In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot co...In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot corrosion behavior of the coatings was in-vestigated.X-ray diffraction(XRD)and scanning electron microscope with energy dispersion spectrum(SEM-EDS)were used to analyze the phase compositions,morphologies and chemical compositions of the coatings.The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content,which resulted in NiO being the major reaction product.It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating.The basic fluxing of Cr_(2)O_(3) lowered its protection during the hot corrosion process and led to the formation of porous Cr_(2)O_(3) on the NiCr41 coating.The molten salts accelerated the oxidation reac-tion resulting in thicker and porous oxide scales formed on the surfaces of coatings.展开更多
The metastableβtitanium alloy TB8(Ti-12.76Mo-2.13Nb-2.73A1-0.16Si)was used as the original material,and the secondary processing method combining equal channel angular pressing(ECAP)and heat treatment was adopted.Wit...The metastableβtitanium alloy TB8(Ti-12.76Mo-2.13Nb-2.73A1-0.16Si)was used as the original material,and the secondary processing method combining equal channel angular pressing(ECAP)and heat treatment was adopted.With the help of optical microscope(OM),scanning electron microscope(SEM)and X-ray diffractometer(XRD),the corrosion behavior of TB8 titanium alloy after different secondary processing(800℃/850℃solid solution-520℃aging,ECAP-800℃/850℃solid solution-520℃aging,and800℃/850℃solid solution-ECAP-520℃aging)was studied.The experimental results show that the hot corrosion products of the six samples are similar,mainly Na_(2)Si_(2)O_(5),MoS_(2),TiCl_(2),Ti(SO_(4))_(2),and TiS.Due to the grains of the TB8 titanium alloy treated by 850℃solid solution-ECAP-520℃aging are obviously refined,the surface structure is the most smooth and dense,forming a continuous Al2O3protective film,and the surface defects are the least after corrosion.Its corrosion layer thickness is the lowest(102.3μm),only 36.5%-81.4%of that of other secondary processing titanium alloys.In addition,the corrosion kinetics curves of the six materials all follow parabolic laws,and the minimum corrosion weight gain of the samples after 850℃solutionECAP-520℃aging treatment is 0.7507 mg·mm^(-2),showing better hot corrosion resistance.展开更多
The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show tha...The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.展开更多
The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel(HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y all...The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel(HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y(80 wt%;microsized)–silicon carbide(SiC)(20 wt%;nano(N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na2SO4–60 wt%V2O5 molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction,field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20 wt%SiC(N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.展开更多
The effect of sputtered Ti-50Al-10Cr and Ti-50A1-20Cr coatings on both isothermal and cyclic oxidation resistance at 800-900℃ and hot corrosion resistance at 850℃ of Ti-24Al-14Nb-3V was investigated. Results indicat...The effect of sputtered Ti-50Al-10Cr and Ti-50A1-20Cr coatings on both isothermal and cyclic oxidation resistance at 800-900℃ and hot corrosion resistance at 850℃ of Ti-24Al-14Nb-3V was investigated. Results indicated that Ti-24Al-14Nb-3V alloys exhibited poor oxidation resistance due to the formation of Al2O3+TiO2+AlNbO4 mixed scales in air at 800-900℃ and poor hot corrosion resistance due to the spoliation of scales formed in Na2SO4+K2SO4 melts at 850℃. Both Ti-50Al-10Cr and Ti-50Al-20Cr coatings remarkably improved the oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V alloy.展开更多
The oxidation and hot corrosion behavior of Co-Ni-Cr-AI-Ta-Y coating produced by magnetron sputtering with and without enamel coating has been investigated in air at 900℃ and in molten 75 wt pct NaCl+25 wt pct Na2SO4...The oxidation and hot corrosion behavior of Co-Ni-Cr-AI-Ta-Y coating produced by magnetron sputtering with and without enamel coating has been investigated in air at 900℃ and in molten 75 wt pct NaCl+25 wt pct Na2SO4 at 850℃. The results show that the enamel coating possesses good hot corrosion resistance in the molten salts, in comparison with the sputtered Co-Ni-Cr-AI-Ta-Y coating. In the hot corrosion test, breakaway corrosion did not occur on the samples with enamel coating and the composition of enamel coating did not significantly change either. The oxidation resistance of the sputtered coating, which offers good adhesion, can be improved by the enamel coating.展开更多
Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler...Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler tube steel, FeCrAl, NiCrTi, Ni50Cr and NiCrAlMoFe-Cr 3C 2 coatings, which are widely used at present for protection of boiler tubes. Meanwhile,the influence of sealer on the hot corrosion resistance of various coatings and the mechanisms of coating corrosion were explored.展开更多
Hot corrosion of intermetallic compound Ni_3Al-0.2B was studied by electrochemical techniques combined with physical analyses.It was found that hot corrosion resistance of Ni_3Al-0.2B is rather inferior.Sulfidation-ox...Hot corrosion of intermetallic compound Ni_3Al-0.2B was studied by electrochemical techniques combined with physical analyses.It was found that hot corrosion resistance of Ni_3Al-0.2B is rather inferior.Sulfidation-oxidation is responsible for the accelerated corrosion.The addition of 6at.-% Cr and 0.5at.-% Zr to Ni_3Al-0.2B may accelerate its corrosion.展开更多
The sputtered nanocrystalline coating of K38G alloy was obtained by magnetron sput-tering. The hot corrosion behaviors of cast K38G alloy and its sputtered nanocrys-talline coating by pre-deposited 75wt%Na2SO4+25wt%K2...The sputtered nanocrystalline coating of K38G alloy was obtained by magnetron sput-tering. The hot corrosion behaviors of cast K38G alloy and its sputtered nanocrys-talline coating by pre-deposited 75wt%Na2SO4+25wt%K2SO4 at 900℃ were studied. The results indicated the occurrence of internal sulfidation in the cast K38G alloy with pre-deposited sulfattes of 0.8 and 3.0mg/cm2. However, the internal sulfidation was not observed in the coating with pre-deposited 0.8mg/cm2 sulfate. The hot corrosion resistance of K38G alloy was clearly enhanced through nanocrystallinzation, although the internal sulfides were still formed for the coating with sulfate deposit of 3mg/cm2. The relevant hot corrosion mechanism was also discussed.展开更多
An investigation of low temperature hot corrosion is carried out on a spray-formed nickel-based superalloy FGH100 pre-coated with Na2SO4-NaC1 at 700 ℃ for 100 h. Mass gain measurement, x-ray diffraction, scanning ele...An investigation of low temperature hot corrosion is carried out on a spray-formed nickel-based superalloy FGH100 pre-coated with Na2SO4-NaC1 at 700 ℃ for 100 h. Mass gain measurement, x-ray diffraction, scanning electron mi- croscopy, and energy dispersive x-ray spectroscopy are used to study the corrosion behavior. Results reveal that corrosion behavior follows a sequence, that is, first rapidly proceeding, then gradually slowing down, and finally forming an outer layer composed of different types of oxides and an inner layer mainly comprised of sulfides. In-depth analysis reveals that the hot corrosion of FGH100 is a combined effect of oxidation-sulfidation and transfer of oxides.展开更多
The hot corrosion behavior of the NiAl coating and the 5Hf-NiAl coating induced by mixed salt at 900℃was investigated.Comparing with the NiAl coating,the 5Hf-NiAl coating exhibited superior hot corrosion resistance b...The hot corrosion behavior of the NiAl coating and the 5Hf-NiAl coating induced by mixed salt at 900℃was investigated.Comparing with the NiAl coating,the 5Hf-NiAl coating exhibited superior hot corrosion resistance because the addition of Hf promoted the formation of protective oxide scale and reduced the growth rate of oxide scale.Therefore,internal sulfides were not present in the 5Hf-NiAl coating after hot corrosion for 140 h.Cr exhibited different distribution in the two coatings since the addition of Hf changed the hot corrosion process of the coating.Hf and Ti in the 5Hf-NiAl coating trapped and captured sulfur,preventing the penetration of sulfur into the coating.The hot corrosion mechanism of the two coating and the effects of Hf on this process were discussed in this work.展开更多
Hot corrosion behaviors of the 921A alloy and Fe-based amorphous coating induced by KCl-10% ZnCl_(2) and KCl-55% ZnCl_(2) salts at 450℃ in air for 40 h were investigated.Results show that the 921A alloy suffers more ...Hot corrosion behaviors of the 921A alloy and Fe-based amorphous coating induced by KCl-10% ZnCl_(2) and KCl-55% ZnCl_(2) salts at 450℃ in air for 40 h were investigated.Results show that the 921A alloy suffers more serious corrosion damage than the coating and KCl-55% ZnCl_(2) salts are more corrosive than KCl-10% ZnCl_(2) salts.In the two salts,an Fe_(2)O_(3) layer is formed on the 921A alloy surface,while an outer Fe-rich oxide layer and an inner Cr-rich oxide layer are formed on the surface of the coating.Moreover,a certain amount of metal chloride can be found at the oxide/alloy(coating)interface,which can be explained by "active oxidation".However,the corrosion resistance of the Fe-based amorphous coating did not achieve the desired results,probably because the intersplats in the coating serve as corrosion diffusing channels,which facilitate the corrosion damage rate.Nevertheless,the coating is still in amorphous state after hot corrosion exposure.展开更多
