Mechanical Properties Of Superalloys Research Articles

Enhancement of creep properties with trace nitrogen in a low-cost nickel-based single crystal superalloy

Nitrogen (N) is an unavoidable element in single-crystal superalloys that combines with other elements to form nitrides. Large-size nitrides often become the sites of crack initiation and propagation, which adversely affect the microstructures and mechanical properties of superalloys. However, in this study, it was found that the addition of trace amounts of N could improve the creep properties of superalloys. The results indicated that the size and number of nitrides gradually increased as the N contents increased from 3 ppm to 25 ppm. In addition, the porosity first decreased and then increased. The cause of the increase and subsequent decrease in creep lives as N contents increased was the lattice expansion caused by the formation of nitrides, which reduced the porosity by compensating for volume contraction. Meanwhile, the small-size nitrides could impede dislocation movement, which benefited the creep life of the specimens, resulting in the best creep life of the specimens containing 12 ppm of N.

Avoiding microstructural instabilities in high tungsten containing superalloys by adjusting Al content

The effects of Al contents on the microstructures and mechanical properties of superalloy with high tungsten content were studied. During solidification, Al was found to be enriched in the residual liquid, which led to the transformation of eutectic morphology from reticular to bulk-like. When the Al content increased to 8 wt%, β-NiAl phase formed in the inter-dendritic region, Thermo-Calc calculations confirms such the experimental phenomenon. The absolute value of the lattice misfit between the γ/γ' phases and the elastic strain energy increases, then the size of the γ' phase increases when the Al concentration rises from 7 wt% to 8 wt%. When the Al content increased to 7 wt%, the tungsten-rich α-W phase is precipitated and the volume fraction is 1.20%. The volume fraction of the α-W phase increases to 7.84% when the Al content reached 8 wt%, which is consistent with the Thermo-Calc calculation results. After the room temperature tensile and stress rupture life test at 975 °C / 235 MPa, it revealed that the precipitation of hard and brittle α-W and β-NiAl phases with high Al content, which resulted in the mechanical properties decreased due to the crack initiation at multiple locations and then interconnected. The higher density of γ' phase with 6 wt% Al makes it difficult for dislocations to bypass. The site of crack initiation is decreased due to the absense of brittle phase. The stress rupture life can reach 49.21 h of the alloy.

Effects of pre-precipitation treatment temperature on the microstructure and mechanical properties of nickel-based powder superalloy

The slow-cooling treatment has been observed to induce the formation of serrated grain boundaries, which effectively enhance the creep strength of nickel-based powder superalloys. However, this heat treatment also leads to the coarsening of γ′ precipitates in nickel-based alloys, which impairs their dispersion-strengthening effects. To address this issue, the high-temperature pre-precipitation treatment (HTPT) was employed to simultaneously form fine γ′ precipitates and serrated grain boundaries in the alloys. A systematic investigation was conducted to analyze the impact of various HTPT intermediate temperatures (ranging from 1150 to 1110 °C) on the microstructure and mechanical properties of the superalloy. In this study, a significant increase in the volume fraction of secondary γ′ with a butterfly-shaped morphology, from 1.6% to 27.7%, was observed as the intermediate temperature was decreased from 1150 to 1110 °C. Simultaneously, the average size of spherical tertiary γ′ precipitates decreased from 73.3 nm to 52.7 nm. Serrated grain boundaries were observed in the samples when the HTPT temperature was below 1140 °C, with increasing amplitudes ranging from 2.1 to 2.8 μm. To investigate the formation mechanism of these serrated grain boundaries, we focused on the interactions between γ′ precipitates and grain boundaries. At temperatures below 1135 °C, a fan-shaped structure consisting of finger-shaped γ′ dendrites and γ phases was observed, which potentially contributes to the formation of serrated grain boundaries. Among the samples tested, the sample subjected to an HTPT temperature of 1130 °C showed the best mechanical properties at room temperature (1542 MPa, 12.9% elongation), while the 1140 °C sample exhibited superior performance at 750 °C (1301 MPa, 6.5% elongation). These findings highlight the potential of heat treatment as a novel approach for enhancing the mechanical characteristics of nickel-based superalloys.

