Superalloy Samples Research Articles

Evolution of Microstructure during Creep Deformation in a Forged 617 Superalloy

Creep tests are conducted on forged 617 M superalloy samples at 650, 700, and 750 °C at stresses ranging from 115 to 320 MPa. At 650 °C, a significant steady‐state secondary creep is observed, while at 700 and 750 °C limited secondary creep and prolonged tertiary creep are observed. Creep data analysis using power‐law creep approach estimates high‐stress exponents (n ≈ 13.4 at 650 °C, ≈11.5 at 700 °C, and ≈9.7 at 750 °C) and activation energy (Q ≈ 530.6 kJ mole−1). After incorporating threshold stress, the activation energy for creep is found to be ≈261 kJ mole−1. This is consistent with the activation energy for lattice self‐diffusion in the alloy. Transmission electron microscopy provides evidences affirming that climb‐controlled dislocation creep may be the operative creep mechanism. Ni3(Al, Ti) (γ′) precipitates and M23C6 carbides evolve during exposure at operating temperatures. These are observed to lead to enhanced creep resistance at 700 °C. Significant coarsening rate of γ′ precipitates are noted during exposure at 750 °C. This intensifies recovery processes and lowers creep threshold stress drastically. Extended tertiary creep prevails near the service conditions of this alloy, which is ascribed to instability in microstructure during creep.

Tribological response of pack-boronized inconel 601 superalloy surfaces at elevated temperatures

Inconel 601 superalloy sample surfaces were pack-borided at 1000 °C for 4 h and 6 h to investigate the effect of boriding treatment on the mechanical and high temperature wear performance. The boride layers were characterized using SEM, EDS, XRD, microhardness tests, nanoindentation and high-temperature wear tests at room temperature and 500 ℃ under 7 N and 15 N normal loads. Boriding led to nearly 300 % increase in the hardness and up to 11-fold increase in the wear performance of the Inconel 601 surfaces. Despite lower COF and specific wear rates, borided surfaces were more susceptible to temperature increase than the non-treated Inconel 601 surfaces due to the lower tendency of wear debris with hard phase content to form a consistent lubricating layer.

Enabling tailored microstructures by hybrid directed energy deposition processing of a nickel-based superalloy

The technological advances in additive manufacturing, particularly laser based directed energy deposition (DED), revolutionized the production of complex metal components. Despite this progress, the oriented heat flux and several reheating thermal cycles can induce a strongly textured microstructure, which induces an anisotropic mechanical behavior. In addition, considerable residual stresses typically require additional post-processing. Therefore, hybrid process chains for additive manufacturing (AM) are being developed, which aim at integrating conventional post-processing into the AM process. However, a detailed investigation of thermal and mechanical effects of such hybrid processes on the mechanical properties and their interrelation is lacking. In an experimental study, we explore the integration of thermal and mechanical processing steps within the DED process chain to locally tailor microstructures and mechanical properties. Through electron backscatter diffraction measurements, we demonstrate significant microstructural changes of DED-manufactured nickel-based superalloy samples using deep rolling and laser heat treatment. A mechanical surface deformation induces microstructural misorientation leading to an increase in hardness down to substantial depth of several hundred micrometers. Additionally, the targeted management of heat input during laser heat treatment results in different grain morphologies and sizes, affecting average microhardness within a significant depth. The results demonstrate the potential for microstructural tailoring using hybrid AM process chains, while a substantial sensitivity of the microstructure to thermal and mechanical load emphasizes the importance of a precise process control. This work provides an understanding of the process-microstructure-property relationship required for developing new process pathways in hybrid AM that integrate thermal and mechanical processes into DED manufacturing.

A hardness-based constitutive model for numerical simulation of blind rivet with gradient hardness distribution

