Inconel Research Articles

Analysis of the effects of isothermal aging and Laser Shock Peening on the flow properties, fatigue crack growth, and fracture toughness of Inconel 718

Laser Shock Peening (LSP) is a surface treatment that improves the fatigue life and fatigue strength of components by inducing a shallow layer that is characterized by compressive residual stress and plastic deformation. This study investigates the use of LSP on Inconel 718 (IN718) on the fatigue crack growth (FCG) and fracture toughness (FT) of as-received (AR), solution-treated (SOL), and samples aged for 0.5, 4, and 100 h. Experimental results on aged samples established that the hardness of samples 0.5 and 4 h increased due to the precipitation of γ′ and γ″ phases while in the 100 h sample the hardness decreases due to the presence of coarser γ″ phase and intergranular δ-phase. These microstructural features impacted the plastic flow behavior of the different samples which was adequately described using a two-fitting approach to the Voce equation. While thermal aging accelerated the FCG of aged samples, the plastic flow and residual stress induced by the LSP significantly reduces the effect of thermal aging, by reducing the FCG rate and increasing the FT of the IN718 aged samples. Finally, results from EBSD analysis showed that the LSP-induced plastic strain depends on the microstructural transformations that occurred during the aging treatment.

Decoupling build orientation-induced geometric and texture effects on the mechanical response of additively manufactured IN625 thin-walled elements

When additively manufactured (AM) metallic components have highly anisotropic microstructures, the relationship between microstructure and mechanical properties becomes more complicated with the introduction of additional design parameters, such as build orientation and geometric variations. This study serves to decouple the contribution of build orientation-induced texture and geometric effects on the mechanical response of thin-walled Inconel 625 (IN625) T-elements fabricated by laser-based powder bed fusion and subjected to a combination of heat treatments. T-elements were printed at 40° and 90° inclinations from the build plate, which led to variation in crystallographic texture as well as a 10% ligament width difference. T-elements from both build orientations underwent a standard stress-relief heat treatment of 870 °C for 1 h, and subsets of these were homogenized at 1150 °C for 90 min. Milli-scale tests indicated that the 40° stress-relieved T-elements were 30% less stiff than their 90° counterparts due to both geometric and texture differences. Effective elastic tensor estimations from EBSD maps allowed the determination of the relative contributions of texture and geometry. Combined results for stress-relieved and homogenized samples indicate that the (+)10% change in ligament width led to a (+)38% change in the elastic response, while in-plane texture differences affected the elastic response by (−)8%. These findings highlight the importance of build orientation-induced geometric variation for the performance of printed-AM thin-walled structures in complex loading conditions.

Corrosion Behavior of Refractory High-Entropy Alloys in FLiNaK Molten Salts

Refractory high-entropy alloys (RHEAs) have recently attracted widespread attention due to their outstanding mechanical properties at elevated temperatures, making them appealing for concentrating solar power and nuclear energy applications. Here, the corrosion behavior of equimolar HfTaTiVZr and TaTiVWZr RHEAs was investigated in molten FLiNaK eutectic salt (LiF-NaF-KF: 46.5−11.5−42 mol.%) at 650 °C. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and immersion test measurements were carried out for these two RHEAs and compared with Inconel 718 (IN718) superalloy and SS316 stainless steel under identical test conditions. Both TaTiVWZr and HfTaTiVZr refractory high-entropy alloys exhibited an order of magnitude lower corrosion rate than SS316. IN718 and TaTiVWZr showed similar corrosion rates. Corrosion products enriched with noble alloying elements formed in the case of TaTiVWZr and IN718 were stable and protective on the substrate. SS316 showed the lowest corrosion resistance and void formation along the exposed surface due to the active dissolution of Cr and Fe, which provided diffusion paths for the corroded species. The surface analysis results showed that IN718 underwent pitting corrosion, while TaTiVWZr experienced selective dissolution in the inter-dendritic area. In contrast, HfTaTiVZr and SS316 experienced corrosion at the grain boundaries.