Hot corrosion has been extensively observed in various high temperature applications,which might cause large economic losses.To deepen the insight and understanding of hot corrosion,herein,we provide a detailed discus...Hot corrosion has been extensively observed in various high temperature applications,which might cause large economic losses.To deepen the insight and understanding of hot corrosion,herein,we provide a detailed discussion on hot corrosion induced by molten sulfate salt,in which Na_(2)SO_(4)is the main chemical reactant.The hot corrosion is triggered and sustained by the negative solubility gradient of protective oxide from the oxide/salt interface to salt/gas interface.In this work,we reviewed several key factors,including temperature,gas composition,molten salt composition,alloy element and external stress,influencing the hot corrosion of alloy beneath the molten salt.The application of anti-corrosion coating seems to be the most effective and commercial mothed to mitigate hot corrosion.Therefore,the progress of the development of effective coatings,e.g.,Ni-Cr coatings,aluminide coatings,silicide coatings and MCrAlY(X)coatings,has also been summarized.展开更多
LaTi2Al9O19 (LTA) exhibits promising potential as a new kind of thermal barrier coating (TBC) material, due to its excellent high-temperature capability and low thermal conductivity. In this paper, LTA/yttria stab...LaTi2Al9O19 (LTA) exhibits promising potential as a new kind of thermal barrier coating (TBC) material, due to its excellent high-temperature capability and low thermal conductivity. In this paper, LTA/yttria stabilized zirconia (YSZ) TBCs are produced by atmospheric plasma spraying. Hot corrosion behavior and the related failure mechanism of the coating are investigated. Decomposition of LTA does not occur even after 1 458 hot corrosion cycles at 1 373 K, revealing good chemical stability in molten salt of Na=SO4 and NaCl. However, the molten salt infiltrates to the bond coat, causing dissolving of the thermally grown oxide (TGO) in the molten salt and hot corrosion of the bond coat. As a result, cracking of the TBC occurs within the oxide layer. In conclusion, the ceramic materials LTA and YSZ reveal good chemical stability in molten salts of Na2SO4 and NaCl, and the bond coat plays a significant role in providing protection for the component against hot corrosion in the LTA/YSZ TBCs. LTA exhibits very promising potential as a novel TBC material.展开更多
In this investigation, impedance spectroscopy (IS) is used, as a non-destructive tool, to examine the hot corrosion behavior of thermal barrier coatings (TBCs) exposed to a mixture of 25wt% NaCl and 75wt% Na2SO4. ...In this investigation, impedance spectroscopy (IS) is used, as a non-destructive tool, to examine the hot corrosion behavior of thermal barrier coatings (TBCs) exposed to a mixture of 25wt% NaCl and 75wt% Na2SO4. The results show that the thermally grown oxide (TGO) formed along the top coat/bond coat interface is a mixed oxide layer, i.e. Cr2O3, (Ni, Co)(Cr, Al)2O4 spinel and NiO. The growth of TGO layer appears to follow the parabolic law. The resistance of TGO increases due to the increase of thickness when the number of cycles is less than 110. While for more than 110 cycles, the resistance of TGO decreases with the increase of porosity of TGO layer, even though the thickness of TGO layer increases. The nucleation and propagation of cracks within top coat increase the electrical resistance of top coat. The parameters in equivalent circuit could be used to characterize the degradation of TBCs.展开更多
