Laser powder bed fusion(L-PBF)has been employed to additively manufacture WE43 magnesium(Mg)alloy biodegradable implants,but WE43 L-PBF samples exhibit excessively rapid corrosion.In this work,dense WE43 L-PBF samples...Laser powder bed fusion(L-PBF)has been employed to additively manufacture WE43 magnesium(Mg)alloy biodegradable implants,but WE43 L-PBF samples exhibit excessively rapid corrosion.In this work,dense WE43 L-PBF samples were built with the relativity density reaching 99.9%.High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations.The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface,a transition layer in the middle and the matrix.The oxide layer consisted of rare earth(RE)oxides,and became dense and thick with increasing the holding duration.The matrix was composed ofα-Mg,RE oxides and Mg_(24)RE_(5) precipitates.The precipitates almost disappeared in the transition layer.Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation.The original L-PBF samples lost 40%weight after 3-day immersion in Hank’s solution,and broke into fragments after 7-day immersion.The casted and solution treated samples lost roughly half of the weight after 28-day immersion.The high temperature oxidation samples,which were heated at 525℃ for 8 h,kept the structural integrity,and lost only 6.88%weight after 28-day immersion.The substantially improved corrosion resistance was contributed to the gradient structure at the surface.On one hand,the outmost dense layer of RE oxides isolated the corrosive medium;on the other hand,the transition layer considerably inhibited the corrosion owing to the lack of precipitates.Overall,high temperature oxidation provides an efficient,economic and safe approach to inhibit the corrosion of WE43 L-PBF samples,and has promising prospects for future clinical applications.展开更多
To further improve the oxidation-resistance of materials and reduce the cost of grid plates in grate-kiln, a new kind of heat-resistant grid plate was developed. The microstructure of this grid plate with a life more ...To further improve the oxidation-resistance of materials and reduce the cost of grid plates in grate-kiln, a new kind of heat-resistant grid plate was developed. The microstructure of this grid plate with a life more than 18 months was studied by XRD, SEM and EDS techniques. The results show that high hardness, high intensity and good impact property make the new kind of heat-resistant grid plate and its oxide film have a higher resistance to deformation and abrasion at 900-1000℃ Besides, small grain size is beneficial to form a complete protective oxide film. The oxide film composed of SiO2 layer, Cr2O3 layer and Fe2O3 layer is rather thin and bonds closely with the backing. The forming of the chemical stable nickel-rich layer increases the density of Cr2O3 layer.展开更多
18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend ...18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.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
The plasma sprayed gradated coating with the bottom layer of NiCrAl and the top layer of(ZrO2+Y2O3) was prepared by the plasma spraying technique. The phase structure and morphology of the gradated coating were analyz...The plasma sprayed gradated coating with the bottom layer of NiCrAl and the top layer of(ZrO2+Y2O3) was prepared by the plasma spraying technique. The phase structure and morphology of the gradated coating were analyzed by means of X-ray diffractometry(XRD) and scanning electron microscopy(SEM). The high temperature oxidation resistance of the plasma sprayed samples at 800 ℃ was investigated. The oxidation kinetics curve was obtained. The results show that the thickness of gradated coating is about 410 μm. The plasma sprayed gradated coating on stainless steel surface can improve the high temperature oxidation resistance of stainless steel. The oxidation rate of stainless steel is less than that of plasma sprayed gradated coating. The oxidation film of plasma sprayed sample is very dense and is not easily exfoliated. The dense oxidation film prevents the stainless steel from more oxidation.展开更多
