Inconel Alloy X-750 Research Articles

Experimental investigations into fretting wear and damage mechanisms of Inconel X-750 alloy

Fretting wear characteristics of Inconel X-750 were investigated under the dry test condition. Ball-on-flat contact configuration was subjected to the oscillatory movement at different sliding amplitudes through the different time duration and normal loading. Fretting tests were carried out according to the American Society for Testing and Materials standards (ASTM D6425) by the high frequency linear-oscillation wear test rig SRV 4 at room temperature with ∼60 % relative humidity. Worn surface morphologies in the case of stick, partial slip and gross slip regimes were examined by 3D optical profiler, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The aim of this research is to study the tribological characteristics of the Ni-based Inconel X-750 superalloy, which is widely used in the air lubricated gas foil bearing applications where contacting surfaces are subjected to fretting motion. It is found that the displacement amplitude and normal load had strong effect on the fretting mode and damage mechanism. Wear mechanisms were associated with the plastically sheared asperities and crack nucleation and propagation during the stick and partial slip regimes, respectively. As the displacement increased, the wear modes were switched to adhesion, abrasion, debris oxidation, delamination and plastic deformation during the gross slip condition. Fretting time dependence was critical in the higher displacement amplitudes where the wear volume loss progressed significantly. However, test duration was less consistent in the stick and partial slip regimes where the wear properties remains unchanged over time.

Multi-Objective Optimization of Machining Process Parameters in Wire-Cut Electric Discharge Machining of Inconel X750 Alloy by Combinatorial Approach

Difficult-to-cut materials, generally high hardness, strength and toughness, are generally difficult to machine in conventional machining. Also tool wear is high in conventional machining processes. Wire Cut Electric Discharge (WEDM) machining is particularly used for machining complex profiles, demanding very high accuracy. The current work focuses on the optimization of roughness of a surface that is machined using WEDM; the process parameters considered for optimization are pulse-on-time (Pon), pulse-off time (Poff), wire feedrate (WFR) and spark gap voltage (SGV). One of the surface integrity aspect is considered as surface roughness (SR) and other related to machining output considered as material removal rate (MRR) for the output responses. The paper presents, a multi-criteria decision making technique, with Grey Relational Analysis (GRA) integrated with Particle Swarm Optimization (PSO) for optimizing the process parameters. Further, confirmation tests that were conducted also validated the improvement in SR and MRR.

Fretting Wear Behavior and Damage Mechanisms of Inconel X-750 Alloy in Dry Contacts

Tribological behavior of the Inconel X-750 alloy disk subjected to fretting against the GCr15 steel ball was investigated in an ambient laboratory air with relative humidity of 55–65%. A high-frequency oscillating Optimol SRV 4 tribometer was employed to execute dry fretting tests in the partial and gross slip regimes under constant 100 N normal load. Tests were carried out for 10, 30, and 90 minutes, and the friction forces vs. displacement amplitudes were monitored during the test duration. Posttest examinations were conducted utilizing advanced tools such as 3D optical surface profiler, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The main objective was to obtain wear scar evolutions, frictional properties, and degradation mechanisms under the different running conditions over time. It was found that fretting wear behaviors of friction pairs were strongly influenced by fretting regimes. Degradation evolutions were greatly influenced by fretting time during partial slip regimes, i.e., evolving from asperity deformation and slight damage to the fatigue crack and material transfer. However, the combination of adhesive, abrasive, delamination, and wear oxidation mechanisms was repeated during the entire gross slip fretting process.

Fretting Wear Behavior and Damage Mechanisms of Inconel X-750 Alloy in Dry Contact Condition.

Frictional and fretting wear behaviors of Inconel X-750 alloy against GCr15 steel ball were investigated in dry contact condition with ∼60% air humidity. Fretting tests were run at the high frequency tribosystem SRV 4 in room temperature and ball-on-flat contact configuration were adopted with the relative oscillatory motion of small displacement amplitude (40 μm). Sliding regimes, wear volumes, frictional properties, and material damage mechanisms were studied with regard to different normal loading and test durations. After the tests, the worn surface morphologies were analyzed by three-dimensional (3D) optical surface profiler, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to distinguish fretting running conditions and material responses for different test cases. It was found that the material removals by abrasive and adhesive wear, debris formation and oxidization, and wear delamination were the main damage mechanisms under the lower normal load where the full slide or gross slip regime (GSR) was dominant between the contact surfaces. On the other hand, fretting regime was found to be a stick-slip or a partial slip at greater loads where damage mechanisms were correlated with deformed asperities, fatigue cracks, and thick layer removal due to highly concentrated cyclic stresses. Time dependence was crucial during GSR where the wear volume increased substantially; however, the wear volumes and scars sizes were consistent over time because of stick-slip effects under the higher normal load.