TiN and TiAlN coatings were deposited by arc ion plating on titanium alloys to study their hot corrosion resistance when they were exposed to NaCl at 600℃.The microstructure and corrosion behaviors of nitride coating...TiN and TiAlN coatings were deposited by arc ion plating on titanium alloys to study their hot corrosion resistance when they were exposed to NaCl at 600℃.The microstructure and corrosion behaviors of nitride coatings were studied using scanning electron microscope,X-ray diffraction,electro-probe microanalyzer and X-ray photoelectron spectroscopy.The results showed that nitride coatings with the different compositions and the ones with the same composition but different thicknesses presented different hot corrosion resistance.TiN and thin TiAlN coatings showed poor corrosion resistance.Serious internal oxidation attacked the alloy substrate.Their corrosion products were mainly consisted of non-protective TiO2 and sodium salt.By contrast,the thick TiAlN coating presented outstanding corrosion resistance.Besides sodium salt,the corrosion products were composed of protective Al_(2)O_(3).The increasing thickness of TiAlN significantly enhanced the hot corrosion resistance.The corrosion mechanisms of alloy,TiN and TiAlN coatings were discussed in detail.展开更多
DZ68 alloy is a new Ni-base directionally solidified superalloy for the blade of advanced turbine engine with high ratio of thrust-mass.In order to investigate the influence of pre-oxidation on the hot corrosion resis...DZ68 alloy is a new Ni-base directionally solidified superalloy for the blade of advanced turbine engine with high ratio of thrust-mass.In order to investigate the influence of pre-oxidation on the hot corrosion resistance of DZ68 alloy,pre-oxidation treatment was conducted at 950℃ in air for 20 h.A mixture of 75% Na2SO4 +25% NaCl (in mass fraction) was used for hot corrosion study at 900℃.The microstructure of specimens was investigated by using a scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS).The compositions of the corroded specimens were determined by X-ray diffraction (XRD).After preoxidation at 950℃ in air for 20 h,a protective scale consisting of Cr2O3,Al2O3,NiO,NiCr2O4,and Ni2Ti4O formed on the DZ68 superalloy surface.The pre-oxidation treatment improved the initial incubation stage of the alloy in the mixture of 75% Na2SO4 +25% NaCl melts at 900℃.The oxide layer degraded gradually with increasing the time of hot corrosion.Once the oxide layer was damaged,the corrosion rate would increase rapidly,accompanied by obvious spallation of the corrosion products.At 900℃,the pre-oxidation treatment could not inhibit the accelerated hot corrosion of DZ68 in the mixture of 75% Na2SO4 +25% NaCl melts,with a high corrosion rate.展开更多
The effects of a MCrAlY coating on low-cycle fatigue(LCF) behavior of directionally solidified(DS)nickle-based superalloy DZ125 were investigated. Before the fatigue testings, the specimens were pre-exposed in high-te...The effects of a MCrAlY coating on low-cycle fatigue(LCF) behavior of directionally solidified(DS)nickle-based superalloy DZ125 were investigated. Before the fatigue testings, the specimens were pre-exposed in high-temperature hot corrosion(HTHC) environment generating by a burner rig at 850 ℃. The results show that the coating in hot corrosion condition has beneficial effects on the fatigue resistance of superalloy. Under corrosion condition, the MCrAlY-coated specimens tested have higher fatigue lives than the uncoated specimens at the same stress level. The coating failure results from fatigue process and numerous fatigue cracks were nucleated at the specimen surface, only one main crack propagates inward and the secondary cracks away from the fracture surface are perpendicular to the loading orientation.展开更多
基金supported by Corporate Talent Fund Program of Zhengzhou Research Institute of Mechanical Engineering Co.,Ltd.(No.201SJ2023013)the Faculty of Materials and Manufacturing,Beijing University of Technology.
文摘In this article,NiCr coatings with chromium content of 13%,27%and 41%were prepared by arc spraying.They were exposed in molten salts(NaCl-Na_(2)SO_(4))at 800℃for 200 hours.The effect of chromium content on the hot corrosion behavior of the coatings was in-vestigated.X-ray diffraction(XRD)and scanning electron microscope with energy dispersion spectrum(SEM-EDS)were used to analyze the phase compositions,morphologies and chemical compositions of the coatings.The results show that NiCr13 coating exhibited the worst hot corrosion resistance due to the low chromium content,which resulted in NiO being the major reaction product.It should be noted that the hot corrosion resistance of NiCr27 coating was better than that of NiCr41 coating.The basic fluxing of Cr_(2)O_(3) lowered its protection during the hot corrosion process and led to the formation of porous Cr_(2)O_(3) on the NiCr41 coating.The molten salts accelerated the oxidation reac-tion resulting in thicker and porous oxide scales formed on the surfaces of coatings.
