In this work, Al-7.5Si-4Cu alloy melt modified by Al-10Sr, RE and Al-5Ti-B master alloys was poured into multi-step moulds made from three moulding sands, including quartz, alumina and chromite, to investigate compara...In this work, Al-7.5Si-4Cu alloy melt modified by Al-10Sr, RE and Al-5Ti-B master alloys was poured into multi-step moulds made from three moulding sands, including quartz, alumina and chromite, to investigate comparatively the effects of different cooling rates of the casting mould on the alloy's microstructures and mechanical properties. The results show that with an increase in wall thickness, the cooling rate decreases, the dendrite arm spacing(DAS) increases significantly and the mechanical properties decrease steadily. The elongation is more sensitive to the cooling rate than the tensile strength. No obvious trend of the effect of wall thickness on hardness of the alloy was found. When the cooling rate is at its greatest, the microstructures and mechanical properties are the best when using chromite sand. The improvement of the properties is mainly attributed to the decrease of the DAS, the grain refinement and the metamorphic effect. Each of the three has a strong impact on the microstructures. Furthermore, a series of fitting models was established based on the data of the DAS to predict the mechanical properties of the multivariate sand-cast Al-7.5Si-4Cu alloy,展开更多
The rheological behavior of partially solidified Al-10% Cu alloy is in-vestigated.It is found that the slurry presents the character of a psoudoplastie fluid inisothermally holding and the apparent viscosity increases...The rheological behavior of partially solidified Al-10% Cu alloy is in-vestigated.It is found that the slurry presents the character of a psoudoplastie fluid inisothermally holding and the apparent viscosity increases with increasing cooling ratein continuously cooling.The effect of cooling rate on the apparent viscosity decreasesin high stirring rate range.The measured value of apparent viscosity is influenced bythe diameter of the screw propeller.展开更多
The bulk glassy Cu 60 Zr 30 Ti 10 alloy with a diameter up to 4 mm and a length of 70 mm containing nanocrystalline phase was successfully developed by using copper mold casting method. The temperature interval of the...The bulk glassy Cu 60 Zr 30 Ti 10 alloy with a diameter up to 4 mm and a length of 70 mm containing nanocrystalline phase was successfully developed by using copper mold casting method. The temperature interval of the supercooled liquid region before crystallization is above 37 K. The glass transition temperature ( T g) and the reduced glass transition temperature ( T g/ T l) of the cast bulk glassy Cu 60 Zr 30 Ti 10 alloy are 713 K and 0.62. The cast bulk glassy alloy, which has high glassy forming ability, shows expected mechanical properties. The elastic modulus, yield strength, fracture strength and elongation including elastic elongation are 114 GPa, 1 785 MPa, 2 150 MPa and 3.3% respectively in compressive deformation, and 112 GPa, 1 780 MPa, 2 000 MPa and 1.9% respectively in tensile deformation. High resolution transmission electron microscope (HRTEM) and nano beam electron diffraction (NBED) studies indicate that the cast metallic bulk glassy Cu 60 Zr 30 Ti 10 alloy consists of nanocrystals with a size of 4 nm embedded in glassy matrix. The nanoparticle is identified as CuZr and has point space group symmetry of pm3m and its lattice parameter is a =0.3 262 nm . The nanocrystalline phase grew up to 10 nm upon annealing at 430 ℃ for 10 min and caused the alloy brittle.展开更多
Al-4. 5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand ...Al-4. 5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand and chill cast alloys. Equiaxed grains were observed for spray formed alloys. Wear testing employing a pin-on-disc type set-up, reveals considerably lower wear of spray deposited alloy compared to that of chill and sand cast alloys. The morphological features of wear track on specimen and debris indicated a mixed oxidative-cum-adhesive wear mechanisms for these alloys tested in the present investigation. (Edited author abstract) 36 Refs.展开更多
After solutionized, 70Cu 30Ni alloy was deformed in different degrees and then exposed both in NaCl solution and in seawater. The results show that with the increase of deformation, the E c and R p -1 ...After solutionized, 70Cu 30Ni alloy was deformed in different degrees and then exposed both in NaCl solution and in seawater. The results show that with the increase of deformation, the E c and R p -1 of 70Cu 30Ni alloy decrease more quickly and fluctuate less when the exposure time increases, and the corrosion product films contain more nickel and less chloride because the distribution of dislocations tends to be homogeneous.展开更多
