Alloy X-750 Research Articles

Study on the effect of machining characteristics of B4C powder mixed EDM of Inconel X-750 alloy

ABSTRACT EDM is identified as one of the favoured machining processes for frontiers material and their alloys. The present investigation is the influence of the B4C into a dielectric fluid of EDM process machining with Inconel X-750 alloy using W-Cu electrode. The process input parameters are selected as discharge current, pulse on time, pulse off time, and B4C powder concentration to examine their performance responses on material removal rate, surface roughness, and white layer thickness. In this process, a newly designed and fabricated dielectric tank is used for doing experiments. Taguchi L27 orthogonal array is adopted for planning and designing of experiments. ANOVA is considered to find the effect of B4C powder concentration on performance responses, and their input parameters interactions with percentage contributions. The result is notified that the addition of B4C powder into dielectric fluid improves material removal rate, surface roughness, and white layer thickness. Further, the optimum condition of the machined samples, surface topography is studied by using a scanning electron microscope. It reviled that uniform craters, small and pocket marks are formed on the machined surface.

Multi-Objective Optimization of Process Parameters for Powder Mixed Electrical Discharge Machining of Inconel X-750 Alloy Using Taguchi-Topsis Approach

Abstract The paper investigates the influence of boron carbide powder (B4C) mixed in dielectric fluid on EDM of Inconel X-750 alloy. The process parameters selected as discharge current (Ip), pulse on time(Ton), pulse off time(Toff), boron carbide(B4C) powder concentration to examine their performance responses on Material Removal Rate (MRR), Surface Roughness(Ra) and Recast Layer Thickness (RLT).In this study, o examine the process parameters which influence the EDM process during machining of Inconel X-750 alloy using combined techniques of Taguchi and similarity to ideal solutions (TOPSIS).Analysis of variance (ANOVA) was conducted on multi-optimization technique of Taguchi-TOPSIS. ANOVA results identified the best process parameters and their percentages. It developed the mathematical equation on Taguchi-TOPSIS performance characteristics results. The multi optimization results indicated that Ip and Toff are more significant parameters; V, and Ton parameters are less significant. Finally, surface structures were studied at optimized EDM conditions by using scanning electron microscope (SEM).

Investigation on the deformation mechanisms and size-dependent hardening effect of He bubbles in 84 dpa neutron irradiated Inconel X-750

Microstructural characterization and calculation of how several intrinsic features contribute to the mechanical properties of highly strained Inconel X-750 alloy specimens irradiated to 84 dpa at two distinct temperature ranges (300 °C–330 °C and 120 °C–280 °C) were performed. The individual contributions of different microstructural features to the critical resolved shear stress (CRSS) of the material, including the γ matrix, γ′ precipitates, irradiation induced defects, and helium bubbles, were calculated. The obstacle strength of He bubbles was found to be size-dependent and a critical size was determined. For bubbles < 2.4 nm, the obstacle strength is only approximately 0.03 while it can be as high as 0.55 for bubbles > 6.6 nm. In the high temperature range (300–330 °C) irradiated specimen, localised dislocation slip was found responsible for the failure of the specimen during micro-tensile testing, associated with significant helium bubble elongation. Elongation of helium bubbles on both the primary and adjacent secondary {1 1 1} planes was likely induced by the cross slip of screw dislocations. Nanotwins were also found adjacent to the shear failure surface in the high temperature specimen, but no elongated bubbles were found within the nano-twinned region. In the low temperature range (120–280 °C) irradiated highly strained specimen, a dislocation network structure was revealed.

Performance of cryogenically treated carbide inserts under sustainable cryo-lubrication assisted milling of Inconel X750 alloy

