Inconel X-750 Research Articles

Experimental Study of Electrical Discharge Machining of Inconel X-750 Using Tungsten-Copper Electrode

Nickel-based alloys have wide applications in many industries due to their outstanding properties like high temperature, corrosion resistant and creep rupture. Inconel X-750, a Nickel based super alloy, precipitation hardenable material used especially in aircraft structures, rocket engine thrust chambers, gas turbines, nuclear reactors and pressure vessels due to its excellent properties. However, it is very difficult to machine using traditional methods due to their low thermal conductivity, strong strain hardening, and high strength at elevated temperatures. Therefore, electrical discharge machining (EDM), which is a thermal process irrespective of work piece hardness, is used to machine Nickel-based alloys by electrical erosion. In this process cu-w electrode was used as an electrode because of its excellent thermal properties and high thermal conductivity of copper component and low thermal expansion, high melting point of tungsten gives the better surface integrity on machining .The objective of this investigation is to optimize the EDM process parameters on Inconel X-750 alloy over the performance parameters like material removal rate (MRR), surface roughness (SR) and recast layer thickness (RLT) and to study the influence of operating parameters of tungsten-copper electrode on the machining characteristics .The experiments were performed based on one factor at a time approach. In this report, the considered input parameters like pulse peak current, pulse on time, pulse off time and type of electrode. It has been noticed that most of the authors focused on reducing the surface roughness and increasing the material removal rate using different materials like copper, graphite, brass. However, very few authors have been experimental investigated on Inconel X-750 with W-Cu electrode

A Comparative study of tool wears in dry turning of Inconel X-750 and Waspaloy

Machining of Nickel based superalloys has posed considerable challenges due to rapid work hardening and low thermal conductivity. The present investigation aims to compare the tool wears in dry turning of Inconel X-750 and Waspaloy by analyzing the variation of flank and nose wears with machining length. The experiments were designed using the following parameters: cutting speed=50 m/min, 75 m/min, 100 m/min; feed rate= 0.05 mm/rev. The depth of cut was kept at a constant value of 0.5 mm. PVD coated carbide inserts were used for the turning operation and tool wear was analyzed using a digital microscope. The wear rate was higher while machining Waspaloy as compared to Inconel X-750 for all experiments.

Experimental investigation on surface integrity in machining of Inconel X750 with WEDM using Taguchi technique

Experimental investigation on surface integrity in machining of Inconel X750 with WEDM using Taguchi technique

Experimental investigation on surface integrity in machining of Inconel X750 with WEDM using Taguchi technique

The objective of the present work is to investigate the effects of various WEDM process parameters such as pulse on time, pulse off time, servo voltage, peak current, wire tension and wire feed rate on the surface roughness of the machined samples. The analysis of variance was carried out for raw data as well as for signal to noise ratio. Four input parameters have been found to be statistically significant for their effects on the response of interest. The optimum value of surface roughness was obtained at pulse on time - 110; pulse off time - 51; spark gap voltage - 65 V; peak current - 90 A; wire feed - 11; wire tension - 5. The confirmation experiments were also performed for validating the predicted results. Scanning electron microscopy was performed on the machined samples to investigate the effect and microstructure of the samples after machining.

A novel in-situ, lift-out, three-point bend technique to quantify the mechanical properties of an ex-service neutron irradiated inconel X-750 component

A first of its kind small scale mechanical testing technique involving micro-three-point bending was invented, developed, and implemented on reactor irradiated, active Inconel X-750 components removed from service after approximately 53 and 67 dpa. These tests were performed at ambient room temperature in-situ using a scanning electron microscope in order to obtain live recordings of sample deformation and loading curves. Sample and testing apparatus preparation required novel lift-out and fabrication processes. Materials from two irradiation temperature regimes, low temperature (120-280 °C) and high temperature (300 ± 15 °C) were examined. Manufacturing and finishing (grinding) of this component create differences between its edge and center, so micro-specimens from both areas were extracted in order to study these differences. According to three-point beam bending theory, a 0.2% offset yield stress parameter is introduced and calculated for all specimens. Differences in mechanical properties due to irradiation temperature and dose effects were observed. Material irradiated at the higher temperature exhibited yield strength increases of ∼540 MPa after 53 dpa and ∼1000 MPa after 67 dpa. There was little difference (≤310 MPa) in yield strength between materials irradiated at the lower temperature at 53 dpa and 67 dpa compared with non-irradiated material. Differences in yield strengths between the edge and center of the component are retained after irradiation. The difference in yield strengths for the edge and center regions was ∼740 MPa for non-irradiated material. After irradiation to a dose of 67 dpa these differences were ∼570 MPa for the lower irradiation temperature and ∼710 MPa for higher irradiation temperature. There were no indications of grain boundary failures via cracking except for material irradiated to 67 dpa at low temperature.

