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
As a new spraying technology used in the remanufacturing engineering, electro-thermal explosion spraying holds a lot of advantages. Electro-thermal explosion spraying coating aliquation phenomena are reduced and non-c...As a new spraying technology used in the remanufacturing engineering, electro-thermal explosion spraying holds a lot of advantages. Electro-thermal explosion spraying coating aliquation phenomena are reduced and non-crystal, micro-crystal and millimicron-crystal and other microstructure are formed. The corrosion-resistance ability of electro-thermal explosion spraying coating in high temperature environment was surveyed respectively. SEM equipped with EDS was employed to analyze the microstructure of spraying coating before and after corrosion. The corrosion-resistance mechanism of the spraying coating was discussed.展开更多
WC powders were uniformly coated by Ni nanoparticles through a combined chemical co-precipitation and subsequent high temperature hydrogen reduction strategy(abbreviated as CM-WCN),and then were consolidated by vacuum...WC powders were uniformly coated by Ni nanoparticles through a combined chemical co-precipitation and subsequent high temperature hydrogen reduction strategy(abbreviated as CM-WCN),and then were consolidated by vacuum sintering at 1450°C for 1 h to obtain WC−Ni cemented carbides.The microstructure and properties of the as-consolidated CM-WCN were investigated.The average grain size of WC in the consolidated CM-WCN was calculated to be in the range of 3.0−3.8μm and only few pores were observed.A relative density of 99.6%,hardness of HRA 86.5 and bending strength of 1860 MPa were obtained for the CM-WCN−10wt.%Ni,and the highest impact toughness of 6.17 J/cm^(2 )was obtained for the CM-WCN−12wt.%Ni,surpassing those of the hand mixed WC−Ni(HM-WCN)cemented carbides examined in this study and the other similar materials in the literature.CM-WCN cemented carbides possess excellent mechanical properties,due to their highly uniform structure and low porosity that could be ascribed to the intergranular-dominated fracture mode accompanied by a large number of plastic deformation tears of the bonding phase.In addition,the corrosion resistance of CM-WCN was superior to that of HM-WCN at the Ni content of 6−12 wt.%.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 N2. Microstructure and h...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 N2. 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） ranges from 0.96 to 1.33. After the introduction of N2, TiN coating exhibits a weak （200） plane and a preferred （111） orientation. The coating prepared with an N2 flow ratio of 15% shows an optimal oxidation resistance in the atmospheric environment at 800 ℃. In either 1 200 ℃ steam environment for one hour, or deionized water at 360 ℃ 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
Porous TiAl intermetallic compound, as a novel substitute for current inorganic porous material, offsets the shortages of both ceramics and metals. The environmental corrosion resistance of porous TiAl intermetallic c...Porous TiAl intermetallic compound, as a novel substitute for current inorganic porous material, offsets the shortages of both ceramics and metals. The environmental corrosion resistance of porous TiAl intermetallic compound was investigated. The kinetic equation for the cyclic oxidation of porous TiAl alloy at 600 ℃ is determined to be △m2=1.08×10-5t. After total oxidation of 140 h, porous TiAl intermetallic compound shows more stability of pore structure and the mass gain of TiAl alloy is 0.042 g/m2, which is only 10.6% that of porous 316L stainless steel. The kinetic equation for the cyclic corrosion behavior of porous TiAl alloy in hydrochloric acid with pH=2 at 90 ℃ is determined to be △m2=5.41×10-5t-2.08×10-4. After 50 h exposure, the mass loss of TiAl alloy is 0.049 g/m2, which is only 14.8% and 5.57% that of porous Ti and stainless steel, respectively. The kinetic equation in hydrochloric acid with pH=3 is determined to be △m2=2.63×10-6t-3.72×10-6.展开更多