High-Throughput Investigation of Multiscale Deformation Mechanism in Additively Manufactured Ni Superalloy

In this paper, Inconel 718 (IN718) superalloy was processed by laser powder-bed fusion additive manufacturing (L-PBFAM), followed by heat treatment. High-resolution nanoindentation was used to investigate the complex deformation mechanisms that occurred at various length scales in both conditions. The nanoindentation elastoplastic maps show a strong crystal orientation dependency of modulus and hardness, which is attributed to the high mechanical anisotropy of IN718. The hardness map effectively resolves complex microscale strength variation imparted due to the hierarchical heat distribution associated with the thermal cycles of L-PBFAM. The disproportionately high hardening effect of Nb, Mo-rich chemical segregations and Laves phases in dendritic structures is also observed. The heat treatment resulted in a 67% increase in yield strength (from 731 MPa in the L-PBFAM condition to 1217 MPa in the heat-treated condition) due to the activation of multiple precipitation-strengthening mechanisms. The nanoindentation mapping of a heat-treated sample delineates the orientation-dependent hardness distribution, which apart from high mechanical anisotropy of the alloy, is also contributed to by a high degree of coherency strengthening of the D022 γ″-precipitates oriented parallel to the <001> crystal plane of the γ-matrix. The mean hardness of the sample increased from 13.3 GPa to 14.8 GPa after heat treatment. Evidence of extensive deformation of twin networks and dislocation cells was revealed by transmission electron microscopy of the deformed region under the nanoindentation tip.

Effect of Heat Treatment on Creep Deformation and Fracture Properties for a Coarse-Grained Inconel 718 Manufactured by Directed Energy Deposition

The creep properties of a laser-directed energy deposition (L-DED) technique manufactured Inconel 718 (IN718) was investigated at 650 °C/700 MPa. Microstructure and creep properties of L-DED IN718 samples were tailored by various post heat treatments involving homogenization heat treatment with temperature ranging from 1080 to 1180 °C + double aging and hot isostatic pressing (HIP). Microstructural changes and their influence on the creep behavior and fracture mechanism were observed and discussed. The results show that L-DED sample heat treated by a simple double aging exhibits a 49% increase in creep lifetime tr and a comparable creep elongation ɛf when compared to the wrought material, due to the reserved coarse dislocation cell substructure from the L-DED process. The loss of dislocation cell structure and the coarsening of grains at higher temperature of heat treatments contributes to a shorter tr, εf, but faster ε̇min (minimum creep rate). The present work demonstrates that a simultaneous improvement of creep strength and creep elongation can be achieved in the case of a coarse-grained L-DED IN718 by a double aging treatment which can preserve both the strengthening precipitates and an appropriate size of dislocation cells.

In-situ study of adjacent grains slip transfer of Inconel 718 during tensile process at high temperature

Adjacent grains slip transfer is an important mechanism for metal adaptation to incompatibilities in intergranular deformation. Thus, this paper investigates slip transmission at grain boundaries (GBs) and annealed twin boundaries (TBs) in Inconel 718 (IN718) alloy using in-situ tensile test at 650 °C by integrating slip trace analysis and the crystal plasticity finite element method (CPFEM). Results show that the mαβ criterion, based on the match of intersection lines between slip planes to GB planes and slip directions, is more reasonable in predicting induced activated slip systems than Luster-Morris mαβ′ criterion. In addition, slip transfer tended to occur at mαβ′>0.83 and Δb(1/b)<0.44 or mαβ>0.82 and Δb(1/b)<0.46 for general GBs; when mαβ′>0.92 or mαβ>0.93, continuous slip transfer is a crucial mechanism to coordinate strain and reduce stress concentration. Furthermore, the acceptable criteria for slip transfer at TBs are θ≈0 and Δb(1/b)<0.6 by experimental and computational results. This study deepens the understanding of the adjacent grains slip transfer behavior of IN718 and also provides a new strategy to study the deformation behavior of Nickel-based superalloys.

Sustainability analysis of additive + subtractive manufacturing processes for Inconel 625

With the purpose to analyse the interrelations between the additive and the subtractive processes, this novel study does a comprehensive and comparative analysis of Wire Arc Additively Manufactured Inconel 625 (IN625) with its wrought counterpart. The fabrication, as well as the machining stage, is analyzed in terms of economic, environmental and machinability aspects. The machinability analysis is conducted based on power consumption, surface roughness and tool wear under Dry, Cryogenic and Electrostatic Minimum Quantity Lubrication (EMQL) cutting environments. The economic viability of additively manufactured and wrought Inconel 625 is assessed by comparing the total fabrication and machining costs, whereas the long-term viability of the fabrication and machining process and the cutting environments is analyzed by assessing the effects of carbon emissions on sustainability. The comprehensive analysis showed that the fabrication cost of AMed IN625 was found to be about 86.62% more than that of wrought component and the total machining costs increased by 5.51%, 37.43%, and 61.605% for machining AMed IN625 in comparison to wrought IN625 for dry, EMQL, and LCO2 cutting environments. The total carbon emissions from fabrication as well as machining of AMed IN625, also increased by about 123.95%, 79.43%, and 60.60% for dry, EMQL, and LCO2 cutting environments respectively as compared to wrought IN625. The tool life while machining AMed IN625 increased by about 191.55%, 115.80%, and 65.95% for dry, EMQL, and LCO2 respectively whereas there was a 1.741% and 8.522% increase in the power consumption values for dry and LCO2 environment as compared to wrought IN625.

