Hot Corrosion Resistance Research Articles

Influence of NiCrAlY coating on anti-corrosion of M951 alloy

M951 alloy is a cast nickel-based super-alloy widely used in gas turbines and aircraft engines, thus a suitable high temperature protective coating must be applied on its surface to enhance the corrosion resistance. In this research, NiCrAlY coating was deposited on M951 by arc ion plating. TGA at 1100 °C, cyclic oxidation at 1000 °C and hot corrosion in molten Na2SO4+25 wt% K2SO4 salt at 850 °C of M951 bare alloy and NiCrAlY coating specimens were investigated respectively. After TGA and cyclic oxidation, mixed oxides of NiO, NiAl2O4, Nb2O5 and Al2O3 formed on M951 surface, which spalled seriously during cyclic oxidation process. Thin, continuous and adhesive α- Al2O3 formed on the surface of NiCrAlY coating after both oxidation process. In molten Na2SO4+25 wt%K2SO4 salt at 850 °C, catastrophic corrosion occurred for the M951 alloy only after 10 hours, while thin and continuous θ- Al2O3 film formed on the surface of the NiCrAlY coating. In a word, NiCrAlY coating greatly improved the high temperature oxidation and hot corrosion resistance of the M951 superalloy. This study will further refine the oxidation and corrosion behaviors of M951 superalloy under different high temperature protective coatings and provides theoretical and experimental basis for the application of M951 superalloy in corrosive environments.

Plasma-assisted particle deposition manufacturing: Multi-functional integrated superhigh temperature thermal protection coating on niobium alloy

Multi-functional integrated thermal protection coating is a promising approach for the high-temperature protection of niobium alloy while facing multiple extremely harsh environments, while hard to avoid the complex/multi-step preparation process. Particularly, a simultaneous demonstration of multi-functional features is still challenging. Herein, a novel HfC-HfO2-MoSi2-Yb2O3 multi-functional layer has been fabricated on the NbSi2 layer surface via plasma-assisted particle deposition manufacturing, endowing the modified silicide-based multilayer composite coating with multiple thermal protective characteristics. The composite coating shows excellent hot corrosion resistance with a corrosion gain of 3.56 mg cm−2 after 200 h, the intact coating structure after three thermal cycles of fast rise and fall from 25 °C–1800 °C, and a high thermal emissivity of above 0.9, as well as the good high-temperature oxidation resistance and ablation resistance demonstrated in our previous study. The superior multiple thermal protective characteristics are attributed to the synergistic effects of multi-functional particles. HfC particle provides the anti-ablation skeleton, MoSi2 particle provides more SiO2 glass phase and seals defects, Yb2O3 particle acts as the stabilizer of glass network, and matching vibration absorption of multiphase/multi-chemical bonds endow the high emissivity of coating. Our work paves the new way and provides an inexpensive and environmentally friendly approach for the development of a new class of multi-functional integrated thermal protection materials.

Enhancing hot corrosion resistance of N-doping NiCoCr-based superalloy coatings fabricated by directed energy deposition in mixed molten salts

Here, a NiCoCr-based superalloy coating has been developed in ultra-supercritical environments. However, optimizing the coating composition to enhance the anti-corrosion performance remains a formidable challenge. This research introduced an innovative N-doping strategy to enhance the hot corrosion resistance of the coating by utilizing directed energy deposition. The hot corrosion behavior at 700 °C of the coating with N-doping reinforcement was investigated. Detailed characterizations of the microstructural evolution and corrosion products were conducted. The results showed that the improvement of hot corrosion resistance was attributed to the continuous protective film retained in the N-doping reinforced coating, which inhibited the inward diffusion of corrosive media to retard the chlorination and sulfuration reaction. This work provides new insight into the design of corrosion-resistant superalloys and highlights the potential of N-doping superalloy coating in extreme environments.

Microstructure and surface properties of Co-based brazed alloys coatings

Abstract The paper investigates the characteristics of two different manufactured high temperature brazed coatings using a cobalt based powder applied onto the surface of a stainless-steel substrate (AISI 904L). The coatings are intended to shield components exposed to high temperatures in an atmosphere where wear is expected. Energy dispersive analysis (EDX) together with scanning electron microscopy (SEM) was used to characterise the coating microstructure and morphology, and X-ray diffraction was used to identify the phase composition. Properties evaluations were carried out on the coatings’ surface characteristics, including hardness, erosion behaviour and hot corrosion resistance. The hot corrosion test was conducted at 650°C in a salt mixture that contained 75 wt. % sodium sulphate (Na2SO4) and 25 wt.% sodium chloride (NaCl). Alumina particles were used in the erosion tests, which hit the samples surface with an impact angle of 90°.The degree of corrosion attack, erosion behavior and hardness depended on the microstructure of the manufactured vacuum brazed coatings.

