Hot Corrosion Resistance Research Articles

Role of bond coat deposition method in the hot corrosion behavior of CSZ thermal barrier coatings

In this research, a NiCrAlY bond coat was applied using two methods – namely, conventional air plasma spraying (APS) and new spark plasma sintering (SPS) technique – on an Inconel-738 substrate. The ceria-stabilized zirconia (CSZ) topcoat was similar in both samples and deposited using the APS method. The hot corrosion performance of the fabricated thermal barrier coatings (TBCs) was studied at 950°C in a sodium sulfate (Na2SO4)–55 wt.% vanadium (V) oxide (V2O5) corrosive salt environment. The results showed that the hot corrosion resistance of the coating system with an SPS-processed NiCrAlY bond coat and a CSZ topcoat was much better than that of the conventional TBC sample because the adhesion of the bond coat to the substrate was very good in this sample, and the interface was free of any defects such as cracks and porosities. According to these results, no spallation was observed in the SPS-processed coating up to 38 h, while for the CSZ topcoat with an APS-processed bond coat, spallation occurred after 24 h.

Hot Corrosion Resistance of TB8 Titanium Alloy after ECAP and Heat Treatment

Hot Corrosion Resistance of TB8 Titanium Alloy after ECAP and Heat Treatment

Quantitative Characterization of Elemental Segregation in Inconel 718 Superalloy by Micro-Beam X-ray Fluorescence Spectroscopy and Its Correlation Study.

Inconel 718 (IN718) nickel-based superalloy is widely used in aerospace and nuclear applications owing to its excellent comprehensive mechanical properties, oxidation resistance, and hot corrosion resistance. However, the elemental segregation caused by heterogeneous solidification during casting has great influence on the mechanical properties. Therefore, accurately characterizing the segregation behavior is necessary. Traditional quantitative characterization of elemental segregation uses various sampling methods, in which only macroscopic segregation results are obtained. In this study, micro-beam X-ray fluorescence (μ-XRF) is used for the quantitative characterization of element micro-segregation in IN718 superalloy. The concentration distributions of Cr, Fe, Mo, Nb, and Ti in IN718 alloy are determined with optimized testing parameters, and the degree of elemental segregation in different regions of the analytical area is calculated. It is found that the segregation degree of Nb and Ti in the testing area is larger than other alloying elements. The correlation between the microstructure distribution and the segregation degree of Nb and Ti has been studied using scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). There is severe segregation of Nb and Ti in areas where Nb-containing precipitates are accumulated. The distribution of abnormal signals of Nb with a high fluorescence intensity has a close relationship with the area of precipitates-enriched Nb.

Development of EPDM composites reinforced by CNTs@SiO2 for thermal protection systems of aerospace propulsion: Significant improvement in oxidation and ablation resistance properties

Carbon Nanotubes (CNTs) reinforced Polymer-Matrix Composites (PMCs) is widely used as insulation materials in thermal protection system of aerospace propulsion. However, CNTs are prone to oxidation and have high thermal conductivities, which makes it difficult to improve the ablation resistance of insulation materials that contain CNTs. SiO2 was encapsulated onto the surface of CNTs (CNTs@SiO2), which were then added to Ethylene Propylene Diene Monomer (EPDM) rubber to prepare the insulation materials. Thermogravimetric analysis and ablation test were used to evaluate the resistance of the insulation materials to thermal oxidation and ablation. Additionally, scanning electron microscopy was performed to analyze their microstructures. Results revealed that the addition of CNTs@SiO2 could visibly reduce the effects of hot corrosion and ablation on insulation materials. The C-CNTs@SiO2-1 formulation had the best ablative resistance. Further, compared with the unencapsulated formulation (C-CNTs-10), the C-CNTs@SiO2-1 formulation reduced the line ablation rate by 51% to 0.0130 mm/s after oxygen-acetylene experiments. Lastly, the ablation mechanism was investigated based on the effects of the CNTs@SiO2 additive on their properties. Thus, the improvement in ablation performance may be attributed to CNTs@SiO2-induced decreases in thermal conductivity, improvement in the hot corrosion resistance in the char layer, and changes in the microstructure.