The oxidation behaviors of Nb67-xW15Si18Hfx (x=0, 5, 10) alloys were studied at 1 250℃in air. It is found that the Nb67W15Si18 alloy has the best oxidation resistance among the three alloys; and Hf addition is harmfu...The oxidation behaviors of Nb67-xW15Si18Hfx (x=0, 5, 10) alloys were studied at 1 250℃in air. It is found that the Nb67W15Si18 alloy has the best oxidation resistance among the three alloys; and Hf addition is harmful to the oxidation resistance of the Nb67W15Si18 alloy. The oxides formed on the Nb67W15Si18 alloy are mainly Nb12WO33 and NbO2, and that on the Nb62W15Si18Hf5 and Nb57W15Si18Hf10 alloys is Nb2O5. Effect of Hf on the oxidation behavior of the Nb67-xW15Si18Hfx alloys has been discussed based on microstructures and kinetics of oxidation.展开更多
The oxidation rate of a high temperature titanium alloy in air at 650℃ could be decreased significantly by means of ion implantation of 3×10 16 and 3×10 17 ions/cm 2 Nb. The microstructure and al...The oxidation rate of a high temperature titanium alloy in air at 650℃ could be decreased significantly by means of ion implantation of 3×10 16 and 3×10 17 ions/cm 2 Nb. The microstructure and alloy elements distribution in the oxidation scale of unimplanted and Nb implanted titanium alloy were investigated by using SEM, XRD and AES. The addition of Nb could reduce the number of point defects and decrease the solubility of oxygen in the alloy substrate. Therefore, the oxidation resistance of the alloy in air at 650℃ is remarkably improved.展开更多
The oxidation behavior (isothermal and cyclic oxidation) of cast superalloy K38G and the effect of Ce^+ ion implantation with dose of 1×10^(17) ions/cm^2 upon its oxidation resistance at 900 and 1000 ℃ in air we...The oxidation behavior (isothermal and cyclic oxidation) of cast superalloy K38G and the effect of Ce^+ ion implantation with dose of 1×10^(17) ions/cm^2 upon its oxidation resistance at 900 and 1000 ℃ in air were investigated. Meanwhile, the influence of Ce^+ implantation on oxidation behavior of K38G with pre-oxide scale at 1000 ℃ in air was compared. The pre-oxidation was performed at 1000 ℃ in static air for 0.25 and 1.5 h, respectively. It is shown that the homogeneous external mixture oxide of rutile TiO_2+Cr_2O_3 and non-continuous internal oxide of Al_2O_3 are formed during the oxidation procedure in all the cases. The isothermal oxidation resistance and the cracking or spallation resistance of superalloy K38G implanted with Ce^+ by both of the two different implantation ways are not improved notably. This may be attributed to the mixed oxide composition characteristics and the blocking effect differences of Ce^+ segregation along the oxide grain boundaries on the transport process for different diffusing ions.展开更多
A coating with high hardness, wear and oxidation resistance was prepared by electric arc spray. The hardness, bonding strength, abrasive wear and values of porosity and oxidation resistance of the coating were investi...A coating with high hardness, wear and oxidation resistance was prepared by electric arc spray. The hardness, bonding strength, abrasive wear and values of porosity and oxidation resistance of the coating were investigated. The microstructures and function of Cr3C2 of the coating were analyzed. The results showed surface Rockness Hardness HR30 reached 72.5 and average bond strength reached 49.1Mpa. Also porosity value was less than 2%. In addition, it was found from the comparison between the coating and 45CT coating that, oxidation resistance of the coating was less than that of 45CT, but the abrasive wear of the coating was obvious better than that of 45CT.展开更多
FeAl intermetallic compound with different contents of rare earth oxide La2O3 addition was prepared by hot pressing the mechanically alloyed powders.Effect of La2O3 on microstructure and high-temperature wear property...FeAl intermetallic compound with different contents of rare earth oxide La2O3 addition was prepared by hot pressing the mechanically alloyed powders.Effect of La2O3 on microstructure and high-temperature wear property of the sintered FeAl samples was investigated in this paper.The results showed that 1 wt.% La2O3 addition could refine the microstructure and increase the density of the FeAl intermetallic compound,and correspondingly improved the high-temperature wear resistance.SEM and EDS analyses of the wo...展开更多