Effect of ion implantation on the grain boundary strength of heat treated Inconel X750

Bending tests performed with notched cantilever micro-beams were used to measure the initiate of plastic deformation from grain boundaries in Ni+ and He+ implanted Inconel X750. Whereas the local grain boundary yield stress followed a complex nonlinear dependence upon grain boundary misorientation angle up to about 60⁰, it showed a simpler continuous decreasing dependence upon grain boundary energy. This suggests that the grain boundary strength of the heat treated Inconel X750 alloy, in all conditions tested, is related to the grain boundary energy and decreases as the energy increases. Both Ni+ and He+ ion implantation increased the local grain boundary yield stress over the complete range of boundary misorientation investigated. We attribute this to the strengthening effect resulting from segregation of ion-induced crystal defects and helium bubbles/cavities to the grain boundaries. Our data suggest that the strengthening effect from 5000 appm He+, implanted at 25 °C, is significantly higher than what is produced by 1 dpa crystal damage associated with Ni+ implantation at 25 °C. Analysis of these findings in terms of a dispersed barrier hardening model illustrate that accumulated helium is more effective than irradiation-induced crystal defects, such as stacking faults tetrahedra and small dislocation loops, at preventing dislocation nucleation and/or movement from grain boundaries in the heat treated Inconel X750 alloy.

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

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.

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.

Badania doświadczalne stabilności procesu frezowania stopu Inconel X750

Badania doświadczalne stabilności procesu frezowania stopu Inconel X750

Experimental investigations of cutting parameters’ influence on cutting forces and surface roughness in turning of Inconel alloy X-750 with biodegradable vegetable oil

Nickel-based Inconel X-750 superalloy is widely applied in aerospace industry and manufacturing of gas turbine blades, power generators and heat exchangers due to its exclusive properties. As a consequence of low heat transfer coefficient and work-hardening properties, this alloy is known as a poorly machinable alloy. In this work, effect of machining parameters (cutting speed, feed rate and depth of cut) on cutting forces and surface roughness was investigated during turning of Inconel alloy X-750 with coated carbide tool. In order to meet the demands of the environment-friendly cutting processes and human health, biodegradable vegetable oil (BioCut 4600) was selected as the cutting fluid. The results were analyzed using response surface methodology and statistical analysis of variance, and mathematical models for cutting forces and surface roughness were proposed. Results indicated that feed rate and cutting speed were the most effective parameters on the surface roughness. However, depth of cut was the most effective parameter on cutting forces in comparison with cutting speed and feed rate. Eventually, in order to achieve the main aims of industrial production in large amounts and green manufacturing, the ranges for the best cutting conditions were presented.

Assessment of Heat Treated Inconel X-750 Alloy by Nonlinear Ultrasonics

The nonlinear ultrasonic technique is known as a promising tool for monitoring material states related with micro-structural changes, with improved sensitivity compared to conventional nondestructive testing techniques. It is well known that degradation of material properties is generally accompanied by the increase of material nonlinearity. However, the trend has been rarely investigated in the opposite way for improved material properties. In this paper, nonlinear ultrasonic waves are used to assess the material condition of heat treated Inconel X-750 alloy based on the nonlinear acoustic parameters. Material property testing is conducted to compare the influence of heat treatment for comparison with the nonlinear parameter based prediction. The material properties of specimens are improved by applying heat treatment, with significant decreases in the acoustic nonlinearity. The better the mechanical property achieves via heat treatment, the smaller the acoustic nonlinearity becomes. It can be concluded that the nonlinear acoustic technique can be used to evaluate the effect of heat treatment nondestructively, and to optimize the process, thus providing another indication of the feasibility of using the nonlinear ultrasonic technique for material characterization.

