In this study, the effect of temperatures and cooling rates of heat treatment on the microstructure of a powder metallurgy (PM) Ti-46Al-2Cr-2Nb-(B,W) (at.%) alloy was studied. Depending on the cooling rate and tempera...In this study, the effect of temperatures and cooling rates of heat treatment on the microstructure of a powder metallurgy (PM) Ti-46Al-2Cr-2Nb-(B,W) (at.%) alloy was studied. Depending on the cooling rate and temperature, the different structures were obtained from the initial near-γ (NG) microstructures by heat treatment in the α+γ field. The results show that the microstructures of samples after furnace cooling (FC) consist primarily of equiaxed γ and α 2 grains, with a few grains containing lamellae. Duplex microstructures consist mainly of γ grains and lamellar colonies were obtained in the quenching into another furnace at 900°C (QFC) samples. However, further increasing of the cooling rate to air cooling (AC) induces the transformation of α→α_2 and results in a microstructure with equiaxed γ and α_2 grains, and no lamellar colonies are found.展开更多
The alternative heating/cooling cycles (thermal fatigue) of K465 superalloy were carried out. The specimens were held at 1 050℃for 300 s, then quenched into 20℃recycling water for 10 s as a cycle. During thermal fat...The alternative heating/cooling cycles (thermal fatigue) of K465 superalloy were carried out. The specimens were held at 1 050℃for 300 s, then quenched into 20℃recycling water for 10 s as a cycle. During thermal fatigue,γ' precipitates changed typically from cubical to irregular shape after 10 cycles, to complex configuration after 20 cycles and raft-like shape after 30 cycles. The very fineγ' particles precipitated inter the originalγ' particles. The elastic energy dominated morphological evolution of largeγ' precipitates, and the thermal stress induced the directional growth of precipitates that minimized the total energy of the system, and the nucleation theory controlled the formation of fineγ' precipitate. The results show that the volume fraction ofγ' precipitates is increased with the increase of heating/cooling cycles, which improves the mechanical property of this alloy.展开更多
The influence of γ-phase composition in WC-Co cemented carbides on its specific coercive force H_(sc) hasbeen studied by analysing the imitative alloys of γ-phase. The results show that the H_(sc) of γ-phase is low...The influence of γ-phase composition in WC-Co cemented carbides on its specific coercive force H_(sc) hasbeen studied by analysing the imitative alloys of γ-phase. The results show that the H_(sc) of γ-phase is lower thanthat of pure cobalt, because the solute W can raise γ-phase H_(sc) but the carbon exhibits more intense negativeeffect on H_(sc). The effect is enhanced with raising the C solubilities in γ-phase.展开更多
In this article, principle and mathematical method of determining the phase fractions of multiphase flows by using a dual-energy γ -ray system have been described. The dual-energy γ -ray device is composed of radioa...In this article, principle and mathematical method of determining the phase fractions of multiphase flows by using a dual-energy γ -ray system have been described. The dual-energy γ -ray device is composed of radioactive isotopes of 241Am and 137Cs with γ -ray energies of 59.5 and 662 keV, respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The modified arithmetic is beneficial to removing the extra Compton scattering from the measured value. The result shows that the dual-energy γ -ray technique can be used in three-phase flow with average accuracy greater than 95%, which enables us to determine phase fractions almost independent of the flow regime. Improvement has been achieved on measurement accuracy of phase fractions.展开更多
The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by usi...The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a sin- gle-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.展开更多
An investigation has been made into strengthening mechanism in a single crystal nickel-base superalloy DD8 by transmission electron microscopy. The results show that the stress rupture strength of the alloy increases ...An investigation has been made into strengthening mechanism in a single crystal nickel-base superalloy DD8 by transmission electron microscopy. The results show that the stress rupture strength of the alloy increases with decreasing misfit, and the antiphase boundaries (APBs) formed in the ordered γ' phase, rather than the misfits, play a dominate role in strengthening of the single crystal Ni-base superalloy DD8.There are three kinds of mechanisms for forming the APBs which were observed in the present materials. One is mis-arrangement of the local ordered atoms in the γ' precipitates due to the local strain; the second arises from the 1/2<110> dislocations cutting into the γ', and the third is the formation of the APBs induced by the 1/2<110> matrix dislocation network. The contribution of the antiphase boundary energy to the strength of the alloy can be expressed by:where τ is the resistance to deformation provided by the APB energy; S is the long-range order degree in γ'; Tc is the transition temperature from order to disorder; f is the volume fraction of γ'; rs is the radius of γ'; b is the Burgers vector; a is the lattice constant; G is the shear modulus, and k is the proportional constant.展开更多