Serrated tensile flow in inconel X750 sheets: Effect of heat treatment

The tensile behavior of gamma prime precipitation hardened nickel-chromium superalloy X-750 sheets was investigated in the as received (i.e. non-heat treated NHT) and heat treated (HT) states. The evolution of mechanical properties were studied as a function of strain rate (10−3, 10−4, and 10−5s−1) and temperature (23–900°C). The Portevin Le Chatelier (PLC) effect was observed in both HT and NHT X-750, with the occurrence of saw-tooth type serrations accompanying hardening until rupture at intermediate temperatures. Above 800–900°C, the stress-strain curves showed a softening effect, with the occurrence of sinusoidal serrations indicative of Dynamic Recristallization. The temperature ranges of the PLC effect were determined for both NHT and HT X750 highlighting the effect of heat treatment. The strain rate was observed to shift the PLC temperature regime for both NHT and HT X-750. Type A, B, and C PLC serrations were observed for both HT and NHT, and serration amplitude increased with temperature and decreasing strain rate. The NHT X-750 was found to exhibit more instances of normal PLC effect whereas the HT material exhibited more cases of inverse PLC behavior. The normal PLC regime activation energies were calculated for both NHT and HT cases respectively, and the results suggest carbon as the responsible solute for serrations in this range.

Characterization of Microstructure, Tensile Strength and Corrosion Behavior of Autogenous GTA Welds of Inconel X750 With and Without Activated Compound Flux

In the present study, an attempt has been made to join 5-mm-thick plates of Inconel X750 using autogenous tungsten inert gas (TIG) welds without and with the use of activated compound flux mixture that contains 50%SiO2 + 25%TiO2 + 25%MoO3. The welded coupons were subjected to direct aging at 705 °C for 22 h. The interfacial and fusion zone microstructures were compared for both as-welded and direct aged coupons. It is assimilated that the fusion zone is enriched with Cr23C6 at the grain boundaries along with polygonal γ′ precipitates upon direct aging. Tensile studies show the fact that the fractures occur at the fusion zones of the joints both in as-welded and direct aged conditions. The joint strengths of the autogenous TIG weldments without and with flux addition were reported as 946 and 1162 MPa in the directly aged conditions, respectively. Studies also attested that there is an increase in the tensile strength by 54% of the autogenous weldment employing compound flux upon direct aging compared to as-welded conditions. Further, the fusion zones of both the conditions and the parent metal were subjected to 3.5%NaCl environment. Potentiodynamic polarization plots clearly envisaged that the fusion zone in the directly aged condition exhibits better corrosion resistance than that of the as-welded ones.

Development of a TiC<sub>p</sub> Reinforced Ni-Based Superalloy MMC, with High Creep Resistance and Reduced Weight

Ni-based superalloys, in both single and polycrystalline varieties, are extensively used in high pressure turbine blades. But contrary to single crystal variants, the polycrystalline forms present easier manufacturing and offer higher potential for improvement in metal matrix composites (MMCs). To benefit from this opportunity, an Inconel X-750 superalloy reinforced with TiC particles is proposed, having a polycrystalline microstructure and the possibility for weight reduction in turbine elements application. The metallic powder with an addition of 15 vol.% of 3.7 μmd TiC particles was prepared through low energy mixing, uniaxial pressing and sintering, followed by a triple heat treatment. The microstructure was analyzed with SEM and XRD techniques. Compressive creep tests were performed at 800 °C with 200 MPa, on both original and reinforced alloys. The study shows how the inclusion of a highly compatible particle reinforcement does not only improves the creep resistance, but also reduces the material weight, thus having potential to promote further reduction in the creep rate on turbine blades submitted to centripetal forces.