Owing to their superior features even under elevated temperatures, the nickel-based superalloy Inconel X750 is among the materials demanded in many critical areas. However, such alloys are hard to cut because of their characteristic properties i.e., strain hardening, poor thermal conductivity, high mechanical resistance at elevated temperature, the presence of abrasive carbide fragments and chemical proximity. Therefore, it is important to develop the machinability characteristics of these materials with sustainable machining methods that offer high performance. For this, in this work, a number of attempts were made during the milling of the Inconel X750 alloy. During the experiments, the performance of each cutting tool was investigated by considering three different tools which are uncoated carbide tool, cryogenically treated cutting tool and TiAlN coated tool. Since the machinability of superalloys is difficult in the dry environment, three different sustainable cooling/lubrication conditions such cryogenic LN2, MQL and hybrid cooling/lubrication (MQL + LN2) have been used in conjunction with these tools. In evaluating the effectiveness of the employed methods, flank wear, tool damage types, surface roughness/topography, cutting force and maximum temperatures were analyzed. As a result, even if the cryogenically treated tool performed slightly better than those of untreated, it still did not reach the performance level of the TiAlN coated tools. The hybrid cooling/lubrication system with coated tool offered the best solution in terms of all criteria. On the other hand, MQL outperforms LN2 cooling for tool wear, surface roughness/topography and cutting force, LN2 cooling is better than MQL in temperature reducing.

Enhancing Tribological Properties of Inconel X-750 Superalloy through Surface Topography Modification by Shot Blasting

Abstract The profound usage of Inconel X-750 in structural and high-pressure conditions mandates improved tribological properties. One of the methods to achieve this is through surface topography modifications. In this work, the viability of the shot blasting technique is explored to enhance the wear resistance of Inconel X-750. For this purpose, aluminum oxide particles with 80 mesh size were shot blasted on the superalloy surface at a constant pressure of 0.6 MPa. The 3D surface topography of Inconel X-750 alloy confirms substantial surface deformation and increased surface roughness after shot blasting. Furthermore, the surface characteristics of shot-blasted superalloy were meticulously examined using a string of techniques: optical profilometer, scanning electron microscope, and electron probe microanalysis. The tribological properties of Inconel X-750 before and after shot blasting were examined using a reciprocating tribometer with a ball-on-flat configuration. Results showed that shot blasting the superalloy has tremendously enhanced the wear resistance by ∼78%, which could be attributed to the reduced sliding contact area, enhanced surface hardness, and the hindrance in the transition of wear mechanism from abrasion tribo-oxidation to adhesion.

Effect of Sequential Helium and Nickel Ion Implantation on the Nano-Indentation Hardness of X750 Alloy

Abstract Sequential He+ and Ni+ implantations were performed to investigate their combined effect on the indentation hardness of heat-treated X750 alloy. The microstructure of the ion-implanted region was also characterized with transmission electron microscope (TEM). The X750 alloy displayed a pronounced softening with very low Ni+ implantation levels, ψ = 0.01–1.0 dpa, however it showed a clear increase in hardness when implanted with He+ up to CHe = 5000 appm. Samples subjected to sequential He+ and Ni+ implantations displayed hardness values between those presented by sole He+ or Ni+ implantation suggesting that the effects of ion-induced microstructural damage and helium accumulation on the hardness of this alloy can be considered as independent and additive over the range of conditions studied. This observation is in contradiction to previously reported TEM-based studies, which suggest that accumulated helium slows the dissolution/disordering of the γ′ hardening phase in this alloy. In our study, established theories were applied to assess the contribution of ion-induced defect clustering, γ′ precipitate disordering, and helium bubble accumulation to the hardness of the X750 alloy. It was observed that generation of ion-induced defect clusters and the formation of helium bubbles increased the indentation hardness slightly while the disordering of γ′ precipitates resulted in a dramatic decrease in the total hardness. Ni+ and He+ implantation also had different effects on the depth dependence of the indentation hardness indentation size effect (ISE). The ISE was pronounced in the samples subjected to only Ni+ implantation while it was almost absent in samples subjected to only He+ implantation.

Analysis of Corrosion of Hastelloy-N, Alloy X750, SS316 and SS304 in Molten Salt High-Temperature Environment

Nickel superalloy Hastelloy-N, alloy X-750, stainless steel 316 (SS316), and stainless steel 304 (SS304) are among the alloys used in the construction of molten salt reactor (MSR). These alloys were analyzed for their corrosion resistance behavior in molten fluoride salt, a coolant used in MSR reactors with 46.5% LiF+ 11.5% NaF+ 42% KF. The corrosion tests were run at 700 °C for 100 h under the Ar cover gas. After corrosion, significant weight loss was observed in the alloy X750. Weight loss registered in SS316 and SS304 was also high. However, Hastelloy-N gained weight after exposure to molten salt corrosion. This could be attributed to electrochemical plating of corrosion products from other alloys on Hastelloy-N surface. SEM–energy-dispersive X-ray spectroscopy (EDXS) scans of cross-section of alloys revealed maximum corrosion damage to the depth of 250 µm in X750, in contrast to only 20 µm on Hastelloy-N. XPS wide survey scans revealed the presence of Fe, Cr, and Ni elements on the surface of all corroded alloys. In addition, Cr clusters were formed at the triple junctions of grains, as confirmed by SEM–EBSD (Electron Back Scattered Diffraction) analysis. The order of corrosion resistance in FLiNaK environment was X750 &lt; SS316 &lt; SS304 &lt; Hastelloy-N.