Heating rate playsanimportantroleon recrystallizationtextureofcold deformed metals.Inthispaper,thelaser heatingtechnique wasusedtotheultrarapidlyannealingon acold rolledCu 30 mass% Zn alloy. The experimental result...Heating rate playsanimportantroleon recrystallizationtextureofcold deformed metals.Inthispaper,thelaser heatingtechnique wasusedtotheultrarapidlyannealingon acold rolledCu 30 mass% Zn alloy. The experimental resultsshow thatthe texture development differs from those observed in the case of conventional annealing. When primary recrystallization completes,the grainsizeisvery fineandthegrain orientation distributionisalmostrandom . Withthecontinuousgrain growing,the dispersioncharacterofthegrainorientationsstillre mains. The possible mechanismson theevolution of ultrarapid recryctallization texture were discussed.展开更多
A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment...A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment a non catalytic nucleation composite glass lined coating (B F) was prepared on the inner surface of mould and the Cu 70 Ni 30 alloy was selected to perform undercooling experiment in the B F non catalytic coating mould. Its ratio of undercooling heredity was 0.76. The results prove that the B F coating is an ideal non catalytic media for purified Cu 70 Ni 30 alloy melts due to its small contact angle between the melt and coating layer. Considering that various microstructures form under different undercoolings, two critical undercoolings, Δ T 1 and Δ T 2, and their corresponding microstructures of Cu 70 Ni 30 alloy are well defined. Moreover, it is found that the manned trigging solidification in the non catalytic coating mould could be used to get directional undercooling dendrite structure while the melt undercooling is larger than the critical undercooling Δ T 2.展开更多
Experiments of X-ray diffraction for liquid Cu70Ni30 alloy above and below its liquidus (1 230℃) have been carried out. By the analysis of experimental results, it is discovered that difference between structures of ...Experiments of X-ray diffraction for liquid Cu70Ni30 alloy above and below its liquidus (1 230℃) have been carried out. By the analysis of experimental results, it is discovered that difference between structures of liquid and undercooled Cu70Ni30 alloy is their cluster sizes. The correlation radius of cluster is 1.125 nm and the atom number of cluster is 403 at 1 250-1 400℃, and they are 1.3 nm and 704 respectively at the undercooled liquid state (1 200℃). The structure of liquid alloy is fee short order and its solid structure, fcc, is kept from liquid fcc short order.展开更多
In this study,Al–4Cu alloy specimens with spherical grains and liquid flms were obtained by isothermal reheating treatment.The hot cracking of the solidifcation process was determined using a modifed constrained rod ...In this study,Al–4Cu alloy specimens with spherical grains and liquid flms were obtained by isothermal reheating treatment.The hot cracking of the solidifcation process was determined using a modifed constrained rod casting experimental apparatus,and the efect of liquid flm characteristics at the end of solidifcation on hot cracking initiation of Al–4Cu alloys was systematically investigated by combining molecular dynamics simulations and other methods.With the extension of soaking time,the liquid fraction(liquid flm fraction at the end of solidifcation)and grain shape factor increased with higher isothermal reheating temperatures.Additionally,the widened flling channel decreased the hot cracking initiation temperature and the critical hot cracking shrinkage stress was found to increase,thus reducing the hot cracking severity in Al–4Cu alloys.Molecular dynamics simulations revealed that with the extension of soaking time,the composition of the liquid flm changed at diferent isothermal reheating temperatures,but the short-range structure and atomic ordering of the liquid flm remained the same.The activity of the liquid flm increased in equilibrium,leading to a decrease in viscosity and an increase in fuidity,which contributed to the flling behaviour.After isothermal reheating at 640℃for 60 min,the liquid fraction reached the maximum,and the viscosity of the liquid flm was the minimum.In addition,almost no hot cracks were found.展开更多