Effect of impact angle on hot corrosion resistance of abrasive water jet peened Ti-6Al-4V alloy

The effect of peening angle (10° to 40°) on NaCl induced hot corrosion behavior of Ti-6Al-4V alloy was evaluated at 750 °C for 100 h. Peening at higher impact angles progressively increases the surface roughness, number of sub-grains, magnitude of compressive residual stresses and hardness of the alloy. During hot corrosion, the surfaces of Ti-6Al-4Al, irrespective of the peened condition, develops oxide scales that contain oxides of Ti, Al and V. Hot corrosion rate, measured in terms of rate of mass gain and the rate constant, Kp, was highest for the unpeened alloy but decreased for surfaces subjected to AWJ peening. Surfaces peened at increasing impact angles have smaller mass gain rate and the one peened at the impact angle of 30° exhibited the lowest corrosion rate and a lowest Kp of ~0.08 mg2/cm4/h. The surface peened at 40° is, however, not as corrosion resistant. The mechanism of corrosion was discussed in the context of corrosion products formed and the opposing influences of initial roughness and compressive residual stresses. While higher roughness promotes hot corrosion by facilitating sites for corrosive attack, higher compressive residual stresses retard the diffusion of corrosive species into the Ti-6Al-4V surface. Based on these discussions, the optimum impact angle for AWJ peening for imparting maximum hot corrosion resistance on Ti-6Al-4V was determined to be ~30°.

Synergistic Improvement in Ductility and Hot Nitric Acid Corrosion Resistance of LPBF Ti-6Al-4V Alloy via Hot Isostatic Pressing

Synergistic Improvement in Ductility and Hot Nitric Acid Corrosion Resistance of LPBF Ti-6Al-4V Alloy via Hot Isostatic Pressing

Enhanced hot corrosion resistance of AlCoCrFeNi2.1 high entropy alloy coatings by extreme high-speed laser cladding

Extreme high-speed laser cladding (EHLC) and multiple laser remelting (EHLC-MR) are used to improve hot corrosion resistance of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) coatings by refining their microstructures, introducing low angle grain boundaries (LAGBs) and high densities of dislocations as well as higher compressive residual stresses (CRSs) in the coatings. The experimental results show that finer microstructure, more LAGBs and high densities of dislocations are beneficial to increase Al2O3 nucleation sites and promote the uniform formation of the oxide layer on the coating surface. On the other hand, higher CRSs suppress the initiation and propagation of cracks as well as enhance the adhesion between the oxide layer and the substrate. Thus the hot corrosion resistance of the EHEA coatings under a molten salt of 75% Na2SO4 + 25% NaCl at 900°C is improved significantly. These novel results provide effective approach for designing elevated-temperature materials.

Cyclic hot corrosion behavior and mechanism of GH4738 superalloy in mixed molten salt

The research on the hot corrosion resistance of nickel-based superalloys is critical to determining and enhancing their service life. Therefore, this study investigates the cyclic hot corrosion behavior of GH4738 alloy coated with a mixed salt (75 wt% Na2SO4+25 wt% NaCl) at 750 °C and 800 °C. X-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and transmission electron microscope (TEM) are used to analyze the phase compositions and film structures of the corrosion products, as well as to explore the corrosion mechanism. The results show that a thicker oxide layer is formed at higher temperatures, indicating poorer hot corrosion resistance at elevated temperatures. The corrosion products form at both temperatures to show a distinct layered structure, the outer layer is mainly composed of Cr2O3 and a small amount of TiO2, while the inner layer consists of Al2O3, CrS, and TiS. In addition, it is found that the corrosion mechanism of O, S, and Cl elements in the corrosion process is synergistic and accompanied by alkaline melting.