Deformation mechanism characteristics in a Ni-based alloy X-750: Dislocation/precipitate interaction

Transmission electron microcopy (TEM) analysis was employed to characterize the deformation mechanisms in X-750 Ni-based superalloy. Both in-situ and ex-situ tensile tests were carried out at room temperature to observe the dislocation structure and trace the interaction between the γ'-precipitates and dislocations. The deformation mechanism was found to be planar slip which resulted in the formation of planar slip bands. This was attributed to the low stacking fault energy of X-750 alloy as well as the shearing of a high density of ordered γ'-precipitates. The shearing of γ'-precipitates occurred through an Anti-phase boundary (APB) mechanism evidenced by paired superlattice dislocations or a Stacking Fault (SF) mechanism by partial dislocations evidenced by isolated stacking faults within the γ'-precipitates.

Comparative study of parametric effects on the performance of simple and powder mixed EDM using aluminium and graphite powder on Inconel X750 alloy

In the present scenario, Electrical Discharge Machining (EDM) is one of the most entrenched non-conventional machining processes which are widely used in different manufacturing sectors worldwide. Generally, the conductive materials, which having geometrically complex shape and extremely difficult to machine by conventional machining processes are machined by EDM. The further improvement of the machining efficiency of this EDM process may be enhanced by using powder suspended dielectric fluid which is called Powder Mixed EDM (PMEDM) process. In this research work, an attempt has been made to analyze the comparative study of parametric effects on the performance characteristics like material removal rate (MRR), tool wear rate (TWR) and surface roughness (SR) in terms of average value of roughness parameter (Ra) of simple (without powder) and powder mixed EDM using Aluminium (Al) and Graphite powder on Inconel X750 alloy by experimental investigation. Here, in our study, Peak current (Ip) pulse on time (Ton) and pulse off time (Toff) have been taken as the variable process parameters and concentration of powder (Cp) is taken as 6 g/l in all cases throughout the experimentation. From the experimental results, it has been observed that PMEDM gives lower MRR but better surface finish in comparison with conventional EDM technique (without powder). Also, it has been noticed that graphite powder mixed EDM is more effective for getting better surface finish of Inconel X750 alloy compared to Al mixed PMEDM process.

Ni+ and He+ Implantation Effects on the Hardness and Microstructure of Heat-Treated X750 Superalloy

Abstract Nickel and Helium ion implantation-induced hardening and microstructural evolution of X750 in the heat-treated (HT) and solution annealed (SA) conditions were investigated using nano-indentation hardness testing and electron microscopy (scanning electron microscopy (SEM) and transmission electron microscopy (TEM)). Irradiation crystal damage up to ψ = 5 dpa was invoked with Ni+ implantation while He+ implantation up to CHe = 5000 appm was performed on samples the HT and SA conditions. The X750 alloy displayed generally increasing hardness with increasing Ni+ implantation damage but a perturbation in the trend occurred when ψ ≤ 0.5 dpa, and the hardness dropped by about 30% and 2% for the HT and the SA samples, respectively. TEM analysis indicated that this softening was associated with disordering and dissolution of the γ′ strengthening phase. The hardening behavior observed at higher implantation damage (ψ = 1 dpa) resulted in reformation of Al/Ti-rich regions within the microstructure phase. The hardness of the X750 increased continuously with increasing implanted He+ up to CHe = 1000 appm. This was associated with the formation of helium bubbles as observed by TEM. Slight drop in hardness in the HT condition at CHe = 5000 appm indicated that high levels of He+ implantation destabilize the γ′ precipitates as was confirmed with TEM observed disappearance of γ′ super-lattice reflections.

