The high melting point element W and the rare earth element Ce were added to 18Cr-Mo(444-type)ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas.A simulated exhaust gas was fi...The high melting point element W and the rare earth element Ce were added to 18Cr-Mo(444-type)ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas.A simulated exhaust gas was filled in the simultaneous thermal analyzer to simulate the service environment,and the oxidation behavior in high-temperature exhaust gas environment of 444-type ferritic stainless steel alloyed with W and Ce was investigated.The oxide structure and composition formed in this process were analyzed and characterized by scanning electron microscopy/energy-dispersive spectroscopy and electron probe analysis,and the mechanism of W and Ce in the oxidation process was revealed.The results show that 18Cr-Mo ferritic stainless steel containing W and Ce has better oxidation resistance in high-temperature exhaust gas.The element W can promote the precipitation of Laves phase at the matrix/interface,inhibit the interface diffusion of oxidizing elements and prevent the inward growth of the oxide film.The element Ce can suppress the volume of SiO_(2)at the oxide film/interface,reducing the breakaway oxidation caused by cracking of the oxide film.The CeO_(2)provides nucleation sites for oxide particles,promoting the healing of cracks and voids within the oxide film.展开更多
In this study,the oxidation behavior of Ti42Al5Mn,Ti42Al5Mn0.5 W,Ti42Al5Mn0.5W0.1B,and Ti42Al5Mn0.8 W was investigated at 800℃.Due to the inability to form a dense protective Al2O_(3) layer,Ti42Al5Mn suffered severe ...In this study,the oxidation behavior of Ti42Al5Mn,Ti42Al5Mn0.5 W,Ti42Al5Mn0.5W0.1B,and Ti42Al5Mn0.8 W was investigated at 800℃.Due to the inability to form a dense protective Al2O_(3) layer,Ti42Al5Mn suffered severe spallation during oxidation at 800℃and the mass gain was significant.The intermediate layer between the scale and the substrate was first composed of Laves/Z phase but changed toα2/Z phase with prolonged oxidation.The intermediate layer with high Ti/Al ratio favors the forma-tion of a thick Al2O_(3)+TiO_(2) mixed layer in the oxide scale which is prone to initiate cracks and cause the spalling of oxides.The doping of W in TiO_(2) effectively inhibited its generation and promoted the for-mation of a dense Al2O_(3) layer,resulting in a significant improvement in the oxidation resistance of the alloy.Compared to Ti42Al5Mn alloy,Ti42Al5Mn0.8 W showed no spallation after 300 h cyclic oxidation and the kinetic curve changed from liner law to parabolic law.The intermediate layer of Ti42Al5Mn0.8 W alloy was composed of a single Laves phase and remained unchanged even after 1000 h oxidation at 800℃,offering a favorable basis for the generation of a stable protective oxide layer in the alloy.The addi-tion of 0.1 at.%B to Ti42Al5Mn0.5 W alloy refined its microstructure and further improved its spallation resistance to a level close to that of Ti42Al5Mn0.8 W alloy.展开更多
In this paper,the isothermal oxidation experiments were used to study the effect of Ag on the high-temperature oxidation behavior of Mg-6.5Gd-5.6Y-0.1Nd-0.01Ce-0.4Zr(wt%)alloy oxidized at 350℃,400℃ and 450℃ for 120...In this paper,the isothermal oxidation experiments were used to study the effect of Ag on the high-temperature oxidation behavior of Mg-6.5Gd-5.6Y-0.1Nd-0.01Ce-0.4Zr(wt%)alloy oxidized at 350℃,400℃ and 450℃ for 120 h.The results show that the oxidation weight gain of the alloy mainly occurs in the early oxidation stage(0-20 h).This reason attributes to the lack of protective oxide film and the rapid inward diffusion of oxygen through the macroscopic defects of the incomplete oxide film.When dense oxide films such as Y_(2)O_(3),Gd_(2)O_(3),and ZrO2 form,they hinder the inward transport of oxygen ions and improve the high-temperature oxidation resistance of the alloy.In addition,the role of the Ag element at three temperatures is different.The addition of Ag mainly promotes the formation of eutectic phases such as Mg3Gd,Mg24Y5,and Ag2Gd,which reduces the content of Gd and Y elements in the alloy matrix,resulting in a decrease in the diffusion rate of Gd and Y elements during the oxidation process at 350℃ and 400℃,and weakens the oxidation resistance of Ag-containing alloys.However,in the oxidation experiment at 450℃,a large amount of eutectic phase is solid dissolved into the matrix,reducing the difference in element content.At this time,it is detected that the Ag element promoted the outward diffusion of Gd and Y elements,accelerating the formation of the oxide film.The oxidation resistance of Ag-containing alloys is improved.展开更多
Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °...Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant （kp） of Ni-11Fe-10Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10Cu at 750 °C was composed of a CuO outer layer, a NiFe2O4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction （XRD）, scanning electron mi-croscopy/energy dispersive spectroscopy （SEM/EDX） analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10Cu alloy was also discussed.展开更多
The oxidation behavior and mechanism of as-received and 30 % cold-rolled alumina-forming austenitic(AFA) steel were investigated in dry air at 700℃.The results show that the mass gain per unit area curves of as-recei...The oxidation behavior and mechanism of as-received and 30 % cold-rolled alumina-forming austenitic(AFA) steel were investigated in dry air at 700℃.The results show that the mass gain per unit area curves of as-received and 30 % cold-rolled steels subject to near-parabolic law before 100 h oxidation time.Two samples both show higher high-temperature oxidation resistance due to the formation of dense Al_(2)O_(3) oxide scale.Gradual spallation of outer scale results in the formation of continuous and dense alumina scale.Dislocations can act as short-circuit diffusion channel for the diffusion of Al from alloy matrix to surface,and also provide nucleation sites for B2-NiAl phase,which ensure the continuous formation of Al_(2)O_(3) scale.展开更多