High-Temperature Hot Corrosion Resistance of CrAl/NiCoCrAlY/AlSiY Gradient Composite Coating on TiAl Alloy

TiAl alloys are used in high-temperature components such as the turbine blades of aeroengines because of their excellent properties. However, TiAl alloys are prone to thermal corrosion when in near-ocean service. In order to solve this problem, a hot-corrosion-resistant CrAl/NiCoCrAlY/AlSiY gradient composite coating was prepared on the surface of the TiAl alloy. The phase composition and morphology of the coating were analyzed. Hot corrosion tests of the traditional NiCoCrAlY coating and CrAl/NiCoCrAlY/AlSiY gradient composite coating on a TiAl substrate were performed. The samples were coated with 75%Na2SO4 + 25%NaCl salt film and treated at 950 °C for 100 h, and the corrosion products were analyzed. The results indicate that compared with the TiAl substrate and traditional NiCoCrAlY-coated samples, the composite coating showed better hot corrosion resistance, only slightly cracking, and no corrosion loss occurred. This is mainly because the continuous Al2O3 layer can effectively resist the damage caused by the melting reaction in salt, and the Cr-rich layer can not only slow the mutual diffusion of elements but also generate a good corrosion resistance chromium oxide protective layer under serious corrosion. Moreover, the corrosion mechanism of the TiAl substrate, traditional NiCoCrAlY coating, and experimental composite coating was analyzed in detail.

Significant improvement in hot corrosion resistance of Inconel 690 by laser shock peening

The effects of laser shock peening (LSP) with different peening times on the hot corrosion behavior (molten salt of 75 wt% Na2SO4 + 25 wt% NaCl) of Inconel 690 at three different temperatures (700 °C, 800 °C, 900 °C) were investigated. The corrosion conditions of the three specimens were also compared in the extreme case, i.e. after 900 °C, 300 h of hot corrosion. The results showed that LSP effectively prevented the surface oxides from shedding. As times of LSP increased, the strengthening effect improved and the rate of weight loss gradually slowed down. The dense oxide film generated by the high Cr content of the material itself, LSP-induced high-density dislocation structure, mechanical twinning and grain refinement is one of the key factors in improving the hot corrosion resistance of Inconel 690. The CRS layer and microhardness layer are another key factor in preventing the cracking of the oxide film to enhance the hot corrosion resistance. Under extreme conditions, the hot corrosion resistance of LSPed specimens is still better than that of unLSPed specimen.

Hot corrosion behavior of selective laser melted TiC/GT D222 nickel-based composite in 75% Na2SO4 and 25% K2SO4 molten salt medium at 900°C

PurposeThis paper aims to investigate the differences in hot corrosion behavior of the GTD222 superalloy and TiC/GTD222 composite in a mixed salt of 75% Na2SO4 and 25% K2SO4 at 900°C.Design/methodology/approachThe GTD222 superalloy and TiC/GTD222 nickel-based composite were prepared using selective laser melting (SLM). Subsequently, the hot corrosion behavior of the two alloys was systematically investigated in a salt mixture consisting of 75% Na2SO4 and 25% K2SO4 (Wt.%) at 900°C.FindingsThe TiC/GTD222 composite exhibited better hot corrosion resistance compared to the GTD222 superalloy. First, the addition of alloying elements led to the formation of a protective oxide film on the TiC/GTD222 composites 20 h before hot corrosion. Second, TiC/GTD222 composite corrosion surface has a higher Ti content, after 100 h of hot corrosion, the composite corrosion surface Ti content of 10.8% is more than two times the GTD222 alloy 4% Ti. The Ti and Cr oxides are tightly bonded, effectively resisting the erosion of corrosive elements.Originality/valueThe hot corrosion behavior of GTD222 superalloy and TiC/GTD222 composites prepared by SLM in a mixed salt of 75% Na2SO4 and 25% K2SO4 was studied for the first time. This study provides insights into the design of high-temperature alloys resistant to hot corrosion.

Effects of Nb on Creep Properties and Hot Corrosion Resistance of New Alumina-Forming Austenitic Steels at 700 °C

Effects of Nb on the creep resistance and hot corrosion behavior of the Fe-25Cr-35Ni-2.5Al-xNb (x = 0, 0.6, 1.2) Alumina-Forming Austenitic stainless steels (AFA steels) at 700 °C were investigated. The addition of Nb promoted the precipitation of both nanoscale NbC and γ′-Ni3(Al, Nb) phases, which exhibited very low coarsening rate constants. The nanoscale NbC and γ′-Ni3(Al, Nb) phases effectively impeded the migration of dislocations and led to an improvement in creep performance of the Nb-addition AFA steel. The corrosion of AFA steels in Na2SO4-25%K2SO4 at 700 °C was primarily driven by an “oxidation-sulfidation” mechanism. The addition of Nb, serving as a third element, facilitated the formation of protective Cr2O3 and Al2O3 films, which improved the hot corrosion resistance performance. However, the formation Nb2O5 was found to compromise the compactness of the oxide film, which adversely affected the corrosion resistance.