基金Funded by the Key Projects of Equipment Pre-research Foundation of the Ministry of Equipment Development of the Central Military Commission of China(No.6140922010201)the Key R&D Plan of Zhenjiang(No.GY2018021)。
文摘The metastableβtitanium alloy TB8(Ti-12.76Mo-2.13Nb-2.73A1-0.16Si)was used as the original material,and the secondary processing method combining equal channel angular pressing(ECAP)and heat treatment was adopted.With the help of optical microscope(OM),scanning electron microscope(SEM)and X-ray diffractometer(XRD),the corrosion behavior of TB8 titanium alloy after different secondary processing(800℃/850℃solid solution-520℃aging,ECAP-800℃/850℃solid solution-520℃aging,and800℃/850℃solid solution-ECAP-520℃aging)was studied.The experimental results show that the hot corrosion products of the six samples are similar,mainly Na_(2)Si_(2)O_(5),MoS_(2),TiCl_(2),Ti(SO_(4))_(2),and TiS.Due to the grains of the TB8 titanium alloy treated by 850℃solid solution-ECAP-520℃aging are obviously refined,the surface structure is the most smooth and dense,forming a continuous Al2O3protective film,and the surface defects are the least after corrosion.Its corrosion layer thickness is the lowest(102.3μm),only 36.5%-81.4%of that of other secondary processing titanium alloys.In addition,the corrosion kinetics curves of the six materials all follow parabolic laws,and the minimum corrosion weight gain of the samples after 850℃solutionECAP-520℃aging treatment is 0.7507 mg·mm^(-2),showing better hot corrosion resistance.
基金Research Project supported by the Corrosion Science Laboratory,Academia Sinica
文摘The structure of the yttrium modified Co-base alloy layers formed by laser cladding on 2Cr13 and 1Cr18Ni9Ti steel surfaces and its hot corrosion performance have been investigated systematically.The re- sults show that the Y-containing cobalt base clad alloy has a finer microstructure and higher corrosion re- sistance to the salt mixture of 75% Na_2SO_4+25%NaCl at high temperature.The unique properties are ob- tained with addition of 0.875% Y for the formation of a continuous and compact oxide scale.The compact scale may act as a barrier for the inward diffusion of oxygen and sulphur and also for the outward diffusion of alloying elements.
基金DST,New Delhi for their research grant(No.SB/FTP/ETA-435/2012,Dated-10/6/2013)that funded the research and development of the project entitled“Nano-composite Coatings to Control Erosion of Boiler Tubes of Steam Generating Plants.”
文摘The present paper deals with the investigation of microstructure and high-temperature hot corrosion behavior of high-velocity oxy fuel(HVOF)-produced coatings. Two powder coating compositions, namely, Ni22Cr10Al1Y alloy powder and Ni22Cr10Al1Y(80 wt%;microsized)–silicon carbide(SiC)(20 wt%;nano(N)) powder, were deposited on a T-22 boiler tube steel. The hot corrosion behavior of bare and coated steels was tested at 900°C for 50 cycles in Na2SO4–60 wt%V2O5 molten-salt environment. The kinetics of corrosion was established with weight change measurements after each cycle. The microporosity and microhardness of the as-coated samples have been reported. The X-ray diffraction,field emission-scanning electron microscopy/energy dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. The results showed that both coatings were deposited with a porosity less than2%. Both coated samples revealed the development of harder surfaces than the substrate. During hot corrosion testing, the bare T22 steel showed an accelerated corrosion in comparison with its coated counterparts. The HVOF-sprayed coatings were befitted effectively by maintaining their adherence during testing. The Ni22Cr10Al1Y–20 wt%SiC(N) composite coating was more effective than the Ni–22Cr–10Al–1Y coating against corrosion in the high-temperature fluxing process.