A comprehensive study on hot corrosion resistance of NiCoCrAlYTa and NiCrAl thermal-sprayed coatings for CSP applications

The new generation of concentrated solar power (CSP) plants could be able to work at temperatures up 650 °C and carbonates molten salts are one of the main candidates to be used as thermal energy storage (TES) materials. Molten salt corrosion has been defined as one of the main issues and the technology demands more resistance alloys and innovative coatings. In this study, the assessment of hot corrosion resistance for NiCoCrAlYTa and NiCrAl thermal-sprayed coatings has been undertaken, tested on a ternary eutectic mixture (Li2CO3-Na2CO3-K2CO3) at a temperature of 650 °C. Electrochemical impedance spectroscopy and linear polarization resistance tests were used to evaluate the behaviour of the coatings but the obtained results reveal high values of corrosion rates accompanied by the formation of cracks. This unsatisfactory performance of the coatings, analysed by scanning electron microscopy and x-ray diffraction, can be attributed to a combination of different factors such as porosity, internal material stresses and thermal diffusion phenomena. As a result, it is concluded that further research is necessary to explore new coating application techniques.

Effects of Aluminium Oxide Content on the Regenerated Magnesia-Calcium Bricks for Cement Rotary Kiln

Regenerated magnesia-calcium brick samples with different aluminium oxide (Al2O3) contents were prepared using spent magnesia-calcium bricks and fused magnesia as the main raw materials and Al2O3 powders as the additive. The phase compositions, microstructures, room temperature, hot flexural strength, and kiln coating adherence of the regenerated samples were investigated. This indicates that the Al2O3 content increased, mainly resulting in the content of tetracalcium aluminoferrite (C4AF) and tricalcium aluminate (C3A) increasing in the regenerated samples. The bulk density, room temperature flexural strength, and kiln coating adherence all increased, whereas the hot flexural strength and corrosion resistance to cement clinker both deteriorated with an increase in the Al2O3 content. This was because, on the one hand, the low melting point phases of C4AF and C3A improved the sinterability of the regenerated samples during the burning stage, and on the other hand, they melted or existed in the liquid phase at the experimental temperature, which degraded the hot flexural strength and corrosion resistance but enhanced the kiln coating adherence as the wettability of the liquid phase. The content of Al2O3 in the regenerated magnesia-calcium brick should not be higher than 1.1 wt.%, considering its comprehensive performance for cement rotary kiln.

Hot corrosion mechanism of laser metal deposited Ni-based single crystal superalloy under fuel gas atmosphere

In this research, the hot corrosion behavior of laser repaired Ni-based single crystal superalloy in fuel gas environment is analyzed and compared with that of the substrate, and the corrosion mechanism is determined. The deposited single crystal layer is comprised of the γ(Ni) matrix and abundant spherical γ′(Ni3Al) nanoparticle phases. The corrosion products exhibited layered structure including the outer layer dominated by NiO, NaTaO3 and (Ni,Co)Cr2O4, the inner layer mainly comprising Al2O3 and Cr2O3, and the internal γ′ depleted layer. The hot corrosion resistance of the deposited part is superior than that of the substrate, owing to the synergistic effects of much finer γ′ phase, higher volume fraction of γ′ phase, and more compact corrosion product of the deposited component. Our work provides a practical strategy for enhancing the hot corrosion resistance of laser repaired superalloy by manipulating the size and morphology of γ′ phase.

Hot corrosion of borosilicate barrier scale on MoSi2-based ceramic

The borosilicate scales with different B2O3 contents were prepared on MoSi2 ceramics by cold pressing, pressureless sintering and pre-oxidation. Hot corrosion with Na2SO4 was carried out at 1000 °C for 8 h. The pre-oxidized borosilicate scale on ceramics with 10 wt% B2O3 has an excellent hot corrosion resistance. B2O3–SiO2 barrier scales mainly contained amorphous borosilicate glass which can reacted with Na2SO4 producing sodium borosilicate glass to cover and heal the corroded surface. The Mo-based particles under the barrier scale were isolated to avoid severe reactions producing Na2MoO4, so the borosilicate barrier scale had an excellent corrosion resistance to Na2SO4 molten salt.

Effect of trace sulfur on the hot corrosion resistance of Ni-base single crystal superalloy

The effect of sulfur on the hot corrosion resistance of Ni-base single crystal superalloy was investigated in Na2SO4 salt at 900 °C in static air. The results indicate that the corrosion resistance of the superalloy is significantly degraded even with several ppm contents of sulfur in the alloy. High sulfur content in the alloy causes the oxide layer to bulge and significantly shortens the corrosion incubation period. The accelerated corrosion process is attributed to the outward diffusion of sulfur from the alloy promoting S segregation at the oxide/metal interface and hence favors crack premature initiation.