Microstructure, high-temperature cyclic oxidation, and hot corrosion behaviors of Inconel 718 alloy produced by laser-induction hybrid cladding

The microstructure evolution, cyclic oxidation, and hot corrosion behavior of the unheated-treated (As-built) and solution + double aging (SDA)-treated Inconel 718 alloys fabricated through laser-induction hybrid cladding (LIHC) were investigated. It was found that the as-built Inconel 718 alloy exhibits a columnar dendritic with intergranular Laves phase. After SDA-treated, γ", γ′, δ and carbide phases precipitated, the Laves phase became fine and dispersed. After cyclic oxidation, the Cr2O3 scales were formed on both as-built and SDA-treated LIHC-produced Inconel 718 alloy, which could provide good cyclic oxidation resistance for the Inconel 718 alloy. However, the as-built and SDA-treated LIHC-produced Inconel 718 alloy suffered severe hot corrosion in 95 wt% Na2SO4 + 5 wt% NaCl mixed salt solution and many corrosion products were generated, including Cr2O3, NiCr2O4, NaNbO3, Na2CrO4, NiFe2O4, Fe3O4, and NiO. Nevertheless, the SDA-treated sample showed better cyclic oxidation and hot corrosion resistance than the as-built sample, owing to the more compact Cr2O3 scale.

Novel Chromium–Silicon Slurry Coatings for Hot Corrosion Environments

Ni-based superalloys are commonly used in gas turbines because of their exceptional high-temperature mechanical properties. To secure a long service life, the materials must also have sufficient corrosion resistance. Therefore, diffusion coatings are widely used to enrich the surface in protective oxide scale-forming elements. For temperatures between 650 and 950 °C, where hot corrosion occurs, Cr-based coatings are advantageous. These are commonly applied via the laborious pack cementation process. Recently, a novel cost-effective Cr/Si slurry coating process has been developed which demonstrated resistance to oxidative high-temperature environments. Here, the protection of the slurry coatings against hot corrosion type I at 900 °C on the Ni-based superalloy Rene 80 is investigated and compared to coatings produced by pack cementation. Prior to the 300-h exposures in air containing 0.1% SO2 at 900 °C, 4 mg/cm2 of Na2SO4 was deposited on the material surfaces. The uncoated Rene 80 exhibited rapid dissolution of the initial oxide scale followed by catastrophic break away oxidation. In comparison, the slurry coatings showed significantly improved hot corrosion resistance compared to the uncoated alloy and a better protection than a Cr pack cementation coating. The Cr pack cemented Rene 80 showed improved hot corrosion resistance, but Cr depletion in the subsurface zone occurred with increasing exposure time, associated with the propagation of Al internal oxidation and increasing sulfidation. In contrast, the slurry coatings formed an external Cr2O3 scale coupled with an agglomeration of SiO2 underneath and a continuous Al2O3 subscale which offered a better diffusion barrier and leading to superior long-term protection against hot corrosion.

Effect of annealing on the corrosion-fatigue strength and hot salt corrosion resistance of fine-grained titanium near-α alloy Ti-5Al-2V obtained using Rotary Swaging

The corrosion-fatigue strength in 3 % aqueous NaCl solution and the resistance against hot salt corrosion (HSC) of the fine-grained near-α alloy Ti-5Al-2V (Russian analogue of Grade 9 titanium alloy with increased aluminium content) have been studied. The properties of the Ti-5Al-2V alloy in the coarse-grained state, in the fine-grained state after cold Rotary Swaging (RS), in the partly recrystallized state and in the fully recrystallized state have been investigated. The mechanical properties of the alloy were characterised using compression tests and microhardness measurements. The effects of RS, the annealing temperature, the time on the characteristics of corrosion destruction of the surface and the composition of the products of the HSC were studied. RS was shown to increase the depth of the intergranular corrosion defects, whereas recrystallization annealing promoted an increase in the corrosion resistance of the Ti-5Al-2V titanium alloy. The parameters of the Basquin equation for the corrosion-fatigue curves for the near-α Ti-5Al-2V alloy in the coarse-grained state, in the severely strained state and after recrystallization annealing were determined for the first time. An effect of non-monotonous dependencies of the slopes of the corrosion-fatigue curves for the strained near-α Ti-5Al-2V alloy on the recrystallization annealing temperature has been observed.