Influence of the γ′ Volume Fraction on the High-Temperature Strength of Single Crystalline Co–Al–W–Ta Superalloys

Understanding the influence of γ′ and secondary-phase fractions on the mechanical properties of superalloys is very important to optimize these high-strength materials. So far, this has not been systematically investigated for the novel class of Co-based superalloys. In this study, a Co–Al–W–Ta model alloy series was designed with compositions of γ/γ′ on the tie-line and an increasing γ′ volume fraction of up to 70% after heat treatment at 900 °C, while a few alloys are unexpectedly out of γ/γ′ two-phase region with an additional secondary phase fraction of up to 15%. The high-temperature strength and creep properties were evaluated by compression tests up to 1050 °C and compressive creep experiments at 950 °C, respectively. At temperatures of up to 1050 °C, an increasing γ′ volume fraction consistently increased the yield strength, which was not dramatically changed by the presence of secondary phases. Significant work hardening was found in alloys with γ′ volume fractions of 65–70% during compression testing, but not in alloys with either a lower γ′ volume fraction (<50%) or a high fraction of secondary phases (~15%). Similar to the yield strength, the creep strength also increased continuously with the γ′ volume fraction, but was greatly reduced with an increasing fraction of secondary phases. The best creep performance at 950 °C and 200 MPa was found in the alloy with the highest γ′ volume fraction and no secondary phases. At higher creep stresses, rafting contributed significantly to the hardening and, again, the alloy with a high γ′ volume fraction and a small amount of secondary phases exhibited the highest strength.

Prediction and optimization of mechanical properties of Ni based and Fe–Ni based super alloys via neural network approach with alloying composition parameter

The Optimization of super alloy through alloying element composition control is very challenging since it contains more than ten type of elements. Generally, the optimization process of the mechanical properties of super alloy by composition alteration was performed via trial-and-error which is time consuming and expensive. In this study, the artificial neural network was successfully employed to reveal the correlation between alloying element and the hardness, tensile strength, and melting point of Ni based and Fe–Ni based super alloy. The model showed a good accuracy between predicted and actual values, especially for hardness and melting temperature, with R2 and RMSE values were found to be above 95% and below 3%, respectively. The Pearson Correlation Coefficient and Feature Importance revealed the linear and non-linear correlation of elements in the matrix. The validation of mathematical expression derived from symbolic regression displayed a high reliability associated with RMSE values of approaching 0%. The feature importance derived from atomic and thermal features characterization on Fe–Ni based super alloy as selected sample revealed the dominant effect of Ni matrix on the mechanical properties of the alloy. These results show the potential of our model to assist in the designing of super alloy for industry.

Investigation on the Microstructure and Mechanical Properties of Ni-Based Superalloy with Scandium

In this work, a method concerning thermal consolidation is proposed to simulate the traditional powder metallurgy process and accomplish the composition screening of powder metallurgy Ni-based superalloys U720Li and RR1000 with rare metal scandium, and superalloys with zero scandium addition, medium scandium addition and high scandium addition are selected. Then effects of scandium on the microstructure and mechanical properties of superalloys are further investigated through fast hot pressed sintering. The results indicate that scandium doping can effectively refine the grain through modifying the size and volume fraction of primary γ’ precipitates at the grain boundary. Meanwhile, scandium can promote the growth and precipitation of secondary γ’ precipitates to some extent. Due to the comprehensive effects of γ’ precipitate modification and grain boundary strengthening, as-sintered U720Li with 0.043 wt.% scandium presents an excellent combination of tensile strength and ductility at ambient and elevated temperature while as-sintered RR1000 with 0.064 wt.% scandium has a good performance at elevated temperature.

Effect of carbon content on the microstructure, tensile properties and cracking susceptibility of IN738 superalloy processed by laser powder bed fusion