High-temperature circulating fans blow 800 ℃ HN protective atmosphere to the surface of the strip as a jet heating power source or suspending source,playing a core role in metal strip continuous annealing furnaces. I...High-temperature circulating fans blow 800 ℃ HN protective atmosphere to the surface of the strip as a jet heating power source or suspending source,playing a core role in metal strip continuous annealing furnaces. In this study,several high-temperature alloys were experimentally compared based on their high-temperature mechanical properties,high-temperature creep resistance,and high-temperature oxidation resistance. The results indicate that though the price of HR-120 alloy is only half of Inconel 601,it is suitable for the manufacture of fans that can withstand a high temperature of 800 ℃ given its good creep resistance,high-temperature oxidation resistance,and price advantage.展开更多
Oxidation and hot corrosion behaviors of Ni<sub>3</sub>Al-Mo （IC6） alloy were studied. Surface protective coatings were also developed for the engineering application of the alloy. The sputtered NiCrAlY ...Oxidation and hot corrosion behaviors of Ni<sub>3</sub>Al-Mo （IC6） alloy were studied. Surface protective coatings were also developed for the engineering application of the alloy. The sputtered NiCrAlY coating may greatly improve the oxidation and hot corrosion resistance of IC6 alloy by forming a protective Al<sub>2</sub>O<sub>3</sub> scale, and the coating shows little effect on the mechanical properties of IC6 alloy.展开更多
In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate t...In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2＋Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals and promoting the stable formation of the Al2O3-riched layer, which is beneficial to improve the oxidation properties.展开更多
CrN/（Ti,Al,Zr,Cr） N bilayer films were successfully deposited on cemented carbide（ WC-8% Co） substrates by multi-arc ion plating process using two Ti-Al-Zr alloy targets and one pure Cr target. As a result of bila...CrN/（Ti,Al,Zr,Cr） N bilayer films were successfully deposited on cemented carbide（ WC-8% Co） substrates by multi-arc ion plating process using two Ti-Al-Zr alloy targets and one pure Cr target. As a result of bilayered structure and addition of alloying elements（ e. g. Al and Cr）,the films exhibited excellent high temperature oxidation resistance under both short-term isothermal（ up to 800 ℃） and long-term cyclic（ up to 600 ℃） exposure conditions. Combined with pre-established outstanding tribological properties（ e. g. maximum hardness of 4 000HV0. 01 and maximum adhesion strength over 200 N）,these observations make such films quite a promising candidate to extend the cutting tool life span and boost the performance in high-productivity,high-speed and high-feed cutting or in dry machining conditions.展开更多
The high-temperature oxidation-resistant MoSi2 coating on the Nb substrate was prepared by slurry firing. The structure, compositions and phase distribution of the coating and the relationship between these features a...The high-temperature oxidation-resistant MoSi2 coating on the Nb substrate was prepared by slurry firing. The structure, compositions and phase distribution of the coating and the relationship between these features and the oxidation resistance of the coating were investigated by SEM, EDS and XRD. The results indicate that the interface between the coating and the substrate has metallurgic combination, and a transitional layer is formed by diffusion. The multi-layer structure improves the oxidation resistance of the coating. The method of slurry firing to prepare the high-temperature MoSi2 coating on Nb is feasible. The SiO2 scale, which is formed on the surface of the coating by the self-oxidation of MoSi2, prevents the further diffusion of oxygen.展开更多
To improve the oxidation resistance and corrosion resistance of Zr-4 alloy, titanium nitride(TiN) coatings were prepared on the Zr-4 alloy with a TiN ceramic target with different ratios of N_2. Microstructure and hig...To improve the oxidation resistance and corrosion resistance of Zr-4 alloy, titanium nitride(TiN) coatings were prepared on the Zr-4 alloy with a TiN ceramic target with different ratios of N_2. Microstructure and high-temperature properties of the TiN coated samples were studied by scanning electron microscopy(SEM), energy dispersive spectrometer(EDS), X-ray diffraction meter(XRD), X-ray photoelectron spectroscopy(XPS), heat treatment furnace and autoclaves, respectively. The x value of the TiN coatings(TiN_x) ranges from 0.96 to 1.33. After the introduction of N_2, TiN coating exhibits a weak(200) plane and a preferred(111) orientation. The coating prepared with an N_2 flow ratio of 15% shows an optimal oxidation resistance in the atmospheric environment at 800 °C. In either 1 200 °C steam environment for one hour, or deionized water at 360 °C and a pressure of 18.6 Mpa for 16 d, the opitimized TiN coated samples have no delamination or spallation; and the gains in the masses of samples are much smaller than Zr-4 alloy. These results demonstrate the effectiveness of the optimized TiN coating as the protective coating on the Zr-4 alloy under extreme conditons.展开更多
