Dissolution kinetics of δ phase in Inconel 718 at 980, 1 000 and 1 020 ℃ respectively was established using the quantitative X-ray diffraction(XRD) method. Microstructure evolution during dissolution process was ana...Dissolution kinetics of δ phase in Inconel 718 at 980, 1 000 and 1 020 ℃ respectively was established using the quantitative X-ray diffraction(XRD) method. Microstructure evolution during dissolution process was analyzed with scanning electron microscopy(SEM). Dissolution rate of δ phase during high temperature heating keeps at a high level at the beginning stage, and then decreases gradually with the increase of heating time. A dynamic equilibrium state approaches after being heated at 980 ℃ for more than 30 min and at 1 000 ℃ for more than 2 h, and the equilibrium mass fraction are 3% and 0.6% respectively. δ phase fully dissolves into the austenitic matrix after being heated at 1 020 ℃ for more than 2 h. The dissolution and fracture effects cause the morphology evolution of δ phase from long needle shape to short bars or particles at high temperature.展开更多
The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were...The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.展开更多
Tensile tests of GH4169 alloy were performed at room temperature. Different fractions, distributions and shapes of δ phase was prepared by aging treated at 880 °C, 930 °C and 980 °C for 5 h or 10 h. Th...Tensile tests of GH4169 alloy were performed at room temperature. Different fractions, distributions and shapes of δ phase was prepared by aging treated at 880 °C, 930 °C and 980 °C for 5 h or 10 h. The effect of δ phase on the mechanical properties of GH4169 alloy was investigated. The results show that 0.2% yield strength and ultimate tensile strength of GH4169 alloy increase by 61 MPa and 78 MPa respectively when the fraction of δ phase increases from 2.20% to 5.21%. Then, the ultimate tensile strength remains at 1 012 MPa even when the fraction of δ phase reaches 7.56%. The fraction effect of δ phase on the strength improvement of GH4169 alloy is more significant than morphology, and the critical fraction value is 5.21%. In addition, the elongation decreases by 14.1% when the fraction of δ phase increases from 2.20% to 7.56%. Excessive needle or short rod shaped δ phase is responsible for the reduction of elongation.展开更多
The GH4169 superalloy with different content ofδ-Ni3Nb phase was welded by tungsten inert gas welding.A detailed study of microstructure and hardness of heat-affected zone(HAZ)was performed in both as-welded and aged...The GH4169 superalloy with different content ofδ-Ni3Nb phase was welded by tungsten inert gas welding.A detailed study of microstructure and hardness of heat-affected zone(HAZ)was performed in both as-welded and aged state.The results show that the precipitation ofδphase,especially the intergranularδphase,can lead to the enrichment of Nb and Mo elements,which promote the formation ofγ/Laves eutectic constituent at grain boundaries in HAZ.In as-welded state,the hardness decreases first and then increases(exhibiting a"V"shape)with distance away from fusion line in HAZ,which is governed by grain size.After aging treatment,however,theγ″phase plays a key role in hardness and leads to the"■"shape profiles of hardness in HAZ.展开更多
Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy ex...Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy exhibits an excellent creep resistance at 700 ℃ and below. When the creep temperature rises to 750 ℃, the creep resistance falls drastically due to the failure of phase transformation strengthening and the precipitation of a large amount of δ phase and σ phase at the grain boundary. The special temperature-sensitive characteristics of Inconel 625 alloy play a very important role in its fracture. When the strain rate is 8.33×10^-3s^-1, the strength of the specimen is higher than that of other parameters attributed to the effect of phase transformation strengthening. With the increase of Ni3(Al, Ti), the phase transformation strengthening inhibits thickening of the stacking faults into twins and improves the overall mechanical properties of the alloy. With the increase of the aging time, the granular Cr-rich M23C6 carbides continue to precipitate at the grain boundary, which hinders the movement of the dislocations and obviously increases the strength of the samples. Especially, the yield strength increases several times.展开更多
The relationship between the tensile properties and S(delta) phase precipitation in cast alloy IN625 was investigated in this paper. Although the influences of δ phase on the mechanical properties have been pointed o...The relationship between the tensile properties and S(delta) phase precipitation in cast alloy IN625 was investigated in this paper. Although the influences of δ phase on the mechanical properties have been pointed out in our previous work, the relationship is still not directly determined due to the coexistence of γ"(gamma double prime) and δ precipitates. In order to exclude the effect from γ" phase, various fractions of δ precipitates with few γ" precipitates were obtained by a set of experimental alloys aging at 750 ℃, and tensile tests were conducted in parallel. The results showed that both yield strength and ultimate tensile strength increased nearly in linear with increasing δ phase fraction, while the elongation was relatively and limitedly affected by δ precipitation when the area fraction of δ phase was above 10%.展开更多
Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperatureductility,stress rupture,especially,certain important mechanical properties,such as cyclicstress rupture,creep/fatigue interaction and crac...Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperatureductility,stress rupture,especially,certain important mechanical properties,such as cyclicstress rupture,creep/fatigue interaction and crack propagation rate.The quantity,morphology and distribution of δ-phase may obviously influence the notched cyclic stress rup-ture life.The relevant microstructure shows that the Mg may also influence to certain extenton the feature of δ-phase.Thus,to keep the Mg and δ-phase under control may further im-prove the mechanical properties of alloy GH169.展开更多
Investigation of the substitution process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work the effects of substitution Lanthanum (La) for Gadolinium (Gd) on...Investigation of the substitution process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work the effects of substitution Lanthanum (La) for Gadolinium (Gd) on the structure and oxygen content for x = 0.0 - 0.5 in the compound Gd1-xLaxBa2Cu3O7-δ (GLBCO-123 phase) have been investigated. Samples were synthesized by using a wet-mixing method from powders of Gd2O2, La2O2, BaO, CuO, and solution of HNO3. Based on the analysis of XRD data and SEM-EDXA, it confirms that the sample has formed the GLBCO-123 phase, as expected. It has been obtained that the lattice parameters a and c are increased while the parameter b is slightly decreased with increasing content of Lanthanum. The oxygen content slightly decreased and structure of the Gd1-xLaxBa2Cu3O7-δ phase changed from orthorhombic to tetragonal with increasing the content of Lanthanum.展开更多
A stable δ- and β-bismuth trioxide was prepared at room temperature by vacuum vapor-phase oxidation. The average crystal size of products was 14.6 nm (by XRD), the d(0.5) value was in the range from 62 nm to 69 nm, ...A stable δ- and β-bismuth trioxide was prepared at room temperature by vacuum vapor-phase oxidation. The average crystal size of products was 14.6 nm (by XRD), the d(0.5) value was in the range from 62 nm to 69 nm, and geometric standard deviation(GSD) was from 1.42 to 1.64. The results show that δ-Bi2O3 is formed when quenching rates is rapid and β-Bi2O3 is formed when it is slow. The size of grains increases with rising reaction temperature, flow rate of carrier gas, residual pressure of system and longer growing time of grains.展开更多
文摘Dissolution kinetics of δ phase in Inconel 718 at 980, 1 000 and 1 020 ℃ respectively was established using the quantitative X-ray diffraction(XRD) method. Microstructure evolution during dissolution process was analyzed with scanning electron microscopy(SEM). Dissolution rate of δ phase during high temperature heating keeps at a high level at the beginning stage, and then decreases gradually with the increase of heating time. A dynamic equilibrium state approaches after being heated at 980 ℃ for more than 30 min and at 1 000 ℃ for more than 2 h, and the equilibrium mass fraction are 3% and 0.6% respectively. δ phase fully dissolves into the austenitic matrix after being heated at 1 020 ℃ for more than 2 h. The dissolution and fracture effects cause the morphology evolution of δ phase from long needle shape to short bars or particles at high temperature.
文摘The effect of δ phase on the hydrogen embrittlement (HE) sensitivity of Inconel 718 was investigated by conducting notch tensile tests. Notch tensile specimens with various precipitation morphologies of δ phase were prepared with different heat treatments, and hydrogen was charged into the tensile specimens before tensile tests via a cathodic charging process. The loss of notch tensile strength (NTS) due to the charged hydrogen was used to evaluate the hydrogen embrittlement sensitivity. The results show that δ phase has deleterious effect on NTSs, and the fracture of hydrogen-charged specimens initiated near the notch surfaces. The loss of NTS caused by precharged hydrogen can be greatly decreased by dissolving δ phase. δ-free Inconel 718 alloy is proposed for the applications in hydrogen environments.
基金Sponsored by the Fund of China State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals,Lanzhou University of Technology(SKLAB02014001)
文摘Tensile tests of GH4169 alloy were performed at room temperature. Different fractions, distributions and shapes of δ phase was prepared by aging treated at 880 °C, 930 °C and 980 °C for 5 h or 10 h. The effect of δ phase on the mechanical properties of GH4169 alloy was investigated. The results show that 0.2% yield strength and ultimate tensile strength of GH4169 alloy increase by 61 MPa and 78 MPa respectively when the fraction of δ phase increases from 2.20% to 5.21%. Then, the ultimate tensile strength remains at 1 012 MPa even when the fraction of δ phase reaches 7.56%. The fraction effect of δ phase on the strength improvement of GH4169 alloy is more significant than morphology, and the critical fraction value is 5.21%. In addition, the elongation decreases by 14.1% when the fraction of δ phase increases from 2.20% to 7.56%. Excessive needle or short rod shaped δ phase is responsible for the reduction of elongation.
