourth-generation Ni-based single-crystal superalloy was investigated. Results show that the Ru element alters the distribution coefficient of other elements in the alloy to produce reverse partitioning behavior, which leads to a difference in microstructure between 0Ru and 3Ru. The addition of Ru triggered the incubation period before the beginning of the primary creep stage, which depends on the creep temperature and stress during creep deformation. TEM results revealed that Ru addition inhibits the slip system {111}<112> at medium-temperature (760-1050 °C) and high-stress (270-810 MPa) creep, which brings a considerably low creep rate and high creep life to the Ru-containing alloy.

Effect of Al addition on creep resistance of the fired SiC-MgAl2O4 composite refractories

SiC-MgAl2O4 composite refractories were prepared by using SiC particles, MgAl2O4 powders, α-Al2O3 micro-powders and metal Al powders as raw materials under flowing nitrogen at 1450 °C. The creep test was conducted at 1400 °C under 0.2 MPa for 50 h and the effects of Al addition on the creep resistance of SiC-MgAl2O4 composite refractories were investigated. The results show that the creep rate of samples without Al addition increases gradually as time prolonging while the samples with Al addition has a better creep resistance and the creep rate always contains a low creep rate. The mechanism for improving creep resistance of the samples with Al addition could be concluded as follow. During the creep test, the samples have a oxygen concentration from surface areas to the inner areas. (Al2OC)x-(AlN)(1-x) whiskers (generated during the sintering process) at the surface area preferentially reacts with oxygen to form Al2O3 and a little SiC oxidizes to SiO and even SiO2, the formed Al2O3 and SiO/SiO2 can react with the MgAl2O4 matrix to generate mullite, cordierite and MgO. MgO and SiO/SiO2 could also transfer and react with Al2O3 to generate new MgAl2O4 particles and even plate β-Sialon dispersed in pores where (Al2OC)x-(AlN)(1-x) whiskers ever existed. The formation of mullite, cordierite, MgAl2O4 particles and plate β-Sialon had a synergistic effect to improve the creep resistance. Besides, these new phases could fill the pores and inhibit the diffusion of oxygen inside the samples. With a relative low oxygen partial pressure inside, most of the (Al2OC)x-(AlN)(1-x) whiskers still existed in samples with a network structure and only partly oxidized to Al2O3, the oxidation of SiC was inhibited and formation of liquid was avoided. Thus, the creep resistance of the sample was further enhanced.

Optimization of creep and thermal features of the Sn-Ag-Cu-Zn alloy by the magnetic field

A key factor in ensuring the service life of microelectronic devices is the creep and thermal characteristics of alloys. As a result, the present work aims to develop the creep features and thermal analysis of Sn-2.0 wt% Ag-0.5 wt% Cu-2.0 wt% Zn (SAC205-2Zn) in the presence of a magnetic field. Based on the microstructure examination, applying the magnetic field reduced the β–Sn fraction and refined the eutectic phases. The average grain size of β–Sn in the SAC205-2Zn alloy was 27–35 ± 3 μm, and the average size of intermetallic compounds (IMCs) was 4–9 ± 1 μm. In contrast, the average sizes of IMCs and β-Sn in Sn-2.0 wt% Ag-0.5 wt% Cu-2.0 wt% Zn with a magnetic field (SAC205-2Zn-B) were 1–5 ± 1 and 10–16 ± 2 μm, respectively. According to the DSC analysis, the melting temperatures (Tm) were 221.7 °C for SAC205-2Zn and 221.8 °C for SAC205-2Zn-B. In addition, the pasty ranges for SAC205-2Zn and SAC205-2Zn-B were 8.6 and 8.2 °C, respectively. Besides, the magnetic field's existence reduced the undercooling (ΔT) of SAC205-2Zn by 15.5 °C, leading to an improvement in the solidified phases' nucleation. Clearly, SAC205-2Zn-B displayed a lower creep rate (38.5 %) and higher creep resistance compared with those of the SAC205-2Zn alloy. Interestingly, the creep lifetime increased by 164 % under the magnetic field effects. The obtained results using a novel feasible method have significant implications for electronic applications.

Creep strengthening mechanisms of a superlattice γ′-strengthened Co–Al–W–Ta–Ti single crystal superalloy at steady-state conditions under compressive stresses

The strengthening mechanism of steady-state creep is a critical factor in developing advanced superalloys. In this study, the steady-state creep mechanisms of a superlattice γ′-strengthened Co–Al–W–Ta–Ti single crystal superalloy are investigated with the creep conditions of 750 °C/800 MPa, 900 °C/420 MPa and 1000 °C/137 MPa. Results suggest that the microstructures of steady-state creep samples are significantly different under the above three experimental conditions. A detailed TEM study shows that, Lomer-Cottrell locks and stacking faults interactions are responsible for the low creep rate at low temperature and high stress creep regime, dislocations cross-slip and the dislocation tangles contribute the main creep resistance at intermediate temperatures and moderate stress creep regime, interactions of stacking faults and dislocation networks are the strengthening mechanism for the high temperature and low stress creep regime. The steady-state creep rate of investigated alloy follows the classical power law equation, and the creep activation energy calculated by the power law equation is 378.46 kJ/mol. The results of this study provide insights into the effects of temperature and stress on steady-state creep mechanisms, and high activation energy makes the γ′-strengthened Co–Al–W–Ta–Ti single crystal superalloy an attractive candidate for further study as a high temperature structural material.

