Creep Strengthening Research Articles

Load transfer behavior in semisolid formed hypereutectic Al-Fe-based alloys during tensile creep

The tensile creep behavior of semisolid formed hypereutectic Al-Fe-based alloys (for short Al-5Fe-based alloys) is investigated at temperatures ranging from 200 °C to 350 °C and stresses ranging from 30 MPa to 100 MPa. A power law model incorporating the “generalized” load transfer term is employed to rationalize creep data for Al-5Fe-based alloys with respect to that of the pure aluminum as a corresponding matrix without second phases and/or reinforcements. This expression proves more suitable for describing the creep characteristics of Al-5Fe-based alloys. The AlFe phases in the alloys transfer and bear load, and have no interaction with dislocations practically, which is the main reason for the creep strengthening of Al-5Fe-based alloys. The results obtained in this study are validated by creep data for Al-Fe alloys obtained by a thorough literature review.

Effect of Si addition on the microstructure and creep properties of the forged titanium alloy

Creep experiments were carried out on pure Ti after annealed (720 °C/2 h, AC), Ti-0.4Si alloy after annealed (720 °C/2 h, AC) and thermal exposed (720 °C/2 h, AC+600 °C/500 h, AC) respectively. The presence mode of Si in Ti-0.4Si alloy after two heat treatments is partial precipitation and complete precipitation respectively. Combined with SEM and TEM characterization, the effects of Si addition on the creep properties and creep mechanism and the dominant roles of solid solution Si and silicide in improving the creep resistance of titanium alloys were investigated. The results show that the annealed Ti-0.4Si alloy has the best creep resistance, indicating that the addition of Si significantly improves the creep resistance of titanium alloys, and the Si has a creep strengthening effect whether it exists in solid solution state or in precipitated state. The high creep activation energy (Q = 253 kJ/mol) of the annealed Ti-0.4Si alloy is due to the strong inhibition of solid solution Si and dynamically precipitated silicide on matrix diffusion, indicating that the precipitation strengthening effect of dynamically precipitated silicide during creep is significantly stronger than that of precipitated silicide before creep, and obviously compensates the diffusion effect of dynamic precipitates during the precipitation process.

Contribution of the Fe-rich phase particles to the high temperature mechanical behaviour of an Al-Cu-Fe alloy

The high temperature strengthening mechanisms in Al-Cu-Fe aluminium alloy was analysed basis on a comprehensive microstructural study of the as-cast alloy and mechanical testing results. An approach which extracts the specific contribution of solid solution atoms, precipitates, and Fe-rich particles to the creep strengthening was utilized. Additionally, the Shear Lag model, was employed to account for the contribution to strengthening of the Fe-rich intermetallic particles through a load transfer mechanism. For this study, an as-cast Al-Cu alloy, which does not contain Fe impurities, has been also used for comparative purposes. The findings suggest that the large and 3D interconnected Fe-rich phase particles (Al6(MnFe) and α-Fe) generate the main strengthening effect at high temperature through a load transfer mechanism, whereas the contribution of the nanometric Al2CuMg precipitates were very limited.

Investigation of the thermal creep behaviour of non-irradiated Zr1%Nb cladding alloys between 623 and 1223K

Short-term constant stress creep tests in tension were performed on two zirconium Zr1%Nb cladding alloys in the form of thin-walled cladding tubes in the temperature range of 623–1173 K and at the applied tensile stress σ range of 5 - 225 MPa to provide further information on their creep behaviour in the α-Zr and (α+β)-Zr phase regions. In parallel, the evolution of the microstructure of the studied alloys was investigated using SEM and TEM microscopy in the as-received state and after creep exposures. Using the dependence of diffusion coefficient-compensated minimum creep rate vs modulus compensated applied stress the values of the stress rate exponent n = (∂lnε˙m/∂lnσ)T were determined ranging from ∼2.5 up to ∼16 depending on the applied stress and testing temperature. The stress-dependant activation energy for creep QC=[∂lnε˙m/∂(-1/kT)]σ was determined and possible creep deformation mechanisms as well as creep strengthening mechanisms are discussed. Under the loading conditions used in this study three distinct stress regions were identified according to the relevant controlling creep deformation mechanisms.