基金funded by the National Key Research and Development Program of China (2018YFE0104200)National Natural Science Foundation of China (51875310, 52175274, 82172065)Tsinghua Precision Medicine Foundation
文摘Laser powder bed fusion(L-PBF)has been employed to additively manufacture WE43 magnesium(Mg)alloy biodegradable implants,but WE43 L-PBF samples exhibit excessively rapid corrosion.In this work,dense WE43 L-PBF samples were built with the relativity density reaching 99.9%.High temperature oxidation was performed on the L-PBF samples in circulating air via various heating temperatures and holding durations.The oxidation and diffusion at the elevated temperature generated a gradient structure composed of an oxide layer at the surface,a transition layer in the middle and the matrix.The oxide layer consisted of rare earth(RE)oxides,and became dense and thick with increasing the holding duration.The matrix was composed ofα-Mg,RE oxides and Mg_(24)RE_(5) precipitates.The precipitates almost disappeared in the transition layer.Enhanced passivation effect was observed in the samples treated by a suitable high temperature oxidation.The original L-PBF samples lost 40%weight after 3-day immersion in Hank’s solution,and broke into fragments after 7-day immersion.The casted and solution treated samples lost roughly half of the weight after 28-day immersion.The high temperature oxidation samples,which were heated at 525℃ for 8 h,kept the structural integrity,and lost only 6.88%weight after 28-day immersion.The substantially improved corrosion resistance was contributed to the gradient structure at the surface.On one hand,the outmost dense layer of RE oxides isolated the corrosive medium;on the other hand,the transition layer considerably inhibited the corrosion owing to the lack of precipitates.Overall,high temperature oxidation provides an efficient,economic and safe approach to inhibit the corrosion of WE43 L-PBF samples,and has promising prospects for future clinical applications.
文摘To further improve the oxidation-resistance of materials and reduce the cost of grid plates in grate-kiln, a new kind of heat-resistant grid plate was developed. The microstructure of this grid plate with a life more than 18 months was studied by XRD, SEM and EDS techniques. The results show that high hardness, high intensity and good impact property make the new kind of heat-resistant grid plate and its oxide film have a higher resistance to deformation and abrasion at 900-1000℃ Besides, small grain size is beneficial to form a complete protective oxide film. The oxide film composed of SiO2 layer, Cr2O3 layer and Fe2O3 layer is rather thin and bonds closely with the backing. The forming of the chemical stable nickel-rich layer increases the density of Cr2O3 layer.
文摘18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.
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(20061D0500500151) supported by Beijing Excellent Talent Nurture and Sponsor programProject supported by Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality
文摘The plasma sprayed gradated coating with the bottom layer of NiCrAl and the top layer of(ZrO2+Y2O3) was prepared by the plasma spraying technique. The phase structure and morphology of the gradated coating were analyzed by means of X-ray diffractometry(XRD) and scanning electron microscopy(SEM). The high temperature oxidation resistance of the plasma sprayed samples at 800 ℃ was investigated. The oxidation kinetics curve was obtained. The results show that the thickness of gradated coating is about 410 μm. The plasma sprayed gradated coating on stainless steel surface can improve the high temperature oxidation resistance of stainless steel. The oxidation rate of stainless steel is less than that of plasma sprayed gradated coating. The oxidation film of plasma sprayed sample is very dense and is not easily exfoliated. The dense oxidation film prevents the stainless steel from more oxidation.