A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-AI alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure ...A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-AI alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.展开更多
An environmental barrier coating(EBC) consisting of a silicon bond coat and an Yb2-SiO5 top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite(CMC) by atmospheric plasma spray(APS). The micros...An environmental barrier coating(EBC) consisting of a silicon bond coat and an Yb2-SiO5 top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite(CMC) by atmospheric plasma spray(APS). The microstructure of the coating annealed at 1300 ℃ and its high-temperature oxidation behavior at 1350 ℃ were investigated. The significant mass loss of silica during the plasma spray process led to the formation of Yb2SiO5 and Yb2O3 binary phases in the top-coat. Eutectics of Yb2SiO5 and Yb2O3 were precipitated in the top-coat, and channel cracks were formed in the top-coat after 20 h annealing because of the mismatch between the coefficients of thermal expansion(CTEs) of Yb2SiO5 and the SiC substrate. The EBC effectively improved the oxidation resistance of the CMC substrate. The channel cracks in the Yb2SiO5 top-coat provided inward diffusion channels for oxygen and led to the formation of oxidation delamination cracks in the bond coat, finally resulting in spallation failure of the coating after 80 h oxidation.展开更多
In this paper, a Fe-Mn-Al-C austenitic steel with certain addition of Cr and N alloy was used as experimental material. By using the SETSYS Evolution synchronous differential thermal analysis apparatus, the scanning e...In this paper, a Fe-Mn-Al-C austenitic steel with certain addition of Cr and N alloy was used as experimental material. By using the SETSYS Evolution synchronous differential thermal analysis apparatus, the scanning electron microscope （SEM）, the electron microprobe （EPMA） and the X-ray diffraction （XRD）, the high-temperature oxidation behavior microstructure and the phase compositions of this steel in air at 600-1,000 ℃ for 8 h have been studied. The results show that in the whole oxidation temperature range, there are three distinct stages in the mass gain curves at temperature higher than 800 ℃ and the oxidation process can be divided into two stages at temperature lower than 800 ℃. At the earlier stage the gain rate of the weight oxidized in temperature range of 850 ℃ to 1,000 ℃ are extremely lower. The oxidation products having different surface microstructures and phase compositions were produced in oxidation reaction at different temperatures. The phase compositions of oxide scale formed at 1,000 ℃ are composed of Fe and Mn oxide without Cr. However, protective film of Cr oxide with complicated structure can be formed when the oxidation temperature is lower than 800 ℃.展开更多
In this study,the CeO_(2)-modified WC-12 Co coatings were deposited on Q345 steel substrate using high-velocity oxygen fuel(HVOF) spraying.Oxidation behavior of the modified coatings was analyzed in the range of 450-...In this study,the CeO_(2)-modified WC-12 Co coatings were deposited on Q345 steel substrate using high-velocity oxygen fuel(HVOF) spraying.Oxidation behavior of the modified coatings was analyzed in the range of 450-900℃ for different oxidation time to investigate the effects of oxidation time and temperature on the coatings.The oxidation kinetics and oxidation mechanism of the modified coatings were clarified.The results show that the oxides are mainly composed of WO_(3) and CoWO_(4) within 450-750℃ while the phases are different at 900 ℃.The CeO_(2)-modified coatings have good oxidation resistance when the oxidation temperature is below550℃ and the oxidation mechanism changes due to the occurrence of anomalous oxidation above 650℃.Moreover,the oxidation mass gain curves obey approximately a parabolic law in the temperature range of 450-650℃ at the initial stage but the later oxidation proceeds by a linear law.In addition,based on the analysis of micromorphology and component of the prepared coating,the role of rare earth(RE) additives is obtained during high-temperature oxidization.展开更多
The key in antioxidant capacity of aero-engine hot components is the protective oxide scales.Many factors can affect the performance of oxide scales.The effect of tensile stress on high-temperature oxidation behavior ...The key in antioxidant capacity of aero-engine hot components is the protective oxide scales.Many factors can affect the performance of oxide scales.The effect of tensile stress on high-temperature oxidation behavior of directionally solidified DZ125 Ni-based superalloy was investigated by thermogravimetric analysis(TGA).Tensile samples were subjected to stress of 100 MPa,and the oxidation behavior was studied at 980℃in air.The surface and cross-sectional morphologies of the oxidized coating were analyzed by scanning electron microscope(SEM).The influence of tensile stress on the oxidation behavior of directionally solidified DZ125 Ni-based superalloy at high temperature was discussed.Results show that an applied tensile stress generally leads to larger Cr/Ni mass ratio in the oxide scales,greater overall chromium depletion values directly under the oxide scales,lower specific weight gain values and thinner oxide scales.These factors are attributed to the formation of fast diffusion paths for Cr atoms to diffuse to the surface under tensile stress,thus causing a reduction in the duration of the less protective transient oxidation period and promoting a faster formation of the protective Cr_(2)O_(3)layer.展开更多