Effects of alloying elements on the super-lattice intrinsic stacking fault energy and ideal shear strength of Ni3Al crystals

The effects of alloying elements (Re,W,Ti,Ta,andMo) on the super-lattice intrinsic stacking fault energy and ideal shear strength (σmax) of Ni3Al crystals at 0 K was studied through first-principles calculation. The calculated formation enthalpy of point defects reveals that single solute atoms (i.e., Re,W,Ti,Ta,andMo) tend to occupy the Al site, while solute–solute complex defects (i.e., Re-Re, Re-W, Re-Mo, Re-Ta, Re-Ti, W-Mo, W-Ta, W-Ti, Mo-Ta, Mo-Ti, and Ta-Ti) tend to occupy the Al-Al site. The addition of single solute atom can increase the unstable stacking fault energy and ideal shear strength (σmax) of perfect Ni3Al crystals. Therefore, the doping of a single solute atom is beneficial for the creep strengthening of Ni3Al crystals. Compared with the doping of W,Ti,Ta,andMo, the doping of Re can more effectively impede the nucleation and movement of dislocations of Ni3Al crystals. Through the careful comparison of the creep properties of Ni3Al crystals with solute–solute complex defects, a conclusion can be drawn that the doping of alloy elements W and Re exhibit similar strengthening effects on the creep properties of Ni3Al crystals. W can be preliminarily predicted to replace part of Re in Ni3Al crystals without affecting creep properties. In addition, comprehensive evaluation reveals that the weak interaction between solute–solute complex defects should improve the strengths of Ni3Al crystals to a certain extent.

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.

Extraordinary creep resistance in a non-equiatomic high-entropy alloy from the optimum solid-solution strengthening and stress-assisted precipitation process

Improving creep resistance has commonly been achieved by the optimization of alloy design that results into strong solid-solution strengthening and/or coherent precipitates for dislocation blockage. High-entropy alloys (HEAs), despite their single-phase solid-solution nature, only exhibit creep properties that are comparable to precipitate-strengthened ferritic alloys. Moreover, many HEAs are found to be plagued with many incoherent second phases after long-term annealing, which reduces the lifetime and thus prohibits their usage at elevated temperatures. The present work demonstrates the extraordinary creep resistance of a non-equiatomic Al0.3CoCrFeNi HEA, in which the creep strain rate is found to be several orders of magnitude lower than the Cantor alloy and its subsets. Using a suite of characterization tools such as atom probe tomography (APT) and transmission electron microscopy (TEM), it was shown that a B2 precipitate phase that has been widely seen during annealing is suppressed during the early stage of the creep deformation. Currently, metastable and coherent L12 precipitates emerge and provide significant creep strengthening. This observation is rationalized by the coupling between the applied stress and the lattice mismatch. In the range of 973 ∼ 1033 K, the stress exponent and activation energy were determined to be 3–6.53 and 390–548.2 kJ·mol−1, respectively. The creep lifetime, on the other hand, is comparable to Cantor subset alloys because the precipitate free zone near the grain boundaries does not provide sufficient constraint for the grain boundary cavity growth. The present work provides a pathway to design novel HEAs with improved creep resistance.

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.

High-temperature strengthening mechanism and thermal stability of Laves phase in ferritic matrix

The high-temperature creep strengthening mechanism and thermal stability of Laves phase are the key factors that affect its strengthening property in ferritic matrix. Therefore, in this study, two types of C14 Laves phase alloys, namely, Fe2Nb Laves phase Alloy S1 (Fe–9Cr–4Al–2Nb) (wt.%) and Fe2W Laves phase Alloy S2 (Fe–9Cr–4Al–2W) (wt.%) were prepared to investigate the strengthening mechanism and strengthening effect of Laves phase with different compositions in ferritic matrix. The creep properties and microstructure characteristics of the two alloys, in particular, the interfacial structure characteristics between Laves phases (Fe2Nb and Fe2W) and ferritic matrix were analyzed. The true stress exponent n for both Alloys S1 and S2 is 5, and the true activation energies Q of Alloys S1 and S2 are 372.47 and 365.82 kJ mol−1, respectively. The creep mechanisms of Alloys S1 and Alloy S2 are both dislocation climbing-dominated processes reinforced with precipitated phases. Alloy S1 exhibits higher high-temperature creep resistance than that of Alloy S2. The grain size of Alloy S1 is smaller than that of Alloy S2. Both the precipitates Fe2Nb in Alloy S1 and Fe2W in Alloy S2 are mostly located at the grain boundary. The density of dislocation in Alloy S1 is higher than that in Alloy S2, and the bending degree of dislocation lines caused by precipitate hindrance is also higher than that in Alloy S2. The orientation relationships between the Laves phase Fe2Nb and ferritic matrix in Alloy S1 are [011]α-Fe//[5 1‾9‾4‾]Fe2Nb, (011‾)α-Fe//(03 3‾ 1)Fe2Nb, with the atomic interface mismatch of 1.6%; the orientation relationships between the Laves phase Fe2W and ferritic matrix in Alloy S2 are [001]α-Fe//[01 1‾ 2]Fe2W, (1 1‾ 0)α-Fe//(01 1‾1‾) Fe2W, with the atomic interface mismatch of 1.9%. The results indicate that the Fe2Nb-type Laves phase may be more suitable to candidate for the strengthener in the ferritic matrix compared with Fe2W-type.