A286 superalloy blind rivets find extensive applications in the structural connections of aerospace equipment owing to their exceptional strength and heat resistance. However, the gradient hardness distribution within the rivet sleeves complicates achieving precise numerical simulation results with traditional constitutive models. This study aims to establish a constitutive model suitable for materials exhibiting gradient hardness to support the development of A286 superalloy blind rivets. Initially, quasi-static compression experiments were conducted on A286 superalloy samples at different hardness levels (160–324 HV), strain rates (0.01–10 s⁻¹), and temperatures (25–600°C). Subsequently, the influence of material microstructural evolution on flow stress during compression was investigated using electron backscatter diffraction technique. Furthermore, a hardness-based Johnson-Cook (J-C) constitutive model was developed by introducing hardness and offset compensation onto the original J-C model and compared with its counterpart. Finally, the hardness-based model was employed to simulate the bulge compression forming of A286 blind rivets and validated through experimental trials. The findings reveal that dislocation strengthening predominantly contributes to the increased material flow stress with escalating strain rates and sample hardness. Compared to the original J-C model, the stress prediction error of the hardness-based model reduced from 26.8 % to 2.9 %, effectively depicting the variation in material flow stress under different hardness values. The simulated values of bulge morphology, dimensions, and load closely align with experimental data, affirming the efficacy of the hardness-based model in numerically simulating blind rivets with gradient hardness distribution.

Microstructural evolution and high-temperature strengthening mechanisms of the IN 738LC superalloy prepared by selective laser melting

Defect-free SLM-IN 738LC superalloy samples were fabricated using selective laser melting (SLM). The as-built samples exhibit a cellular structure with fine carbides, γ′ phases, and high-density dislocations at the cell boundary and nano-size γ′ phases in the interior, resulting in excellent deformation resistance and favorable mechanical properties at room temperature, with a yield strength (YS) of 970 MPa, an ultimate tensile strength (UTS) of 1263 MPa, and an elongation (EL) of 33%. This study investigates the evolution behavior of the γ′ phase at different solid solution treatment (SHT) temperatures and its impact on alloy strength and toughness. The 1020 + AHT sample exhibits a uniform distribution of coarse γ′ phases. The samples subjected to 1070 + AHT and 1120 + AHT display a bimodal distribution of γ′ phases. When the SHT temperature was further increased, fine spherical γ′ phases are evenly distributed in the 1160 + AHT and 1200 + AHT samples. Moreover, the γ/γ′ eutectics at the grain boundaries gradually dissolve with increasing SHT temperature, whereas the size and fraction of carbides increase. The room temperature tensile test of the 1070 + AHT sample demonstrated a favorable balance between strength and plasticity (YS = 1217 MPa, UTS = 1472 MPa, EL = 9.25%). This is attributed to the synergistic strengthening effect of the bimodal distribution of the γ′ phase. The temperature-dependent deformation behavior of the 1070 + AHT sample was analyzed at 23 °C, 800 °C, 900 °C, and 1000 °C. At 23 °C, numerous dislocations accumulated around the γ/γ′ interfaces. When the temperature increased to 800–900 °C, the dislocations shearing γ′ phases is activated and the alloy remained high strength. At 1000 °C, both the dislocation shearing and dislocation bypassing mechanisms coexist, resulting in a decrease in the strength of the alloy and an increase in its plasticity. This work provides scientific and theoretical support for SLM-IN 738LC parts with favorable properties.

Creep rupture life prediction of high-temperature titanium alloy using cross-material transfer learning

High-temperature titanium alloys are the key materials for the components in aerospace and their service life depends largely on creep deformation-induced failure. However, the prediction of creep rupture life remains a challenge due to the lack of available data with well-characterized target property. Here, we proposed two cross-materials transfer learning (TL) strategies to improve the prediction of creep rupture life of high-temperature titanium alloys. Both strategies effectively utilized the knowledge or information encoded in the large dataset (753 samples) of Fe-base, Ni-base, and Co-base superalloys to enhance the surrogate model for small dataset (88 samples) of high-temperature titanium alloys. The first strategy transferred the parameters of the convolutional neural network while the second strategy fused the two datasets. The performances of the TL models were demonstrated on different test datasets with varying sizes outside the training dataset. Our TL models improved the predictions greatly compared to the models obtained by straightly applying five commonly employed algorithms on high-temperature titanium alloys. This work may stimulate the use of TL-based models to accurately predict the service properties of structural materials where the available data is small and sparse.