The high cracking susceptibility is the major barrier hindering the broad adoption of additive manufacturing (AM) in traditional non-weldable superalloys. It is particularly important to explore the role of elements during the AM processing and establish a new alloy design criterion. In this study, the effect of carbon, a critical element that influences the solidification and mechanical properties of superalloys, on the printability and mechanical properties of a typical non-weldable Inconel 738 (IN738) alloy processed by laser powder bed fusion (LPBF) was studied. Different from the limitation of low carbon content in traditional superalloy design, it was found that a moderate increase of carbon content from 0.11 wt% (alloy IN738LC) to 0.3 wt% (alloy IN738–0.3 C) and 0.6 wt% (alloy IN738–0.6 C) can produce crack-free LPBF samples in a wide range of processing parameters. The effect of carbon content on the microstructure, tensile properties and cracking susceptibility of the LPBF-printed alloys was evaluated. With the increase of carbon content, more granular monocarbides of no more than 200 nm in size form into a quasi-continuous or continuous network at the boundaries of cellular structures, while the low melting-point phases containing boron and γ/γ′ eutectics at cellular boundaries are significantly reduced. The susceptibility to solidification cracking and liquation cracking is substantially decreased owing to the reduced level of element segregation, elimination of initiation source for liquid films, and decrease of local strain concentration. As a result, LPBF IN738–0.3 C and IN738–0.6 C show excellent ultimate tensile strength (1320 and 1598 MPa) and superior total elongation (14.7% and 9.0%), respectively. The results above demonstrate the different roles of carbon element in AM and the potential for designing AM non-weldable superalloys with improved printability and mechanical properties via alloy composition optimization.

The strengthening effects of Re-X (X[dbnd]Mo, W, Cr Ta, Re) mediated by their local partitioning behaviors at γ/γ′ interface in Ni-based single crystal superalloys

In Ni-based single crystal (SX) superalloys, the local partitioning behaviors of solute elements at γ/γ′ interface directly determine the structure and strength of the interface, which in turn have a significant effect on the mechanical properties of superalloys. As a characteristic strengthening element, Re has become indispensable in modern Ni-based SX superalloys in spite of its high cost. In order to unveil the strengthening mechanisms of Re combined with other alloying elements, the local partitioning behaviors of alloying atoms X (XMo, W, Cr, Ta, Re) at the γ/γ′ interfaces with and without Re were investigated by first-principles calculations. An innovative quantity called layer concentration was defined and calculated to study the distributions of the alloying elements near γ/γ′ interface. The results show that Mo, W, Re and Cr are soluble in the nearest layer to the coherent plane on γ side most, while Ta is soluble in the nearest layer to the coherent plane on γ′ side most. An extra Re atom fixed at its most preferable site increases the partitioning tendencies of X to γ all, although it does not change the most preferable site of X. The presence of X also increases the layer concentration of Re in its favorable layer. Both single-alloying X and co-alloying Re-X could stabilize and strengthen the γ/γ′ interface with enhanced Griffith rupture works. Especially, for γ phase solid solution elements, Re-W co-alloying has the strongest strengthening effect on the interface, followed by Re-Re unexpectedly. Therefore, properly replacing Re with W could theoretically play an important role in improving the interfacial strength. The obtained results give an insight into the strengthening mechanism on atomic scale focusing at γ/γ′ interface area and pave a way to design high-performance low-cost Ni-based SX superalloys in future.

Effects of different elevated temperature and long-term exposure on microstructural evolution and mechanical characteristics of IN617 Ni-based superalloy

The microstructural changes and mechanical properties of service-exposed IN617 Ni-based superalloy were studied at temperatures of 750, 800, 850 and 900 °C and different time ranging from 4250 to 105000 h. Some microscopic techniques and mechanical experiments, including Optical Microscopy (OM), Field Emission Scanning Electron Microscopy (FESEM) equipped with Energy Dispersive X-ray Spectroscopy (EDS), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), impact, hardness and room/elevated temperatures tensile tests were employed to investigate the microstructure and mechanical performance of the superalloy. In the samples operated at 750 °C/105000 h and 800 °C/98000 h conditions, the γ′ strengthening phase was observed, leading to noticeable improvement in mechanical features of the material. At 850 °C/24000 h and 900 °C/4250 h, the γ′ weight percentage was very low to be detected, so that no significant variation in the mechanical properties of the superalloy was observed. Moreover, metallographic evaluations showed that carbide particles nucleated and grew along the grain boundaries and also within the grains with increasing exposure time during service condition, while their growth rate depended upon the operating temperature. Changes in microstructural characteristics and mechanical properties were assessed using Larson-Miller parameter. As the value of P parameter went up, the area fraction of carbides and the weight percentage of M23C6 carbide increased in return, whereas weight percentage of M6C carbide revealed a decreasing trend. This is due to the fact that a part of M6C carbide was transformed to equilibrium state of M23C6 carbide by increasing P parameter. Impact energy, ultimate tensile strength at room temperature and ultimate tensile strength at 750 °C drastically reduced with increasing P parameter. Although elongation percentage and yield strength showed a decreasing trend in terms of the P parameter, they did not follow regular changes contrary to other mechanical attributes. Measurements indicated that the average hardness value remained constant at around 215 HV with increasing P parameter up to 27500 and then decreased with a steep slope down to about 178 HV.