Electrochemical dissolution behavior of phosphorus and boron doped Inconel 718 alloy in NaNO3 solution

As a promising material for the blisk of high-pressure compressors in aeroengines, modified Inconel 718 (IN718) alloy with phosphorus and boron additions is a new derivative of IN718 with higher temperature capabilities. Herein, electrochemical tests and electrochemical machining (ECM) experiments of the modified IN718 alloy in NaNO3 solution were conducted to investigate the electrochemical dissolution behavior. Microstructure and microtexture analysis revealed that modified IN718 fabricated by forging mainly comprises γ phase, carbide, and δ phase, and its grain size distribution is uneven. Furthermore, the anodic behavior of the modified IN718 alloy in NaNO3 solution was investigated by the polarization curve and electrochemical impedance spectroscopy. The results show that an uneven passivation film forms on the surface of modified IN718 due to the inhomogeneous grain size, which reduces the corrosion resistance. Then, ECM experiments at different corrosion times (1 s, 3 s,5 s, 7 s) and current densities (50 A/cm2, 100 A/cm2, 130 A/cm2, 160 A/cm2) were conducted. The results show that the δ phase existed like a needle-plate and the machined surface quality was poor. The corrosion resistance of the fine grains and δ phase was better than that of the coarse grains, which is the main factor influencing the surface quality. Finally, dissolution models were proposed to characterize the dissolution behavior of modified IN718 in NaNO3 solution.

Nondestructive quantification of single crystal elasticity for additively manufactured SB-CoNi-10C, IN625, and Ti64

Resonant ultrasound spectroscopy (RUS) is capable of determining the single crystal elastic constants from polycrystalline specimens with known crystallographic texture. However, the calculated single crystal elastic constants vary with the measured texture, resulting in inconsistent estimates for additively manufactured (AM) specimens with heterogeneous texture regions. In this work, the accuracy of the determined single crystal elastic constants is improved by incorporating the uncertainty of the texture in the determination of single crystal elasticity, and requiring only small quantities of electron backscatter diffraction data (EBSD) to do so. The single crystal elastic constants are determined by Bayesian inference with parallelized sequential Monte Carlo (SMC), enabling an order of magnitude reduction in computational cost. AM specimens of a cobalt-nickel-base superalloy (SB-CoNi-10C) demonstrate that the incorporation of texture variability enables the single crystal elastic constants to converge to the reported literature values within one standard deviation, avoiding any dependence on the initial texture values. The single crystal elastic constants of nickel-base-superalloy Inconel 625 (IN625) and Ti-6Al-4V (Ti64) are determined from AM specimens, using only RUS and EBSD data. The determined single crystal elastic constants of IN625 agree between two different texture conditions (induced by AM raster strategy), as well as with the literature values, within one standard deviation. The single crystal elastic constants determined from three AM Ti64 specimens, printed with different beam powers, agree with the range of literature values within two standard deviations but demonstrate variability between AM specimens, indicating that the frequencies may be susceptible to the effects of secondary phases.

Effect of a gradient structure on the mechanical performance of Inconel 718 Ni-based superalloy at elevated temperatures

The effect of a gradient structure (GS) with present precipitates on the tensile properties of Inconel 718 (IN718) alloy at elevated temperatures was studied. A high-density δ-Ni3Nb phase and fine recrystallized γ grains were obtained in the surface gradient layer using an ultrasonic surface-rolling process (USRP) and subsequent heat treatment. The amount of the δ phase in the gradient layer decreased with the layer depth, while the size of the recrystallized γ grains exhibited an opposite trend. Remarkably, the GS did not show a microhardness gradient at room temperature but exhibited excellent strength and plasticity during high-temperature tensile tests. Compared with a uniform sample, the yield strength (YS) and ultimate tensile strength (UTS) of the specimen with a GS increased by 55 and 105 MPa, respectively, and the plasticity increased by 25% in the tensile tests at 650 °C. The δ phase pinned the RANS-scale grain hierarchy in the gradient layer and improved the thermal stability at 650 ℃. This GS promoted the accumulation of high-density geometrically necessary dislocations (GNDs) in the gradient layer during plastic deformation, resulting in additional back-stress strengthening. Therefore, forming a gradient structure with precipitates provides a new approach toward a good combination of strength and ductility at elevated temperatures.