Machinability performance of nickel alloy X-750 with SiAlON ceramic cutting tool under dry, MQL and hBN mixed nanofluid-MQL

Nickel alloy X-750 which is difficult-to-machine material, is employed in many critical fields owing to its superior mechanical and thermal properties. However, these superior features lead to some difficulties in its machinability especially when using carbide tool materials. Hence, ceramic cutting tools (CCTs) having excellent hardness, heat and abrasion resistance, and poor chemical proximity to workpiece material are a perfect choice in machining operations of such materials. Considering this, the current study focused on the influence of various cutting environment, i.e., dry, base fluid-MQL without any mixed nanoparticles (BF-MQL) and hBN dispersed nanofluid-MQL (NF-MQL) on surface roughness, 2D-surface topography, maximum cutting temperature, cutting force, micro-hardness, flank wear and its mechanism when milling of alloy X-750 with Sialon ceramic tools. As a result, surface roughness was reduced by about 39% and 47.2% with BF-MQL (0 vol% additive) and hBN mixed NF-MQL, respectively compared to dry machining environment. Also the noticeable improvement with NF-MQL environment in 2D-surface topography of workpice, cutting temperature and cutting force has been achieved, the dry machining offered less tool wear for CCT than both BF-MQL and NF-MQL.

Short Range Ordering (SRO) Reaction in Ni-base Alloy X-750

The short range ordering (SRO) reaction of the X-750 Ni-base alloy used as a garter spring material for CANDU reactors was systematically investigated through differential scanning calorimeter (DSC) analysis. Water quenching (WQ) after solution annealing (SA) and 20% cold rolled (CR) X-750 were prepared and these samples were subjected to ordering treatment at 475 &lt;sup&gt;o&lt;/sup&gt;C for up to 2,160 hours. The WQ and CR specimens showed an exothermic reaction due to the release of entropy formed by the WQ and CR processes, respectively, whereas the ordered WQ and CR specimens exhibited endothermic reactions. The exothermic reaction from the WQ and CR specimens means the SRO reaction occurred. In the WQ specimen, two exothermic reactions at 577 &lt;sup&gt;o&lt;/sup&gt;C and 671 &lt;sup&gt;o&lt;/sup&gt;C were observed, which corresponds to SRO formation of Ni&lt;sub&gt;2&lt;/sub&gt;Cr and CrFe, respectively. The critical temperature and thermal activation energy for these specimens were measured by varying the heating rate. The lattice variation with ordering time at 475 &lt;sup&gt;o&lt;/sup&gt;C up to 2,160 hours was measured by XRD using CuKa X-ray. A 0.03-0.09% lattice contraction of the (200) plane occurred, depending on prior treatment condition. We discuss whether a lattice contraction due to SRO reaction may cause voids, providing formation sites for He bubbles in the X-750 garter spring exposed to the operating environment of the CANDU reactor.

Bayesian model updating for the corrosion fatigue crack growth rate of Ni-base alloy X-750

Nickel base Alloy X-750, which is used as fastener parts in light-water reactor (LWR), has experienced many failures by environmentally assisted cracking (EAC). In order to improve the reliability of passive components for nuclear power plants (NPP's), it is necessary to study the failure mechanism and to predict crack growth behavior by developing a probabilistic failure model.In this study, The Bayesian inference was employed to reduce the uncertainties contained in EAC modeling parameters that have been established from experiments with Alloy X-750. Corrosion fatigue crack growth rate model (FCGR) was developed by fitting into Paris’ Law of measured data from the several fatigue tests conducted either in constant load or constant ΔK mode.These parameters characterizing the corrosion fatigue crack growth behavior of X-750 were successfully updated to reduce the uncertainty in the model by using the Bayesian inference method. It is demonstrated that probabilistic failure models for passive components can be developed by updating a laboratory model with field-inspection data, when crack growth rates (CGRs) are low and multiple inspections can be made prior to the component failure.

