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The metallic materials subjected to machining‐induced severe plastic deformation can experience alterations of microstructures and mechanical properties, affecting the functional performances of the components. This study concentrates on the microstructure evolution and mechanical properties analysis of Ni‐based superalloy Inconel 690 under severe plastic deformation induced by milling process. The obtained results show that the microstructures of the machined surface and subsurface exhibit the characteristic of gradient distribution. Plastic behaviors involving dislocation multiplication, grain deformation and refinement, increment of local misorientation and average intragranular misorientation, and transition from high‐angle grain boundaries to low‐angle grain boundaries occur in the superficial layer of the machined workpiece. Both the intensity and the affected depth of plastic deformation for the superficial layer are strengthened following the cutting speed and feed increase, which is attributed to higher cutting forces. No white layer and phase transformation is found under all cutting conditions. In addition, the nanohardness of the superficial layer shows the reduction tendency of hardening effect from the surface to the bulk of the machined workpiece material. With the increase in cutting speed and feed, the affected zones of residual stresses and work hardening below the machined surface become wider. [ABSTRACT FROM AUTHOR]

Wire electric-discharge machining (WEDM) is the most desirable material processing technique for making complex designs, especially in hard-to-machine conductive materials with high fidelity and accuracy. Current study aims to streamline the WEDM parameters to process Inconel 690. Experimental trials are effectuated using Box-Behnken design of response surface methodology. Processing conditions of parameters are varied to scrutinize the performance of the technique. Federated mode of analysis of variance and grey relational analysis (GRA) are implemented to the study the significance and streamlining of the parameters respectively, to attain increasing material removal rate and small surface roughness for inconel 690 which is highly preferred for nuclear reactor and gas turbine industry. After applying GRA technique, streamlined condition of parameters is found which gives results with acceptable error. Surface topography of the post processed workpiece is also anatomize using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) technology has the advantages of designability, short process times, high flexibility, etc., making it especially suitable for manufacturing complex high-performance components for high-end industrial systems. However, the intensive temperature gradients caused by the rapid heating and cooling processes of AM can generate high levels of residual stresses, which directly affect the precision and serviceability of the components. Taking Inconel 690 alloy, which is widely used in nuclear power plants, as the research object, a thermo-coupled mechanical model of temperature field and residual stress field of directed energy deposition (DED) of Inconel 690 was established based on ABAQUS 2019 finite element software to study the influence of process parameters on the temperature history and the distribution of residual stresses in the DED process. The experimental results show that the peak temperature of each layer in the fabrication process increases with the increase in laser power and preheating temperature, and decreases with the increase in scanning speed and interlayer dwell time. Substrate preheating only has a large effect on the peak temperature of the first four layers. Residual stresses are mainly concentrated in the upper and middle parts, the bottom of the substrate, and the sides combined with the substrate, and the residual stresses increase with the increasing laser power and decrease with the increasing interlayer dwell time. Decreasing laser power, longer dwell time, higher preheating temperature, and appropriate scanning speed are beneficial for the reduction in residual stresses in Inconel 690 components. This research has important significance for the process design and residual stress modulation in the additive manufacturing of Inconel 690 alloy. [ABSTRACT FROM AUTHOR]

In this study, we synthesized three low-sulfur and low-phosphorus ionic liquids (ILs). These were N88816P8, P88816P8, and P88816DOSS. The viscosity and thermal stability of the three ILs were analyzed. The tribological properties and lubrication mechanisms of the three ILs were investigated as lubricants for a carbide ball–Inconel 690 nickel-based alloy friction pair and compared at 50 °C and 150 °C. The wear spots of the carbide ball and nickel-based alloy disc samples were characterized using SEM and EDS. The experimental results revealed that P88816P8 had excellent tribological properties. The lubrication mechanism of P88816P8 as a lubricant for the carbide ball–Inconel 690 nickel-based alloy friction pair was investigated using XPS. The excellent friction reduction and anti-wear properties of P88816P8 could be attributed to the tribo-chemistry between P88816P8 and Inconel 690 as well as the formation of a tribo-film on the wear-spot surface. This high-performance IL, suitable for carbide ball–Inconel 690 contact, will be applied to a cutting process of Inconel 690. [ABSTRACT FROM AUTHOR]

