A286 Superalloy Research Articles

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.

Hydrogen embrittlement behaviors during SSRT tests in gaseous hydrogen for cold-worked type 316 austenitic stainless steel and iron-based superalloy A286 used in hydrogen refueling station

To consider an appropriate evaluation method for hydrogen compatibility, slow strain rate tensile (SSRT) tests were conducted on high strength piping materials, cold-worked type 316 austenitic stainless steel (SUS316CW) and iron-based superalloy A286, used in hydrogen stations for two years.SUS316CW, used at room temperature in 82 MPa gaseous hydrogen, contained 7.8 mass ppm hydrogen. The SSRT test of SUS316CW was conducted in nitrogen at −40 °C. The fracture surface showed dimples, and no hydrogen embrittlement behavior was observed. While, the SSRT test of SUS316CW in 70 MPa gaseous hydrogen at −40 °C showed a slight decrease in reduction area and a brittle fracture morphology in the outer layer. This was considered to be the effect of high-pressure gaseous hydrogen during the SSRT test in addition to the pre-contained hydrogen.A286, used at −40 °C in 82 MPa gaseous hydrogen, contained negligible hydrogen (0.14 mass ppm). SSRT tests were conducted at 150 °C in 70 MPa gaseous hydrogen and in air, and showed a low relative reduction in area (RRA) value. To investigate the decrease in the RRA, we switched the gas from hydrogen to air in the middle of the SSRT test and closely examined the RRA values and fracture morphology including side cracks. The hydrogen embrittlement was found to originate from the elastic deformation region. Stress cycling in the elastic deformation region also accelerated the effect of hydrogen. These were attributed to an increase in the lattice hydrogen content. While in the plastic deformation region, hydrogen trapped in the defects and hydrogen through the generated surface cracks increased the hydrogen content at the crack tips, reducing the RRA value. And there was a good correlation between the crack lengths and RRA values.Then, hydrogen embrittlement mechanism depends on the operating conditions (stress and temperature) of the material, and evaluating the hydrogen compatibility of materials by controlling their hydrogen content and strain according to the service environment is desirable.

Carbon and Titanium Effect on Tensile Behavior of Aged A286 Nickel-Iron Based Superalloy

A286 nickel-iron based superalloy used in high temperature applications. Age hardening is done to enhance the creep behavior which is much affected by TiC and eta (ⴄ (Ni3Ti)) phases. Effect of carbon and titanium (0.02C-2.46Ti, 0.04C-2.54Ti, 0.05C-2.58Ti, and 0.06C-2.62Ti) on tensile behavior of aged A286 superalloy is systematically investigated via TiC and ⴄ (Ni3Ti) phases. It has been revealed that carbon and titanium contents are in proportional to nucleation of TiC and eta phases in the austenitic matrix of this alloy. Precipitation of these phases enhanced yield strength from 354MPa to 501MPa and ultimate tensile strength (UTS) 543MPa to 651MPa. However, plasticity decreased nearly 4%. Fracture topography showed that the ductile transgranular fracture in low C-Ti alloys are due to TiC particles, whereas in high C-Ti alloys fracture nature is found brittle intergranular due to eta phases.

Analyzing Forged Quality of Thin-Walled A-286 Superalloy Tube under Multi-Stage Cold Forging Processes.

Cold forging is suitable for manufacturing thin-walled tubes; however, a poorly planned forging process results in serious quality problems. This paper aims to determine an appropriate cold forging process for thin-walled A286 superalloy tube with ideal forming quality. We analyzed the effects of the two forging processes with reverse forging sequences on forming defects and hardness distribution in the thin-walled tubes via finite element simulation. The methods of optical microscope, micro-hardness, scanning electron microscope, and electron-backscattered diffraction were used to validate the tube forming quality. The simulation results revealed that the Type-I process was an appropriate forging process for meeting the quality requirements. For the Type-I process, an underfilling defect was observed at the bottom of the rod section of the tube. The stress concentration in the head section was lower than that in the Type-II process, potentially reducing the probability of crack initiation. Compared to the rod section, the head section may exhibit higher hardness magnitudes due to the greater strain distribution. The experimental results confirmed the feasibility of the Type-I process. The increased hardness in the head section may be primarily attributed to the more intense plastic deformation applied to the material in this section by the Type-I process.