Coupling effect of feature size and δ phase on compressive deformation of a nickel-based superalloy at the mesoscopic scale

Nickel-based superalloys have become essential materials due to their excellent comprehensive properties as the miniaturization of products in the aerospace and energy fields develops. The complex microstructure and various strengthening mechanisms of nickel-based superalloys make the plastic deformation behavior extremely complicated at the mesoscopic scale. In this paper, compression experiments of nickel-based superalloy samples with different feature sizes (i.e. the sample diameter to grain size ratio, D/d) and different aging times at the mesoscopic scale were carried out. The coupling effect of feature size and δ phase on the compressive deformation behavior was studied. The results show that the δ phase plays a role in precipitation strengthening during compressive deformation at the mesoscopic scale. When D/d is in the range of 9.7–10.9, the flow stress decreases significantly with the increase of grain size, and a “smaller is weaker” size effect appears. When D/d is less than 9.7, the flow stress increases with the grain size, and a “smaller is stronger” size effect appears. Considering grain boundary strengthening, solid solution strengthening, and precipitation strengthening, a size effect model of flow stress was established. The calculated values were in good agreement with the experimental values. The inhomogeneity of the end surface and side surface increases with the decrease of feature size and the decrease of aging time. The presence of the δ phase reduces the inhomogeneous deformation of nickel-based superalloys during compressive deformation at the mesoscopic scale.

Effect of Zr on microstructure and hot cracking susceptibility of ZGH451 superalloy fabricated by direct energy deposition

Four groups of newly developed Ni-based superalloy samples with different Zr contents were manufactured by Direct energy deposition (DED). This study focuses on the influence of Zr element concentration on microstructure and cracking formation mechanism in DED-processed Ni-based superalloy ZGH451. Although Zr content is low, it strongly affects the formation of the precipitated phase and hot tearing tendency. Measurement of the crack area showed that the crack density value increases with the Zr concentration. According to thermodynamic simulation results and microstructures observed, Zr microsegregation in the interdendritic regions and considerable amounts of Zr is present in oxides or carbides. Zr contributes to forming large-size carbides mainly due to zirconia providing nucleation sites and the dissolution of Zr. Simultaneously, the solidification has been retarded due to the continuous accumulation of large Zr atoms, which increases the γ-γ′ eutectic fraction. Moreover, Zr addition could effectively decrease the solidus temperature of ZGH451 alloys, leading to the critical liquid film at the end of solidification. Based on these results, staying below 0.05 wt% of Zr content to reduce the risk of hot tearing in additive manufacturing superalloy was proposed.

Investigation on compaction pressure and sintering temperature suitable for Nimonic 90 superalloy

Fabrication of high strength, high temperature and corrosion resistant materials provide much assistance in aerospace, automotive, chemical and oil industries, as they have to withstand severe operating conditions. Traditionally, superalloys are widely used under these conditions that are prepared by casting method. Nowadays, powder metallurgy technique is gaining importance for preparing superalloys because of its capability of making homogeneous microstructure with near-net-shape. In this significant context, the processing of Nimonic 90 superalloy sample using conventional powder metallurgy route is discussed. Desired amount of metallic powders by weight percent are blended, uni-axially pressed and sintered in tubular vacuum furnace at different sintering temperatures. The influence of compaction pressure and sintering temperature on density, hardness, surface roughness and electrical resistivity is determined. Surface porosity and the effect of sintering temperature on the microstructural features are analyzed noticeably. It is found that the compaction pressure of 700 MPa and the sintering temperature of 1365℃ are the most desirable process parameters, essentially required for synthesizing the Nimonic 90 superalloy. Sample prepared under these conditions has achieved the desired density and hardness, as that of the standard Nimonic 90 alloy. Thus, the study paves the way for future researchers to appropriately identify the conditions suitable for preparing the superalloys as per the application needed.

Study on the Tribological Behavior and the Interaction between Friction and Oxidation of Graphite Reinforced by Impregnated Phosphate at High Temperatures.

The stability of the graphite seal device is a key factor for the normal operation of aero engines. However, conventional graphite exhibits poor comprehensive performance due to its porous structure, which limits its application at high temperatures. Therefore, in this paper, phosphate was used to impregnated graphite pores, and the interaction between the friction, wear, and oxidation of phosphate-impregnated graphite against superalloy at high temperatures was studied through pin-on-disk friction tests. The results revealed that the coefficient of friction (COF) of matrix graphite fluctuated greatly, from 0.07 to 0.17, in the range of 100 °C to 500 °C, while the COF of impregnated graphite was stable, at around 0.13, from 100 °C to 500 °C. The wear rates of the two types of graphite were close from 20 °C to 300 °C, while the wear rate of the impregnated graphite was significantly lower than that of the matrix graphite at higher temperatures, from 400 °C and 500 °C. The reason was that the impregnated phosphate reacted with graphite at a high temperature, forming the inert site which helped to inhibit the oxidation and maintain the mechanical properties of the impregnated graphite at high temperatures. In addition, the impregnated graphite could maintain better integrity of the contact surface and reduce the inclusion of large hard metal oxides, thus effectively reducing the abrasive wear of the disk. Therefore, the wear depth of the superalloy disk samples with impregnated graphite was significantly lower than that of the matrix graphite. The results promote the application of phosphate-impregnated graphite under the high temperature conditions of aero engines.