Effect of B on hot corrosion behavior of silicide coatings under different corrosive environments at 900 °C

Silicide coatings and B-modified silicide coatings were prepared on Nb-Si based alloys using halide activated pack cementation. The hot corrosion behavior of the coatings exposed to Na2SO4 and Na2SO4 + NaCl mixture salts at 900 °C was investigated. The results show that B-modified silicide coatings possess better hot corrosion resistance than the silicide coatings. The hot corrosion products of silicide coatings show a regional microstructure, including uplift regions of AlNaSiO4 imbedded with Al2O3 phases, and depressed silica regions with NaNbO3 and TiO2 particles. The addition of B to the silicide coatings promotes the formation of the uniform and dense boroaluminosilicate scale with better fluidity during hot corrosion, which impedes the self-sustaining cyclic chlorination/sulfidation reactions, and thus, improves the hot corrosion resistance of the silicide coatings.

Synergistic enhancement of hot corrosion resistance and mechanical properties of IN738LC alloy prepared by selective laser melting

The present study investigates the synergistic enhancement of hot corrosion resistance (900 °C, 75%Na2SO4+25%NaCl) and mechanical properties of IN738LC alloy prepared by selective laser melting after heat treatment. The results indicate that the M23C6 precipitation at the grain boundaries coupled with smaller-sized γ′ phase distribution in the inner grain is conducive to the formation of thicker Cr2O3 outer layer and Al2O3 inner layer for the samples, which effectively hinders the diffusion of S and Cl elements penetrate to the matrix, enhancing the hot corrosion resistance. Additionally, the presence of small-sized γ′ phase and re-crystallization-induced grain refinement contribute to an increase in yield strength (σYS = 1261 MPa) and ultimate tensile strength (σUTS = 1360 MPa) for the alloy.

Behaviour of thermally sprayed coating for hot corrosion applications

As modern air engines’ working temperatures are increasing, materials and coatings' hot corrosion resistance characteristics gain significant attention. Hot corrosion is a type of degradation at high temperatures that involves oxidizing or sulphidation of the substrate behind a layer of salt melt deposit, which either causes the development of a thick layer of sulphide scale or the penetration of sulphur via grain boundaries into the matrix to a deeper depth. It may notably change the microstructure, phase composition, and characteristics of the thermally sprayed coating. In recent years, thermally sprayed cermet coatings on steel have been more well-liked as a possible method for enhancing hot corrosion resistance. This review paper qualitatively summarizes the recent development of thermal sprayed coatings to improve hot corrosion performance.

Overview of corrosion behaviour of ceramic materials in molten salt environments

This study reviewed previous studies between the years 2015 and 2021 on how ceramic materials degraded in the presence of molten salt environments. The processes of corrosion resistance of various ceramic compositions subjected to various molten salt compositions and temperatures were also scrutinized. The results offer important new insights into the variables affecting ceramics' corrosion behaviour and the production of corrosion products. The reported result reveals that the ceramic material with the composition (Sm0.5Sc0.5)2Zr2O7 performed better than that of Sm2Zr2O7 in terms of hot corrosion resistance in molten salt (V2O5 + Na2SO4). It has also been reported that corrosion behaviour is influenced by particle size. Notably, zirconia (n-YSZ) with nanoscale grain sizes was more susceptible to hot corrosion, which was explained by increased specific surface areas. On the other hand, sintering and additives have been found to enhance corrosion resistance. The Y-Y2Si2O7 ceramic's resistance to corrosion in (V2O5 + Na2SO4) molten salt was enhanced by the addition of alumina. The results of these investigations help us understand how corrosion works and what influences ceramic materials' susceptibility to deterioration in molten salt media. This information can direct the creation of more corrosive-resistant ceramic materials for use in high-temperature environments or molten salt-based energy systems, among other corrosive uses.

Insight into the hot corrosion behavior of GH4251 high-temperature superalloy fabricated by selective laser melting

In this study, the GH4251 high-temperature superalloy was fabricated using selective laser melting (SLM) and hot isostatic pressing (HIP) post-treatment. The hot corrosion behavior of the SLMed and SLM-HIPed GH4251 was systematically investigated and compared with the as-forged one in a mixed salt of 75 % Na2SO4 and 25 % NaCl at 900 °C. The results indicated that three GH4251 superalloys rank in order of superiority for high-temperature corrosion resistance as follows: SLMed > SLM-HIPed > as-forged. The hot corrosion resistance of the alloy is closely related to its microstructures. A high density and a high proportion of small-angle grain boundaries effectively prevent substrate corrosion from molten salts. High dislocation densities and fine grains can increase the elemental diffusion channels and promote the formation of dense protective oxide films, thereby enhancing the hot corrosion resistance. The SLMed superalloy has high densities, high dislocation densities, a high proportion of small-angle grain boundaries, and an appropriate grain size. This is the reason why the SLMed alloy exhibits the most superior hot corrosion resistance. In addition, the hot corrosion mechanisms of the GH4251 superalloy were also discussed in depth.