Metallurgical evaluation and failure analysis of turbo expander Tie-bolt

Failure in a turbo-expander Tie-Bolt (stud) made of superalloy A-286 was investigated. The evaluation of the chemical composition and tensile properties confirmed compliance with the relevant standard. However, the coarsening of γ′ due to over aging condition, the non-uniform grain size and banded coarse MC carbide particles, the segregation of phosphorus to grain boundaries and the growth of carbide particles at the grain boundaries led to a decrease in fatigue strength of the alloy. Fractography studies showed that fracture occurred due to primary axial and secondary bending loads. Multiple ratchets and tire tracks on the fracture surface were consistent with low-cycle fatigue (LCF) failure mechanism. Fatigue striations spacing and micro hardness profile of the threads were used to calculate the stress amplitude and estimate the fatigue strength of Tie-bolt. Neuber’s rule was used to estimate the local stress and strain in the thread root. The calculation results showed that the failure occurred due to the application of cyclic loads at a stress level lower than fatigue strength of the stud. A large amount of sulfur detected at the multiple cracks initiation areas by EDS analysis, indicated the presence of H2S in the environment, which has caused cathodic hydrogen charge and reducedthe steel ductility and accelerated fatigue crack nucleation and growth.

Prediction of WEDM Performances Using Clustering Techniques in ANFIS During Machining of A286 Superalloy

Prediction of WEDM Performances Using Clustering Techniques in ANFIS During Machining of A286 Superalloy

Effect of high-pressure hydrogen environment in elastic and plastic deformation regions on slow strain rate tensile tests for iron-based superalloy A286

To investigate the effects of a high-pressure hydrogen environment in the elastic and plastic deformation regions, we performed slow strain-rate tensile tests of iron-based superalloy A286 at 150 °C by switching the atmosphere from 70 MPa hydrogen to air during the tests. The relationship between the nominal strain exposed to a hydrogen environment and the relative reduction in area (RRA) revealed that in the plastic deformation region, the RRA value decreased gradually depending on the nominal strain exposed to hydrogen, but in the elastic deformation region, the RRA value decreased rapidly. The RRA value further decreased when the stress cycle was applid in the elastic region. The fracture surface exhibited an intragranular slip plane fracture similar to that of the hydrogen-charged specimen. These phenomena suggest that the lattice decohesion theory is dominant in the elastic region, where hydrogen embrittlement occurs owing to an increase in the content of dissolved hydrogen.

The Effect of Second Phase Particles on the Corrosion Resistance of A286 Alloys

A286 alloy (AISI 660) is an austenitic precipitation hardness stainless steel that is widely used in the gas turbine industry, due to its high-temperature strength and oxidation resistance [1]. A286 alloy contains higher Ni (24.23 wt.%) and lower Cr (14.5 wt.%) than AISI 316 and AISI 304. The main precipitation strengthening phase of this alloy is gamma phase γ' [Ni3(Al, Ti)], and second phase particles, which form during solution treatment and aging, include eta phase η (Ni3Ti) and metal carbides and nitrides (TiC, TiN).Unlike the relation between precipitates (γ', η) and pitting corrosion [2], the influence of TiC and TiN on the pitting corrosion is rarely studied. To investigate the influence of the various second phase particles on the corrosion behavior of A286 alloys, three samples were employed, including the hot-rolled (HR), HR + solution treatment at 980 °C for 1 h, and HR + solution treatment + aging at 720 °C for 16 h.The corrosion resistance of the various A286 alloy samples were examined by potentiodynamic tests in 3.5 wt.% NaCl solution. The microstructure was investigated via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS).The second phase particles of HR A286 were mainly TiC and a few TiN, which were several micrometers in size and distributed intragranularly in the austenite matrix (Fig. 1a, 1d, and 1e). After the solution treatment, many TiC particles with sizes of a couple of micrometers precipitated along the austenite grain boundaries (Fig. 1b). Further aging resulted in the formation of γ' and η particles (Fig.1c). The potentiodynamic curves (Fig.1f) showed that the HR A286 had the lowest pitting potential (Epit) and smallest passivation range, suggesting the formation of TiC particles did not deteriorate the corrosion resistance. Meanwhile, the γ' and η particles resulted in a slight decrease in the Epit and passivation range.Reference:[1] H. De Cicco, M.I. Luppo, L.M. Gribaudo, J. Ovejero-García, Microstructural development and creep behavior in A286 superalloy, Materials Characterization 52 (2004) 85-92.[2] P. De Tiedra, O. Martín, M. San-Juan, Potentiodynamic study of the influence of gamma prime and eta phases on pitting corrosion of A286 superalloy, Journal of Alloys and Compounds 673 (2016) 231-236. Figure 1