This paper analyzes the extreme application conditions of high temperature, high thermal shock and strong erosion of Al_(2)O_(3)-SiC-C refractories for molten iron ladles. It is considered that the main damage mechani...This paper analyzes the extreme application conditions of high temperature, high thermal shock and strong erosion of Al_(2)O_(3)-SiC-C refractories for molten iron ladles. It is considered that the main damage mechanism of the refractories is chemical corrosion of oxides (high contents of CaO, FeO and MnO) in the materials, reaction melting erosion, oxidation or decomposition of C or SiC in the materials, melting erosion at high temperatures, and damage under high thermal shock. The analysis results show that the low carbon and low silica Al_(2)O_(3)-SiC-C materials with high oxidation resistance should be used. The ratio of Al_(2)O_(3) to SiO_(2) in the materials should be greater than 2.5, and the andalusite or pyrophyllite with microcracks, Al_(2)O_(3) or Si_(3)N_(4) with in-situ particles or fibers, and the clay or metal with ductility at high temperatures should be added to improve the high temperature corrosion resistance and thermal shock resistance.展开更多
The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18MolVN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted z...The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18MolVN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted zone of different heat-treated samples were investigated by X-ray diffraction, electron probe microanalyzer analysis, and trans- mission electron microscopy. The corrosion resistance was evaluated using electrochemical measurements, and the analysis of passive film was carded out by X-ray photoelectron spectroscopy. The results indicated that the volume fraction of precipitates decreased, and the homogeneity of elements was improved with increasing austenitizing temperature. The degree of Cr-depleted zone around coarse M23C6 was severer than that around M2N, and pitting corrosion initiated preferentially around M23C6. The corrosion resistance of the samples increased with the austenitizing temperature. With the increase in austenitizing temperature, the passive film was thickened and Cr（III）cr2O3 in the inner layer of passive film was enriched, which enhanced the corrosion resistance of the steel. The higher content of nitrogen in solid solution at higher austenitizing temperature contributed to the increased intensity of CrN and NH3, leading to the increase in pH value in the pit, and promoting the repassivation of 55Cr18Mo1N steel.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As a new spraying technology used in the remanufacturing engineering, electro-thermal explosion spraying holds a lot of advantages. Electro-thermal explosion spraying coating aliquation phenomena are reduced and non-crystal, micro-crystal and millimicron-crystal and other microstructure are formed. The corrosion-resistance ability of electro-thermal explosion spraying coating in high temperature environment was surveyed respectively. SEM equipped with EDS was employed to analyze the microstructure of spraying coating before and after corrosion. The corrosion-resistance mechanism of the spraying coating was discussed.
基金the financial supports from the National Natural Science Foundation of China (Nos. 51778213, 52078189)the Fundamental Research Funds for the Central Universities, China (No. B200202073)。
文摘WC powders were uniformly coated by Ni nanoparticles through a combined chemical co-precipitation and subsequent high temperature hydrogen reduction strategy(abbreviated as CM-WCN),and then were consolidated by vacuum sintering at 1450°C for 1 h to obtain WC−Ni cemented carbides.The microstructure and properties of the as-consolidated CM-WCN were investigated.The average grain size of WC in the consolidated CM-WCN was calculated to be in the range of 3.0−3.8μm and only few pores were observed.A relative density of 99.6%,hardness of HRA 86.5 and bending strength of 1860 MPa were obtained for the CM-WCN−10wt.%Ni,and the highest impact toughness of 6.17 J/cm^(2 )was obtained for the CM-WCN−12wt.%Ni,surpassing those of the hand mixed WC−Ni(HM-WCN)cemented carbides examined in this study and the other similar materials in the literature.CM-WCN cemented carbides possess excellent mechanical properties,due to their highly uniform structure and low porosity that could be ascribed to the intergranular-dominated fracture mode accompanied by a large number of plastic deformation tears of the bonding phase.In addition,the corrosion resistance of CM-WCN was superior to that of HM-WCN at the Ni content of 6−12 wt.%.