Investigation of Work Hardening Behavior of Inconel X-750 Alloy

The constant strain rate uniaxial compression tests were conducted in this paper for studying the work hardening behavior and revealing the underlying microstructure evolution involved in the plastic response of the nickel-based Inconel X-750 alloy. The work hardening rate versus true strain plots of Inconel X-750 alloy resembled that of low-stacking-fault energy (SFE) alloys with distinct four stages. The dislocations were found in the planar arrangements at a strain of 0.1 located at the onset of stage II, and the dislocation density was increased and the planar arrangement configuration was partially destroyed at a strain of 0.36 located in stage III. It was unexpected that deformation twins were observed at a strain of 0.69 located in stage IV although the alloy has been classified into materials with a higher SFE value. The result is different with a similar study, in which the deformation twins were absent in Ni–Cr-based alloy Inconel 625 even when the strain was as high as 0.65. It was deemed that the low level of solution strengthening favored the deformation of matrix and the activation of slip system for twining in Inconel X-750 alloy. Unlike the low-SFE alloys that the twins were always formed at the end of stage I, the higher SFE delayed the twin formation to stage IV for Inconel X-750 alloy. The well-developed planar dislocation configuration gave rise to the stage II with a slightly decreasing rate, the collapse of planar dislocation arrangements caused the occurrence of stage III with an accelerated decreasing rate, and the twin formation led to the stage IV with a nearly constant work hardening rate.

Effects of γ′ Precipitation, Dislocation Density, and Grain Size on Stress-Relaxation Properties of INCONEL X-750 Helical Springs

INCONEL X-750 specimens were manufactured into helical springs by drawing and coiling followed by aging. They were subsequently subjected to stress-relaxation tests. Stress relaxation is the important property of springs that are compressed at elevated temperatures. To understand stress relaxation, this study investigated the effect of the drawing ratio (DR) on the γ′ size and volume fraction, grain size, carbide volume fraction, and dislocation density. Small-angle neutron scattering was used to measure the size and volume fraction of γ′ phase, and X-ray diffraction was employed to analyze the dislocation density in the springs as a function of the DR. The smallest DR specimen (DR0) had a longer free length than the larger DR specimens (DR17 and DR42) after the stress-relaxation test was completed at 773 K (500 °C) for 300 hours. However, the size and volume fraction of γ′, along with the dislocation density, had no influence on the stress relaxation of the INCONEL X-750 springs. The decreased grain size (d) due to an increase in the DR was the main factor in the increase in the stress relaxation of the springs. The decrease in grain size displayed a nonlinear relationship with the increase in stress relaxation. The stress-relaxation behavior relationship was d −3. Grain boundaries were determined to play a role in dislocation sink via transmission electron microscopy (TEM) observations. Grain boundary diffusion accommodated by slip was responsible for the stress-relaxation properties of the spring at an elevated temperature (773 K = 500 °C).

The effects of proton irradiation on the microstructural and mechanical property evolution of inconel X-750 with high concentrations of helium

Ni-based alloys, which are used in nuclear applications with a high thermal flux, are shown to contain a high density of helium bubbles within the matrix and aligned along grain boundaries, resulting in lost strength and ductility. In the current investigation, material with and without helium is irradiated with protons up to approximately 60 dpa and 18 000 appm helium. With the use of advanced microscopy and nano-indentation, the microstructural evolution and mechanical hardening has been characterized. The addition of helium decreases the rate of disordering of the gamma prime phase, and suppresses void swelling by forming a region with a high density of helium bubbles, and thereby inhibiting the mobility of freely-migrating point defects. Mechanical hardening from proton-irradiation is consistent with neutron-irradiated Inconel X-750 and Alloy 718.