Orientation dependence of microstructure deformation mechanism and tensile mechanical properties of Nickel-based single crystal superalloys: A molecular dynamics simulation

In this paper, molecular dynamics (MD) simulations are performed to investigate the tensile deformation mechanisms and mechanical properties of superalloys with different orientations. The research results show that the superalloys exhibit anisotropy of mechanical properties and are consistent with previous experimental research results. The anisotropy of mechanical properties is related to the differences of stability at the interfacial dislocation network and the 1/6〈112〉{111} slip system startup of superalloys with different orientations. When the yield point is reached, dislocations and stacking faults on both sides of the slip plane will contact each other and merge into a stacking fault band to penetrate into the γ' precipitates. Meanwhile, the dislocation density and the proportion of face-centered cubic (FCC) structure with different orientation models have a sudden change at the yield point. As the temperature increases, the yield strength and elastic modulus decrease in the (110) and (111) orientation models, whereas the (100) orientation model has an anomalous yield behavior. This is mainly related to the destruction of dislocation network, the change of deformation mechanism and the thermally activated cross-slip mechanism when the temperature increases.

Formation mechanism and thermal stability of C15-Laves phase in a Hf-containing Co-based superalloy

Topologically close-packed (TCP) phases such as μ and Laves phases formed during solidification has an important influence on the mechanical properties of superalloys. Understanding the formation and elimination mechanism of TCP phases is the key to promote the development of superalloys. In this study, C15-Laves phase was first found in a Hf-containing Co-based superalloy, meanwhile, the formation mechanism and thermal stability of the C15-Laves phase were clarified. The results showed that the formation of C15-Laves phase was associated with the segregation behavior of alloying elements during solidification: Co, W and Cr segregated to the dendrite core, and Hf, Ta, Ti, Mo, Ni, Al, Si segregated to the interdendritic region. In the final stage of solidification, the C15-Laves phase enriched in Hf, Ta and Ti formed, and it had similar lattice parameters to the C15-Co2Hf phase. The incipient melting point of C15-Laves phase was between 1170 ℃ and 1180 ℃, and it gradually decomposed to form the Hf-rich MC carbide during solution treatment. The large formation energy differences between the MC carbide and C15-Laves phase promoted a rapid elimination of the C15-Laves phase, which reduced solution treatment time of the alloy. The results can provide a theoretical basis and experimental data support for the composition design and heat treatment process optimization of multicomponent novel Co-based superalloys.

Precipitate Shearing, Fault Energies, and Solute Segregation to Planar Faults in Ni-, CoNi-, and Co-Base Superalloys

The mechanical properties of superalloys are strongly governed by the resistance to shearing of ordered precipitates by dislocations. In the operating environments of superalloys, the stresses and temperatures present during thermomechanical loading influence the dislocation shearing dynamics, which involve diffusion and segregation processes that result in a diverse array of planar defects in the ordered L12γ′ precipitate phase. This review discusses the current understanding of high-temperature deformation mechanisms of γ′ precipitates in two-phase Ni-, Co-, and CoNi-base superalloys. The sensitivity of planar fault energies to chemical composition results in a variety of unique deformation mechanisms, and methods to determine fault energies are therefore reviewed. The degree of chemical segregation in the vicinity of planar defects reveals an apparent phase transformation within the parent γ′ phase. The kinetics of segregation to linear and planar defects play a significant role in high-temperature properties. Understanding and controlling fault energies and the associated dislocation dynamics provide a new pathway for the design of superalloys with exceptional properties.

Effects of vacuum on gas content, oxide inclusions and mechanical properties of Ni-based superalloy using electron beam button and synchrotron diffraction

The effects of vacuum induction melting (VIM) vacuum (<1 Pa–100 Pa) on gas content, oxide inclusions and mechanical properties of Ni-based superalloy K4648 has been investigated by electron beam (EB) button experiment under high vacuum (10-3 Pa) and high resolution synchrotron X-ray powder diffraction (SXPD). The results indicated that VIM remelting vacuum drop has obvious effect on the existing form of trace oxygen. The total amount of oxygen did not increase significantly but a dramatic increase in the amount of oxide inclusions by 1–2 orders of magnitude was found. The inclusions are mainly oxides including Al2O3, Cr2O3, NiAl2O4 and complex oxides or sulfides. Remelting under 100–110 Pa has no significant effect on mechanical properties such as stress rupture life and tensile strength but decreased ductility obviously. In comparison to the normal vacuum counterpart, the tensile elongation and impact ductility of the alloy remelted under lower vacuum level decreased by 67% and 39%, respectively. This study reveals the relationship between the vacuum level and mechanical properties of superalloys and highlights the trace amount of oxide inclusions which should be considered as one of the key issues for the cleanliness of virgin or revert superalloys apart from the typical measurement of the gas content only.