Microstructural characterization, boriding kinetics and tribo-wear behavior of borided Fe-based A286 superalloy

Iron-based superalloys are alloys produced for use in corrosive environments as an alternative to high-cost nickel-based superalloys. However, their average strength and hardness, attributed to their austenitic structures, limit their use in tribological applications. In an attempt to counter these drawbacks, boriding was applied to an iron-based A286 superalloy having an initial surface hardness of 320 HV. Boriding kinetics, some mechanical properties, and tribo-wear (ambient air and 3.5 NaCl environment) behaviors of the formed boride layers were investigated. Multicomponent boride layers (consist of FeB, Fe 2 B, CrB, NiB, Ni 4 B 3 ) were formed on the surface of the alloy, with hardness and thickness values of 1498–1961 HV and 20–130 μm, respectively, depending on the boriding temperature and the treatment time. The integral diffusion model was adopted to deal with the kinetics of monoboride and hemiboride layers formed on the surface. The boron activation energies of FeB, Fe 2 B, and DZ layer were estimated as equal to 175.86, 198.7, and 205.73 kJ mol −1 , respectively. As a result of increased surface hardness, all of the borided samples displayed reduced friction coefficients and higher wear resistance compared to the untreated alloy, in both ambient air and 3.5% NaCl. However, the increase in wear resistance was not proportional to the increase in hardness; while the best wear resistance was obtained in samples borided at 850–950 °C for 6 h, the lowest wear resistance was obtained in samples borided for 4–6 h at 1050 °C. This situation was caused by the Kirkendall effect and residual stresses in the structure of alloying elements with different diffusion rates due to the high-temperature effect of the boriding process. • Fe-based superalloy with average strengths and low hardness was successfully pack-borided. • Formed borides were examined using XRD, SEM-EDS, nanoindentation, microhardness, surface roughness and tribo-wear tests. • The hardness and elasticity modules of Fe-based superalloy were developed by boriding. • The friction and wear performance of A286 was improved with the boriding both in ambient air and 3.5% NaCl solutions. • Boriding open new possibilities for the use of Fe-based superalloys in tribo-corrosive environments.

Effect of Carbon and Titanium Variations in Fe‐Based Heat‐Resistant Superalloy A286 on TiC and η Phase Formation