To improve the oxidation properties of ferritic heat-resistant steels,an Al-bearing 9Cr‒5Si‒3Al ferritic heat-resistant steel was designed.We then conducted cyclic oxidation tests to investigate the high-temperature o...To improve the oxidation properties of ferritic heat-resistant steels,an Al-bearing 9Cr‒5Si‒3Al ferritic heat-resistant steel was designed.We then conducted cyclic oxidation tests to investigate the high-temperature oxidation behavior of 9Cr‒5Si and 9Cr‒5Si‒3Al ferritic heat-resistant steels at 900 and 1000℃.The characteristics of the oxide layer were analyzed by X-ray diffraction,scanning electron microscopy,and energy dispersive spectroscopy.The results show that the oxidation kinetics curves of the two tested steels follow the parabolic law,with the parabolic rate constant kp of 9Cr‒5Si‒3Al steel being much lower than that of 9Cr‒5Si steel at both 900 and 1000℃.The oxide film on the surface of the 9Cr‒5Si alloy exhibits Cr2MnO4 and Cr2O3 phases in the outer layer after oxidation at 900 and 1000℃.However,at oxidation temperatures of 900 and 1000℃,the oxide film of the 9Cr‒5Si‒3Al alloy consists only of Al2O3 and its oxide layer is thinner than that of the 9Cr‒5Si alloy.These results indicate that the addition of Al to the 9Cr‒5Si steel can improve its high-temperature oxidation resistance,which can be attributed to the formation of a continuous and compact Al2O3 film on the surface of the steel.展开更多
The oxidation behavior of the Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy at 900℃ was investigated at different oxidation times(5,20,60 and 100 h).The results show that the total weight gain of the alloy after 100 h at 900℃ ox...The oxidation behavior of the Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy at 900℃ was investigated at different oxidation times(5,20,60 and 100 h).The results show that the total weight gain of the alloy after 100 h at 900℃ oxidation is 9.1 g·m^(-2),and the oxidation rate decreases with oxidation time.The oxides on the alloy surface are mainly TiO_(2) and Al_(2)O_(3).At the beginning of oxidation(5 h),the oxide film is relatively complete,thin,and the interface between the oxide layer and the matrix is virtually flat.At the end of oxidation(100 h),the thickness of the oxide film is expanded,cracking and spalling occur,and the spalling form is intra-film spalling.At the same time,oxygen is mainly distributed in the oxide film and the oxygen content in the alloy substrate is reduced,confirming that the TiAl alloy has a certain oxidation stability at 900℃.From the outer surface of the oxide layer to the matrix,the TiO_(2) content increases and the Al_(2)O_(3) content decreases.Oxidation proceeds to completion in this system via the dissolution and diffusion of O atom.展开更多
High-temperature oxidation behavior of directionally solidified(DS) Nb-Si-based alloys with Re additions was investigated at 1200 and 1250℃,respectively.Microstructures and high-temperature oxidation behavior of the ...High-temperature oxidation behavior of directionally solidified(DS) Nb-Si-based alloys with Re additions was investigated at 1200 and 1250℃,respectively.Microstructures and high-temperature oxidation behavior of the alloys were characterized.Results show that the microstructures in vertical section of Nb-24Ti-15Si-4Cr-2Al-2Hf-xRe(x=0,1,3;at%) alloys grow parallel to the withdrawal direction and the cross section exhibits bud-like structures.The bud-like structures become finer with more Re additions.The weight gain of the Nb-24Ti-15Si-4Cr-2Al-2Hf-3Re alloy after oxidation at 1200℃ for 100 h is 198.1 mg·cm^(-2),and it is a bit higher at 1250℃.The other two alloys perform somewhat worse.The influence of Re addition on the oxidation resistance at 1250℃ is more significant than that at 1200 ℃.Although Re addition does not benefit obviously the high-temperature oxidation resistance of the DS samples,it does not compromise the oxidation resistance with a certain amount of Re additions in contrast with the alloy without Re addition.展开更多
The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed t...The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed the parabolic line law, and after 250 h of oxidation, the mass gain was about 80 g/m2. The surface morphology and structure of the oxide layers were studied by scanning electron microscopy and X-ray diffraction. A complicated oxide layer obtained at 1 050 ℃ was mainly composed, from inner to outer, of （FeSi） 3 04, Cr2 03, Fe2 03, and spinel oxides FeCr204 and NiMn204.展开更多
Ni-W-P matrix composites containing CeO2 and SiO2 nano-particles were prepared on common carbon steel surface by means of pulse electrodeposition,and the high-temperature oxidation behavior was investigated.The result...Ni-W-P matrix composites containing CeO2 and SiO2 nano-particles were prepared on common carbon steel surface by means of pulse electrodeposition,and the high-temperature oxidation behavior was investigated.The results show that when the oxidation time is controlled in 1 h,oxidation kinetics curve between oxidation mass gain rate and oxidation temperature of CeO2-SiO2/Ni-W-P composites accords with the index increasing law.When the oxidation temperature is controlled at 300℃,the kinetics curve between oxidation mass gain rate and oxidation time accords with the linear increasing law.The composites as-deposited are in the amorphous state and turn into the crystal state at 400℃.The microstructures of oxidation film on the composites will change from the compact state to the loose state with increasing oxidation temperature to 800℃.They are still continuous and compact,and there are no crackle,strip and falling-out.CeO2 and SiO2 nano-particles co-deposited into Ni-W-P alloy can improve the high-temperature oxidation resistance.展开更多
The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component....The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component.In this study,the oxidation experiment of RuT400 vermicular graphite iron was performed at 500 ℃,and the oxidation time was chosen as 100 h,200 h,300 h,400 h,and 500 h,respectively.Meanwhile,the corresponding microstructure evolution,oxidation kinetics,and oxidation mechanism were discussed.It is found that oxidation pores and oxide layer often appear at the vermicular graphite on the specimen surface;the vermicular graphite plays the role of oxidation channel,and it tends to diff use along the adjacent pearlite and then connect with each other to form oxidation bridges as the oxidation time prolongs.A linear relationship between oxidation weight gain and the thickness of the oxide layer was established and verifi ed well.These results will give a more comprehensive understanding on the oxidation mechanism of vermicular graphite iron and provide certain guidance for design and preparation of anti-oxidation cast irons.展开更多
Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature...Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature oxidation kinetic curve of Cr20 Ni12 Si2 RE at 1 050 ℃ was obtained using the weighting method. The oxidation curves exhibit the parabolic law at 1 050 ℃; after 250 h of oxidation,the mass gain was 22 g/m^2. The morphology,structure,and composition of the oxide film were examined using scanning electron microscopy and Xray diffraction methods. A thin,stable,and dense spinel oxide film obtained after 250 h of oxidation at 1 050 ℃ was mainly composed of( Mn_(0.87)Fe_(0.13))( Mn_(0.13)Fe_(0.87)Cr) O_4 and Cr_2 O_3 with a silicon-containing oxide underneath. The addition of rare earth elements was found to restrict further diffusion of metallic atoms from the austenite toward the oxide film,and consequently,led to a low growth rate of the oxide film. The inner silicon-containing oxide was produced by the diffusion of oxygen atoms and enhanced the coherent strength of the oxide film.展开更多
Ni-based single crystal superalloy IC21 with different Ce con tents was prepared by screw selection method,and Al-Si coatings were prepared by pack cementation.Cyclic oxidation and transient oxidation were carried out...Ni-based single crystal superalloy IC21 with different Ce con tents was prepared by screw selection method,and Al-Si coatings were prepared by pack cementation.Cyclic oxidation and transient oxidation were carried out at 1150℃ to investigate the effect of Ce on the high-temperature oxidation behavior of Al-Si coatings.After cyclic oxidation at 1150℃,the addition of trace Ce decreased the mass gain of the Al-Si-coated samples and effectively improved oxidation perform a nee and spallation resistance.In specimens without Ce doping,microstructure examinatio n revealed that bulkyγ-Ni3Al precipitated in oxidized coating because of high Al con sumption,and this finding suggests that Ce inhibits the consumption of Al in the coating during oxidation.Ce slows down the Ininsformation of O-Al2O3 to oc-Al2O3 and improves the adhesion of the oxide scale.展开更多
Not only the isothermal oxidation behaviors at 900-1 300℃for 20 h in air of bulk Ti3AlC2 with 2.8% TiC which was sintered by hot pressing with the additive of silicon, but also the cyclic oxidation behavior at 1 100-...Not only the isothermal oxidation behaviors at 900-1 300℃for 20 h in air of bulk Ti3AlC2 with 2.8% TiC which was sintered by hot pressing with the additive of silicon, but also the cyclic oxidation behavior at 1 100-1 300℃for 30 cycles, were investigated by using TG, XRD, SEM. The isothermal and cyclic oxidation behaviors generally follow a parabolic rate law. The parabolic rate constants of the former increased from 1.39×10-10 kg2/(m4·s) at 900℃to 5.56×10-9 kg2/(m4·s) at 1 300℃. The calculated activation energy is 136.45 kJ/mol. The oxidation products areα-Al2O3 and little TiO2 at 900-1 000℃, however when the temperature is raised up to 1 200℃, TiO2 partially reacts to Al2TiO5, and the reaction is completed at 1 300℃. This demonstrates that Ti3AlC2 has excellent oxidation resistance and good thermal shock because the dense continuous oxide scale consists of massα- Al2O3 and little TiO2 and/or Al2TiO5. Generally, the oxide scale is grown by the inward diffusion of O2- and the outward diffusion of Ti4+ and Al3+.展开更多
Accident-tolerant fuels(ATF)have been extensively studied to reduce the production rate and total amount of heat and hydrogen generated from high-temperature steam oxidation during severe accidents.Chromium-coated zir...Accident-tolerant fuels(ATF)have been extensively studied to reduce the production rate and total amount of heat and hydrogen generated from high-temperature steam oxidation during severe accidents.Chromium-coated zirconium alloy cladding has become one of the most promising candidates for ATF because of its excellent corrosion and oxidation resistance.This paper provides a comprehensive overview of the research progress on oxidation behaviors and degradation mechanisms in chromium-coated zirconium alloy cladding under high-temperature conditions.Potential techniques to strengthen the oxidation resistance are highlighted and compared.Finally,challenges and opportunities for various future directions are addressed.展开更多
基金the joint financial support from the National Natural Science Foundation of China and Baowu Group Co.,Ltd.(Grant No.U1660205)the Fundamental Research Funds for the Central Universities(Grant No.N2007001).
文摘The high melting point element W and the rare earth element Ce were added to 18Cr-Mo(444-type)ferritic stainless steel to improve its high-temperature oxidation resistance in exhaust gas.A simulated exhaust gas was filled in the simultaneous thermal analyzer to simulate the service environment,and the oxidation behavior in high-temperature exhaust gas environment of 444-type ferritic stainless steel alloyed with W and Ce was investigated.The oxide structure and composition formed in this process were analyzed and characterized by scanning electron microscopy/energy-dispersive spectroscopy and electron probe analysis,and the mechanism of W and Ce in the oxidation process was revealed.The results show that 18Cr-Mo ferritic stainless steel containing W and Ce has better oxidation resistance in high-temperature exhaust gas.The element W can promote the precipitation of Laves phase at the matrix/interface,inhibit the interface diffusion of oxidizing elements and prevent the inward growth of the oxide film.The element Ce can suppress the volume of SiO_(2)at the oxide film/interface,reducing the breakaway oxidation caused by cracking of the oxide film.The CeO_(2)provides nucleation sites for oxide particles,promoting the healing of cracks and voids within the oxide film.