Effects of Process Parameters and Heat Treatment on Microstructure and Mechanical Characteristics of Laser Powder Bed Fusion Alloy Inconel 718

A laser powder bed fusion (LPBF) Inconel 718 (IN718) alloy was fabricated under different process parameters, and the samples with optimal process parameters were treated by subsequent heat treatment. The outcomes demonstrated that the pores’ size and shape were influenced by the process parameters. The porosity of the samples first grew and subsequently reduced as the volume energy density increased, and the types of pores changed from lack-of-fusion pores to gas holes and keyhole pores. The porosity of the samples with three process parameters were 3.46%, 0.15% and 1.26%, respectively. The sample of 60.0 J/mm3 was chosen for a single solution (heat treatment at 980 °C for 1 h, SS) and direct aging (heat treatment at 720 °C for 8 h and then 620 °C for 8 h, DA), and the microstructure evolution of the samples was examined. Because of the segregation of the elements Nb and Mo, the Laves phase was distributed among the dendrites in the as-built (AB) sample. The solution heat treatment dissolved the Laves phase and precipitated the δ phase, while aging heat treatment precipitated the γ′/γ” phases. Additionally, the impact of the second phase on the tensile characteristics was looked into. The DA sample had the highest strength, with a tensile strength of 1458 MPa and a yield strength of 1271 MPa. With tensile and yield strengths of 980 MPa and 620 MPa, respectively, the AB sample had the lowest strength due to the Laves phase’s role as the crack initiator. The Laves phase dissolved and the γ′/γ”-strengthened phase precipitated, leading to an increase in the strength of the heat-treated specimens.

Influence of parameters on mechanical and micro-structural properties of tungsten inert gas (TIG) welded joint of 1 mm thin Inconel 625 plates

Inconel 625 (IN625), since its invention, has been a material of choice for industries where components in service conditions are exposed to extremely high temperatures, corrosion, and oxidation environments. As per the American welding society for butt-joining such alloys in sheets, non-traditional techniques are the best means for producing permanent joints. These techniques require high-cost setup and high maintenance costs which are only economical for high-volume assembly line fabrication in mass-production facilities. Therefore, Tungsten Inert Gas (TIG) welding is highly suitable for producing defect-free autogenous weldments in high-strength alloy sheets with a thickness below 3mm. The current work focuses on the experimental investigation of the TIG welding of Inconel 1mm sheets. In this work, mechanical properties and microstructure are studied for controlled heat input of TIG welding. Current is varied from 40A to 65A and voltage from 10V to 12V. Only three combinations of parameters show sound weld visually and are analyzed by performing various testing. The main objective of the study is to find the feasible process parameters for the micro joining of IN625 sheets. From this discussion, it appears that arc energy, welding current, and voltage significantly affect the quality of the weld.

High power laser powder bed fusion of Inconel 718 alloy: Effect of laser focus shift on formability, microstructure and mechanical properties

In this study, a 1 kW high-power laser powder bed fusion (HP-LPBF) equipment was employed for the additive manufacturing of Inconel 718 (IN718) alloy, and the effects of laser focus shift (F s 0, +5, +10, +15, +20 mm) on the formability, microstructure and mechanical properties of the HP-LPBF samples were investigated. Results suggest that HP-LPBF is able to produce near full-dense samples with high build rates by applying larger scanning speeds and hatch spacings. The process limit can be further expanded when a suitable F s is adopted through its impact on the energy density, laser spot size and laser intensity distribution. As the increase of F s , the surface roughness of HP-LPBF sample decreases initially but increases subsequently. The corresponding melting mode transforms from keyhole to transition and then to conduction. Besides, the F s is found to be influential in the mechanical properties by changing the primary dendritic arm spacing, the fraction of Laves phase and the grain size. The optimal performance at the F s of +10 mm is comparable to the low-power laser powder bed fusion (LP-LPBF), whereas its maximal build rate (16 mm 3 /s) rises to around 3-12 times that of the latter. Moreover, the scaling law of energy density for LP-LPBF remains applicable for HP-LPBF when the focal plane is located at the build surface, but not if the focal plane is shifted away. Based on those findings, the potential efficiency and limitations of HP-LPBF with higher laser powers (≥2 kW) were briefly prospected.