Cyclopropylamine is synthesized with γ butyrolactone and isopropanol by five steps of ring opening esterification, cyclization, hydrolysis, acylation and Hofmann degradation. Cyclization and hydrolysis are key steps ...Cyclopropylamine is synthesized with γ butyrolactone and isopropanol by five steps of ring opening esterification, cyclization, hydrolysis, acylation and Hofmann degradation. Cyclization and hydrolysis are key steps in the process, and Phase Transfer Catalysis (PTC) is used in the two steps respectively. In the cyclization reaction, because solid liquid PTC, sodium hydroxide is applied instead of expensive sodium alcoholate, the reaction can be carried out in mild conditions. The optimum re action conditions are as follows: 0.03∶1∶1.5 mole ratio of BTEAC to ester to sodium hydroxide, reacting at 50 ℃ for 2 h with yield of 92%. Hydrolysis of isopropyl cyclopropanecarboxylate is accelerated by liquid liquid PTC, and the order of catalytic activity is BTEAC>BTMAC>CTMAB>TBAB. The results show that the new synthesis method is superior to those from literature and feasible for production with simple routes, mild reaction conditions, cheap materials and total yield of 52.6%.展开更多
1.IntroductionSince the biginning of 1960s,the effectof Mg upon superalloy has been studiedand some satisfactory developments havebeen achieved.The role of Mg on the alloycan be summarized as follows:(1)Themechanical ...1.IntroductionSince the biginning of 1960s,the effectof Mg upon superalloy has been studiedand some satisfactory developments havebeen achieved.The role of Mg on the alloycan be summarized as follows:(1)Themechanical plasticity of Ni-base superalloycan be improved by adding Mg asdesulphurizer,because of forming insolubleMgS instead of other low melting eutectic展开更多
Alumina (Al2O3) has been synthesized through combustion synthesis (CS) technique. The calcined products were characterized using X-ray diffractional analysis (XRD), scanning electron microscopy (SEM), transmission ele...Alumina (Al2O3) has been synthesized through combustion synthesis (CS) technique. The calcined products were characterized using X-ray diffractional analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermo-gravimetric analysis (TGA). TG-DTA results reveal the various stages involved in transition from γ-phase to α-Al2O3 phase. The first phase γ-Al2O3 was presented in the temperature range from 600°C-875°C as deduced from the XRD patterns with cubic crystal structure. The second stage occurs in the temperature range from 900°C-1000°C. In the final step, above 1000°C, the aluminium oxide appears completely as α-Al2O3, showing high crystallinity. The particle sizes are closely related to γ- to α-Al2O3 phase transition.展开更多
基金supported by the National Natural Science Foundation of China (No. 51101003)
文摘In this study, the effect of temperatures and cooling rates of heat treatment on the microstructure of a powder metallurgy (PM) Ti-46Al-2Cr-2Nb-(B,W) (at.%) alloy was studied. Depending on the cooling rate and temperature, the different structures were obtained from the initial near-γ (NG) microstructures by heat treatment in the α+γ field. The results show that the microstructures of samples after furnace cooling (FC) consist primarily of equiaxed γ and α 2 grains, with a few grains containing lamellae. Duplex microstructures consist mainly of γ grains and lamellar colonies were obtained in the quenching into another furnace at 900°C (QFC) samples. However, further increasing of the cooling rate to air cooling (AC) induces the transformation of α→α_2 and results in a microstructure with equiaxed γ and α_2 grains, and no lamellar colonies are found.
文摘The alternative heating/cooling cycles (thermal fatigue) of K465 superalloy were carried out. The specimens were held at 1 050℃for 300 s, then quenched into 20℃recycling water for 10 s as a cycle. During thermal fatigue,γ' precipitates changed typically from cubical to irregular shape after 10 cycles, to complex configuration after 20 cycles and raft-like shape after 30 cycles. The very fineγ' particles precipitated inter the originalγ' particles. The elastic energy dominated morphological evolution of largeγ' precipitates, and the thermal stress induced the directional growth of precipitates that minimized the total energy of the system, and the nucleation theory controlled the formation of fineγ' precipitate. The results show that the volume fraction ofγ' precipitates is increased with the increase of heating/cooling cycles, which improves the mechanical property of this alloy.