Study on oxidation kinetics of three kinds of candidate superalloys for VHTR under air ingress accident

Inconel 617 alloy, Incoloy 800H alloy and Hastelloy X alloy are three alternative superalloys for heat transfer tubes used in the steam generator (SG) in the very high temperature gas cooled reactors (VHTR). In this paper, the oxidation kinetics of isothermal oxidation of three superalloys in the circulating air at 950 ℃ during the air ingress accident is investigated. Oxidation kinetic parameters of superalloys, such as the oxidation rate indexes (np and nt), mass parabola rate constant (kp) and oxide layer thickness parabola rate constant (kt) are calculated by the experimental data. In addition, tested samples of superalloys were analyzed by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray diffraction (XRD). The results show that these three superalloys exhibit parabolic oxidation behavior in air atmosphere. The oxidation behavior of Incoloy 800H alloy is closer to the cubic oxidation law as time increases. The mass gain of three alloys does not fully match with the growth law of the oxide layer, which should be attributed to the internal oxidation degree of the alloy. The arithmetic square root of kp and kt, L, are proposed to quantify the internal oxidation degree. And the L of Inconel 617 alloy is the largest compared to Inconel 800H alloy and Hastelloy X alloy. This work is helpful to explain the behavior of oxidation of superalloys.

An investigation on the effect of change in experimental sequence of warm laser shock peening and laser shock peening on the performance of DD6 nickel-based single-crystal superalloy

Incorporated with the benefits of dynamic strain aging (DSA) and laser shock peening (LSP), warm laser shock peening (WLSP) is able to induce a compressive residual stress (CRS) layer with high thermal stability on the near-surface of the material. It has been widely used in recent years as a new surface modification technique to prolong the fatigue life of aero-engine turbine blades. Single WLSP has limited effect on material modification, while multiple WLSP when the confining layer is quartz glass will affect the thickness and thermal stability of the CRS layer during replacement of the confining layer, absorbing layer, and cooling and heating. To address this issue, this study investigates the mechanism of the CRS response, mechanism of strengthening, mechanism of action, and change of electrochemical corrosion performance of DD6 superalloy samples to different surface treatments after double LSP, single WLSP plus single LSP and double WLSP surface treatments by changing the experimental sequence of WLSP and LSP.The experimental results show that all three surface treatments deform the sample by inducing 〈110〉 cross-slip bands on the sample surface. Also all three surface treatments strengthen the sample surface by pipeline diffusion of elements to form a dislocation network similar to the γ/γ′ substructure.Meanwhile, single WLSP plus single LSP treatments can effectively prevent the thermal relaxation of the previously induced CRS layer. The final induced CRS layer thickness, dislocation distribution and dislocation density are better than those of double LSP and double WLSP. Pipeline diffusion of elements can improve the electrochemical and thermal corrosion resistance of the single-crystal superalloy.

Calculating probability of detection of short surface cracks using inductive thermography

ABSTRACT Inductive thermography experiments on artificial defects were used to calculate the POD of this inspection technique. In nickel-based austenitic superalloy samples defects in the range of 0.3–1.9 mm length and with 0.25–1.5 mm depth were inspected. 11 samples, each of them with 9 different defects, were used for the experiments. Additionally, finite element simulations were carried out to support the POD calculation and in order to investigate how different parameters affect the results. The measured and the simulated temperature sequences were evaluated by Fourier transform to a phase image, and the signal-to-noise ratio of the phase contrast around the crack was used as signal â for the â versus a POD calculation. As the phase contrast depends not only on the defect length but also on the defect depth, POD depending on both variables was calculated, which can be visualised as a POD surface. Finally, experimental results on samples with real cracks (fatigue cracks and cracks obtained through the Varestraint test machine) were compared to the results obtained by the FEM simulation and in the experiments for the artificial defects.