Study of laser directed energy deposition of Inconel 625 and austenitic steel

Functionally graded material (FGM) is an advanced material that illustrates the number of properties in a single component. To develop FGM, it is very important to study each component gradient separately to understand the properties and their behaviour. This paper presents the study of the properties of deposited blocks of the different gradients of Inconel 625 (IN625) and stainless steel 304L (SS304L) (25% IN625 + 75% SS304L, 50% IN625 + 50% SS304L, 75% IN625 + 25% SS304L, and 100% IN625) by a laser directed energy deposition technique. Various tests were performed to understand its mechanical, metallurgical, and chemical behaviour. Deposited samples were heat-treated and then optical microscopy and microhardness were measured and compared to untreated ones and results found to be comparatively improved.

Improving the surface properties of additive-manufactured Inconel 625 by plasma nitriding

As a surface-hardening technique, plasma nitriding is a common procedure for improving the properties of conventional Ni-based alloys. The diffusion of nitrogen hardens a layer on the surface of the alloy, leading to better wear resistance and a higher coefficient of friction, as well as a higher surface hardness. This study reports the effect of plasma nitriding on additive-manufactured (AM) Inconel 625 (IN625) compared to its conventional manufactured and nitrided counterparts. The samples produced with the laser powder-bed fusion (LPBF) process were subsequently plasma nitrided in the as-built condition, stress-relief annealed at 870 °C and solution treated at 1050 °C. The plasma nitridings were carried out at 430 °C and 500 °C for 15 h. The growth kinetics of the nitride layer of the AM samples depends on the prior heat treatments and is faster in the as-built state due to the specific cellular structure. The lower nitriding temperature leads to the formation of expanded austenite in the nitride layer, while at the higher nitriding temperature, the expanded austenite decomposes and CrN precipitation occurs. The XRD and SEM analyses confirmed the presence of two layers: the surface layer and the diffusion layer beneath. The lower nitriding temperature caused the formation of expanded austenite or a combination of expanded austenite and CrN. The higher nitriding temperature led to the decomposition of the expanded austenite and to the formation/precipitation of CrN. The higher nitriding temperature also decreased the corrosion resistance slightly due to the increased number of precipitated Cr-nitrides. On the other hand, the wear resistance was significantly improved after plasma nitriding and was much less influenced by the nitriding temperature.

Multi‐Material Inconel 718 Parts with Highly Conductive Copper Cooling Channels for Aerospace Applications

Multi‐material parts can offer valuable solutions to engineering problems when compared to single materials. The conceptualization of a multifunctional Inconel 718 (IN718)–Copper (Cu) solution aims to improve the heat extraction capacity of an aerospace component. High‐strength IN718 was used as the base material and highly thermal conductive Cu was employed for internal cooling channels. The cooling channels are produced by electrical discharge machining (EDM) and subsequently filled with Cu to be sintered by hot pressing (HP). The morphological, microstructural, hardness, and thermal properties of the hot‐pressed multi‐material IN718–Cu specimens are studied to evaluate the feasibility of HP processing as a viable manufacturing approach for these multi‐material solutions. The multi‐material IN718–Cu specimens presents a well‐defined design with good metallurgical bonding between the two materials and a thin diffusion region is found, assuring the final properties of each individual material. The Vickers’ microhardness of IN178 and Cu are in accordance with the reported for conventional processes which indicates good densification. The thermal conductivity of the multi‐material IN718–Cu specimen is 25% higher than mono‐material IN718, which can be a significant improvement in the thermal efficiency of an aerospace component.

The precipitation behavior effect of δ and γ" phases on mechanical properties of laser powder bed fusion Inconel 718 alloy

The mechanical properties of additively manufactured materials were mainly influenced by the precipitations in the microstructure. In this work, Inconel 718 (IN718) superalloy was fabricated by laser powder bed fusion (LPBF) and treated by solution and dual-aging treatments. The δ and γ" phases with different sizes and morphologies have been obtained by different solution temperatures. The precipitation behavior effect of δ and γ" phases on the room temperature tensile and high temperature stress rupture properties has been investigated. The results showed that the Laves phase formed in the as-fabricated sample. After solution heat treatment, the Laves phase dissolved and transformed to δ phase. As the solution temperature increased, the needle-like δ phase gradually dissolved, while only a little short rod-like δ phase remained. During aging heat treatment, the Nb element released from dissolved δ phase was beneficial to promote the precipitation of γ" phase. The content and size of nano-scale γ" phase significantly affected the yield strength of IN718 alloy. At higher solution temperature, the γ" phase with suitable size exhibited the highest yield strength of 1283 MPa. On the other hand, δ phase had a significant impact on high temperature stress rupture properties. The stress rupture life increased from 37.2 h to 52.5 h with decreasing volume fraction of δ phase. • Revealing the precipitation behavior of δ and γ" phases in different heat treatments. • The Nb released from the dissolved δ phase was beneficial to the precipitation of the γ" phase. • Quantitatively describe the effect of phase content, size and morphology on mechanical properties.