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 N2. 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） ranges from 0.96 to 1.33. After the introduction of N2, TiN coating exhibits a weak （200） plane and a preferred （111） orientation. The coating prepared with an N2 flow ratio of 15% shows an optimal oxidation resistance in the atmospheric environment at 800 ℃. In either 1 200 ℃ steam environment for one hour, or deionized water at 360 ℃ 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.
基金Projects(20636020, 20476106 and 50825102) supported by the National Natural Science Foundation of ChinaProject(2003CB615707) supported by the National Basic Research Program of China+1 种基金Project(2006AA03Z511) supported by the Hi-tech Research and Development Program of ChinaProject(50721003) supported by the Creative Research Group of National Natural Science Foundation of China
文摘Porous TiAl intermetallic compound, as a novel substitute for current inorganic porous material, offsets the shortages of both ceramics and metals. The environmental corrosion resistance of porous TiAl intermetallic compound was investigated. The kinetic equation for the cyclic oxidation of porous TiAl alloy at 600 ℃ is determined to be △m2=1.08×10-5t. After total oxidation of 140 h, porous TiAl intermetallic compound shows more stability of pore structure and the mass gain of TiAl alloy is 0.042 g/m2, which is only 10.6% that of porous 316L stainless steel. The kinetic equation for the cyclic corrosion behavior of porous TiAl alloy in hydrochloric acid with pH=2 at 90 ℃ is determined to be △m2=5.41×10-5t-2.08×10-4. After 50 h exposure, the mass loss of TiAl alloy is 0.049 g/m2, which is only 14.8% and 5.57% that of porous Ti and stainless steel, respectively. The kinetic equation in hydrochloric acid with pH=3 is determined to be △m2=2.63×10-6t-3.72×10-6.
文摘This paper analyzes the extreme application conditions of high temperature, high thermal shock and strong erosion of Al_(2)O_(3)-SiC-C refractories for molten iron ladles. It is considered that the main damage mechanism of the refractories is chemical corrosion of oxides (high contents of CaO, FeO and MnO) in the materials, reaction melting erosion, oxidation or decomposition of C or SiC in the materials, melting erosion at high temperatures, and damage under high thermal shock. The analysis results show that the low carbon and low silica Al_(2)O_(3)-SiC-C materials with high oxidation resistance should be used. The ratio of Al_(2)O_(3) to SiO_(2) in the materials should be greater than 2.5, and the andalusite or pyrophyllite with microcracks, Al_(2)O_(3) or Si_(3)N_(4) with in-situ particles or fibers, and the clay or metal with ductility at high temperatures should be added to improve the high temperature corrosion resistance and thermal shock resistance.
基金financially supported by National Natural Science Foundation of China (Grant Nos.51304041, 51434004 and U1435205)Fundamental Research Funds for the Central Universities (Grant No. N150204007)
文摘The influence of austenitizing temperature on the microstructure and corrosion resistance of 55Cr18MolVN high-nitrogen plastic mould steel was investigated. The microstructure, elemental distribution and Cr-depleted zone of different heat-treated samples were investigated by X-ray diffraction, electron probe microanalyzer analysis, and trans- mission electron microscopy. The corrosion resistance was evaluated using electrochemical measurements, and the analysis of passive film was carded out by X-ray photoelectron spectroscopy. The results indicated that the volume fraction of precipitates decreased, and the homogeneity of elements was improved with increasing austenitizing temperature. The degree of Cr-depleted zone around coarse M23C6 was severer than that around M2N, and pitting corrosion initiated preferentially around M23C6. The corrosion resistance of the samples increased with the austenitizing temperature. With the increase in austenitizing temperature, the passive film was thickened and Cr（III）cr2O3 in the inner layer of passive film was enriched, which enhanced the corrosion resistance of the steel. The higher content of nitrogen in solid solution at higher austenitizing temperature contributed to the increased intensity of CrN and NH3, leading to the increase in pH value in the pit, and promoting the repassivation of 55Cr18Mo1N steel.