基金National Natural Science Foundation of China(Grant No.51971215).
文摘In this study,the oxidation behavior of Ti42Al5Mn,Ti42Al5Mn0.5 W,Ti42Al5Mn0.5W0.1B,and Ti42Al5Mn0.8 W was investigated at 800℃.Due to the inability to form a dense protective Al2O_(3) layer,Ti42Al5Mn suffered severe spallation during oxidation at 800℃and the mass gain was significant.The intermediate layer between the scale and the substrate was first composed of Laves/Z phase but changed toα2/Z phase with prolonged oxidation.The intermediate layer with high Ti/Al ratio favors the forma-tion of a thick Al2O_(3)+TiO_(2) mixed layer in the oxide scale which is prone to initiate cracks and cause the spalling of oxides.The doping of W in TiO_(2) effectively inhibited its generation and promoted the for-mation of a dense Al2O_(3) layer,resulting in a significant improvement in the oxidation resistance of the alloy.Compared to Ti42Al5Mn alloy,Ti42Al5Mn0.8 W showed no spallation after 300 h cyclic oxidation and the kinetic curve changed from liner law to parabolic law.The intermediate layer of Ti42Al5Mn0.8 W alloy was composed of a single Laves phase and remained unchanged even after 1000 h oxidation at 800℃,offering a favorable basis for the generation of a stable protective oxide layer in the alloy.The addi-tion of 0.1 at.%B to Ti42Al5Mn0.5 W alloy refined its microstructure and further improved its spallation resistance to a level close to that of Ti42Al5Mn0.8 W alloy.
基金supported by the National Key Research and Development Program of China(No.2021YFB3701100)the National Key Research and Development Program of China(No.2016YFB0301105)+2 种基金the Applied Basic Research Program Project of Liaoning Province of China(No.2023020253-JH2/1016)the Key Research and Development Plan of Shanxi Province(No.202102050201005)the Dongguan Innovative Research Team Program(No.2020607134012).
文摘In this paper,the isothermal oxidation experiments were used to study the effect of Ag on the high-temperature oxidation behavior of Mg-6.5Gd-5.6Y-0.1Nd-0.01Ce-0.4Zr(wt%)alloy oxidized at 350℃,400℃ and 450℃ for 120 h.The results show that the oxidation weight gain of the alloy mainly occurs in the early oxidation stage(0-20 h).This reason attributes to the lack of protective oxide film and the rapid inward diffusion of oxygen through the macroscopic defects of the incomplete oxide film.When dense oxide films such as Y_(2)O_(3),Gd_(2)O_(3),and ZrO2 form,they hinder the inward transport of oxygen ions and improve the high-temperature oxidation resistance of the alloy.In addition,the role of the Ag element at three temperatures is different.The addition of Ag mainly promotes the formation of eutectic phases such as Mg3Gd,Mg24Y5,and Ag2Gd,which reduces the content of Gd and Y elements in the alloy matrix,resulting in a decrease in the diffusion rate of Gd and Y elements during the oxidation process at 350℃ and 400℃,and weakens the oxidation resistance of Ag-containing alloys.However,in the oxidation experiment at 450℃,a large amount of eutectic phase is solid dissolved into the matrix,reducing the difference in element content.At this time,it is detected that the Ag element promoted the outward diffusion of Gd and Y elements,accelerating the formation of the oxide film.The oxidation resistance of Ag-containing alloys is improved.
基金supported by the National Natural Science Foundation of China(51325102)the International Science and Technology Cooperation Program of Ministry of Science and Technology(2015DFA90750)
文摘Aiming to develop materials for construction of the set-up and electrode of high-temperature molten salt reactors, the effect of Al and Y on the high-temperature oxidation behavior of Ni-11Fe-10Cu at 750 and 950 °C in air were investigated. The oxidation kinetics of Ni-11Fe-10Cu alloy followed parabolic law at 750 °C without spallation and linear law at 950 °C with severe spallation, while that of Ni-11Fe-10Cu-6Al-3Y alloy followed parabolic law at 750 and 950 °C without spallation. The parabolic rate constant （kp） of Ni-11Fe-10Cu was smaller than that of Ni-11Fe-10Cu-6Al-3Y at 750 °C. The oxide scale formed on Ni-11Fe-10Cu at 750 °C was composed of a CuO outer layer, a NiFe2O4 middle layer and a NiO inner layer. The oxide scale formed on Ni-11Fe-10Cu-6Al-3Y at 750 °C was also composed of the similar triplex layers in addition to an internal oxidation zone containing Al, Ni and Cu oxide and the microstructure of the scale changed with increasing temperature. Although the doping Al and Y could improve the adherence of oxide scale, it could aggravate the extent of internal oxidation. Based on the combination of X-ray diffraction （XRD）, scanning electron mi-croscopy/energy dispersive spectroscopy （SEM/EDX） analysis, the microstructure and growth mechanism of the multi-layer oxide scale was studied and the effect of doping Al and Y on the oxidation behavior of Ni-11Fe-10Cu alloy was also discussed.