Fe‐based heat‐resistant A286 superalloy is an age‐hardened austenitic stainless steel. Age‐hardening is greatly affected by TiC particles and η‐Ni3Ti phases. Herein, the evolution of TiC and η (hcp‐Ni3Ti) precipitations is investigated in six different A286 alloys with simultaneous variations of C and Ti contents, such as 0.00C–2.38Ti, 0.02C–2.46Ti, 0.04C–2.54Ti, 0.05C–2.58Ti, 0.06C–2.62Ti, and 0.08C–2.69Ti wt%. During microstructure evolution from solutioning state (900 °C for 2 h) to aging state (720 °Cfor 16 h), nodular/needle‐like TiC (fcc) and platelet lamellar structures of eta (η (hcp‐Ni3Ti)) phases are observed in the austenitic matrix of superalloys. Statistical analysis of TiC and eta phases after microstructural examination indicates that mean size goes up to 3.3 and 6.8 μm2 in 0.08C–2.69Ti wt% alloy, respectively. Yield strength and ultimate tensile strength are increased from 350 to 510 MPa and 530 to 650 MPa as a result of the strengthening mechanism of TiC from 0.00C–2.38Ti to 0.08C–2.69Ti wt% alloys, respectively. However, precipitation of these phases leads to brittleness of the alloys and elongation decreases from 20% to 12% with the increment of these phases. The strengthening mechanism is explained by stress–strain curves and fracture topography.

Research on green dielectric fluids of high-efficient electrical discharge assisted arc milling

Superalloys, titanium alloys, stainless steels, and other difficult-to-cut materials have been widely used in aerospace and military due to their unique physical and chemical properties. Compared with conventional EDM and mechanical milling methods, the electrical discharge assisted arc milling (EDAAM) method can achieve efficient and stable machining when processing these difficult-to-cut materials. The oil-based dielectric fluid, which is often used in conventional EDM, may cause environmental problems if not recycled. In order to improve the environmental performance and study the influence of dielectric fluids, this paper studies the effects of different dielectric fluids on the machining performance of EDAAM. Deionized water and different gases including air, oxygen, nitrogen, and argon were used as the dielectric fluid, graphite was used as tool electrode, and iron-based superalloy A286 (GH2132) was used as the workpiece. Machining performance, including material removal rate, relative electrode wear rate, machining error, and surface properties, including recast layer, surface morphology, and element distribution, were studied. The experimental results show that the combinations of different dielectrics play a vital role in the processing effect. The mixed flushing method of using deionized water and gas medium can ensure the machining efficiency and improve the surface quality of the workpiece.

Evaluation of surface integrity in electrochemical micromachining of A286 super alloy

Surface integrity of micro components is a major concern particularly in manufacturing industries as most geometry of the products must meet out necessary surface quality requirements. Advanced machining process like electrochemical micro machining possess the capabilities to machine micro parts with best surface properties exempting them from secondary operations. In this research work, different electrolytes have been employed for producing micro holes in A286 super alloy material to achieve the best surface quality and the measurement of surface roughness and surface integrity to evaluate the machined surface are carried out. The machined micro hole provides detailed information on the geometrical features. A study of parametric analysis meant for controlling surface roughness and improvement of surface integrity has been made to find out the suitable parameters for machining. The suitability of various electrolytes with their dissolution mechanism and the influence of various electrolytes have been thoroughly studied. Among the utilized electrolytes, EG + NaNO3 electrolyte provided the best results in terms of overcut and average surface roughness.

Differences between internal and external hydrogen effects on slow strain rate tensile test of iron-based superalloy A286

To investigate the evaluation method of hydrogen compatibility of A286 superalloy in high pressure hydrogen gas, SSRT tests of hydrogen-charged specimens were conducted at ambient temperature at various strain rates. The relative reduction in area (RRA), one of the ductility parameters, was determined. The hydrogen content in the hydrogen-charged specimen was the same as the equilibrium hydrogen content on the specimen surface at 150 °C in 70 MPa hydrogen gas. The strain rate dependence of RRA was smaller than that of RRA obtained in 70 MPa hydrogen gas at 150 °C. All the hydrogen-charged specimens showed slip-plane fractures in the grains in their cores. However, the specimens in 70 MPa hydrogen gas at 150 °C showed fracture surfaces morphology ranging from dimples to quasi-cleavages and intergranular fractures with decreasing strain rate. These dissimilarities are expected to arise from differences in the hydrogen concentration behaviors of the specimens during the deformation process.