Effect of building direction on anisotropy of mechanical properties of GH4169 alloy fabricated by laser powder bed fusion

Ni Base superalloy samples were fabricated by laser powder bed fusion in vertical, oblique, and horizontal building directions. The microstructures, tensile properties, and fracture morphologies of the three specimens were studied. The precipitated strengthening phase structure, grain characteristics, and geometric necessary dislocation density of the samples were characterized. The reason for the anisotropy of yield strength for the three specimens was discussed based on the strengthening theory. The results show that the microstructures of the as-built alloys are composed of coarse columnar grains, fine dendritic structures, and high-density dislocations. Partial recrystallization occurs with the precipitation of the ellipsoidal γ″ strengthening phase in the alloys after solution and double aging heat treatment. Compared with the vertical and horizontal specimens, the oblique sample has the highest yield and tensile strength and has a good elongation of 19%. The effective grain sizes of the horizontal, vertical, and oblique samples are 11.92 μm, 15.15 μm, and 11.67 μm, respectively. There are no significant differences in the average Taylor factors of the three samples. The geometrically necessary dislocation densities of the three samples are 4.021 × 1014 m−2, 3.078 × 1014 m−2, and 4.362 × 1014 m−2, respectively. The anisotropy of yield strength for the samples with different building directions is explained by the effect of dislocation strengthening, followed by precipitation strengthening and grain boundary strengthening which is essentially related to the dislocation density, Taylor factor and effective grain size.

Microstructural Characteristics and Mechanical Properties of an Additively Manufactured Nickel-Based Superalloy

The nickel-based superalloys processed by additive manufacturing are very promising structural materials in aircraft engines as high-pressure turbine discs. In this work, a nickel-based superalloy with good mechanical performance and few defects was manufactured by optimized selective laser melting (SLM) processing. We then investigated the influences of post heat treatments on its microstructural characteristics and mechanical performance. The results indicated that a fine grain size with uniform grain orientation was presented in the as-printed nickel-based superalloy sample. After heat treatments, the grains were slightly grown and grain orientation was also changed. Under transmission electron microscopy, fine subgrains with an approximate size of 0.5 μm were found in the as-printed sample which accompanied massive dislocations and discontinuous Laves phases. After the post heat treatments, fine subgrains and less dislocations were retained. On the other hand, massive γ′ and γ″ precipitates with an orientation relationship of (001)[100]γ′//(100)[001]γ or (001)[100]γ″//(100)[001]γ were formed. As a result, the yield stress and tensile strength increased to 1362 and 1410 MPa, respectively, in a heat-treated sample, which retained the identical elongation of the as-printed specimen.

An intelligent design for Ni-based superalloy based on machine learning and multi-objective optimization

The simultaneous consideration of multiple conflicting properties in alloy optimization design is necessary yet remains challenging. A comprehensive strategy of machine learning (ML) and multi-objective optimization based on thermodynamic simulation data was proposed to accelerate the composition design of Ni-based superalloys. The microscopic parameters were determined by Pearson correlation analysis and domain knowledge as the key affect factors of tensile strength and elongation. The Multi-objectives Evolutionary Algorithm (MOEA) was adopted to search the well-built surrogate by ML meta-heuristically for the Pareto front of three objectives and its responding Pareto optimal solution set of composition. Furthermore, nine high-performance superalloy samples selected from the obtained Pareto front were well verified by fabricating and testing in the laboratory. Specially, a new composition among the nine as-fabricated samples was the best one according to the pre-defined design preferences with the γ′ solvus temperature, γ′ volume fraction, and TCP phases content approximating to 1210 °C, 65%, and 0.01%, respectively. This intelligent cooperation strategy based on ML and MOEA extends the methodology for multi-composition and multi-property design materials, which can optimize multiple conflicting objectives simultaneously rather than do one by one.

Machine Learning Applied to Identify Corrosive Environmental Conditions

The reliability of turbine engines depends significantly on the environment experienced during flight. Air humidity, corrosive contaminant substances, and high operating temperatures are among the attributes that affect engine lifespans. The specifics of the environment that affect materials are not always known, and damage is often evaluated by time-consuming manual inspection. This study innovates by demonstrating that machine learning approaches can identify the environmental conditions that degrade jet engine metallic materials. We used the state-of-the-art pre-trained neural network models to assess images of damaged nickel-based superalloy samples to identify the environment temperature, the exposure time, and the deposited amounts of salt contaminants. These parameters are predicted by training the model with a database of approximately 3,600 sample images tested in laboratory conditions. A novel tree classification process results in excellent predictive power for classifying the type of environment experienced by nickel-based superalloys.