基金Project(50671002) supported by the National Natural Science Foundation of China
文摘The oxidation behaviors of Nb67-xW15Si18Hfx (x=0, 5, 10) alloys were studied at 1 250℃in air. It is found that the Nb67W15Si18 alloy has the best oxidation resistance among the three alloys; and Hf addition is harmful to the oxidation resistance of the Nb67W15Si18 alloy. The oxides formed on the Nb67W15Si18 alloy are mainly Nb12WO33 and NbO2, and that on the Nb62W15Si18Hf5 and Nb57W15Si18Hf10 alloys is Nb2O5. Effect of Hf on the oxidation behavior of the Nb67-xW15Si18Hfx alloys has been discussed based on microstructures and kinetics of oxidation.
文摘The oxidation rate of a high temperature titanium alloy in air at 650℃ could be decreased significantly by means of ion implantation of 3×10 16 and 3×10 17 ions/cm 2 Nb. The microstructure and alloy elements distribution in the oxidation scale of unimplanted and Nb implanted titanium alloy were investigated by using SEM, XRD and AES. The addition of Nb could reduce the number of point defects and decrease the solubility of oxygen in the alloy substrate. Therefore, the oxidation resistance of the alloy in air at 650℃ is remarkably improved.
基金Project supported by National Outstanding Young Scientist Foundation of China (50371095) the Special Funds for the Major State Basic Research Projects (G19990650) and State Laboratory for Corrosion and Protection of Metals
文摘The oxidation behavior (isothermal and cyclic oxidation) of cast superalloy K38G and the effect of Ce^+ ion implantation with dose of 1×10^(17) ions/cm^2 upon its oxidation resistance at 900 and 1000 ℃ in air were investigated. Meanwhile, the influence of Ce^+ implantation on oxidation behavior of K38G with pre-oxide scale at 1000 ℃ in air was compared. The pre-oxidation was performed at 1000 ℃ in static air for 0.25 and 1.5 h, respectively. It is shown that the homogeneous external mixture oxide of rutile TiO_2+Cr_2O_3 and non-continuous internal oxide of Al_2O_3 are formed during the oxidation procedure in all the cases. The isothermal oxidation resistance and the cracking or spallation resistance of superalloy K38G implanted with Ce^+ by both of the two different implantation ways are not improved notably. This may be attributed to the mixed oxide composition characteristics and the blocking effect differences of Ce^+ segregation along the oxide grain boundaries on the transport process for different diffusing ions.
基金sponsored by National Natural Science Foundation of China(50375004).
文摘A coating with high hardness, wear and oxidation resistance was prepared by electric arc spray. The hardness, bonding strength, abrasive wear and values of porosity and oxidation resistance of the coating were investigated. The microstructures and function of Cr3C2 of the coating were analyzed. The results showed surface Rockness Hardness HR30 reached 72.5 and average bond strength reached 49.1Mpa. Also porosity value was less than 2%. In addition, it was found from the comparison between the coating and 45CT coating that, oxidation resistance of the coating was less than that of 45CT, but the abrasive wear of the coating was obvious better than that of 45CT.
基金supported by the National Natural Science Foundation of China (50575034)
文摘FeAl intermetallic compound with different contents of rare earth oxide La2O3 addition was prepared by hot pressing the mechanically alloyed powders.Effect of La2O3 on microstructure and high-temperature wear property of the sintered FeAl samples was investigated in this paper.The results showed that 1 wt.% La2O3 addition could refine the microstructure and increase the density of the FeAl intermetallic compound,and correspondingly improved the high-temperature wear resistance.SEM and EDS analyses of the wo...
文摘High-temperature circulating fans blow 800 ℃ HN protective atmosphere to the surface of the strip as a jet heating power source or suspending source,playing a core role in metal strip continuous annealing furnaces. In this study,several high-temperature alloys were experimentally compared based on their high-temperature mechanical properties,high-temperature creep resistance,and high-temperature oxidation resistance. The results indicate that though the price of HR-120 alloy is only half of Inconel 601,it is suitable for the manufacture of fans that can withstand a high temperature of 800 ℃ given its good creep resistance,high-temperature oxidation resistance,and price advantage.