Structure and properties of Ni22Cr10Al1Y coatings deposited by the vacuum plasma spray process

In this study, the aim was to deposit layers of the Ni22Cr10Al1Y coating using the vacuum plasma spray process to protect gas turbine engine components from oxidation and high-temperature corrosion. The coating can significantly affect the properties of the substrate because it forms a composite together with the substrate. The type of the coating deposition process and coating heat treatment, together with the substrate, significantly affect its resistance to high temperature creep. Ni22Cr10Al1Y powder was deposited with a vacuum plasma spray system of the Plasma Technik AG company using the control panel A-2000 and the plasma gun F4. The coating deposited on the substrate of INCONEL X-750 alloy was thermally treated at 1100 o C for 2 hours in a protective atmosphere of argon. The particle morphology was tested by scanning electron microscopy.The microhardness of layers was tested by the HV0.3 method and the bond strength was tensile tested, in accordance with the standard Pratt & Whitney. The microstructure of the deposited coating layers was examined under a light microscope. Coating etching was done by mixing 2.5 ml of nitric acid HNO3 with 7.5 ml of hydrofluoric acid HF. The microstructure of the etched coating before and after heat treatment, as well as the thickness of the diffusion zone, were analysed under a light microscope, based on which the coating quality was later assessed.

Morphology Evolution of γ′ Precipitates during Isothermal Exposure in Wrought Ni-Based Superalloy Inconel X-750

The morphological evolution of γ′ precipitates and lattice misfit with isothermal aging were closely investigated in wrought Ni-based superalloy Inconel X-750. The γ′ morphology dramatically changes in terms of shape, distribution, coalescence and coherency at the γ/γ′ interface. These processes and their dependence on temperature are summarized as a γ′ morphology map together with a time–temperature–precipitation (TTP) diagram through quantifying relevant morphological parameters. The lattice misfit was measured by X-ray diffraction and is positive; it decreases from 0.6% at room temperature to 0.1% at the aging temperature. These results suggest that the morphological changes of the γ′ precipitates are attributable to very low lattice misfit, the interaction of the elastic field, the volume fraction of the precipitates and incoherence in γ/γ′ interface.

Inconel X-750镍基合金激光喷丸抗热腐蚀性能及机理

Inconel X-750镍基合金激光喷丸抗热腐蚀性能及机理

Multi response optimization in wire electrical discharge machining of Inconel X-750 using Taguchi’s technique and grey relational analysis

AbstractThe effective optimization of machining process parameters affects dramatically the cost and production time of machined components as well as the quality of the final products. This study presents an investigation on cutting speed and surface roughness of Inconel X-750 using Wire-cut electric discharge machining process. Six input process parameters of Wire-cut Electro Discharge Machining—spark gap voltage, pulse-on time, pulse-off time, wire feed rate, peak current and wire tension—were chosen to study their effects on the selected responses. Taguchi’s design of experiments methodology has been used for planning, designing and conducting the experiments. The grey relational analysis has been applied in conjunction with the Taguchi’s parameter design approach for the optimization of multiple responses. The analysis of variance has been applied to identify the significance of different parameters. Finally the confirmation experiments were performed to validate the predicted optimized results.

Structural Stiffness of X-750 Alloy Bump Foil Strips for Compliant Foil Bearings With Different Heat Treatments

This paper focuses on the structural stiffness of bump foils which are used for compliant foil bearings with different heat treatments. After heat treatments in vacuum environments, the mechanical properties of the foil strips were tested, and the structural stiffness was estimated from the static load versus displacement curves obtained from the experiments. High cycle dynamic load tests were also applied to the bump foil under different cycle loads, and the shape of the foil was scanned after the tests to measure the height variation of the bumps. The results show that the modulus of elasticity and strength of Inconel X-750 strip with thickness of 0.1 mm after different treatments are lower than that with the thickness of 0.18 mm at room temperature. Moreover, the sample foil strips which have been treated with a lower solution anneal temperature at 980 °C (2 hrs) and precipitation heat treatment at 732 °C (16 hrs) have the largest modulus of elasticity and strength at room temperature. Therefore, heat treatments have a great influence on the structure stiffness of the bump foil. At last, the results of the high cycle dynamic load tests show that the bump foil with suitable heat treatment will have a good load capacity and stress-relaxation property.