Fractal Dimension of Grain-boundary Fracture for Characterization of High-temperature Fracture in Heat-resistant Alloys

The fractal dimension of the grain-boundary fracture, Df, (2<Df<3), which represents the fracture surface pattern with grain-boundary microcracks in three-dimensional space, is proposed for characterization of high-temperature fracture in materials. The value of Df as well as its two dimensional value, Dfp (the fractal dimension of the grain-boundary fracture surface profile, 1<Dfp<2), was estimated in the length scale range more than about one grain-boundary length using the height data of fracture surfaces of heat-resistant alloys obtained by the stereo matching method. The value of Df increased with increasing fractal dimension of the grain-boundary surface profile (DGB, 1<DGB<2) in the specimens of the HS-21 alloy ruptured at 1089 K. Both rupture life and creep ductility increased with increasing value of Df in these specimens. Similar results were obtained by the two-dimensional fractal analysis on other specimens of cobalt-base, nickel-base and iron-base heat-resistant alloys. Creep fracture process including the growth of the main creep crack was examined by the fractal analysis using the fractal dimension map (FDM, a color-coded map) on the surface notched specimens. The result of the fractal analysis was compared with that of the FRASTA (fracture surface topography analysis) in the Inconel X-750 alloy. The fractal analysis used in this study is more convenient and more advantageous than the FRASTA, and is widely applicable to the investigation of high-temperature fracture in materials.

Microstructures and Properties of High-strength Alloys Severely Deformed by Machining

Microstructures and properties were examined on the chip specimens severely deformed to a given shear strain (y) by machining in the high-strength Ni-base Inconel X-750 alloy and 6061-T6 aluminum alloy. Chip specimens has a deformation structure principally composed of elongated grains (for example, a few μm to about 100 μm in length and about 1 μm to a few tens μm in width for the chip specimen of γ≈3 of the Inconel X-750 alloy). Many subgrains separated by small or medium angle grain boundaries (misorientation, 0<15°) were also observed within relatively large grains. In the case where detailed analysis by FESEM/EBSP was possible, the fraction of large angle grain boundaries (θ≥15°) and that of medium angle grain boundaries (5°<0<15°) were relatively small, and most of grain boundaries were small grain boundaries (1°≤θ<5°) in the chip specimens of both alloys. Internal friction of the chip specimen was much larger than that of the original material. Large internal friction of the chip specimens was principally attributed to many cracks formed during machining. The hardness of chip specimens largely increased with increasing shear strain imposed by machining in the Inconel X-750 alloy, although the increase of hardness with shear strain was not so large in the 6061-T6 alloy.

Effect of Heat Treatment on the Properties of Inconel X-750

The authors experimentally investigated the change of mechanical properties of Inconel X-750 alloy under various heat treatments. For the selected specimens, solid solution treatment under different temperatures was carried out, followed air cooling or furnace cooling. Results show that suitable solid solution treatment and air cooling enhances the strength, plasticity, impact toughness at room temperature of the alloy and lowers the hardness of the alloy at room temperature.

Performance enhancement of Inconel alloy X-750 during creep via optimal solution treatment and control of morphology of grain boundary carbide

AbstractThe effect of solution treatment temperature on both the morphology of grain boundary carbides and the creep rupture behaviour of Inconel alloy X-750 has been investigated. Solution treatment at 1050°C led to precipitation of Ti/Nb carbide along grain boundaries, and as a result the formation of chromium carbide during subsequent aging treatment was considerably affected. This led to changes in the morphology of the grain boundary carbide and reduction in the width of ‘clear’ zone. This modification in the morphology of grain boundary carbide reduced the creep resistance of the alloy, leading to a reduction in rupture lifetimes, whereas strains tofracture were unaffected.MST/1981

Performance enhancement of Inconel alloy X-750 during creep via optimal solution treatment and control of morphology of grain boundary carbide

The effect of solution treatment temperature on both the morphology of grain boundary carbides and the creep rupture behaviour of Inconel alloy X-750 has been investigated. Solution treatment at 1050°C led to precipitation of Ti/Nb carbide along grain boundaries, and as a result the formation of chromium carbide during subsequent aging treatment was considerably affected. This led to changes in the morphology of the grain boundary carbide and reduction in the width of ‘clear’ zone. This modification in the morphology of grain boundary carbide reduced the creep resistance of the alloy, leading to a reduction in rupture lifetimes, whereas strains tofracture were unaffected.MST/1981