Development of Vickers hardness prediction models via microstructural analysis and machine learning

Superalloys are high-temperature materials with outstanding strength and resistance to corrosion. A prior knowledge about its hardness is essential for development of new superalloys for its applications in aeronautics and power industries. Determining the hardness of a material with experiments is usually a destructive process. In this study, using structural, compositional and processing condition parameters as descriptors, machine learning (ML) models are developed to predict Vickers hardness. We employed image processing tools, which extract structural descriptors such as volume fraction, area, perimeter and aspect ratio of the phases in the microstructures. Using the structural features in combination with elemental and processing information as features, a Gaussian process regression model for the prediction of Vickers hardness of superalloys is developed. The model gives an unprecedented accuracy with a minimum root mean square error of 0.15. The descriptors provide insights into structure–property relationships, which are important for designing superalloys with improved Vickers hardness. The proposed method for extracting features from microstructures and combining them with elemental and processing information can be extended to develop ML model for prediction of other mechanical properties of superalloys.

Segregation of alloying elements and their effects on the thermodynamic stability and fracture strength of γ-Ni/γ′-Ni3Al interface

The γ/γ’ phase interface, being the main plane defect in nickel-based single-crystal superalloys, can have a significant effect on the microstructural stability and mechanical properties of superalloys. To improve the thermodynamic stability and fracture strength of the γ-Ni/γ’-Ni3Al interface and gain insight into the underlying micro-mechanisms, the segregation tendency of 12 alloying elements X at the γ-Ni/γ’-Ni3Al interface and their effects on the interfacial formation and Griffith fracture works were investigated by using first-principles calculations. It is found that all alloying elements X can segregate to the corner-point site of the γ-Ni (001) layer except the element Y. The Re-, Ti-, Mo-, W-, Cr-, Nb-, Ta-, Hf- and Zr-segregated interfaces are more stable than the unalloyed interface due to the presence of pseudogap and lower values of densities of states at the Fermi level. The segregation of Ru, Co, Re, Mo, W, Cr, Nb and Ta strengthens the interfacial fracture strength, which can be mainly attributed to the enhanced bonding strengths of X–Ni bonds formed in these segregated interfaces. The interfacial segregation of Cr, Re, Mo, W, Nb and Ta can not only improve the thermodynamic stability but also enhance the fracture strength of the phase interface. The segregation of Ta and Re is able to improve the thermodynamic stability and fracture strength of the γ-Ni/γ’-Ni3Al interface to the maximum extent, respectively. The effect of interfacial segregation of alloying elements on the fracture strength and thermodynamic stability of the γ-Ni/γ’-Ni3Al phase interface and the underlying mechanisms are studied.

Different effects of γ′ and η phases on the physical and mechanical properties of superalloys

In this research, the effect of γ′ and η phases has been investigated on the physical and mechanical properties of a superalloy. For this purpose, after heat treatment under different conditions, the samples were evaluated by XRD, and the microstructural phases were identified. Microstructure of the alloy was investigated by optical and scanning electron microscopy. Physical properties measurements including sound velocity and electrical resistivity were performed on the heat treated samples. In addition, hardness of the specimens was determined.The results showed that the presence of η phase instead of γ′ greatly increases the sound velocity in the alloy. It was also found that the dissolution of the η phase, in contrast to the γ′ phase, decreases electrical resistivity of the superalloy. Furthermore, we observed that although the η phase has a considerably higher inherent hardness than the γ′ phase, the γ′ precipitates can increase the hardness of the alloy more than the η phase if they are nano-sized.Based on the findings in this work, it is demonstrated that the optimization of heat treatment cycles of superalloys that can simultaneously have η and γ′ phases in their microstructure (such as IN939, IN792, IN740, GTD-111, Alloy 706, Rene 80, X-750, PWA1483, TMW, Nimocast 263 and many other superalloys) cannot be completed solely nondestructively by measurement of the physical properties, and performing the mechanical test experiments is essential.