文摘The effect of sputtered Ti-50Al-10Cr and Ti-50A1-20Cr coatings on both isothermal and cyclic oxidation resistance at 800-900℃ and hot corrosion resistance at 850℃ of Ti-24Al-14Nb-3V was investigated. Results indicated that Ti-24Al-14Nb-3V alloys exhibited poor oxidation resistance due to the formation of Al2O3+TiO2+AlNbO4 mixed scales in air at 800-900℃ and poor hot corrosion resistance due to the spoliation of scales formed in Na2SO4+K2SO4 melts at 850℃. Both Ti-50Al-10Cr and Ti-50Al-20Cr coatings remarkably improved the oxidation and hot corrosion resistance of Ti-24Al-14Nb-3V alloy.
基金This work was supported by the National Natural Science Foundation of China(Grant No.59971052).
文摘The oxidation and hot corrosion behavior of Co-Ni-Cr-AI-Ta-Y coating produced by magnetron sputtering with and without enamel coating has been investigated in air at 900℃ and in molten 75 wt pct NaCl+25 wt pct Na2SO4 at 850℃. The results show that the enamel coating possesses good hot corrosion resistance in the molten salts, in comparison with the sputtered Co-Ni-Cr-AI-Ta-Y coating. In the hot corrosion test, breakaway corrosion did not occur on the samples with enamel coating and the composition of enamel coating did not significantly change either. The oxidation resistance of the sputtered coating, which offers good adhesion, can be improved by the enamel coating.
文摘Three kinds of NiCr-Cr 3C 2 cermet coatings were designed and deposited by the subsonic velocity flame spraying, and their performances of hot corrosion performance were evaluated in comparison with 102G, 20G boiler tube steel, FeCrAl, NiCrTi, Ni50Cr and NiCrAlMoFe-Cr 3C 2 coatings, which are widely used at present for protection of boiler tubes. Meanwhile,the influence of sealer on the hot corrosion resistance of various coatings and the mechanisms of coating corrosion were explored.
文摘Hot corrosion of intermetallic compound Ni_3Al-0.2B was studied by electrochemical techniques combined with physical analyses.It was found that hot corrosion resistance of Ni_3Al-0.2B is rather inferior.Sulfidation-oxidation is responsible for the accelerated corrosion.The addition of 6at.-% Cr and 0.5at.-% Zr to Ni_3Al-0.2B may accelerate its corrosion.
文摘The sputtered nanocrystalline coating of K38G alloy was obtained by magnetron sput-tering. The hot corrosion behaviors of cast K38G alloy and its sputtered nanocrys-talline coating by pre-deposited 75wt%Na2SO4+25wt%K2SO4 at 900℃ were studied. The results indicated the occurrence of internal sulfidation in the cast K38G alloy with pre-deposited sulfattes of 0.8 and 3.0mg/cm2. However, the internal sulfidation was not observed in the coating with pre-deposited 0.8mg/cm2 sulfate. The hot corrosion resistance of K38G alloy was clearly enhanced through nanocrystallinzation, although the internal sulfides were still formed for the coating with sulfate deposit of 3mg/cm2. The relevant hot corrosion mechanism was also discussed.
文摘An investigation of low temperature hot corrosion is carried out on a spray-formed nickel-based superalloy FGH100 pre-coated with Na2SO4-NaC1 at 700 ℃ for 100 h. Mass gain measurement, x-ray diffraction, scanning electron mi- croscopy, and energy dispersive x-ray spectroscopy are used to study the corrosion behavior. Results reveal that corrosion behavior follows a sequence, that is, first rapidly proceeding, then gradually slowing down, and finally forming an outer layer composed of different types of oxides and an inner layer mainly comprised of sulfides. In-depth analysis reveals that the hot corrosion of FGH100 is a combined effect of oxidation-sulfidation and transfer of oxides.
基金This work was supported by the Key Research Program of the Chinese Academy of Sciences(Grant No.ZDRW-CN-2021-2-2)the Science Center for Gas Turbine Project(P2021-A-IV-002-003)+2 种基金the IMR Innovation Fund(2022-PY17)the Basic Research Project of Science,the Education and Industry Integration Pilot Project for Qilu University of Technology(Shandong Academy of Sciences)(2022PY063)the National Natural Science Foundation of China(No.5227011470).