文摘The influence of γ-phase composition in WC-Co cemented carbides on its specific coercive force H_(sc) hasbeen studied by analysing the imitative alloys of γ-phase. The results show that the H_(sc) of γ-phase is lower thanthat of pure cobalt, because the solute W can raise γ-phase H_(sc) but the carbon exhibits more intense negativeeffect on H_(sc). The effect is enhanced with raising the C solubilities in γ-phase.
基金Supported by National Natural Science Foundation of China (No.10572143) and Joint Project between the Royal Society and the Chinese Academy of Sciences (No.15933).
文摘In this article, principle and mathematical method of determining the phase fractions of multiphase flows by using a dual-energy γ -ray system have been described. The dual-energy γ -ray device is composed of radioactive isotopes of 241Am and 137Cs with γ -ray energies of 59.5 and 662 keV, respectively. A rational method to calibrate the absorption coefficient was introduced in detail. The modified arithmetic is beneficial to removing the extra Compton scattering from the measured value. The result shows that the dual-energy γ -ray technique can be used in three-phase flow with average accuracy greater than 95%, which enables us to determine phase fractions almost independent of the flow regime. Improvement has been achieved on measurement accuracy of phase fractions.
基金Supported by National Natural Science Foundation of China (No. 10572143)
文摘The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a sin- gle-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.
文摘An investigation has been made into strengthening mechanism in a single crystal nickel-base superalloy DD8 by transmission electron microscopy. The results show that the stress rupture strength of the alloy increases with decreasing misfit, and the antiphase boundaries (APBs) formed in the ordered γ' phase, rather than the misfits, play a dominate role in strengthening of the single crystal Ni-base superalloy DD8.There are three kinds of mechanisms for forming the APBs which were observed in the present materials. One is mis-arrangement of the local ordered atoms in the γ' precipitates due to the local strain; the second arises from the 1/2<110> dislocations cutting into the γ', and the third is the formation of the APBs induced by the 1/2<110> matrix dislocation network. The contribution of the antiphase boundary energy to the strength of the alloy can be expressed by:where τ is the resistance to deformation provided by the APB energy; S is the long-range order degree in γ'; Tc is the transition temperature from order to disorder; f is the volume fraction of γ'; rs is the radius of γ'; b is the Burgers vector; a is the lattice constant; G is the shear modulus, and k is the proportional constant.
基金The Science and Research Foundation of Education Commission of Hunan Province
文摘Cyclopropylamine is synthesized with γ butyrolactone and isopropanol by five steps of ring opening esterification, cyclization, hydrolysis, acylation and Hofmann degradation. Cyclization and hydrolysis are key steps in the process, and Phase Transfer Catalysis (PTC) is used in the two steps respectively. In the cyclization reaction, because solid liquid PTC, sodium hydroxide is applied instead of expensive sodium alcoholate, the reaction can be carried out in mild conditions. The optimum re action conditions are as follows: 0.03∶1∶1.5 mole ratio of BTEAC to ester to sodium hydroxide, reacting at 50 ℃ for 2 h with yield of 92%. Hydrolysis of isopropyl cyclopropanecarboxylate is accelerated by liquid liquid PTC, and the order of catalytic activity is BTEAC>BTMAC>CTMAB>TBAB. The results show that the new synthesis method is superior to those from literature and feasible for production with simple routes, mild reaction conditions, cheap materials and total yield of 52.6%.
文摘1.IntroductionSince the biginning of 1960s,the effectof Mg upon superalloy has been studiedand some satisfactory developments havebeen achieved.The role of Mg on the alloycan be summarized as follows:(1)Themechanical plasticity of Ni-base superalloycan be improved by adding Mg asdesulphurizer,because of forming insolubleMgS instead of other low melting eutectic
文摘Alumina (Al2O3) has been synthesized through combustion synthesis (CS) technique. The calcined products were characterized using X-ray diffractional analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermo-gravimetric analysis (TGA). TG-DTA results reveal the various stages involved in transition from γ-phase to α-Al2O3 phase. The first phase γ-Al2O3 was presented in the temperature range from 600°C-875°C as deduced from the XRD patterns with cubic crystal structure. The second stage occurs in the temperature range from 900°C-1000°C. In the final step, above 1000°C, the aluminium oxide appears completely as α-Al2O3, showing high crystallinity. The particle sizes are closely related to γ- to α-Al2O3 phase transition.