Microstructural Evolution and Room Temperature Mechanical Properties in Additively Manufactured Mar M 509 With Short Cycle Heat Treatment

Abstract The Co-based superalloy Mar M 509, known for its high-temperature oxidation and hot corrosion resistance, is processed via laser powder bed fusion (LPBF). Microstructure and mechanical properties of Mar M 509 in as-printed (As-P) and heat-treated (HT) states are compared based on two build orientations (longitudinal (L) and transverse (T)) to establish structure-property links with heat treatment. The As-P condition displays a distinct cellular microstructure (500–600 nm) with 50–60 nm carbide particles adorning cell boundaries. Longitudinal (L) build has columnar grains (8–35 μm along the major axis) with a grain aspect ratio of 4, while transverse (T) orientation exhibits equiaxed, bimodal microstructure (5–10 μm and 15–25 μm grain sizes). Strong <001> texture is noted in L. Mechanical properties at room temperature differ between L and T; T (569 ± 12 HV) has 15% higher hardness compared to L (489 ± 18 HV) and 34% higher 0.2% yield strength (YS), but 30% lower elongation than L. Post a short heat treatment cycle at 1250 °C, weld bead structure and cell boundaries break down. Both L (25–33 μm along the major axis) and T orientations (5–42 μm) experience grain growth, and carbides coarsen (250–350 nm). Post-heat treatment, dislocation density decreases, indicating recrystallization; lattice parameter of matrix reduces, implying solute depletion contributing to carbide enrichment. Yield strength drops from 860 MPa to 740 MPa in L and from 1150 MPa to 840 MPa in T, with ductility rising from 14% to 23% in L.

Effect of chromium and silicon additions on the hot corrosion resistance of nickel aluminide coatings

The effects of chromium and silicon modification on the microstructure and hot corrosion resistance of slurry aluminide coatings applied on pure nickel was studied by in-depth microscopic analyses. The simple and the Cr-modified aluminide coatings provided limited protection in Type II hot corrosion conditions but the Si-modified coating exhibited outstanding resistance with no sign of attack after 300 h of isothermal exposure at 700 °C. The synergistic dissolution between NiO and Al2O3/Cr2O3 appears responsible for the onset of the corrosion attack for the simple and Cr-modified coatings while silicon is shown to extend the incubation period.

Effect of coating degradation on the hot corrosion behavior of yttria-stabilized zirconia (YSZ) and blast furnace slag (BFS) coatings

In order to provide thermal insulation thermal barrier coatings (TBCs) used in gas turbine engine components under conditions of impure fuels and high turbine inlet temperatures are expected to have hot corrosion resistance. Techniques and material combinations used in the production of TBCs are primarily effective in the progression of failure mechanisms as a result of hot corrosion. In this study, the hot corrosion damage mechanism, which is caused by the impurities of the fuels used in the industry and causes great damage to the TBC systems, was simulated and evaluated in the laboratory environment. For the creation of TBC systems, CoNiCrAlY metallic bond coating powders were deposited on Ni-based super alloy substrates by the detonation gun (D-gun) process. Commercial yttria-stabilized zirconia (YSZ) and blast furnace slag (BFS) powders were deposited on the bond coating by Atmospheric plasma spraying (APS) technique. Hot corrosion testing of TBCs was performed at 800 °C for 8, 24, 50, and 75 h in an environmental condition consisting of a 45 wt% Na2SO4 and 55 wt% V2O5 corrosive salt mixture. Blast furnace slag, which is completely cost-free and a waste product, provided excellent protection against hot corrosion damage without deteriorating its stability at high temperatures. In this way, it is open to be evaluated as a new type of coating material alternative to the traditional top coating material YSZ, which has a very high production and cost, and to be used in different areas.

Hot salt corrosion behavior of Ti–6Al–4V alloy treated with different surface deformation strengthening processes

In this study, the effects of shot peening (SP) and ultrasonic surface rolling process (USRP) on the high-temperature oxidation and hot salt corrosion (HSC) behavior of the Ti–6Al–4V alloy were systematically investigated. The results showed that the high-temperature oxidation resistance of this titanium alloy can be significantly improved by the above two treatments. However, the hot salt corrosion resistance of Ti–6Al–4V alloy cannot be improved by SP due to surface roughness increasement, the surface defects and the complete relaxation of compressive residual stress (CRS) at high temperature. On the contrary, the hot salt corrosion resistance of USRP treated specimen was remarkably improved because USRP treatment significantly reduced the surface roughness and introduced deep CRS field with good thermal stability. In addition, the refined surface microstructure promoted the formation of a protective oxide film, which was also beneficial for inhibiting hot salt corrosion.