基金financially supported by the National Natural Science Foundation of China and Shanghai Baosteel Group Company(No. U1960204)the National Natural Science Foundation of China(Nos. 51871042 and 51501034)the Fundamental Research Funds for the Central Universities (No. N2023026)。
文摘The oxidation behavior and mechanism of as-received and 30 % cold-rolled alumina-forming austenitic(AFA) steel were investigated in dry air at 700℃.The results show that the mass gain per unit area curves of as-received and 30 % cold-rolled steels subject to near-parabolic law before 100 h oxidation time.Two samples both show higher high-temperature oxidation resistance due to the formation of dense Al_(2)O_(3) oxide scale.Gradual spallation of outer scale results in the formation of continuous and dense alumina scale.Dislocations can act as short-circuit diffusion channel for the diffusion of Al from alloy matrix to surface,and also provide nucleation sites for B2-NiAl phase,which ensure the continuous formation of Al_(2)O_(3) scale.
文摘A study was conducted to examine the isothermal oxidation behavior of a new Ni-Cr-W-AI alloy in air at 1250℃ with different time. Oxidation kinetics was determined from weight-change measurements. The microstructure and composition of the oxide scale were investigated by means of scanning electron microcopy and X-ray diffraction. The results showed that the oxide scales of the alloy were a compact and continuous outer Cr2O3 and NiCr2O4 layer and an inner Al2O3 layer that was in dendrite shape. Oxides scales with good adherence were formed on the surface of the alloy, which made the alloy perform excellent high-temperature oxidation resistance.
基金sponsored by the National Natural Science Foundation of China (NSFC) under grant Nos. 51590894, 51425102, and 51231001
文摘An environmental barrier coating(EBC) consisting of a silicon bond coat and an Yb2-SiO5 top-coat was sprayed on a carbon fibers reinforced SiC ceramic matrix composite(CMC) by atmospheric plasma spray(APS). The microstructure of the coating annealed at 1300 ℃ and its high-temperature oxidation behavior at 1350 ℃ were investigated. The significant mass loss of silica during the plasma spray process led to the formation of Yb2SiO5 and Yb2O3 binary phases in the top-coat. Eutectics of Yb2SiO5 and Yb2O3 were precipitated in the top-coat, and channel cracks were formed in the top-coat after 20 h annealing because of the mismatch between the coefficients of thermal expansion(CTEs) of Yb2SiO5 and the SiC substrate. The EBC effectively improved the oxidation resistance of the CMC substrate. The channel cracks in the Yb2SiO5 top-coat provided inward diffusion channels for oxygen and led to the formation of oxidation delamination cracks in the bond coat, finally resulting in spallation failure of the coating after 80 h oxidation.
基金supported by the National High Technology Research and Development Program of China (No. 2012AA03A508)the National Natural Science Foundation of China (No. 51271051)
文摘In this paper, a Fe-Mn-Al-C austenitic steel with certain addition of Cr and N alloy was used as experimental material. By using the SETSYS Evolution synchronous differential thermal analysis apparatus, the scanning electron microscope （SEM）, the electron microprobe （EPMA） and the X-ray diffraction （XRD）, the high-temperature oxidation behavior microstructure and the phase compositions of this steel in air at 600-1,000 ℃ for 8 h have been studied. The results show that in the whole oxidation temperature range, there are three distinct stages in the mass gain curves at temperature higher than 800 ℃ and the oxidation process can be divided into two stages at temperature lower than 800 ℃. At the earlier stage the gain rate of the weight oxidized in temperature range of 850 ℃ to 1,000 ℃ are extremely lower. The oxidation products having different surface microstructures and phase compositions were produced in oxidation reaction at different temperatures. The phase compositions of oxide scale formed at 1,000 ℃ are composed of Fe and Mn oxide without Cr. However, protective film of Cr oxide with complicated structure can be formed when the oxidation temperature is lower than 800 ℃.
基金financially supported by the National Natural Science Foundation of China (No.51505393)。
文摘In this study,the CeO_(2)-modified WC-12 Co coatings were deposited on Q345 steel substrate using high-velocity oxygen fuel(HVOF) spraying.Oxidation behavior of the modified coatings was analyzed in the range of 450-900℃ for different oxidation time to investigate the effects of oxidation time and temperature on the coatings.The oxidation kinetics and oxidation mechanism of the modified coatings were clarified.The results show that the oxides are mainly composed of WO_(3) and CoWO_(4) within 450-750℃ while the phases are different at 900 ℃.The CeO_(2)-modified coatings have good oxidation resistance when the oxidation temperature is below550℃ and the oxidation mechanism changes due to the occurrence of anomalous oxidation above 650℃.Moreover,the oxidation mass gain curves obey approximately a parabolic law in the temperature range of 450-650℃ at the initial stage but the later oxidation proceeds by a linear law.In addition,based on the analysis of micromorphology and component of the prepared coating,the role of rare earth(RE) additives is obtained during high-temperature oxidization.