Study on Tensile Fracture Behavior of New Type High Temperature Titanium Alloy Ti-Al-Nb at Room Temperature

In this paper, in order to explore the development of a titanium-based superalloy with a working temperature of 700°C to 750°C and good ductility at room temperature, using Ti+Al+Ti2AlNb ternary powder as the raw material, the temperature is 1200°C to 1300°C, 30MPa, 1.5h Directly mixed and sintered under hot pressing conditions, a new type of titanium-based superalloy (TiAl+Ti2AlNb) samples were prepared. The fracture morphology of hot-pressed sintered samples and tensile samples used scanning electron microscope (Scanning electron microscope, referred to as SEM) and Electron backscattered diffraction (EBSD) for observation. Discuss the room temperature tensile fracture behavior of a new type of high temperature titanium alloy Ti-Al-Nb, and lay a technical foundation for the development of a new type of high temperature titanium-based alloy with low brittleness at room temperature.

Studija mehaničkih svojstva Inconel 625 i Incoloi 800H sa istopljenim solima na bazi nitrata

Energy storage is the most indispensable technology in the recent days with augmented power demand, which helps in balancing the energy demand and production time. Among the broad spread of energy storage types, molten salts technology in concentrated solar plants is most economical, highly efficient with excellent duration on the storage timings. In this current effort, Inconel 625 and Incoloy 800H nickel based super alloys have been taken and heated with sodium nitrate and potassium nitrate molten salts. The super alloy substrates were coated with Yttria stabilized zirconia as thermal barrier coating which could enhances the heat resistance and corrosion resistance property of the base substrates. Both layered and non-coated super alloy samples were intense to a fairly accurate temperature of 1000 o C for different duration as 9, 12 and 15 hours. The mechanical properties of both unheated and heated specimens were compared with the results obtained from tensile test, compression test, hardness test, and impact test. The changes in the micro-structural properties were investigated with the support of SEM images and by XRD analysis. The mechanical properties of YSZ coated specimens are found to be better than the uncoated specimens; which increases the sustainability of the super alloys with the molten salts.

Elemental mapping and quantitative characterization of dendrite structure in IN718 supperalloy based on micro beam X-ray fluorescence and EPMA

Micro beam X-ray fluorescence (μ-XRF) has been applied to characterize the quantitative distribution of elements in the dendrite structure of IN718 superalloy for the first time with the advantage of simple sample preparation, no requirement for conductivity, high spatial resolution and non-destructive surface. Dendrite structure is an important microstructure in cast polycrystalline superalloys such as IN718 superalloy. In this paper, the distribution characterization of Ni, Cr, Fe, Nb, Mo and Ti in the dendrite structure of superalloy was performed by μ-XRF with the improvement of the quantitative method. The elemental mapping with higher spatial resolution in the dendrite structure was obtained by electron probe micro-analysis (EPMA). The elemental content distribution on primary dendrite arm, secondary dendrite arm and inter-dendritic zone of superalloy was investigated and the segregation ratios of different elements have been obtained. It was found that the elemental distribution in dendrite structure of IN718 alloy was inhomogeneous and the content of Nb, Mo and Ti was much higher than that on dendrite arm and the elements of Fe,Cr and Ni have the opposite distribution tendency. Severe micro segregation of Nb has been revealed on the dendrite structure. The minimum Nb value of 2.90 wt%, the mean Nb value of 4.90 wt% and the maximum value of 8.84 wt% in the tested IN718 superalloy sample determined by μ-XRF have good agreement with the composition data of key nonequilibrium point in the Pseudo-binary solidification constitution diagram of Inconel 718. The content distribution of alloy elements (Mo, Nb and Ti) presents a sine distribution between the secondary dendrite arm and inter-dendritic region and the average SDAS value obtained from the line content distribution figure is about 70–80 μm. The segregation ratio of different elements has obtained and the SR values of Nb and Ti are much greater than 1. There were some large precipitates particles containing Nb and Ti elements distributed on the inter-dendritic zone, which led to the fluctuation of Nb and Ti contents.