CAN-Net: A Multi-hidden Layer Attention Deep Learning Method for Surface Roughness Prediction During Abrasive Belt Grinding of Superalloy with Local Weights

Nickel-based superalloys are widely employed in aerospace due to their excellent high-temperature strength, good oxidation resistance, and hot corrosion resistance. Abrasive belt grinding can effectively solve the problems of excessive residual stress and tool wear during the processing of superalloys. However, due to the grinding process being complex and changeable, and a wide range of affecting factors, the surface roughness prediction of abrasive belt grinding has become a challenging topic. In this study, a CAN-Net multi-hidden layer deep learning prediction model is established. The concatenate path is utilized to fuse local weights to optimize the intermediate weights of network training. To increase the predictability of the model, the attention mechanism is included to distribute the weights of the grinding parameters, and the impact of the attention mechanism on the prediction is then carefully analyzed. The results demonstrate that the CAN-Net network model has outstanding parameter flexibility and prediction accuracy, with accuracy reaching 0.984 and a correlation coefficient of 0.981 between the anticipated value and the true value.

Towards high-entropy alloys with high-temperature corrosion resistance and structural stability

Complex component alloys (CCAs) consisting of multiple principal elements potentially encompass superior mechanical properties and good corrosion resistance. Eutectic high-entropy alloys (EHEAs) stand out from CCAs as the desired candidates for high-temperature (HT) applications due to the combined advantages of HEA alloys and unique equilibrium eutectic structure. This work first explores the thermodynamic calculation route toward HEAs with eutectic structure. Series of pseudo-binary diagrams of transition metal (TM) CCAs were calculated with the Calphad approach to locate the potential eutectic points. The representatives of a CrFeCoNi2.2Al alloy with eutectic structure and a non-eutectic CrFeCoNiCu alloy were cast, and their HT performance was further evaluated by hot corrosion with Na2SO4 + 25 wt% NaCl molten salts at 700, 800 and 900 °C, respectively. The HT degradation mechanism was explicitly revealed from a comprehensive thermodynamic perspective. Relationships between the HT performance and the inherent physicochemical properties of the constituent phases and the alloying components were addressed for the first time. It was found that the mixing enthalpy (ΔHmix) and valance electron concentration (VEC) played more decisive roles in the hot corrosion resistance than the mixing entropy (ΔSmix) of CCAs. A strategy for tailoring and developing HEAs for HT application by modulating alloy chemistry and microstructural features was proposed.

Hot salt corrosion behavior of the Ti-44Al-4Nb-1.5Mo-(B,Y) alloy in the temperature range of 750–950 °C

Hot salt corrosion behavior of TNM alloy (Ti-44Al-4Nb-1.5Mo-(B, Y) (at.%)) was investigated in cyclic conditions at 750 °C, 850 °C and 950 °C for 100 h in the 75 wt% Na2SO4 + 25 wt% NaCl salt mixture. The hot salt corrosion resistance of γ、α2 and β phase in the alloy was studied by short-term quasi-in-situ hot corrosion experiments. Results show that the hot salt corrosion resistance of the three phases decreases in the following order: γ、α2、β. The weight changes of TNM alloy after hot salt corrosion at 750 °C, 850 °C and 950 °C for 100 h are 13.8 mg/cm2, -19.6 mg/cm2 and -26.7 mg/cm2. Under the condition of hot salt corrosion at 750 °C, the corrosion scales are mainly composed of a mixed corrosion scale of TiO2 and Al2O3, Al2O3 scale, and Al depletion zone, similar to the morphology of a high-temperature oxidation scale. The corrosion scales are seriously peeled off and destructive transverse cracks are generated inside the corrosion scales under the conditions of hot salt corrosion at 850 °C and 950 °C. The acid-base corrosion dissolution of oxides in the corrosive medium and the formation of volatile chlorides are the main causes of cracks in the TiO2 and Al2O3 scales. In addition, the Nb element in the TNM alloy is mainly enriched beneath the corrosion scales to form a NaNbO3 layer, which can inhibit the decomposition and penetration of the corrosive medium. Mo element reacts with the S element to form MoS2, which anchors the S element to a certain extent.

Hot corrosion resistance of Al2O3 nanoparticles reinforced CoNiCrAlY coatings deposited by LPPS and HVOF processes in molten Na2SO4-V2O5 at 850[formula omitted