基金the High Technology Research and Development Programme of China
文摘Oxidation and hot corrosion behaviors of Ni<sub>3</sub>Al-Mo （IC6） alloy were studied. Surface protective coatings were also developed for the engineering application of the alloy. The sputtered NiCrAlY coating may greatly improve the oxidation and hot corrosion resistance of IC6 alloy by forming a protective Al<sub>2</sub>O<sub>3</sub> scale, and the coating shows little effect on the mechanical properties of IC6 alloy.
基金supported by the Special Program of the Education Bureau of Shaanxi Province of China (No.08JK240)the Breeding Program for Provincial Level Key Research Base of Shaanxi University of Technology (No.SLGJD0806)
文摘In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2＋Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals and promoting the stable formation of the Al2O3-riched layer, which is beneficial to improve the oxidation properties.
基金financially supported by Natural Science Foundation of Liaoning Province of China(No.2014020096)Shenyang Science and Technology Plan Project of Liaoning Province of China(No.F14-231-119 )Shenyang Yongyuan Guanghui Machinery Factory Transverse Project of Liaoning Province of China(No.201521010100051)
文摘CrN/（Ti,Al,Zr,Cr） N bilayer films were successfully deposited on cemented carbide（ WC-8% Co） substrates by multi-arc ion plating process using two Ti-Al-Zr alloy targets and one pure Cr target. As a result of bilayered structure and addition of alloying elements（ e. g. Al and Cr）,the films exhibited excellent high temperature oxidation resistance under both short-term isothermal（ up to 800 ℃） and long-term cyclic（ up to 600 ℃） exposure conditions. Combined with pre-established outstanding tribological properties（ e. g. maximum hardness of 4 000HV0. 01 and maximum adhesion strength over 200 N）,these observations make such films quite a promising candidate to extend the cutting tool life span and boost the performance in high-productivity,high-speed and high-feed cutting or in dry machining conditions.
基金Project(20010533003) supported by the Special Research Foundation of PhD Study
文摘The high-temperature oxidation-resistant MoSi2 coating on the Nb substrate was prepared by slurry firing. The structure, compositions and phase distribution of the coating and the relationship between these features and the oxidation resistance of the coating were investigated by SEM, EDS and XRD. The results indicate that the interface between the coating and the substrate has metallurgic combination, and a transitional layer is formed by diffusion. The multi-layer structure improves the oxidation resistance of the coating. The method of slurry firing to prepare the high-temperature MoSi2 coating on Nb is feasible. The SiO2 scale, which is formed on the surface of the coating by the self-oxidation of MoSi2, prevents the further diffusion of oxygen.
基金Funded by the National Science and Technology Major Project of the Ministry of Science and Technology of China(2015ZX06004001-002)the Postgraduate Research and Innovation Project of the University of South China(2017XCX11)
文摘To improve the oxidation resistance and corrosion resistance of Zr-4 alloy, titanium nitride(TiN) coatings were prepared on the Zr-4 alloy with a TiN ceramic target with different ratios of N_2. Microstructure and high-temperature properties of the TiN coated samples were studied by scanning electron microscopy(SEM), energy dispersive spectrometer(EDS), X-ray diffraction meter(XRD), X-ray photoelectron spectroscopy(XPS), heat treatment furnace and autoclaves, respectively. The x value of the TiN coatings(TiN_x) ranges from 0.96 to 1.33. After the introduction of N_2, TiN coating exhibits a weak(200) plane and a preferred(111) orientation. The coating prepared with an N_2 flow ratio of 15% shows an optimal oxidation resistance in the atmospheric environment at 800 °C. In either 1 200 °C steam environment for one hour, or deionized water at 360 °C and a pressure of 18.6 Mpa for 16 d, the opitimized TiN coated samples have no delamination or spallation; and the gains in the masses of samples are much smaller than Zr-4 alloy. These results demonstrate the effectiveness of the optimized TiN coating as the protective coating on the Zr-4 alloy under extreme conditons.