基金financially supported by the National Natural Science Foundation of China (No.51774213)the Regional Demonstration Project of Marine Economic Innovation and Development (No.BHSF2017-10)
文摘The GH4169 superalloy with different content ofδ-Ni3Nb phase was welded by tungsten inert gas welding.A detailed study of microstructure and hardness of heat-affected zone(HAZ)was performed in both as-welded and aged state.The results show that the precipitation ofδphase,especially the intergranularδphase,can lead to the enrichment of Nb and Mo elements,which promote the formation ofγ/Laves eutectic constituent at grain boundaries in HAZ.In as-welded state,the hardness decreases first and then increases(exhibiting a"V"shape)with distance away from fusion line in HAZ,which is governed by grain size.After aging treatment,however,theγ″phase plays a key role in hardness and leads to the"■"shape profiles of hardness in HAZ.
基金Funded by the National Natural Science Foundation of China(Nos.51664041,51561021,and 51665032)in part by Longyuan Youth Innovation and Entrepreneurship ProjectsBRICS STI Framework Programme
文摘Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy exhibits an excellent creep resistance at 700 ℃ and below. When the creep temperature rises to 750 ℃, the creep resistance falls drastically due to the failure of phase transformation strengthening and the precipitation of a large amount of δ phase and σ phase at the grain boundary. The special temperature-sensitive characteristics of Inconel 625 alloy play a very important role in its fracture. When the strain rate is 8.33×10^-3s^-1, the strength of the specimen is higher than that of other parameters attributed to the effect of phase transformation strengthening. With the increase of Ni3(Al, Ti), the phase transformation strengthening inhibits thickening of the stacking faults into twins and improves the overall mechanical properties of the alloy. With the increase of the aging time, the granular Cr-rich M23C6 carbides continue to precipitate at the grain boundary, which hinders the movement of the dislocations and obviously increases the strength of the samples. Especially, the yield strength increases several times.
基金financially supported by the National Key Research and Development Program of China (No. 2017YFB0305204)the National Natural Science Foundation of China (No. 51571191)
文摘The relationship between the tensile properties and S(delta) phase precipitation in cast alloy IN625 was investigated in this paper. Although the influences of δ phase on the mechanical properties have been pointed out in our previous work, the relationship is still not directly determined due to the coexistence of γ"(gamma double prime) and δ precipitates. In order to exclude the effect from γ" phase, various fractions of δ precipitates with few γ" precipitates were obtained by a set of experimental alloys aging at 750 ℃, and tensile tests were conducted in parallel. The results showed that both yield strength and ultimate tensile strength increased nearly in linear with increasing δ phase fraction, while the elongation was relatively and limitedly affected by δ precipitation when the area fraction of δ phase was above 10%.
文摘Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperatureductility,stress rupture,especially,certain important mechanical properties,such as cyclicstress rupture,creep/fatigue interaction and crack propagation rate.The quantity,morphology and distribution of δ-phase may obviously influence the notched cyclic stress rup-ture life.The relevant microstructure shows that the Mg may also influence to certain extenton the feature of δ-phase.Thus,to keep the Mg and δ-phase under control may further im-prove the mechanical properties of alloy GH169.
文摘Investigation of the substitution process can provide a better understanding of the superconducting mechanisms in cuprous oxide materials. In this work the effects of substitution Lanthanum (La) for Gadolinium (Gd) on the structure and oxygen content for x = 0.0 - 0.5 in the compound Gd1-xLaxBa2Cu3O7-δ (GLBCO-123 phase) have been investigated. Samples were synthesized by using a wet-mixing method from powders of Gd2O2, La2O2, BaO, CuO, and solution of HNO3. Based on the analysis of XRD data and SEM-EDXA, it confirms that the sample has formed the GLBCO-123 phase, as expected. It has been obtained that the lattice parameters a and c are increased while the parameter b is slightly decreased with increasing content of Lanthanum. The oxygen content slightly decreased and structure of the Gd1-xLaxBa2Cu3O7-δ phase changed from orthorhombic to tetragonal with increasing the content of Lanthanum.
基金Project(03SSY4056) supported by the Bureau of Science and Technology of Hunan Province, China Project(04C034) supported by the Bureau of Education of Hunan Province, China
文摘A stable δ- and β-bismuth trioxide was prepared at room temperature by vacuum vapor-phase oxidation. The average crystal size of products was 14.6 nm (by XRD), the d(0.5) value was in the range from 62 nm to 69 nm, and geometric standard deviation(GSD) was from 1.42 to 1.64. The results show that δ-Bi2O3 is formed when quenching rates is rapid and β-Bi2O3 is formed when it is slow. The size of grains increases with rising reaction temperature, flow rate of carrier gas, residual pressure of system and longer growing time of grains.