In this research, satellited CoNiCrAlY/nano-Al2O3 feedstocks with 2 and 4 wt% oxide nanoparticles and conventional CoNiCrAlY powder were deposited through the HVOF and LPPS processes on Inconel 738 substrates. The hot corrosion test was done in molten Na2SO4-55wt.%V2O5 salt at 850 °C for 24 h. The microstructure and phase composition of the as-sprayed and corroded coatings were characterized by the FESEM and XRD. The results showed that by adding Al2O3 nanoparticles in the HVOF CoNiCrAlY coatings up to 4 wt%, the porosity increased from 0.6 to 2.7 vol% and the surface roughness increased from 4.4 to 7.1 μm. By adding Al2O3 nanoparticles in the LPPS CoNiCrAlY coatings up to 4 wt%, the porosity increased from 2 to 3.76 vol%, and the surface roughness increased from 6.1 to 7.5 μm. Penetration of corrosive salt in the conventional and composite HVOF coatings, including 2 and 4 wt% nanoparticles, was obtained as 72, 16, and 140 μm, respectively. Penetration of the corrosive species in the conventional and composite LPPS coatings consisting of 2 and 4 wt% nanoparticles was measured as 91, 125, and 170 μm, respectively. The hot corrosion mechanism was basic and acidic fluxing, creating (Co, Ni)2V2O7, Na(AlO2), CoCo2O4, and NiCr2O4 corrosion products.

Hot corrosion behavior of a novel TiC/GTD222 nickel-based composite prepared by selective laser melting

In this study, a novel TiC/GTD222 nickel-based composite with enhanced hot corrosion resistance was designed by incorporating appropriate amounts of C, Al, and Ti elements into the GTD222 superalloy. The composite was successfully prepared using the selective laser melting (SLM) technique. The hot corrosion behavior of GTD222 superalloy and the TiC/GTD222 composite in a salt mixture of 75% Na2SO4 + 25% NaCl (wt%) at 900 °C was systematically studied. The results show that the TiC/GTD222 composite exhibits much better hot corrosion resistance than the GTD222 superalloy. This is because a continuous and dense double-layer oxide film is formed in the composite (The inner layer is TiO2 and the outer layer is Cr2O3), while oxide film of the superalloy is loose and porous, and has a discontinuous TiO2 and Al2O3 distribution. The adding alloy elements can promote the formation of more γ' phase and TiC particles in the TiC/GTD222 composite, and also result in the refined grain and formation of more dislocations. The above microstructures increase the diffusion channels of elements, and the higher contents of Al and Ti can enhance the diffusion potential energy of these elements, leading to the formation of continuous and dense double-layer oxide film of the composite. This work provides new ideas for the design of additive manufactured superalloy.

The hot corrosion resistance of APS YSZ coatings micro glazed via an ultraviolet picosecond ultrashort pulsed laser

In this paper, yttria-stabilized zirconia (YSZ) was innovatively glazed via an ultraviolet picosecond ultrashort pulsed laser (laser micro glazing, LMG). A smooth LMGed layer (surface roughness: ∼0.714 µm) with incredibly narrow cracks (< 0.547 µm in width) was achieved. The hot corrosion tests of molten salt (V2O5 +Na2SO4) at 1100 °C for 20 h were performed. The results show that laser irradiation not only increased oxygen vacancies but also reduced the reaction area between the molten salt and coatings. During the hot corrosion test, the LMGed layer with ultra-fine grains also promoted a homogeneous redistribution of Y3+ during the segregation process. These factors greatly improved the phase and structural stability of t′-ZrO2 in the LMGed surface. Interestingly, the self-healing phenomenon of narrow cracks was found in the LMGed layer, which tremendously decreased the penetration channels of the molten salt. Compared with the original as-sprayed coatings, the corrosion product YVO4 on the LMGed coatings was not only reduced in number but also greatly diminished in size. Meanwhile, the m-ZrO2 content and penetration depth in the LMGed coatings were decreased by 80.336 % and 60.057 %, which demonstrated the excellent hot corrosion resistance of LMGed YSZ coatings.

Airborne hydrocarbon induced multifunctional coating towards bouncing characteristics, icing delaying, hot-water repellency, and anti-corrosion on copper

Some studies have confirmed copper coating can realize superhydrophobicity after exposure to air. However, the comprehensive characteristics of the special wettable coating such as surface energy, bouncing behavior, hot water repellency, icing delaying, and corrosion resistance are still not well understood. Here, without further chemical processing, an electrodeposition technique creates a superhydrophobic layer on a copper substrate. The wettability versus different exposure routes is investigated. As a result, the slow oxidation of Cu and adsorption of airborne hydrocarbon contribute to a low rolling angle and enhanced water droplet bouncing ability. The coating displays strong 95 °C hot water repellency, icing delaying (∼78s), and great anti-corrosion ability, which also has a high protection efficiency (98.84%) and an improved coating resistance of 2.198 × 105 Ω cm2. The multifunctional properties are attributed to the airborne hydrocarbon and the constructed hierarchical structure. This preparation process avoids complex chemical modification and it can provide a new strategy for designing multifunctional coating for surface protection on metals.