Modeling and combined application of MOEA/D and TOPSIS to optimize WEDM performances of A286 superalloy

Superalloys are categorized as difficult to process materials with a broad spectrum of applications in industries. Process modeling and optimization of WEDM performances on nickel- and titanium-based superalloys are widely investigated. However, such investigations on iron-based superalloy are still lacking and hence probed in the present article. Thus, the paper targets modeling the correlation between the performance parameters and the control parameters with two popular techniques: response surface methodology (RSM) and artificial neural network (ANN) for WEDM of a typical iron-based superalloy, i.e., A286 superalloy. A comparison between the model estimates and the experimental values is made to check ANN and RSM's prediction accuracy. The estimates by the ANN model are exact and consistent with the experimental results. An analysis of variance (ANOVA) test is performed to perceive the degree of statistical significance of parameters. Moreover, a novel two-stage procedure, i.e., MOEA/D in collaboration with TOPSIS method, is implemented to search the optimal condition for process performances. The quality of Pareto-optimal solutions acquired using MOEA/D is compared to that of Pareto-optimal solutions obtained using NSGA II, PESA II, and MMOPSO through the use of a hypervolume (HV) parameter. Wilcoxon’s test is performed to identify the statistical difference between MOEA/D and competing algorithms. The optimal parametric combination recommended by the proposed optimization approach is Ton = 130 µs, Toff = 52 µs, Ipeak = 12 A, Wf = 5 m/min and SV = 30 V. The proposed optimization technique can also be exploited in other manufacturing processes.

Solidification Path, Microstructure, and Weldability Differences Between Fe-Based Superalloy A286 and an Experimental γ′ Strengthened TRIP Steel

Solidification Path, Microstructure, and Weldability Differences Between Fe-Based Superalloy A286 and an Experimental γ′ Strengthened TRIP Steel

Eco-green machining of superalloy A286: Assessment of tool wear morphology and surface topology

Unstable crude oil derivatives are among the main substances added to the mineral-based lubricants (MBL). However, the high purification and disposal costs of such lubricants and consequent environmental difficulties are the major drawbacks of cutting fluid consumption. The lower use of MBL or replacing them with less harmful ones, in principle, vegetable-based lubricants (VBL) are the prime importance of achieving less operating costs and pollution. Furthermore, the use of VBLs is much more recommended if machinability aspects, including tool life, surface, and edge quality, would also be improved. Therefore, in the present study, cutting parameters and lubricant types were used as the experimental variables in the MQL-turning of A286 superalloy. A286 is classified as a difficult-to-cut material with a wide range of applications in the energy and turbine industries. No experimental study was found on the machining of A286 under separate cooling and lubrication with two MQL systems simultaneously. The effects of cutting parameters on both average surface roughness Ra and tool wear morphology were evaluated. Experimental results denoted that the use of VBLs led to better surface topology. On the other hand, the tendency of the built-up layer (BUL) and built-up edge (BUE) phenomenon were intensified when MBL was used. On the word, better tool life is also expected when using VBL. This observation revealed that the use of VBL not only tends to improve productivity and environmental safety aspects but also machinability aspects; in principle, better surface topology and longer tool life are also expected.

Microstructure evolution and stress rupture properties of A286 superalloy in the 600 to 750 °C temperature range

To study the stress rupture properties of the A286 alloy in high temperature service environment, the stress rupture tests of A286 alloy at different temperature ranges and stress levels were carried out. Moreover, the Larson-Miller Parameter (LMP) for predicting the rupture life was established as LMP = (T + 273)(log t r + C) × 10−3, C = 22.3. The fracture morphology and the microstructure evolution of the stress rupture specimens were observed by scanning electron microscopy. The results show that for the stress rupture tests at 700 °C–750 °C/150–400 MPa, the precipitation of the closely arranged cellular η phase and the coarse MC at the grain boundary acted as the crack source. For the stress rupture test at 600 °C–700 °C/400–700 MPa, the coarse MC at the grain boundary led to stress concentration to give rise to crack initiation and propagation during deformation. With decreasing of temperature and increasing of stress, the fracture mode of the A286 alloy changed from the ductile fracture mode of microvoids to the brittle fracture mode of intergranular. The deformation mechanisms of A286 alloy at different temperatures and stress levels also have been systematically analyzed by transmission electron microscopy. The deformation mechanisms of A286 at different temperatures and stress levels were Orowan looping, microtwins and dislocation pairs shearing with Orowan looping and microtwins as the dominant deformation mechanisms. The critical transition radius of γ′ phase during the transition from dislocation shearing mechanism to Orowan looping mechanism was calculated.