Prediction of rupture lifetime in thin sections of a nickel base superalloy

The prediction of rupture lifetime of a component can be based on the data generated from round, flat and tubular specimens. An investigation on the influence of specimen geometry on the creep behavior of Inconel alloy X-750 showed that the tubular specimen exhibited better creep performance when rupture lifetime data were compared on the basis of section size. However, the time to rupture data of all three specimen geometries merged together when compared on the basis of the volume to surface area ratio (V/S) indicating that there is a definite relationship between V/S and the rupture lifetime. This analysis is now extended in another gamma prime strengthened nickel base superalloy. The chemical composition of the alloy in wt%, is as follows: 0.07C-0.66Si-0.07Cu-0.79Fe-19.1Cr-2.35Ti-1.52Al and remainder nickel. Analysis of the rupture lifetime data of a gamma prime strengthened nickel base superalloy shows that time-to-rupture is controlled by the volume to surface area ratio. Furthermore, the normalization of the volume to surface area ratio with the grain size shows that the time-to-rupture data of two grain sizes, 55 and 250 [mu]m, can be represented by a single curve.

An analysis of the creep embrittlement of Inconel alloy X-750 due to its prior exposure to reduced air pressure at 1150°C

Inconel alloy X-750 test pieces exposed to a reduced air pressure at 1150°C for various times exhibited significant embrittlement during subsequent creep tests in air at 700°C. This embrittlement was characterized by a systematic reduction in time and strain to fracture and an acceleration of the minimum creep rate with increasing time of prior exposure. Earlier work has shown that the near-surface environmental damage in the form of heavily cavitated boundaries and γ-free zones are responsible for this form of embrittlement. The purpose of this investigation is to provide a comprehensive analysis of the effect of the above two forms of damage on the time and strain to fracture and the minimum creep rate. Towards this end, a three-zone creep fracture model has been developed to explain the experimental results.

An analysis of the creep-environment interaction of Inconel alloy X-750 exposed at 1150°C

The effect of exposure of Inconel alloy X-750 to air at 1150°C on creep at 700°C and 400 MPa has been investigated. Contrary to the findings for exposure at 1050°C, exposure to air at 1150°C does not impair creep ductility. This is attributable to oxygen diffusion into the alloy at 1150°C being impeded. Evidence is given here to show that during exposure to air at 1150°C diffusion of chromium is fast enough to reach the surface and form a chromium oxide scale, which acts as a barrier to further oxygen diffusion.

On the Less Known Effects of Environment and Specimen Geometry on Creep Fracture of Nickel Alloys

Attention has been drawn to the fact that during exposure of nickel to air at elevated temperatures, oxygen diffuses through the grain boundary and reacts with carbon forming gas bubbles of carbon monoxide and/or carbon dioxide. Voids are produced due to the high pressure generated by the gas bubbles which cause creep embrittlement. Alloying nickel with 3.8 weight per cent aluminium, which is a stronger oxide forming element as compared to carbon, could not prevent diffusion of oxygen during exposure of the alloy to air at elevated temperatures. The diffusing oxygen reacts even in the Ni-Al-C system, with carbon and forms gas bubbles of CO and CO/sub 2/ which lead to creep embrittlement. The presence of 15 weight per cent chromium in nickel (Inconel 600 and Inconel alloy X-750), however, plays an interesting role on the kinetics of oxygen diffusion. At temperature 1050 degree Celsius and below, during exposure to air at atmospheric pressure, oxygen can diffuse along the grain boundary and reacts with carbon forming gas bubbles of carbon monoxide, where as at 1120 degree Centigrade and above, the formation of 'barrier' oxide scale, chromium oxide, at the surface prevents diffusion of oxygen. On the other hand, the presence of chromium, as observed in Inconel alloy X-750, does not play an effective role in preventing diffusion of oxygen along the grain boundary in poor vacuum. Circumstantial evidence suggests that diffusing oxygen reacts with carbon and forms gas bubbles of CO with consequential creep embrittlement, reduction in creep life and enhancement in creep rate. It has been shown that exposure of the alloy in poor vacuum has a much more damaging effect on the creep properties than that of an atmospheric pressure. It is, therefore, emphasized that exposure of nickel base superalloys to poor vacuum at elevated temperatures must be avoided; in particular this effect is more pronounced in the alloy with thin section size. It is also shown that even in the absence of oxygen interaction prior to creep testing, section size has considerable influence on the creep properties which is believed to be caused by oxygen interaction during creep deformation. For the same section size, the creep properties may be different in specimens of different geometrices. But for the same ratio of cross-sectional area to perimeter (A/P), rupture lifetime becomes independent of specimen geometry. Failure analysis of an aero engine blade has been presented as a case study to emphasize that while designing a component, utmost care must be excercised to avoid thin sections.