Effect of post weld heat treatment on the microstructure and tensile properties of activated flux TIG welds of Inconel X750

This study addresses the effect of post weld heat treatment on the fusion zone microstructure and the mechanical properties of activated flux tungsten inert gas (A-TIG) weldments of Inconel X750. In this study, a compound flux of 50% SiO2+50% MoO3 was used for A-TIG welding of the samples. Comparative studies on the microstructure and mechanical properties have been made on the weldments both in the as-welded and post weld heat treated conditions. Direct ageing post weld heat treatment (PWHT) was carried out at 705°C for 22h on the A-TIG weldment to assess the structure–property relationships. It was inferred that direct ageing post weld heat treatment resulted in better tensile strength (1142MPa) compared to the as-welded coupons (736MPa). The joint efficiencies of the as-welded and post weld heat treated conditions were found to be 60.7% and 94.07% respectively. The impact toughness of the as-welded coupons were found to be greater than the post weld heat treated samples; however the impact toughness of the welds are greater than the parent metal employed in both the cases. This study also attested the detailed structure–property relationships of A-TIG weldments using the combined techniques of optical and scanning electron microscopy, Electron Dispersive X-ray Analysis (EDAX) techniques.

An investigation and comparative analysis on marine gas turbine rotor blade with cooling holes using FEA

Cooling technology plays a critical role in operating the turbine blade at elevated temperature. The aim of this research work is to keep the entire blade cool enough and thus maintaining the temperature gradients within the blade to an acceptable level. Several cooling techniques have been proposed for the cooling of turbine blades and one such technique is to have radial holes to pass high velocity cooling air along the blade span. Four different models have been developed consisting of a solid blade and blades with varying number of holes. These models have been designed using CATIA and analysed using ANSYS 14.5. Two turbine blade materials namely INCONEL X-750 and NIMONIC-105 have been chosen for comparative analysis. It has been found that NIMONIC-105 might be better suited material for turbine blades. From the analysis, it has been found that the temperature distribution, Von-Misses stress and total deformation are within the safe limits and are optimum for the turbine blade with 13 holes made of NIMONIC-105.

Modelling and optimisation of the post-weld heat treatment of γ′ precipitation and hardness on Inconel X-750 using the response surface methodology

This work describes a post-weld heat treatment (PWHT) for Inconel X-750. The following PWHT variables were examined: the solution temperature, PWHT temperature, and PWHT time. In this research, the application of the response surface methodology and Box-Behnken design in a mathematical model was investigated and optimised. The resulting materials were examined using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) in the fusion zone (FZ). The experimental results reveal that using a full quadratic model with the proposed mathematical model of the γ′ precipitation size and γ′ hardness in the FZ, the obtained correlation of the hardness and γ′ precipitate size showed a reasonable linear relationship.

Effect of simultaneous helium implantation on the microstructure evolution of Inconel X-750 superalloy during dual-beam irradiation

This study focuses on investigation into the effect of helium implantation on microstructure evolution in Inconel X-750 superalloy during dual-beam (Ni+/He+) irradiation. The 1 MeV Ni+ ions with the damage rate of 10−3 dpa/s as well as 15 keV He+ ions using rate of 200 appm/dpa were simultaneously employed to irradiate specimens at 400 °C to different doses. Microstructure characterization has been conducted using high-resolution analytical transmission electron microscopy (TEM). The TEM results show that simultaneous helium injection has significant influence on irradiation-induced microstructural changes. The disordering of γ′ (Ni3 (Al, Ti)) precipitates shows noticeable delay in dose level compared to mono heavy ion irradiation, which is attributed to the effect of helium on promoting the dynamic reordering process. In contrast to previous studies on single-beam ion irradiation, in which no cavities were reported even at high doses, very small (2–5 nm) cavities were detected after irradiation to 5 dpa, which proved that helium plays crucial role in cavity formation. TEM characterization also indicates that the helium implantation affects the development of dislocation loops during irradiation. Large 1/3 〈1 1 1〉 Frank loops in the size of 10–20 nm developed during irradiation at 400 °C, whereas similar big loops detected at higher irradiation temperature (500 °C) during sole ion irradiation. This implies that the effect of helium on trapping the vacancies can help to develop the interstitial Frank loops at lower irradiation temperatures.