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The present work aims to carry out a feasible study of wire electro-discharge machining (WEDM) during the machining of Inconel 690 superalloy gears. Processing conditions of power-on time, power-off time, current, and spark-gap voltage are varied to evaluate the process performance in terms of material removal rate (MRR), surface roughness (SR), and wire consumption. Parametric optimization has been carried out using combined approach of response surface methodology (RSM) and artificial neural network (ANN). Results revealed that ANN predicted values are 99% in agreement with the experimental results which validates its effectiveness as compared to RSM predicted values. A viability study of noise characteristics of the processed gear is also done using a noise testing setup. Additionally, FE-SEM has been used to analyze the machined surface’s topography. Greater discharge energy brought by a longer pulse length raises the values of MRR, SR, and recast layer thickness (RLT). This study explores the capability of WEDM to produce a more precise and smooth gear profile as compared to other conventional machining methods. Additionally, RLT and microhardness of the machined surface have been critically studied to comprehend the better understanding of the process mechanism.

Current research aims to execute a viability study of electro-spark erosion technique to process Inconel 690, a high-volume fraction of Cr-Fe-Ni superalloy (∼32% Cr). The Box-Behnken design of response surface methodology with varying processing conditions is used to execute the experimental trails. Process performance is examined in terms of material removal rate and surface topography. The surface conditions of the processed surface are studied using scanning electron microscopy. The tool wear character and tribological behavior of the processed surface are also scrutinized to check the post-process consequences. The study explores the formation of oxide layers, craters, spherical droplets, and micro-cracks on the surface processed at Ton: 118 mu; Toff: 45 mu; Ip: 130 mu; Sv: 50 V (parametrical settings for maximum material removal rate), and at Ton: 118 mu; Toff: 30 mu; Ip: 220 mu; Sv: 50 V (parametrical settings for maximum surface roughness) attributing a deteriorating surface quality. The maximum material removal rate of 9.38 mm3/min and minimum surface roughness of 0.47 μm are achieved. A significant improvement of approximately 20 HV in micro-hardness is detected owing to the formation of a recast layer on the processed surface. Consequently, a noticeable improvement is observed in the wear resistance of the processed surface. [ABSTRACT FROM AUTHOR]

One of the major concerns in the field of machinery manufacturing of Ni-based superalloys is machining-induced surface integrity, since the surface integrity is closely bound up with the service performance of machined components. In the current study, a range of orthogonal experiments are carried out to investigate the surface integrity characteristics, including surface morphology, surface roughness, residual stress, work hardening, and surface microstructure during high-speed milling of Inconel 690. The results show that both cutting speed and feed rate plays a constructive role in determining cutting force and surface integrity of Inconel 690. The cutting force displays a downtrend with the increase of cutting speed while presents an uptrend with the increase of feed rate as well as depth of cut. While, no clear tendency between the relative position of tool and workpiece and the cutting force could be found. The surface roughness decreases firstly and then increases slightly with the increase of cutting speed while increases with the increase of feed rate. The surface residual stress presents more tensile tendency as the cutting speed and feed rate increase. Similarly, the increased cutting speed and feed rate strengthen the degree of work hardening as well as depth of work hardening. It is worth mentioning that not only the depth of cut but also the relative position of tool and workpiece has little effect on surface integrity. Severe plastic deformation occurs in the microstructure of machined surface layer. No phase transformation is observed at all workpiece surface. This study provides a meaningful chance to achieve excellent machining-induced surface integrity via selecting suitable cutting parameters. [ABSTRACT FROM AUTHOR]