Effect of aging heat treatment on the microstructure and hardness of a serviced ZHS32 superalloy

According to the gradual changes of the microstructure of superalloys during harsh service condition of turbine blades and the detrimental effects of these changes on the mechanical properties of superalloys, performing of a rejuvenation heat treatment (solution treatment + aging process) on ex-serviced superalloys is necessary. In this work, the aging heat treatment was conducted on a serviced single crystal ZHS32 superalloy in the temperature range of 950-1150°C. It was found that while performing the aging process at 950 and 1050°C for 10 h did not provide appropriate conditions for the nucleation and growth of primary Υ' phases, conducting aging at the temperature of 1150°C for 10 and 16 h yields to the formation of Υ' precipitates with the desired cuboidal morphology. The comparison of the microstructure of the rejuvenated samples with the un-rejuvenated samples confirms that with applying this procedure, the size of strengthening Υ' precipitates reduces and the volume fraction of these phases considerably increases, which yields to the recovery of the superalloy microstructure and improvement of its mechanical properties such as hardness.

Metallography Evaluation of Cast and Wrought Ni-Base Superalloys

. The Ni-base superalloys have an interesting history and evolution since they start to be used in aero jet engines. Microstructures of superalloys have dramatically changed through the years as modern technology of its casting or forging becomes more sophisticated. The first superalloys have polyedric microstructure consist of gamma solid solution, some fraction of gamma prime and of course grain boundaries. As demands on higher performance of aero jet engine increases, the changes in superalloys microstructure become more significant. Further step in microstructure evolution was directionally solidified alloys with columnar gamma prime particles. The latest microstructures are mostly monocrystalline, oriented in [001] direction of FCC gamma matrix. What does not changed through the years is elementary FCC structure of matrix and fundamental group of alloying elements. All microstructure changes bring necessity of proper preparation and evaluation of microstructure. Except already mentioned structures have gamma double prime and various carbides form appear. These structural parameters have mainly positive influence on important mechanical properties of superalloys. However, some detrimental phases as Laves, σ-phase appears as well and have negative influence on heat resistance of superalloys. Paper deals with such microstructural evaluation of both groups of alloys – cast and wrought as well. Microstructure evaluation helps to describe mechanism at various loading and failure of progressive superalloys. Such example where microstructure evaluation is employed is fractography of failure surfaces after fatigue tests, which are as example of metallography evaluation described in this paper as secondary objective. Fatigue test done in this article were at high frequency with push-pull loading, so called high frequency fatigue loading (HFFL) and at low frequency three point flexure, so called low frequency fatigue loading (LFFL).

Analysis of metallurgical aspects and their role in processing and performance of superalloys: A review

Metallurgical processing factors like kinetic and thermodynamic parameters which are essential for modeling of γ′ phase precipitation have been studied. These parameters include γ′ solvus temperature, Gibbs free energy of dissociation of the γ matrix to form γ′, nucleation rate, effective diffusivity and interfacial energy. Nucleation methods and effect of cooling rate on the final phase structure have been analyzed. Co based superalloys have been studied as a potential and promising material for aerospace applications. Effect of microporosity on the mechanical properties of Superalloys has also been analyzed.

Influence of Heat Treatment on the Microstructures and Mechanical Properties of K465 Superalloy

The microstructures and mechanical properties of superalloy K465 under different heat treatment, including as as-cast, solution treatment and aging, were investigated. The results showed that γ' precipitates in as-cast condition exhibited two kinds of morphologies of fine regular cuboidal shape at dendritic arm and coarse irregular form in interdendritic region. MC carbides decomposed into M6C carbides partly after 1210°C/4h solution treatment. The high temperature stress-rupture life can be improved obviously with the increasing cooling rate. When cooling rate was lower than 70°C/min, the room temperature tensile elongation increased with cooling rate increasing. When cooling rate was higher than 90°C/min the room temperature tensile elongation decreased with cooling rate increasing. The proper cooling rate of 70oC/min~90oC/min is advantageous for the achievement of excellent comprehensive properties. When aging treatments continued the regularization of γ' resulted in the improvement of stress-rupture life and the reduction of tensile elongation. The mechanical property gap between the solution treatment and aging can be decreased with increasing cooling rate.