Effect of High Undercooling on Dendritic Morphology and Mechanical Properties of Rapidly Solidified Inconel X750 Alloy

The rapid dendrite growth kinetics of Inconel X750 alloy was explored under electromagnetic levitation and free fall conditions. The dendrite growth velocity of the primary γ phase varies as a double exponential function with undercooling (ΔT). The critical undercooling for the transformation of the primary γ phase from dendrites to equiaxed grains in electromagnetic levitation (EML) and drop tube (DT) experiments is similar. With comparable undercoolings, the grain size of γ phase solidified in the DT is much smaller than that in the EML owing to the effect of large cooling rate. As the undercooling continuously increases to 230 K, the phase constitution changes from γ and precipitated phases to single γ phase. Based on EDS and TEM results, the precipitated phase is confirmed as (Ti, Nb)C phase, and the γ/(Ti, Nb)C interface is semicoherent. The compressive and nanomechanical properties of Inconel X750 alloy solidified in EML experiments were also investigated. The results show that the elastic modulus of γ phase is smaller than that of (Ti, Nb)C phase. According to the compression tests, the elastic modulus of Inconel X750 alloy is improved by high undercooling. Interestingly, the elastic modulus decreases when the undercooling is larger than 230 K, which is attributed to the increasing solubility of Ti and Nb in γ phase and the disappearance of (Ti, Nb)C phase.

Microstructural characterization of Inconel X750 alloy used in reactors components

Microstructural characterization of Inconel X750 alloy used in reactors components

Effect of Machining Parameters on Turning of Inconel X750 Using PVD Coated Carbide Inserts

It is one of the few studies conducted on the machining of Ni-based Inconel X750 alloy, which has a wide range of applications in the main industries (gas turbines etc.) and aerospace (rotor blades etc.) industries. In this study, cutting tool wear, cutting forces and surface roughness were investigated in dry turning of Inconel X750 super alloy with coated carbide cutting tool. For the determining of the wear types and mechanisms electronic microscope and SEM were used. 4 different cutting speeds (40, 60, 80 and 100 m/min) and 3 different feed rate (0.1, 0.15 and 0.2 mm/rev) values were used in the experiments. The cutting depth was kept constant at 1 mm. According to the results; with increasing feed rate, the value of Fc, Ff and Fp cutting force components increased. The feed rate was significantly influential on Ra. The cutting geometry and the cutting edge sharpness induced by the formation of stable BUE caused Ra to increase. The most suitable parameters for turning the Inconel X750 alloy in terms of all evaluation criteria were the cutting speed of 60 m/min and 0.1 mm/rev.

A transmission electron microscopy study of EBR-II neutron-irradiated austenitic stainless steel 304 and nickel-base alloy X-750

The microstructure of EBR-II neutron-irradiated austenitic stainless steel 304 and nickel-base alloy X-750 was investigated. Both alloys were irradiated at low dose rates (∼2 × 10−8 dpa/s) to a neutron fluence of 6.9 × 1022 n/cm2 (E > 0.1 MeV) at 371–389 °C. Different types of defects, including Frank loops, cavities, and precipitates were characterized. The Frank loops in Type 304 stainless steel (SS) are larger in size (∼50 nm in diameter) and lower in number density (2.58 × 1021 m−3), compared to most previous higher dose rate neutron irradiation studies. The Frank loops in X-750 have an average size 26.0 nm of and a number density of 9.44 × 1021 m−3. In 304 SS and X-750, cavities are of ∼20 nm and ∼14 nm in diameter, respectively. The swelling of both alloys was found to be insignificant. In 304 SS, Ni and Si were found enriched at the cavity surfaces and Ni,Si-rich precipitates were also found. Multivariate statistical analysis using non-negative matrix factorization reveals that these Ni,Si-rich precipitates contain only ∼5.7 at.% Si, differing from the Ni3Si γ’ precipitates found in several previous studies. In X-750, L12-structured γ’ precipitates were found, and multivariate statistical analysis confirmed the 3:1 stoichiometry (Ni3(Ti,Al)) of the γ’ precipitates and the superlattice reflections confirmed the stability of the crystal structure of these γ’ precipitates, indicating higher-than-expected precipitate stability under high-dose neutron irradiation.

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.

Steam oxidation behavior of Ni-base superalloys 690, 725 and X-750 at 600 and 650 °C

The 1-bar steam oxidation behavior of Ni-base superalloys 690, 725, and X-750 was evaluated at 600 and 650 °C for up to 5000 h. In addition to monitoring mass changes, microstructures of the 5000-h-exposed samples were characterized using scanning and transmission electron microscopy and energy dispersive x-ray spectroscopy. Together with thermodynamic calculations, the scale constitution and possible exfoliation was discussed. Alloy X-750 exhibited the best resistance to steam oxidation with the least metal thickness loss at 600 °C while alloy 690 at 650 °C. Alloy 725 exhibited more than two times metal thickness loss than the other two alloys at 650 °C.