基金financially supported by the National Natural Science Foundation of China (No.51571010)the National Basic Research Program of China (No.2015CB057400)
文摘The key in antioxidant capacity of aero-engine hot components is the protective oxide scales.Many factors can affect the performance of oxide scales.The effect of tensile stress on high-temperature oxidation behavior of directionally solidified DZ125 Ni-based superalloy was investigated by thermogravimetric analysis(TGA).Tensile samples were subjected to stress of 100 MPa,and the oxidation behavior was studied at 980℃in air.The surface and cross-sectional morphologies of the oxidized coating were analyzed by scanning electron microscope(SEM).The influence of tensile stress on the oxidation behavior of directionally solidified DZ125 Ni-based superalloy at high temperature was discussed.Results show that an applied tensile stress generally leads to larger Cr/Ni mass ratio in the oxide scales,greater overall chromium depletion values directly under the oxide scales,lower specific weight gain values and thinner oxide scales.These factors are attributed to the formation of fast diffusion paths for Cr atoms to diffuse to the surface under tensile stress,thus causing a reduction in the duration of the less protective transient oxidation period and promoting a faster formation of the protective Cr_(2)O_(3)layer.
基金This work was financially supported by the Science&Technology Department of Sichuan Province,China(No.2017KJT0110).
文摘To improve the oxidation properties of ferritic heat-resistant steels,an Al-bearing 9Cr‒5Si‒3Al ferritic heat-resistant steel was designed.We then conducted cyclic oxidation tests to investigate the high-temperature oxidation behavior of 9Cr‒5Si and 9Cr‒5Si‒3Al ferritic heat-resistant steels at 900 and 1000℃.The characteristics of the oxide layer were analyzed by X-ray diffraction,scanning electron microscopy,and energy dispersive spectroscopy.The results show that the oxidation kinetics curves of the two tested steels follow the parabolic law,with the parabolic rate constant kp of 9Cr‒5Si‒3Al steel being much lower than that of 9Cr‒5Si steel at both 900 and 1000℃.The oxide film on the surface of the 9Cr‒5Si alloy exhibits Cr2MnO4 and Cr2O3 phases in the outer layer after oxidation at 900 and 1000℃.However,at oxidation temperatures of 900 and 1000℃,the oxide film of the 9Cr‒5Si‒3Al alloy consists only of Al2O3 and its oxide layer is thinner than that of the 9Cr‒5Si alloy.These results indicate that the addition of Al to the 9Cr‒5Si steel can improve its high-temperature oxidation resistance,which can be attributed to the formation of a continuous and compact Al2O3 film on the surface of the steel.
基金financially supported by the National Natural Science Foundation of China (51805335)
文摘The oxidation behavior of the Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy at 900℃ was investigated at different oxidation times(5,20,60 and 100 h).The results show that the total weight gain of the alloy after 100 h at 900℃ oxidation is 9.1 g·m^(-2),and the oxidation rate decreases with oxidation time.The oxides on the alloy surface are mainly TiO_(2) and Al_(2)O_(3).At the beginning of oxidation(5 h),the oxide film is relatively complete,thin,and the interface between the oxide layer and the matrix is virtually flat.At the end of oxidation(100 h),the thickness of the oxide film is expanded,cracking and spalling occur,and the spalling form is intra-film spalling.At the same time,oxygen is mainly distributed in the oxide film and the oxygen content in the alloy substrate is reduced,confirming that the TiAl alloy has a certain oxidation stability at 900℃.From the outer surface of the oxide layer to the matrix,the TiO_(2) content increases and the Al_(2)O_(3) content decreases.Oxidation proceeds to completion in this system via the dissolution and diffusion of O atom.
基金financially supported by the National Nature Science Foundation of China (No.51471013)。
文摘High-temperature oxidation behavior of directionally solidified(DS) Nb-Si-based alloys with Re additions was investigated at 1200 and 1250℃,respectively.Microstructures and high-temperature oxidation behavior of the alloys were characterized.Results show that the microstructures in vertical section of Nb-24Ti-15Si-4Cr-2Al-2Hf-xRe(x=0,1,3;at%) alloys grow parallel to the withdrawal direction and the cross section exhibits bud-like structures.The bud-like structures become finer with more Re additions.The weight gain of the Nb-24Ti-15Si-4Cr-2Al-2Hf-3Re alloy after oxidation at 1200℃ for 100 h is 198.1 mg·cm^(-2),and it is a bit higher at 1250℃.The other two alloys perform somewhat worse.The influence of Re addition on the oxidation resistance at 1250℃ is more significant than that at 1200 ℃.Although Re addition does not benefit obviously the high-temperature oxidation resistance of the DS samples,it does not compromise the oxidation resistance with a certain amount of Re additions in contrast with the alloy without Re addition.
文摘The kinetic curves of the high-temperature oxidation of austenitic heat resistant stainless steel 1. 4828 at 1 050 ℃ were measured using a weighing method. It is shown that the oxidation curves at 1 050 ℃ followed the parabolic line law, and after 250 h of oxidation, the mass gain was about 80 g/m2. The surface morphology and structure of the oxide layers were studied by scanning electron microscopy and X-ray diffraction. A complicated oxide layer obtained at 1 050 ℃ was mainly composed, from inner to outer, of （FeSi） 3 04, Cr2 03, Fe2 03, and spinel oxides FeCr204 and NiMn204.