A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu70Ni30 adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic aver...A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu70Ni30 adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2 × 1012 K/s, the Cu70Ni30 formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be further understood.展开更多
基金financially supported by the Technology Innovation Fund Project of High-tech Small and Medium Enterprises,Ministry of Science and Technology of China(No:09C26279200863)the Special Fund Project on Science and Technology Achievement Transformation of Jiangsu Province(No:BA201184)
文摘In this work, Al-7.5Si-4Cu alloy melt modified by Al-10Sr, RE and Al-5Ti-B master alloys was poured into multi-step moulds made from three moulding sands, including quartz, alumina and chromite, to investigate comparatively the effects of different cooling rates of the casting mould on the alloy's microstructures and mechanical properties. The results show that with an increase in wall thickness, the cooling rate decreases, the dendrite arm spacing(DAS) increases significantly and the mechanical properties decrease steadily. The elongation is more sensitive to the cooling rate than the tensile strength. No obvious trend of the effect of wall thickness on hardness of the alloy was found. When the cooling rate is at its greatest, the microstructures and mechanical properties are the best when using chromite sand. The improvement of the properties is mainly attributed to the decrease of the DAS, the grain refinement and the metamorphic effect. Each of the three has a strong impact on the microstructures. Furthermore, a series of fitting models was established based on the data of the DAS to predict the mechanical properties of the multivariate sand-cast Al-7.5Si-4Cu alloy,
文摘The rheological behavior of partially solidified Al-10% Cu alloy is in-vestigated.It is found that the slurry presents the character of a psoudoplastie fluid inisothermally holding and the apparent viscosity increases with increasing cooling ratein continuously cooling.The effect of cooling rate on the apparent viscosity decreasesin high stirring rate range.The measured value of apparent viscosity is influenced bythe diameter of the screw propeller.
文摘The bulk glassy Cu 60 Zr 30 Ti 10 alloy with a diameter up to 4 mm and a length of 70 mm containing nanocrystalline phase was successfully developed by using copper mold casting method. The temperature interval of the supercooled liquid region before crystallization is above 37 K. The glass transition temperature ( T g) and the reduced glass transition temperature ( T g/ T l) of the cast bulk glassy Cu 60 Zr 30 Ti 10 alloy are 713 K and 0.62. The cast bulk glassy alloy, which has high glassy forming ability, shows expected mechanical properties. The elastic modulus, yield strength, fracture strength and elongation including elastic elongation are 114 GPa, 1 785 MPa, 2 150 MPa and 3.3% respectively in compressive deformation, and 112 GPa, 1 780 MPa, 2 000 MPa and 1.9% respectively in tensile deformation. High resolution transmission electron microscope (HRTEM) and nano beam electron diffraction (NBED) studies indicate that the cast metallic bulk glassy Cu 60 Zr 30 Ti 10 alloy consists of nanocrystals with a size of 4 nm embedded in glassy matrix. The nanoparticle is identified as CuZr and has point space group symmetry of pm3m and its lattice parameter is a =0.3 262 nm . The nanocrystalline phase grew up to 10 nm upon annealing at 430 ℃ for 10 min and caused the alloy brittle.
文摘Al-4. 5Cu-5Pb alloy was prepared by sand and chill casting. The same alloy was also spray deposited at a gas pressure of 1.6 MPa. The microstructural features exhibit a coarse to fine dendritic morphology for sand and chill cast alloys. Equiaxed grains were observed for spray formed alloys. Wear testing employing a pin-on-disc type set-up, reveals considerably lower wear of spray deposited alloy compared to that of chill and sand cast alloys. The morphological features of wear track on specimen and debris indicated a mixed oxidative-cum-adhesive wear mechanisms for these alloys tested in the present investigation. (Edited author abstract) 36 Refs.
文摘After solutionized, 70Cu 30Ni alloy was deformed in different degrees and then exposed both in NaCl solution and in seawater. The results show that with the increase of deformation, the E c and R p -1 of 70Cu 30Ni alloy decrease more quickly and fluctuate less when the exposure time increases, and the corrosion product films contain more nickel and less chloride because the distribution of dislocations tends to be homogeneous.