The Coupling Effect of Hierarchical Structures and MN‐Type Precipitates on the Creep Resistance for the High N Heat‐Resistant Martensitic Steel

Microstructure of the high nitrogen heat-resistant martensitic-steel (HNHM) crept using 140-170 MPa loading stresses at 923K, is investigated in correlation with creep lifetime and creep rupture strength. Upon creep deformation, both recrystallized grains and the pre-existed hierarchical structures grow via SIBM induced the degradation of strengthening. For pre-existed hierarchical structures in HNHM, martensitic packets and blocks are more inclined to form at higher stresses (170 MPa), causing the degradation of strength, while laths retain easily at lower stresses (140 MPa-155 MPa), retarding the creep damage. Additionally, under all stresses and upon 923K, the highly stabilized MN precipitates not only pin the hierarchical structural boundaries effectively, but also act as the core for the nucleation of Laves, realizing strengthening. The findings elucidate the coupling contribution of hierarchical structures and MN-type precipitates on the creep strengthening for HNHMs, challenging the common viewpoint that the coupling coarsening of lath and precipitates dominates the degradation of strengthening, and thus, deepens the understanding of the creep resistance of the HNHM and provides the first insights into obtaining reliable predicted creep life of the novel HNHMs. This article is protected by copyright. All rights reserved.

Mechanical characterization and creep strengthening of AZ91 magnesium alloy by addition of yttrium oxide nanoparticles

In the current research, the authors have attempted to improve the mechanical properties and creep behavior of the magnesium alloy Mg–9Al–1Zn (AZ91) in three different stress levels. To this end, the present study investigated experimentally the addition effects of different values of yttrium oxide nanoparticles to the AZ91. In this regard, weight percentages of 0.5%, 1%, 1.5%, and 2% nanoparticles were added to the material using the vortex casting method. Then, various test specimens were fabricated based on the ASTM standards by utilizing a Computer Numerical Control lathe machine. Different experiments were performed, and the results of different groups were compared with each other. The results revealed that the addition of yttrium oxide (Y2O3) nanoparticles increases the strength of AZ91 magnesium alloy until the nanoparticles do not clump in the microstructure. In other words, the tensile strength of the nanocomposite increased by adding nanoparticles up to 1.5%, but by adding 2% of nanoparticles, we found that the tensile strength is lower than that of pure magnesium. Moreover, one of the most important achievements of this study is that if the nanoparticles do not clump in the material microstructure, the addition of Y2O3 increases the rate of stable creep (the secondary creep stage). Also, the experimental results indicated that the highest stable creep rate is related to the nanocomposite with 1.5% yttrium oxide nanoparticles. Furthermore, the maximum hardness of the material was obtained in the same case.

Design for 1200 °C creep properties of Ni-based single crystal superalloys: Effect of γ′-forming elements and its microscopic mechanism

Enhancing ultra-high temperature mechanical properties of turbine blade-manufacturing Ni-based single-crystal superalloys is crucial to advanced aero-engines. However, the service temperature still does not rise to 1200 °C, at which severe microstructure degradation and accelerated plastic deformation due to thermal activation deteriorate creep resistance. This work investigates the effect of γ′-forming elements, including Al and Ta, on 1200 °C/80 MPa creep properties and its corresponding mechanism. The creep property is sensitive to Al and Ta addition, reaching its peak in our designed composition region. The microstructure evolution during creep is also sensitive to Al and Ta; particularly, adding γ′-forming elements facilitates abnormal rattan-shaped γ′ phase formation. Evidenced by typical three-stage creep behavior, “cubic-raft-collapse” microstructural evolution, and dislocation configuration analysis, 1200 °C creep resistance would originate primarily from classical 1100 °C creep strengthening mechanisms. Besides, the detrimental impact of the rattan-shaped γ′ phase is revealed, which should also be considered. Further research indicates that Al addition produces a lower degree of γ′-solubility, more negative lattice misfit, higher γ′-fraction, and more rattan-shaped γ′ phase, while Ta addition produces lower γ′-solubility, more positive misfit, higher γ′-fraction and more rattan-shaped γ′ phase. The alloying composition-phase/interface-properties relationship has been established for 1200 °C creep, which explains the peak performance of SCA4 alloy. These results provide new opportunities to design superalloys that resist ultra-high temperature service and elevate the service temperature limit.