The effects of laser shock peening (LSP) with different peening times on the hot corrosion behavior (molten salt of 75 wt% Na 2 SO 4 + 25 wt% NaCl) of Inconel 690 at three different temperatures (700 °C, 800 °C, 900 °C) were investigated. The corrosion conditions of the three specimens were also compared in the extreme case, i.e. after 900 °C, 300 h of hot corrosion. The results showed that LSP effectively prevented the surface oxides from shedding. As times of LSP increased, the strengthening effect improved and the rate of weight loss gradually slowed down. The dense oxide film generated by the high Cr content of the material itself, LSP-induced high-density dislocation structure, mechanical twinning and grain refinement is one of the key factors in improving the hot corrosion resistance of Inconel 690. The CRS layer and microhardness layer are another key factor in preventing the cracking of the oxide film to enhance the hot corrosion resistance. Under extreme conditions, the hot corrosion resistance of LSPed specimens is still better than that of unLSPed specimen. [Display omitted] • The effects of LSP on the hot corrosion behaviors of Inconel 690 were investigated. • The average grain sizes decreased with increasing LSP times. • LSP-induced grain refinement, nano-twins, high CRS and increased dislocation density. • LSP-induced these four factors increased the hot corrosion resistance. [ABSTRACT FROM AUTHOR]

The intergranular corrosion of Inconel 690 alloy in NaCl solution was investigated using in-line digital holography to observe the dynamic processes occurring at the electrode| electrolyte interface in both the absence and presence of a magnetic field (MF). MF reduced the anodic currents by 6 and 3% at 1.1 V in 0.5 M NaCl (pH = 6.44) and 0.5 M NaCl +0.01 M NaOH (pH = 11.5) NaCl solutions respectively because it may increase the amount of Cr on the electrode surface and change the structure of the surface film, thus enhancing the formation of an oxide film; however, MF affected the anodic current little due to the low Lorentz force at the low potential. It was observed that the intergranular corrosion began from a certain grain boundary and developed into other grain boundaries with and without MF. Because the anodic dissolution rate of Fe or Ni is much higher with MF than that without MF and the content of Fe or Ni was higher at a grain boundary than that at the other areas on the surface of the electrode, MF accelerated the intergranular corrosion.

In this study, the effect of Nb content and aging temperature on the weld of Inconel 690 was investigated by the behavior of M 23 C 6 . After changing the Nb content of FM-52 to 0.65 wt%, 1.48 wt%, 2.45 wt%, and 3.46 wt%, shielded metal arc welding was conducted under constrained conditions to reduce the thermal deformation. As a result of measuring the hardness after aging treatment, the hardness increased with the Nb content, and it was determined that the transgranular and intergranular precipitation effect of MC on the increase in hardness was greater than that of M 23 C 6 , which mainly precipitated at the migrated grain boundary (MGB) compared to MC. Optical Microscope analysis showed that the MGB changed from a straight type to a vermicular type as the Nb content increased. As a result of SEM/EDS and EBSD analysis, most of the carbide ( M 23 C 6 ) was observed in specimen A with a low Nb content and decreased with an increase in the aging temperature, and the fraction of M 23 C 6 decreased with an increase in the Nb content. Micro-voids were generated by a large amount of M 23 C 6 at an aging temperature of 600–800 °C in the A and B specimens with a relatively low Nb content. The pitting resistance was improved due to the amount of Cr-rich M 23 C 6 decreased as the Nb content increased. However, no decrease in corrosion resistance was observed owing to the micro-voids produced near Cr-rich M 23 C 6 . [ABSTRACT FROM AUTHOR]

[Display omitted] • A Tube-to-Tube sliding wear test rig is developed. • Sliding wear volume of Inconel 690 tube increases with increasing cycle number. • Sliding wear volume of Inconel 690 tube is larger under larger contact force. • Wear volume is smaller under lubrication of water, especially at beginning. • Water reduces oxidative wear due to lower oxygen concentration. A Tube-to-Tube sliding wear test rig was developed in the current work. The reciprocating sliding wear behaviors on Inconel 690 heat transfer tubes were experimentally studied under various conditions. The sliding amplitude and frequency have little influence on wear, and the wear volume is in general positively proportional to the sliding cycle number and the contact force. Therefore, the Archard wear equation can be adopted to calculate the macroscale wear volume of the heat transfer tubes. Based on the results obtained by optical microscopy and scanning electron microscopy, the main wear mechanisms of the tube are the adhesive wear, abrasive wear and oxidative wear. Under the water environment, the wear rate is evidently lower than that of the dry condition and the wear mechanisms were not altered. [ABSTRACT FROM AUTHOR]