文摘Heating rate playsanimportantroleon recrystallizationtextureofcold deformed metals.Inthispaper,thelaser heatingtechnique wasusedtotheultrarapidlyannealingon acold rolledCu 30 mass% Zn alloy. The experimental resultsshow thatthe texture development differs from those observed in the case of conventional annealing. When primary recrystallization completes,the grainsizeisvery fineandthegrain orientation distributionisalmostrandom . Withthecontinuousgrain growing,the dispersioncharacterofthegrainorientationsstillre mains. The possible mechanismson theevolution of ultrarapid recryctallization texture were discussed.
文摘A new concept of undercooling heredity is developed to evaluate the undercooling ability in a non catalytic nucleation coated mould, where alloy melts were highly undercooled previously. Before the heredity experiment a non catalytic nucleation composite glass lined coating (B F) was prepared on the inner surface of mould and the Cu 70 Ni 30 alloy was selected to perform undercooling experiment in the B F non catalytic coating mould. Its ratio of undercooling heredity was 0.76. The results prove that the B F coating is an ideal non catalytic media for purified Cu 70 Ni 30 alloy melts due to its small contact angle between the melt and coating layer. Considering that various microstructures form under different undercoolings, two critical undercoolings, Δ T 1 and Δ T 2, and their corresponding microstructures of Cu 70 Ni 30 alloy are well defined. Moreover, it is found that the manned trigging solidification in the non catalytic coating mould could be used to get directional undercooling dendrite structure while the melt undercooling is larger than the critical undercooling Δ T 2.
文摘Experiments of X-ray diffraction for liquid Cu70Ni30 alloy above and below its liquidus (1 230℃) have been carried out. By the analysis of experimental results, it is discovered that difference between structures of liquid and undercooled Cu70Ni30 alloy is their cluster sizes. The correlation radius of cluster is 1.125 nm and the atom number of cluster is 403 at 1 250-1 400℃, and they are 1.3 nm and 704 respectively at the undercooled liquid state (1 200℃). The structure of liquid alloy is fee short order and its solid structure, fcc, is kept from liquid fcc short order.
基金supported by the National Natural Science Foundation of China(No.51875365).
文摘In this study,Al–4Cu alloy specimens with spherical grains and liquid flms were obtained by isothermal reheating treatment.The hot cracking of the solidifcation process was determined using a modifed constrained rod casting experimental apparatus,and the efect of liquid flm characteristics at the end of solidifcation on hot cracking initiation of Al–4Cu alloys was systematically investigated by combining molecular dynamics simulations and other methods.With the extension of soaking time,the liquid fraction(liquid flm fraction at the end of solidifcation)and grain shape factor increased with higher isothermal reheating temperatures.Additionally,the widened flling channel decreased the hot cracking initiation temperature and the critical hot cracking shrinkage stress was found to increase,thus reducing the hot cracking severity in Al–4Cu alloys.Molecular dynamics simulations revealed that with the extension of soaking time,the composition of the liquid flm changed at diferent isothermal reheating temperatures,but the short-range structure and atomic ordering of the liquid flm remained the same.The activity of the liquid flm increased in equilibrium,leading to a decrease in viscosity and an increase in fuidity,which contributed to the flling behaviour.After isothermal reheating at 640℃for 60 min,the liquid fraction reached the maximum,and the viscosity of the liquid flm was the minimum.In addition,almost no hot cracks were found.
基金supported by the National Natural Science Foundation of China(Grant No.50271026).
文摘A molecular dynamics (MD) simulation study has been performed for the rapid solidification of Cu70Ni30 adopting the quantum Sutton-Chen many-body potentials. By analyzing the bond-types and the relation of atomic average energy versus temperature, it was demonstrated that as cooling rate being 2 × 1012 K/s, the Cu70Ni30 formed fcc crystal structures and freezing point was found. In addition, having analyzed the transformation of microstructures and the detail of crystal growth by using atomic trace and visual method, not only could the formation of binary disordered solid solution be showed, but also the solidification of liquid metals and the crystal growth processes could be further understood.