Creep properties of TiC/Al7075 composites prepared by coupling process of FSP and heat treatment

In this work, composites of TiC and 7075 aluminum alloy are prepared by friction stir processing coupled with heat treatment to improve the material properties and tested for creep performance. Experimental results showed that the composites displayed a low creep rate and a high creep life after the coupling treatment. The TiC particles exhibited good interfacial bonding coherence in the matrix, and the creep mechanism is changed from the viscous sliding of dislocations to the grain boundary sliding creep control mechanism.

Effects of lattice distortion and chemical short-range order on creep behavior of medium-entropy alloy CoCrNi

Creep behavior of multi-principal element alloys (MPEAs) is an intriguing topic to explore for their potential high-temperature applications. The challenge on this topic is to elucidate what effect the local chemical fluctuation has on the creep behavior of MPEAs. By using large-scale molecular dynamics (MD) simulations, we investigate the creep performances of CoCrNi medium-entropy alloys (MEAs) with and without chemical short-range order (CSRO) as well as the Average-atom (A-atom) counterpart (no lattice distortion (LD)) under different uniaxial tensile stresses at various elevated temperatures. A power-law model is adopted to analyze the implicit stress exponent and activation energy, which are associated with the creep mechanism and creep resistance, respectively. The results reveal CSRO rather than LD plays an important role in creep performance. Specifically, with the introduction of CSRO, the activation energy for creep in CoCrNi MEA is significantly increased and finally close to the activation energy for the diffusion of the Cr element that is the highest among the three elements (Co, Cr, and Ni). The CoCr clusters in the MEA with CSRO make it difficult to increase the shear strain in the creep process, resulting in a much lower creep rate than that of the CoCrNi MEA without CSRO. For the CoCrNi MEA without CSRO, grain boundary diffusion is the main creep mechanism. For the MEAs with CSRO, the predominant creep mechanism depends on the applied stress. At low stress, grain boundary diffusion still prevails and there is no obvious dislocation glide or grain boundary sliding. When the applied stress is high enough, grain boundary diffusion and dislocation slip dominate the creep behavior, accompanied by the occurrence of grain boundary sliding.

Achieving high strength and creep resistance of a Mg-13Gd-6Y-0.2Zr alloy forging fabricated by isothermal forging and artificial aging

Mg alloys are limited in applications due to low strength and poor creep resistance. The requirement for Mg alloy components to be used at 200 °C is proposed in the aerospace industry. Although Mg-Gd-Y-Zr alloys have superior mechanical properties, the creep properties of practical Mg-Gd-Y-Zr alloy forgings have not been reported, which is related to their industrial utilization. In this work, a typical Mg-13Gd-6Y-0.2Zr (wt%) alloy forging used in the aerospace industry was fabricated by a combination of isothermal forging and artificial aging. The forging exhibits excellent creep resistance with a steady-state creep rate of 2.26×10−9 /s at 200 °C and a stress of 60 MPa, while achieving the ultimate tensile strength of 475 MPa (Engineering stress) higher than those of reported wrought Mg-RE alloys with similar elements. The occurrence of recrystallization during isothermal forging refines the grains, increasing strength. The uniformly distributed β' phase (30–50 nm) formed during aging provides effective strengthening. The low steady-state creep rate is mainly attributed to the formation of the finer precipitates (5–10 nm) during creep tests, which contribute to reducing the precipitation-free zones near the grain boundaries and retarding creep behaviors by hindering dislocation movements.

Enhancing the high-temperature creep properties of Mo alloys via nanosized La2O3 particle addition

Molybdenum (Mo) alloys with different La 2 O 3 particle additions (0.6, 0.9, 1.5 wt.%) were prepared by powder metallurgy to investigate the effect of La 2 O 3 particles on microstructural evolution and creep behavior of the alloy. Pure Mo, annealed at 1500 °C for 1 h, presented a fully recrystallized microstructure characterized by equiaxed grains. The alloys doped with La 2 O 3 particles (Mo-La 2 O 3 alloys), on the other hand, exhibited fibrous grains elongated in the rolling direction of the plate. In contrast to the shape of the grains, the average grain size of the alloys was found to be insensitive to the addition of La 2 O 3 particles. Nanosized La 2 O 3 particles with diameters ranging from 65 nm to 75 nm were distributed within the grain interior. Tensile creep tests showed that dislocation creep was the predominant deformation mode at intermediate creep rate (10 −7 s −1 -10 −4 s −1 ) in the present alloys. The creep stress exponent and activation energy were found to decrease with increasing temperature, particularly within the low creep rate regime (<10 −7 s −1 ). The Mo-La 2 O 3 alloys exhibited remarkably greater apparent stress exponent and activation energy than pure Mo. A creep constitutive model based on the interaction between particles and dislocations was utilized to rationalize the nanoparticle-improved creep behavior. It was demonstrated that low relaxed efficiency of dislocation line energy, which is responsible for an enhanced climb resistance of dislocations, is the major creep strengthening mechanism in the Mo-La 2 O 3 alloys. In addition, the area reduction and creep fracture mode of the Mo-La 2 O 3 alloys were found to be a function of the creep rate and temperature, which can be explained by the effect of the two parameters on the creep and fracture mechanisms.