Inconel 690 is one of the most comprehensively used heat-resistive superalloys, exclusively applied in aerospace or aircraft engineering. Due to its implausible strength and rigidity, it possesses dull machinability. Hence, the machinability of Inconel alloys has turned out to be an extremely significant topic for study. Minimum quantity lubrication–vegetable oil synergy already made a reliable venture into the challenging facets of Inconel machining. However, for the effective controlling of end milling parameters, it is an imperative idea to imply Pareto-based hybrid multi-objective optimization strategy in machining domain. Thus, for the first time, a three-stage computational approach combining the theory of gene expression programming (GEP), non-dominated sorting genetic algorithm-II (NSGA-II) and technique for order preference by similarity to ideal solution model (TOPSIS) were utilized. Here, GEP-generated explicit equations are applied in NSGA-II to search the different solutions, and TOPSIS method is applied to choose the best compromise solution from non-dominated Pareto optimal solutions. Furthermore, a comparative study showed that the average error obtained between the experimental and predicted response is 3.13%, which determines the modesty of the proposed optimization model. So, the results of this study enlighten the possibility of adopting Pareto-based hybrid algorithms in the domains of the metal cutting operation. [ABSTRACT FROM AUTHOR]

Inconel 690 is an extensively used superalloy in the aerospace and nuclear industries. Owing to the low thermal conductivity and poor machinability, the cutting tools are severely affected during the milling of Inconel 690. Thus, the machining of such superalloys consumes an extensive cost and time. In this context, an artificial intelligence–assisted cost-effective meta-model has been established in this manuscript for the accurate prediction of maximum flank wear. Here, a series of experiment was conducted on Inconel 690 using a TiAlN-coated solid carbide insert. Afterward, using the main effect plot (MEP) diagram, the effects of machining parameters on flank wear were evaluated. Additionally, the analysis of variance (ANOVA) demonstrated that the MQL flow rate is the most significant parameter affecting the flank wear. In the second part, 70% of machining output has been selected for training the gene expression programming (GEP) and artificial neural network (ANN) model, and the rest 30% data has been used for testing purpose. Furthermore, considering a statistical platform, the GEP model has been compared with an ANN model. The comparative analysis demonstrated that the GEP meta-model is superior to the ANN model in predicting the maximum flank wear under MQL environment. The outcomes of this study can aid the metal cutting industries to better plan the machining system on the perspective of the tool wear reduction with optimized parameters levels. [ABSTRACT FROM AUTHOR]

Through minimum quantity lubrication (MQL) technology, small droplets of cutting fluid accompanied by compressed air are sprayed into the tool-workpiece interface. Hence, it offers effective lubrication/cooling and advances machining performance without using the significant amount of cutting fluids. Conversely, due to the biodegradable and non-pollutant properties of vegetable oils, these are widely employed as a base fluid in MQL technology. Considering the benefits of MQL-vegetable oil synergy, this paper aims to determine the best possible sequence of MQL milling parameters of Inconel 690 using castor oil as a lubricant. Here, response surface methodology (RSM) has been exploited to make a correlation between input and machining responses. To deal with the optimization problem, a two-stage computational approach was adopted. The first theory was non-dominated sorting genetic algorithm-II (NSGA-II) and the second method was technique for order preference by similarity to ideal solution (TOPSIS). NSGA-II has been exploited to explore for the candidate solution, and TOPSIS has been deployed to find out the best compromise solution. Finally, this manuscript compares the outcomes of the adopted approach with experimental outcomes to determine the efficacy of the proposed model. It was revealed from the comparison that the average error obtained between the predicted and the experimental response is less than 1%. [ABSTRACT FROM AUTHOR]

Abstract A specimen with a newly designed composition was produced using shielded metal arc welding by changing the Nb content. To evaluate the susceptibility of ductility-dip cracking (DDC), tensile test and hardness measurement were performed, and to examine the behaviors of precipitates during heat treatment, the microstructures were observed using an optical microscope and a scanning electron microscope. As the Nb content increased, the hardness of the specimen improved through solution hardening, and as the hardness increased, the yield strength in the tensile test results increased. Furthermore, as the Nb content increased, the amount of Cr-rich carbide precipitated at the grain boundary decreased and the amount of transgranular Nb-rich carbides increased. This increased the susceptibility of DDC and the critical strain at which the DDC begins to appear at tension increased. The microstructure analysis of a specimen heat-treated at 715 °C revealed that the intergranular Cr-rich carbides became continuous and coarse through the diffusion of Cr, and the tensile test results showed that DDC occurred at a strain lower than that of the as-weld specimen. In the specimen heat-treated at 1100 °C, the intergranular Cr-rich carbides were melted and the intergranular precipitates were removed. Highlights • DDC susceptibility decreases as the amount of carbide increases at grain boundaries. • As the Nb content increased, the amount of Cr-rich carbide decreased. • The amount of carbide at grain boundary increases during the heat treatment. • The carbide is melted during the heat treatment at a temperature near the melting point. [ABSTRACT FROM AUTHOR]