基金Project(20806035)supported by the National Natural Science Foundation of ChinaProject(2007E187M)supported by the Applied Basic Research Plans Program of Yunnan Province,China+2 种基金Project supported by the Foundation for Leaders of Disciplines in Science and Technology of Yunnan Province,ChinaProject(08C0025)supported by the Scientific Research Fund of Yunnan Provincial Education Department,ChinaProject supported by the Training Foundation for Talents of Kunming University of Science and Technology,China
文摘Ni-W-P matrix composites containing CeO2 and SiO2 nano-particles were prepared on common carbon steel surface by means of pulse electrodeposition,and the high-temperature oxidation behavior was investigated.The results show that when the oxidation time is controlled in 1 h,oxidation kinetics curve between oxidation mass gain rate and oxidation temperature of CeO2-SiO2/Ni-W-P composites accords with the index increasing law.When the oxidation temperature is controlled at 300℃,the kinetics curve between oxidation mass gain rate and oxidation time accords with the linear increasing law.The composites as-deposited are in the amorphous state and turn into the crystal state at 400℃.The microstructures of oxidation film on the composites will change from the compact state to the loose state with increasing oxidation temperature to 800℃.They are still continuous and compact,and there are no crackle,strip and falling-out.CeO2 and SiO2 nano-particles co-deposited into Ni-W-P alloy can improve the high-temperature oxidation resistance.
基金the National Natural Science Foundation of China (NSFC) under Grant.No.51871224the Natural Science Foundation of Liaoning Province under Grant.No.20180550880。
文摘The vermicular graphite iron is an important material with excellent combination properties for cylinder heads of diesel engines,and the high-temperature oxidation is a crucial problem during service of the component.In this study,the oxidation experiment of RuT400 vermicular graphite iron was performed at 500 ℃,and the oxidation time was chosen as 100 h,200 h,300 h,400 h,and 500 h,respectively.Meanwhile,the corresponding microstructure evolution,oxidation kinetics,and oxidation mechanism were discussed.It is found that oxidation pores and oxide layer often appear at the vermicular graphite on the specimen surface;the vermicular graphite plays the role of oxidation channel,and it tends to diff use along the adjacent pearlite and then connect with each other to form oxidation bridges as the oxidation time prolongs.A linear relationship between oxidation weight gain and the thickness of the oxide layer was established and verifi ed well.These results will give a more comprehensive understanding on the oxidation mechanism of vermicular graphite iron and provide certain guidance for design and preparation of anti-oxidation cast irons.
文摘Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature oxidation kinetic curve of Cr20 Ni12 Si2 RE at 1 050 ℃ was obtained using the weighting method. The oxidation curves exhibit the parabolic law at 1 050 ℃; after 250 h of oxidation,the mass gain was 22 g/m^2. The morphology,structure,and composition of the oxide film were examined using scanning electron microscopy and Xray diffraction methods. A thin,stable,and dense spinel oxide film obtained after 250 h of oxidation at 1 050 ℃ was mainly composed of( Mn_(0.87)Fe_(0.13))( Mn_(0.13)Fe_(0.87)Cr) O_4 and Cr_2 O_3 with a silicon-containing oxide underneath. The addition of rare earth elements was found to restrict further diffusion of metallic atoms from the austenite toward the oxide film,and consequently,led to a low growth rate of the oxide film. The inner silicon-containing oxide was produced by the diffusion of oxygen atoms and enhanced the coherent strength of the oxide film.
基金the National Natural Science Foundation of China(No.51371004).
文摘Ni-based single crystal superalloy IC21 with different Ce con tents was prepared by screw selection method,and Al-Si coatings were prepared by pack cementation.Cyclic oxidation and transient oxidation were carried out at 1150℃ to investigate the effect of Ce on the high-temperature oxidation behavior of Al-Si coatings.After cyclic oxidation at 1150℃,the addition of trace Ce decreased the mass gain of the Al-Si-coated samples and effectively improved oxidation perform a nee and spallation resistance.In specimens without Ce doping,microstructure examinatio n revealed that bulkyγ-Ni3Al precipitated in oxidized coating because of high Al con sumption,and this finding suggests that Ce inhibits the consumption of Al in the coating during oxidation.Ce slows down the Ininsformation of O-Al2O3 to oc-Al2O3 and improves the adhesion of the oxide scale.
文摘Not only the isothermal oxidation behaviors at 900-1 300℃for 20 h in air of bulk Ti3AlC2 with 2.8% TiC which was sintered by hot pressing with the additive of silicon, but also the cyclic oxidation behavior at 1 100-1 300℃for 30 cycles, were investigated by using TG, XRD, SEM. The isothermal and cyclic oxidation behaviors generally follow a parabolic rate law. The parabolic rate constants of the former increased from 1.39×10-10 kg2/(m4·s) at 900℃to 5.56×10-9 kg2/(m4·s) at 1 300℃. The calculated activation energy is 136.45 kJ/mol. The oxidation products areα-Al2O3 and little TiO2 at 900-1 000℃, however when the temperature is raised up to 1 200℃, TiO2 partially reacts to Al2TiO5, and the reaction is completed at 1 300℃. This demonstrates that Ti3AlC2 has excellent oxidation resistance and good thermal shock because the dense continuous oxide scale consists of massα- Al2O3 and little TiO2 and/or Al2TiO5. Generally, the oxide scale is grown by the inward diffusion of O2- and the outward diffusion of Ti4+ and Al3+.
基金financially supported by the LingChuang Research Project of China National Nuclear Corporation(CNNC-LCKY-202242)。
文摘Accident-tolerant fuels(ATF)have been extensively studied to reduce the production rate and total amount of heat and hydrogen generated from high-temperature steam oxidation during severe accidents.Chromium-coated zirconium alloy cladding has become one of the most promising candidates for ATF because of its excellent corrosion and oxidation resistance.This paper provides a comprehensive overview of the research progress on oxidation behaviors and degradation mechanisms in chromium-coated zirconium alloy cladding under high-temperature conditions.Potential techniques to strengthen the oxidation resistance are highlighted and compared.Finally,challenges and opportunities for various future directions are addressed.
