Split Hopkinson Tension Bar(SHTB) experiments were conducted to explore the dynamic mechanical behavior and deformation mechanism of powder metallurgical(PM) Ti-47 Al-2 Nb-2 Cr-0.2 W(at.%)intermetallics with near lame...Split Hopkinson Tension Bar(SHTB) experiments were conducted to explore the dynamic mechanical behavior and deformation mechanism of powder metallurgical(PM) Ti-47 Al-2 Nb-2 Cr-0.2 W(at.%)intermetallics with near lamellar(NL) and duplex(DP)microstructures. Results show that,under dynamic loading,the high temperature strength of the PM TiAl intermetallics is higher than that under quasi-static loading, and the ductile to brittle transition temperature(DBTT) increases with the increase of strain rate. Formation of twinning and stacking faults is the main deformation mechanism during dynamic loading. The work hardening rates of the PM TiAl intermetallics are nearly insensitive to strain rate and temperature at high strain rates(800-1600 s-1)and high temperatures(650-850 ℃). Zerilli-Armstrong model is successfully used to describe the dynamic flowing behavior of the PM TiAl intermetallics. In general, the PM TiAl intermetallics are found to have promising impact properties, suitable for high-temperature and high-impact applications.展开更多
Finite element(FEM)analysis was used to systematically evaluate the inhomogeneity of deformation in cylindrical samples with various sample-anvil friction coefficients,m.It was found that the level of friction strongl...Finite element(FEM)analysis was used to systematically evaluate the inhomogeneity of deformation in cylindrical samples with various sample-anvil friction coefficients,m.It was found that the level of friction strongly influences the deformation homogeneity,which increases significantly with the friction coefficient although the overall geometry of the samples almost remains the same when m >0.4.The position,at which the effective strain along the maximum radial direction in a compressed sample is equal to the equivalent strain of the sample,does not vary greatly with respect to both equivalent strain of the sample and m.Hardness measurements of compressed cylindrical 5056B Al alloy samples revealed a change of effective strain distribution similar to that revealed by FEM analysis.There exists a quantitative relationship between the hardness and the effective strain if no recrystallization or recovery occurs during the compression process.展开更多
In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and ...In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.展开更多
In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow dat...In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow data,superplastic region is estimated at relatively low temperature and strain rate domains,specifically around 1000℃/10^-3s^-1.Thereafter,the cylinder specimens are isothermally compressed at 1000℃/10^-3s^-1 and 1025℃/10^-3s^-1 with different strains,to exam the superplasticity and related mechanisms.The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization(DRX),and the grain boundary sliding(GBS)contributes to the total strain during superplastic compression as well.In addition,the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected,which is different from superplastic tensile deformation.展开更多
基金Project(51774335)supported by the National Natural Science Foundation of ChinaProject(2017JJ2311)supported by the Natural Science Foundation of Hunan Province,China+1 种基金Project(KFJJ11-7M)supported by the Opening Project of State Key Laboratory of Explosion Science and Technology,ChinaProject(HKHTZD20140702020004)supported by the Special Funds for Future Industrial Development of Shenzhen City,China
文摘Split Hopkinson Tension Bar(SHTB) experiments were conducted to explore the dynamic mechanical behavior and deformation mechanism of powder metallurgical(PM) Ti-47 Al-2 Nb-2 Cr-0.2 W(at.%)intermetallics with near lamellar(NL) and duplex(DP)microstructures. Results show that,under dynamic loading,the high temperature strength of the PM TiAl intermetallics is higher than that under quasi-static loading, and the ductile to brittle transition temperature(DBTT) increases with the increase of strain rate. Formation of twinning and stacking faults is the main deformation mechanism during dynamic loading. The work hardening rates of the PM TiAl intermetallics are nearly insensitive to strain rate and temperature at high strain rates(800-1600 s-1)and high temperatures(650-850 ℃). Zerilli-Armstrong model is successfully used to describe the dynamic flowing behavior of the PM TiAl intermetallics. In general, the PM TiAl intermetallics are found to have promising impact properties, suitable for high-temperature and high-impact applications.
基金Project(2016JJ1016) supported by the Science Fund for Distinguished Young Scholars of Hunan Province,ChinaProject(201301G0105337290) supported by the Program of Innovation and Entrepreneur Team Introduced by Guangdong Province,China
文摘Finite element(FEM)analysis was used to systematically evaluate the inhomogeneity of deformation in cylindrical samples with various sample-anvil friction coefficients,m.It was found that the level of friction strongly influences the deformation homogeneity,which increases significantly with the friction coefficient although the overall geometry of the samples almost remains the same when m >0.4.The position,at which the effective strain along the maximum radial direction in a compressed sample is equal to the equivalent strain of the sample,does not vary greatly with respect to both equivalent strain of the sample and m.Hardness measurements of compressed cylindrical 5056B Al alloy samples revealed a change of effective strain distribution similar to that revealed by FEM analysis.There exists a quantitative relationship between the hardness and the effective strain if no recrystallization or recovery occurs during the compression process.
基金supported financially by the National Key Research and Development Program of China(No.2018YFB0704100)the Outstanding Graduate Project of Advanced Non-ferrous Metal Structural Materials and Manufacturing Collaborative Innovation Center+2 种基金the Funding from the Opening Project of State Key Laboratory of Nickel and Cobalt Resources Comprehensive Utilizationthe Project of Innovation and Entrepreneur Team Introduced by Guangdong Province(No.201301G0105337290)the Special Funds for Future Industrial Development of Shenzhen(No.HKHTZD20140702020004)。
文摘In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.
基金supported financially by the National Key Research and Development Program of China (No.2016YFB0701404)the National Natural Science Foundation of China (No.91860105)the Fund from Innovation and Entrepreneur Team Introduced by Guangdong Province (No. 201301G0105337290)
文摘In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow data,superplastic region is estimated at relatively low temperature and strain rate domains,specifically around 1000℃/10^-3s^-1.Thereafter,the cylinder specimens are isothermally compressed at 1000℃/10^-3s^-1 and 1025℃/10^-3s^-1 with different strains,to exam the superplasticity and related mechanisms.The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization(DRX),and the grain boundary sliding(GBS)contributes to the total strain during superplastic compression as well.In addition,the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected,which is different from superplastic tensile deformation.