In this study, a combination of local heat treatment (LHT) with (w/) and without (w/o) ultrasonic nanocrystal surface modification (UNSM) technique was applied to Inconel 690 alloy at room and high temperatures (RT and HT). The main purpose of this study is to investigate the influence of LHT w/ and w/o UNSM processing on the mechanical and fretting wear mitigation of Inconel 690 alloy. The surface roughness of the specimens was increased with increasing the LHT temperature w/ and w/o UNSM from RT to HT at 700 °C, while the surface hardness of the RT and HT at 300 °C specimens was increased and softening occurred at HT at 700 °C. The mechanical properties of the specimens were investigated using a tensile stress test. It was found that the stress-strain curve of the UNSM-treated at RT exhibited better mechanical characteristics in comparison with the as-received one. Moreover, the specimens treated at HT at 300 and 700 °C exhibited better results in terms of strain, but there was no significant difference in stress. The UNSM treated specimens at HT of 300 °C had better results in comparison with other specimens. In addition, the fretting wear resistance of those specimens was assessed using a ball-on-disk fretting wear tester at temperatures of 25 and 80 °C. The fretting wear resistance of Inconel 690 alloy was also increased by the combination of LHT + UNSM processing, which may be attributed to the increase in mechanical properties, increase in surface roughness, induced compressive residual stress and the presence of a nanostructured surface layer. Hence, Inconel 690 alloy with the increased mechanical properties and fretting wear resistance by the combination of LHT + UNSM processing could be beneficial for nuclear applications. [ABSTRACT FROM AUTHOR]

The thermally activated dislocation motion due to plastic deformation in Inconel 690 has been carried out by performing tensile tests in air and in environmental hydrogen using the strain relaxation technique. The results show that the variation of - δ (Δ A/b 2 ) or ln( V H / V Air ) with ε p depends on the nickel content in the alloy and the microstructure, and generally increases with increasing Ni% for low value of ε p (tensile test). The maximum increase in the rate change was observed for the austenized and aged microstructure. On the other hand, fatigue crack propagation rate ( da / dN ) has been measured in the same environments. An attempt has been carried out to correlate the rate change - δ (Δ A/b 2 ) or ln( V H / V Air ) with the variation of ( da / dN ) H against ( da / dN ) Air (the variation of Ω ) and has shown that for the austenized and aged microstructure, Ω is higher than those for stress relieved or only aged at 700 °C. These results are similar to those obtained by the thermal activation parameter – δ (∆ A / b 2 ) or the ratio ln( V H / V Air ). The maximum values of – δ (∆ A / b 2 ) and Ω are obtained when the density of precipitates on the grain boundaries is higher than that in the matrix. In this case, intergranular fractures with fin slip lines features on the grain surfaces were observed. Finally, in the presence of environmental hydrogen, about the fatigue crack propagation rate, two relationships were established and expressed as: 1) in stages I and II: ( Δε p /2) = Θ Δ K + Γ and 2) only in stage II: ( da / dN ) II = c II ( Δε p / 2) λ , where λ ≈ m = 2, the power factor in Paris' law. [ABSTRACT FROM AUTHOR]