文摘The hot corrosion behavior of the NiAl coating and the 5Hf-NiAl coating induced by mixed salt at 900℃was investigated.Comparing with the NiAl coating,the 5Hf-NiAl coating exhibited superior hot corrosion resistance because the addition of Hf promoted the formation of protective oxide scale and reduced the growth rate of oxide scale.Therefore,internal sulfides were not present in the 5Hf-NiAl coating after hot corrosion for 140 h.Cr exhibited different distribution in the two coatings since the addition of Hf changed the hot corrosion process of the coating.Hf and Ti in the 5Hf-NiAl coating trapped and captured sulfur,preventing the penetration of sulfur into the coating.The hot corrosion mechanism of the two coating and the effects of Hf on this process were discussed in this work.
基金supported by GuangDong Basic and Applied Basic Research Foundation(No.2020A1515110128).
文摘Hot corrosion behaviors of the 921A alloy and Fe-based amorphous coating induced by KCl-10% ZnCl_(2) and KCl-55% ZnCl_(2) salts at 450℃ in air for 40 h were investigated.Results show that the 921A alloy suffers more serious corrosion damage than the coating and KCl-55% ZnCl_(2) salts are more corrosive than KCl-10% ZnCl_(2) salts.In the two salts,an Fe_(2)O_(3) layer is formed on the 921A alloy surface,while an outer Fe-rich oxide layer and an inner Cr-rich oxide layer are formed on the surface of the coating.Moreover,a certain amount of metal chloride can be found at the oxide/alloy(coating)interface,which can be explained by "active oxidation".However,the corrosion resistance of the Fe-based amorphous coating did not achieve the desired results,probably because the intersplats in the coating serve as corrosion diffusing channels,which facilitate the corrosion damage rate.Nevertheless,the coating is still in amorphous state after hot corrosion exposure.
基金funded by the U.S.Department of Energy,National Energy Technology Laboratory(NETL)under the contract number DE-FE0031548。
文摘Hot corrosion has been extensively observed in various high temperature applications,which might cause large economic losses.To deepen the insight and understanding of hot corrosion,herein,we provide a detailed discussion on hot corrosion induced by molten sulfate salt,in which Na_(2)SO_(4)is the main chemical reactant.The hot corrosion is triggered and sustained by the negative solubility gradient of protective oxide from the oxide/salt interface to salt/gas interface.In this work,we reviewed several key factors,including temperature,gas composition,molten salt composition,alloy element and external stress,influencing the hot corrosion of alloy beneath the molten salt.The application of anti-corrosion coating seems to be the most effective and commercial mothed to mitigate hot corrosion.Therefore,the progress of the development of effective coatings,e.g.,Ni-Cr coatings,aluminide coatings,silicide coatings and MCrAlY(X)coatings,has also been summarized.
基金National Natural Science Foundation of China(50771009,50731001,51071013)National Basic Research Programof China(2010CB631200)
文摘LaTi2Al9O19 (LTA) exhibits promising potential as a new kind of thermal barrier coating (TBC) material, due to its excellent high-temperature capability and low thermal conductivity. In this paper, LTA/yttria stabilized zirconia (YSZ) TBCs are produced by atmospheric plasma spraying. Hot corrosion behavior and the related failure mechanism of the coating are investigated. Decomposition of LTA does not occur even after 1 458 hot corrosion cycles at 1 373 K, revealing good chemical stability in molten salt of Na=SO4 and NaCl. However, the molten salt infiltrates to the bond coat, causing dissolving of the thermally grown oxide (TGO) in the molten salt and hot corrosion of the bond coat. As a result, cracking of the TBC occurs within the oxide layer. In conclusion, the ceramic materials LTA and YSZ reveal good chemical stability in molten salts of Na2SO4 and NaCl, and the bond coat plays a significant role in providing protection for the component against hot corrosion in the LTA/YSZ TBCs. LTA exhibits very promising potential as a novel TBC material.