Revisiting copper as a case study of creep in pure metals: Prediction of creep response in pure Cu in half-hard and friction-stir-processed states

A physical model was used to obtain a pre-assessment of the dependence of minimum creep rate on stress and temperature for ETP copper under two different initial conditions, i.e., in the R240 half-hardened state and after friction stir processing. Although the R240 samples contained a high dislocation density owing to pre-straining, the material that underwent friction stir processing (FSP) had a much finer grain size and a far lower dislocation density.The original Sandström physically based model developed for copper was modified to take into account the strengthening role of the grain boundaries, and its declining importance with increasing temperature and/or decreasing applied stress. In addition, the grain growth effect was estimated using appropriate empirical equations. The model curves obtained by introducing a few initial information, such as the grain size and the ultimate tensile strength at room temperature, in the resulting set of constitutive equations, largely overlapped. This finding was somewhat in conflict with the traditional view, which assumes that a fine grain size is an ineffective source of creep strengthening, if not detrimental.Subsequent creep experimental testing carried out between 178 and 355 °C substantially confirmed the picture provided by the pre-assessment, and the minimum creep rate values for the two materials largely overlapped on the same curves. Only at 355 °C did the FSP samples exhibit a somewhat higher creep rate, when compared with the R240 samples and the pre-assessment curve. The experimental data obtained for R240 copper at 475 °C were not properly described by the physical model, as expected on the basis of the previous literature reports.

Examining the creep strengthening nanoprecipitation in novel highly reinforced heat resistant steels

In this work, the creep strengthening nanoprecipitation in novel heat resistant steels strengthened by a high density of stable nanoprecipitates has been studied. The results show that the high number density of MX nanoprecipitates within the martensitic laths in these steels comes from the great amount of MX former elements present in their chemical compositions and the high dislocation density generated by the martensitic transformation that takes place during cooling after austenitization. These dislocations act as nucleation sites for these nanoprecipitates during the tempering applied after the austenitization and quenching. Atom probe tomography measurements show that these nanoprecipitates are rich in Nb, V, Cr and N for the HDSN1 and HDSN2 steels and V, Cr and N for the HDSN3 steel. The distribution of the nanoprecipitates within the martensitic laths suggests that the creep strengthening produced by the Nb, V, Cr and N nanoprecipitates in the HDSN1 and HDSN2 steels is more effective at pinning dislocations at high temperature than that obtained in the HDSN3 steel by the V, Cr and N nanoprecipitates. However, the high amount of W in the HDSN3 steel enhances the solid solution strengthening at high temperatures, resulting in a similar high temperature strength for all HDSN steels.

A novel damage-based creep model considering the complete creep process and multiple stress levels

Abstract To develop a unified creep model, the complete creep process of rock is divided into the deceleration region and acceleration region based on the typical deformation characteristics and mechanism of the rock creep behavior. By introducing the time-hardening theory and the damage theory, the analytical solutions of creep strengthening and weakening behaviors during the complete creep process are obtained. A unified creep model has been established that can fully capture all the typical creep behavior stages for rock under multiple stress levels, including instantaneous elastic deformation, decelerating creep, stable creep, accelerating creep, and final failure. The model has the advantages of a simple form and easy access to parameter determination. The parameter determination methods are discussed, and the performance of the proposed model has been verified by comparing the predicted creep strain curves with the experimental results from various rock tests.

Analysis of the Combined Strengthening Effect of Solute Atoms and Precipitates on Creep of Aluminum Alloys

The creep strengthening mechanisms in (age‐hardenable) aluminum alloys are analyzed on the basis of a new microstructural study of powder samples, an analysis of a comprehensive revision of creep data from the literature, and a new modeling approach. A strategy based on the strength difference (SD) method to separate the contributions of solid solution atoms and precipitates to creep strengthening is proposed. The new methodology considers the combination of the two contributions avoiding the need of a threshold stress term in the creep equation. The contribution of both precipitates and solid solution is taken into account by means of the analysis of the lattice parameter variation with aging time. For this study, powders of two commercial AA2xxx alloys have been analyzed using diffraction methods. The experimental results are modeled using Lubarda's approach combined with the SD method.