In this research, the surface roughness affecting the pressure drop in a pipe used as the steam generator of a PWR was studied. Based on the CFD (Computational Fluid Dynamics) technique using a commercial code named ANSYS-FLUENT, a straight pipe was modeled to obtain the Darcy frictional coefficient, changed with a range of various surface roughness ratios as well as Reynolds numbers. The result is validated by the comparison with a Moody chart to set the appropriate size of grids at the wall for the correct consideration of surface roughness. The pressure drop in a full-scale U-shaped pipe is measured with the same code, correlated with the surface roughness ratio. In the next stage, we studied a reduced scale model of a U-shaped heat pipe with experiment and analysis of the investigation into fluid-structure interaction (FSI). The material of the pipe was cut from the real heat pipe of a material named Inconel 690 alloy, now used in steam generators. The accelerations at the fixed stations on the outer surface of the pipe model are measured in the series of time history, and Fourier transformed to the frequency domain. The natural frequency of three leading modes were traced from the FFT data, and compared with the result of a numerical analysis for unsteady, incompressible flow. The corresponding mode shapes and maximum displacement are obtained numerically from the FSI simulation with the coupling of the commercial codes, ANSYS-FLUENT and TRANSIENT_STRUCTURAL. The primary frequencies for the model system consist of three parts: structural vibration, BPF(blade pass frequency) of pump, and fluid-structure interaction.

The convincing potential of sophisticated milling tools exploited for machining of Inconel alloys in CNC milling machine offers minimal surface roughness-cutting force-cutting temperature trade-off footprint as compared to the conventional machining operation, which afforded a strong motivation to accomplish an in-depth discovery of the parametric design of CNC milling operation. In this study, the synergistic potential of contemporary Cubic boron nitride coated tool is used for machining of Inconel 690 in CNC milling machine, which has been scrutinized in order to build up a correlation among the objective function and the control variables by a metamodel called Adaptive Neuro-fuzzy inference system (ANFIS). The developed ANFIS model was capable of predicting the performance parameters with commendable accuracy as observed from correlation coefficients within the range of 0.946542–0.988996, Mean absolute percentage error (MAPE) in the range of 3.879652–7.456275% along with noticeably low root mean square errors (RMSE). Moreover, the ANFIS acquired results were compared with an Artificial Neural Network (ANN) model, developed on the identical parametric ranges. The comparison of the obtained results indicated that the ANFIS overtakes the ANN model in predicting the preferred response variables, which suggests the modesty of the ANFIS model. [ABSTRACT FROM AUTHOR]

The effect of normal force on fretting corrosion behaviors of Inconel 690 in 3.5% sodium chloride was investigated. The results indicated that fretting corrosion behaviors strongly depended on fretting regime and normal force. In gross slip regime, the wear volume increased but coefficient of friction (COF) decreased with increasing normal force. The damage mechanism was nanostructures and delamination cracks, and the tribologically transformed structure was separated into Ni-rich/Cr-rich oxide zones. The wear mechanism was delamination/oxidation wear. In partial slip regime, wear volume and COF decreased with increasing normal force. The main damage mechanism was fatigue cracks and asperity corrosion. The fatigue cracks propagated along the direction of 40–50° to the surface. The wear mechanism was oxidation/abrasive wear. [ABSTRACT FROM AUTHOR]

Inconel 690 superalloy was corroded at 700 °C and 800 °C for up to 70 h in N-0.1% HS gas. It corroded almost linearly with large weight gains, displaying little protectiveness. Its corrosion rates were quite fast when compared with its corrosion in air or Ar-1%SO gas. The formed scales were thick, fragile, and nonadherent. They consisted primarily of CrO with some NiCrO, NiS, CrS, and CrS. The HS gas accelerated the corrosion significantly by forming nonprotective sulfides and dissolving hydrogen in the scale and in the internal corrosion zone that consisted of discrete chromium-sulfides and some oxide particles. The marker test indicated that the scales grew by the outward diffusion of metallic ions such as Ni, Cr, Fe, and Mn, whilst the internal corrosion zone thickened by the inward migration of oxygen and sulfur through the lattice, grain boundaries, and microcracks. [ABSTRACT FROM AUTHOR]

The impact fretting wear behavior of a 690 alloy tube affected by low-impact cycling kinetic energy was investigated. The Inconel 690 alloy specimen was clamped by cantilever and simple supported beam structures for support. The interface response was affected by the clamping situation, and material wear was affected by the change in the interface response. The energy loss, contact force versus time and frequency, energy absorption, and deformation of the material (thin wall tube) during impact were analyzed. The worn surfaces and cross-sectional morphologies were observed with an optical microscope and a 2D surface profiler to analyze the impact fretting wear mechanism under the two support structures. In the two clamping structures, wear decreased when the span increased, and material wear showed a high correlation with the peak impact force and absorbed energy. The wear mechanism of the alloy 690 specimen was delamination. [ABSTRACT FROM AUTHOR]