文摘In this investigation, impedance spectroscopy (IS) is used, as a non-destructive tool, to examine the hot corrosion behavior of thermal barrier coatings (TBCs) exposed to a mixture of 25wt% NaCl and 75wt% Na2SO4. The results show that the thermally grown oxide (TGO) formed along the top coat/bond coat interface is a mixed oxide layer, i.e. Cr2O3, (Ni, Co)(Cr, Al)2O4 spinel and NiO. The growth of TGO layer appears to follow the parabolic law. The resistance of TGO increases due to the increase of thickness when the number of cycles is less than 110. While for more than 110 cycles, the resistance of TGO decreases with the increase of porosity of TGO layer, even though the thickness of TGO layer increases. The nucleation and propagation of cracks within top coat increase the electrical resistance of top coat. The parameters in equivalent circuit could be used to characterize the degradation of TBCs.
基金financially supported by the National Natural Science Foundation of China (No. 51171150)the Program of the Ministry of Education of China for Introducing Talents of Discipline to Universities (No. B08040)
基金the National Natural Science Foundation of China(Nos.51901071,51871229 and 51701223)the Program for Innovative Research Team(in Science and Technology)in University of Henan Province(No.20IRTSTHN016)+3 种基金the High-Level Talents Introduction Project of Henan Institute of Science and Technology(No.203010618003)the Science and Technology Research Project of Henan Province(No.202102310288)the Landmark Innovation Project of Henan Institute of Science and Technologythe Young Key Teachers Projects in Henan Higher Education Institutions(No.2018GGJS113)。
文摘TiN and TiAlN coatings were deposited by arc ion plating on titanium alloys to study their hot corrosion resistance when they were exposed to NaCl at 600℃.The microstructure and corrosion behaviors of nitride coatings were studied using scanning electron microscope,X-ray diffraction,electro-probe microanalyzer and X-ray photoelectron spectroscopy.The results showed that nitride coatings with the different compositions and the ones with the same composition but different thicknesses presented different hot corrosion resistance.TiN and thin TiAlN coatings showed poor corrosion resistance.Serious internal oxidation attacked the alloy substrate.Their corrosion products were mainly consisted of non-protective TiO2 and sodium salt.By contrast,the thick TiAlN coating presented outstanding corrosion resistance.Besides sodium salt,the corrosion products were composed of protective Al_(2)O_(3).The increasing thickness of TiAlN significantly enhanced the hot corrosion resistance.The corrosion mechanisms of alloy,TiN and TiAlN coatings were discussed in detail.
文摘DZ68 alloy is a new Ni-base directionally solidified superalloy for the blade of advanced turbine engine with high ratio of thrust-mass.In order to investigate the influence of pre-oxidation on the hot corrosion resistance of DZ68 alloy,pre-oxidation treatment was conducted at 950℃ in air for 20 h.A mixture of 75% Na2SO4 +25% NaCl (in mass fraction) was used for hot corrosion study at 900℃.The microstructure of specimens was investigated by using a scanning electron microscope (SEM) equipped with an energy dispersive spectroscopy (EDS).The compositions of the corroded specimens were determined by X-ray diffraction (XRD).After preoxidation at 950℃ in air for 20 h,a protective scale consisting of Cr2O3,Al2O3,NiO,NiCr2O4,and Ni2Ti4O formed on the DZ68 superalloy surface.The pre-oxidation treatment improved the initial incubation stage of the alloy in the mixture of 75% Na2SO4 +25% NaCl melts at 900℃.The oxide layer degraded gradually with increasing the time of hot corrosion.Once the oxide layer was damaged,the corrosion rate would increase rapidly,accompanied by obvious spallation of the corrosion products.At 900℃,the pre-oxidation treatment could not inhibit the accelerated hot corrosion of DZ68 in the mixture of 75% Na2SO4 +25% NaCl melts,with a high corrosion rate.
基金financially supported by the National Basic Research Program of China(No.2015CB057400)the National Natural Science Foundation of China(No.51571010)
文摘The effects of a MCrAlY coating on low-cycle fatigue(LCF) behavior of directionally solidified(DS)nickle-based superalloy DZ125 were investigated. Before the fatigue testings, the specimens were pre-exposed in high-temperature hot corrosion(HTHC) environment generating by a burner rig at 850 ℃. The results show that the coating in hot corrosion condition has beneficial effects on the fatigue resistance of superalloy. Under corrosion condition, the MCrAlY-coated specimens tested have higher fatigue lives than the uncoated specimens at the same stress level. The coating failure results from fatigue process and numerous fatigue cracks were nucleated at the specimen surface, only one main crack propagates inward and the secondary cracks away from the fracture surface are perpendicular to the loading orientation.