Individual/synergistic effects of Al and AlN on the microstructural evolution and creep resistance of Elektron21 alloy

The creep properties of Mg-2.85Nd-0.92Gd-0.41Zr-0.29Zn (El21) alloys with additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al nanoparticles (NPs) were studied over a stress range from 80 to 140 MPa at 240 °C, respectively. The individual/synergistic roles of Al and AlN in the El21 alloy were investigated systematically to reveal their creep strengthening mechanisms. Creep results show that individually all three additions of 0.25 wt% Al, 0.75 wt% AlN and 1 wt% AlN/Al could increase the creep resistance of El21 alloy apparently. However, the addition of mixed 1 wt% AlN/Al NPs shows the best strengthening effect on creep properties in El21 alloy. Microstructural characterizations reveal that the additions of Al and AlN increased the area fraction of intermetallic particles obviously. Blocky Al2Zr, Al2Zr3 particles and Al2(Nd, Gd) (Al2RE) particulates were observed in both El21 + 0.25% Al and El21 + 0.75%AlN. Nevertheless, when Al and AlN were simultaneously added into El21 alloy the formation of these blocky phases Al2Zr/Al2Zr3 was suppressed, and a larger amount of Al2RE phase was observed. This is attributed to the preferential reaction between AlN and Zr, which restricted the formation of Al–Zr phase and subsequently promoted the reaction of Al-RE phase. The dominant mechanism during creep at 240 °C was calculated to be viscous glide of dislocation. The simultaneous additions of Al and AlN NPs could lead to a more homogeneous distribution of intermetallic particles and increase the amount of Al2RE phase. Such kind of microstructures is beneficial for hindering the dislocation movement, transfer the load from matrix and alleviate the local stress concentration. Consequently, El21 + 1% AlN/Al exhibits the best creep properties among four alloys.

Strengthening of 2D-C/SiC composite through creep with low stress and high temperature

ABSTRACTTo improve the resistance to matrix cracking of 2D-C/SiC composite, the composite was treated at certain creep conditions, which involve relative lower stress, higher temperature. The creep strain and matrix cracking stress (σmc) were used to determine the creep strengthening effect. Moreover, the stress redistribution model was applied to explain the stress transfer from the matrix to fibre, and therefore the creep strengthening mechanisms. The results indicate that 2D-C/SiC can be strengthened by creep at certain conditions. The ability to resist the creep strain and σmc can be improved by certain creep treatments with creep temperature of 1400°C, lower stress and longer time. The strengthening effect is resulted from the stress redistribution during the creep. The tensile residual stress is relaxed in the matrix and transferred to the fibre. The stress redistribution leads to compressive stress in the matrix and takes the advantage of superior creep resistance of carbon fibres.

Effect of cold forming strain on creep rupture properties of 47Ni-23Cr-23Fe-7W alloy

47Ni-23Cr-23Fe-7W (HR6W) is a candidate material for high temperature areas in the Advanced Ultra-Supercritical (A-USC) boilers. In this study, creep rupture properties of cold-formed materials were investigated in comparison to the solution annealed materials in order to clarify the creep strengthening mechanism of the cold-formed HR6W. It was found that the creep strength and rupture life of the cold formed HR6W increased substantially as compared with solution annealed material and creep ductility decreased. According to investigation results of microstructure and hardness changes in the crept specimens, grain boundaries in cold-formed HR6W were covered with M23C6 precipitates from the early stages of creep and the fine M23C6 particles in the grains were very stable for long period of time as compared to the lower grain boundary coverage in the solution annealed materials. These results suggested that a high density of dislocation is maintained during the test and hence it exceeded 60,000 h. This was postulated to be reason why creep rupture strength of cold formed HR6W enhanced so remarkably in comparison to the solution annealed material.

A kinetic Monte Carlo study of vacancy diffusion in non-dilute Ni-Re alloys

The beneficial effect of Re on the creep strengthening properties in single crystal Ni-based superalloys is well known, albeit understanding the underlying mechanism is still an ongoing area of investigation. The microstructure in these alloys comprises of cuboids of the hard precipitate phase embedded in a softer matrix phase. At high temperatures, the glide of creep dislocations is restricted to the matrix only, and dislocation climb is required to get around a precipitate. Vacancy diffusion is an essential component of dislocation climb and elements like Re which are slow-diffusing in Ni are expected to affect this phenomenon. In the present work, we aim to study this by calculating the effect of Re composition on the rate of vacancy diffusion in Ni using kinetic Monte Carlo simulations. First principles electronic structure calculations based on density functional theory have been used to calculate the thermodynamic and kinetic parameters in both dilute as well as non-dilute alloys. Results suggest appreciable modification of the vacancy diffusion coefficients, indicating that the beneficial role of Re in Ni-based superalloys can be largely explained by its effect on vacancy diffusion.