The structural integrity of steam generator tubes is a relevant issue concerning nuclear plant safety. In the present work, J -resistance curves of Inconel 690 and Incoloy 800 nuclear steam generator tubes with circumferential and longitudinal through wall cracks were obtained at room temperature and 300 °C using recently developed non-standard specimens' geometries. It was found that Incoloy 800 tubes exhibited higher J -resistance curves than Inconel 690 for both crack orientations. For both materials, circumferential cracks resulted into higher fracture resistance than longitudinal cracks, indicating a certain degree of texture anisotropy introduced by the tube fabrication process. From a practical point of view, temperature effects have found to be negligible in all cases. The results obtained in the present work provide a general framework for further application to structural integrity assessments of cracked tubes in a variety of nuclear steam generator designs. [ABSTRACT FROM AUTHOR]

The ultrasonic surface rolling process (USRP) is conducted by making the metal surface undergo micro-plastic deformation to improve its surface state and some mechanical properties, thus strengthening its tribocorrosion resistance. In this study, the surface of the Inconel 690 alloy block was treated by special USRP, and the change in its tribocorrosion behaviors had been effectively revealed by a fretting electrochemical corrosion test rig. Results showed that the Inconel 690 alloy's tribocorrosion degree and corrosion rate were evidently reduced after USRP. These results could be attributed to the surface finish reduction and surface grain refinement caused by USRP. [ABSTRACT FROM AUTHOR]

WC-10Co-4Cr coating was deposited through supersonic flame of high-velocity oxygen fuel (HVOF) process on the outside surface of Inconel 690 alloy tube. The fretting corrosion behavior of substrate- and coating- treated alloy tubes under dry state and seawater are compared. Results show remarkable differences between substrate- and coating-treated samples in electrochemical corrosion response and wear behavior. The fretting wear resistance of the WC-10Co-4Cr coating-sprayed alloy tube considerably improved because its surface mechanical properties are better than that of the substrate. Though the initial static corrosion performance of the coating is poorer than the substrate alloy tube, its excellent wear resistance helps decrease corrosion rate. In addition, the predominant damage mechanism of fretting corrosion was abrasive wear, fatigue delamination, and corrosion. [ABSTRACT FROM AUTHOR]

The effect of carbide size and spacing on the fretting wear resistance of Inconel 690 steam generator (SG) tube mated with SUS 409 was investigated in this study. Based on previous materials tribology research, we reasoned that increasing carbide size and spacing would increase the wear resistance of the Inconel 690. Experiments were performed to test this hypothesis. Commercialized Inconel 690 tube with mean carbide length, thickness and spacing of 0.29, 0.10, and 0.59 μm, respectively, was used for the wear test. Carbide length, thickness, and spacing increased to 0.36, 0.15, and 0.68 μm, respectively after heat treatment at 450 °C for 16 h without changes in carbide volume fraction, grain size or hardness. The results of the wear test showed that at the amplitude of 25 μm, wear coefficient did not change due to stick phenomenon. At the amplitude of 50 μm–150 μm, wear coefficient decreased about 50%. At the amplitude of 300 μm, the wear coefficient decreased from 2.7 × 10 − 13 m 3 / Nm to 2.0 × 10 − 13 m 3 / Nm due to increase in carbide size and spacing. [ABSTRACT FROM AUTHOR]

Abstract: Steam generator (SG) tubes in certain types of nuclear power plants experience flow-induced vibrations that can result in fretting wear. The wear mode under these conditions can change with wear variables. Using a custom-designed fretting test apparatus, the effects of amplitude and frequency on wear mode changes for Inconel 690 SG tubes mated with SUS 409 were investigated. Changes in the wear mode were found by using periodic measurements of weight loss to calculate wear coefficients. The wear mode was observed to change from stick to gross slip and sliding as amplitude increased from 25μm to 300μm. However, the wear mode did not change with increasing frequency or testing duration within the range of applied conditions. [Copyright &y& Elsevier]