Microstructural defects governing torsional fatigue failure of additively manufactured as-built and heat-treated Inconel 718

Nickel-based superalloys, such as Inconel 718 (IN718), have the unique properties of high strength, oxidation, and corrosion resistance, hence necessitating their wide use in aircraft engine structural components, power-generation engines, pressure vessels, high performance automobiles, and rocket engines. Additive manufacturing (AM) of these metal superalloys is an emerging technology, which is being investigated in its capability in driving material microstructural development towards enhanced mechanical performance. With torsional fatigue as an often underlying cause for failure of components within these applications, this study investigates the microstructural defects induced through the additive manufacturing process that have driven Inconel 718 samples to failure when subjected to torsional fatigue loading conditions. As-built and heat-treated Inconel 718 torsional fatigue fracture surfaces were compared through use of a variety of material characterization techniques, to show similarities, or lack thereof, in the defects formed due to the AM process that have contributed to torsional fatigue fracture. Results from both as-built and heat-treated direct metal-laser sintered (DMLS) Inconel 718, manufactured using optimized processing parameters reveal that primary torsional fatigue cracks initiated at surface and sub-surface defects where lack of fusion regions and un-melted powder particles are apparent. Through these analyses, a correlation was made between the fracture mechanics response exhibited by each build orientation/post-processing condition and resulting torsional fatigue properties.

A study of the processing and characterization of RSM optimized YSZ-Inconel625 wear-resistant TIG weld cladding

The present investigation focuses on developing a wear-resistant Yttria Stabilized Zirconia (YSZ) reinforced Inconel-625 (IN625) based TIG weld composite cladding on the AISI 304 stainless steel substrate. TIG welding current, scanning speed, standoff distance and YSZ reinforcement % were the primary input process parameters for cladding deposition. For the optimization of process parameters, cladding was deposited at different parametric settings, and their microhardness and sliding wear resistance was calculated as the output responses, according to Box Behnken Design (BBD) under Response Surface Methodology (RSM). Feedstock powders, developed claddings and worn samples were examined to study their surface morphology, microstructure, element composition and different phases using the SEM, Optical Microscopy, EDS, and XRD techniques. The result revealed that welding current and scanning speed are the most significant factors which govern the mechanical and tribological properties of cladding. The cladding was deposited at an optimized welding current 70 A, scanning speed of 192 mm min−1, standoff distance of 2 mm, and 25 wt.% YSZ reinforcement concentration revealed the fine and dense microstructure, resulting in maximum hardness and minimum wear. The microstructure was observed to be columnar dendrites, which grew epitaxially from the substrate. The addition of YSZ particles into the IN625 matrix resulted in the formation of Cr2O3 and ZrO2 stable oxides along with γ-Ni (FCC) phases. The wear test showed that the weight loss in claddings was mainly due to abrasive wear.

Experimental study on steam oxidation resistance at 600 °C of Inconel 625 coatings deposited by HVOF and laser cladding

Inconel 625 (IN625) coatings were deposited by High-Velocity Oxy-fuel (HVOF) and laser cladding, on a 10.50–12%Cr steel to improve its oxidation resistance. Both as-deposited coatings exhibited a γ-Ni-Cr matrix and two protective oxides (Cr2O3 and NiCr2O4). In addition, laser cladding as-deposited coatings also presented precipitates A2B-type Laves phases due to the dilution effect from laser cladding technique. Coated and uncoated steel were oxidized under isothermal conditions at 600 °C for 2000 h and subsequently analyzed using gravimetry, SEM-EDS and XRD techniques. The application of IN625 coatings revealed a weight gain ten times lower than that registered for the uncoated steel, this improvement being mainly due to the presence of protective and stable Cr2O3 and NiCr2O4 oxides. Additionally, the XRD analysis showed that the initial Laves phases present in the laser cladding coating, were re-dissolved and transformed in δ-Ni3Nb compound suggesting that that the temperature and exposure time are enough to induce this transformation.