Microstructural and mechanical characterization of powder-pack boronized Incoloy A286 superalloy

In this study, Incoloy A286 superalloy were boronized successfully by powder-pack boronizing process at 850 °C, 900 °C and 950 °C for 4 h by using a boronizing powder mixture containing H3BO3 as boron source. The thickness and morphology of the boride layer was identified by microstructural examinations. The boride layer with complex, compact and smooth morphology was formed on the surface of the samples. As a result of XRD analyses, it was determined that the compact boride layer was formed many phases such as FeB, Fe2B, Fe3B, CrB and Ni4B3 etc. It was specified that the average hardness value of the boride layer was approximately between 2400 and 3000 HV by microhardness tests. Also the graphs of friction coefficient and values of the specific wear rate were obtained by performing ball on disk wear tests. It was identified that the specific wear rate of boronized samples was approximately 9.5 times lower than that of unboronized samples.

The effect of solid solution treatment parameters on the microstructure and mechanical properties of A286 superalloy

In this investigation, the effects of solution parameters on the microstructure and hardness of a Fe-Ni superalloy were studied. Samples were solutionized in temperature ranges of 900 °C to 1060 °C for the times of 0.5 h to 2.5 h, water quenched and aged at 720 °C for 16 h. for more structural examinations, some solutionized samples were aged at 800 °C and 860 °C for 8 h. The microstructure of the alloy was investigated using optical and scanning electron microscopes and the volume fraction of phases was measured by image analyzer software. The hardness of solutionized and aged specimens and tensile strength of aged samples at room temperature were also assessed. The results showed that hardness and ultimate tensile strength decrease with increasing solution temperature. It was found that increase in the solution temperature led to a decrease in volume fraction of η and carbide phases and an increase in the carbide sizes. It was also found that solution annealing time had no significant effect on the properties of the alloy.

An investigation on thermodynamics and kinetics of η phase formation in Nb-modified iron-nickel base A286 superalloy

In this study, precipitation of η phase (Ni3Ti) in conventional and Nb-modified (Nb-A286) A286 superalloys was evaluated at different aging times and temperatures. The TTP curve of the η phase formation was plotted using thermodynamic analyses, kinetics and microstructural studies. Depending on temperature and heat treatment, the η phase precipitated at the grain boundaries or twin sites, as a result of the γ′ phase or matrix austenite transformation. Heat treatment of conventional A286 superalloy and Nb-A286 was performed within a temperature range of 650 to 900 °C for 2 to 30 h. The η phase transformation was evaluated by scanning electron microscope (SEM) which is equipped to energy dispersive X-ray spectroscopy (EDS) and optical microscopy (OM). In the analyses based on thermodynamic calculations, the interaction of the Gibbs free energy of η phase formation and the diffusion activation energy of the elements, especially titanium and niobium, was considered. The microstructural studies showed that increasing the heat treatment time results in increasing the volume fraction of the η phase. By increasing the aging temperature to 840 and 860 °C for conventional A286 superalloy and Nb-A286 superalloy, respectively, the η phase volume fraction increased, however, further increase led to volume fraction decrease. The results of the thermodynamic analyses showed the tip of the TTP diagrams at temperatures of 860 and 820 °C for the A286 and Nb-A286 alloys, respectively. Investigation of kinetics calculations showed that η phase transformation depends on the diffusion of titanium, nickel, and niobium.