Factors that affect weld mechanical properties of commercially pure titanium have been investigated using artificial neural networks. Input data were obtained from mechanical testing of single-pass, autogenous welds, ...Factors that affect weld mechanical properties of commercially pure titanium have been investigated using artificial neural networks. Input data were obtained from mechanical testing of single-pass, autogenous welds, and neural network models were used to predict the ultimate tensile strength, yield strength, elongation, reduction of area, Vickers hardness and Rockwell B hardness. The results show that both oxygen and nitrogen have the most significant effects on the strength while hydrogen has the least effect over the range investigated. Predictions of the mechanical properties are shown and agree well with those obtained using the 'oxygen equivalent' (OE) equations.展开更多
In order to establish the rolling process parameters of grade-2 commercially pure titanium(CP-Ti),it is necessary to understand the transformation mechanism and mechanical properties of this material.The β→α transf...In order to establish the rolling process parameters of grade-2 commercially pure titanium(CP-Ti),it is necessary to understand the transformation mechanism and mechanical properties of this material.The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator.Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature.The critical cooling rate for β-phase transforms to α phase is about 15 °C/s.When the cooling rate is higher than 15 °C/s,some β phases with fine granular shape remain residually into plate-like structure.The plate-like α phase forms at cooling rate lower than 2 °C/s,serrate α phase forms at medium cooling rates,about 5-15 °C/s.The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700-900 °C and strain rate of 3.6-40 mm/min.The results show that dynamic recrystallization,dynamic recovery and work-hardening obviously occur during hot deformation.Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature,strain rate,deformation degree and deformation resistance.展开更多
Effects of Ce addition on microstructure,castability(fluidity and hot tearing sensitivity),mechanical properties and electric conductivity of commercial purity aluminum(CP-AI) were investigated through microstructure ...Effects of Ce addition on microstructure,castability(fluidity and hot tearing sensitivity),mechanical properties and electric conductivity of commercial purity aluminum(CP-AI) were investigated through microstructure observation and performance tests.Results show that adding Ce in a CP-AI can considerably refine the grains,and has an important influence on the amount,crystallographic forms,and distribution of secondary phases.Addition of Ce also has a large impact on the fluidity and hot tearing sensitivity(HTS) of the CP-AI.With the addition of Ce from 0.1wt.%to 0.5wt.%,the fluidity of CP-AI is first increased remarkably and then decreased,and the HTS has an opposite response.The best castability of the studied alloys appears to be at 0.2wt.%-0.3wt.%Ce addition.The remarkable improvement in castability is attributed to the considerable refinement of grain structure.Ce addition can also lead to a significant rise in electric conductivity.The maximum conductivity of the as-cast CP-AI is 59.7%IACS with an addition of 0.2wt.%Ce.The T7 heat treatment can further improves the conductivity to 60.7%IACS.The Ce-induced evolution of the secondary phases is believed to be the mechanism for it.展开更多
Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produc...Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.展开更多
基金This work is supported by the Scientific Research Foun-dation for the Returned Overseas Chinese Scholars,Ministry of Education,China
文摘Factors that affect weld mechanical properties of commercially pure titanium have been investigated using artificial neural networks. Input data were obtained from mechanical testing of single-pass, autogenous welds, and neural network models were used to predict the ultimate tensile strength, yield strength, elongation, reduction of area, Vickers hardness and Rockwell B hardness. The results show that both oxygen and nitrogen have the most significant effects on the strength while hydrogen has the least effect over the range investigated. Predictions of the mechanical properties are shown and agree well with those obtained using the 'oxygen equivalent' (OE) equations.
基金Project(J51504) supported by Shanghai Leading Academic Discipline Project,China
文摘In order to establish the rolling process parameters of grade-2 commercially pure titanium(CP-Ti),it is necessary to understand the transformation mechanism and mechanical properties of this material.The β→α transformation kinetics of the grade-2 CP-Ti during continuous cooling was measured and its hot compression behavior was investigated using Gleeble-1500 thermal mechanical simulator.Dynamic CCT diagram confirms that cooling rate has an obvious effect on the start and finishing transformation and microstructures at room temperature.The critical cooling rate for β-phase transforms to α phase is about 15 °C/s.When the cooling rate is higher than 15 °C/s,some β phases with fine granular shape remain residually into plate-like structure.The plate-like α phase forms at cooling rate lower than 2 °C/s,serrate α phase forms at medium cooling rates,about 5-15 °C/s.The flow stress behavior of grade-2 CP-Ti was investigated in a temperature range of 700-900 °C and strain rate of 3.6-40 mm/min.The results show that dynamic recrystallization,dynamic recovery and work-hardening obviously occur during hot deformation.Constitutive equation of grade-2 CP-Ti was established by analyzing the relationship of the deformation temperature,strain rate,deformation degree and deformation resistance.
基金supported by GM Research Foundation under contract No.GB1279-NV
文摘Effects of Ce addition on microstructure,castability(fluidity and hot tearing sensitivity),mechanical properties and electric conductivity of commercial purity aluminum(CP-AI) were investigated through microstructure observation and performance tests.Results show that adding Ce in a CP-AI can considerably refine the grains,and has an important influence on the amount,crystallographic forms,and distribution of secondary phases.Addition of Ce also has a large impact on the fluidity and hot tearing sensitivity(HTS) of the CP-AI.With the addition of Ce from 0.1wt.%to 0.5wt.%,the fluidity of CP-AI is first increased remarkably and then decreased,and the HTS has an opposite response.The best castability of the studied alloys appears to be at 0.2wt.%-0.3wt.%Ce addition.The remarkable improvement in castability is attributed to the considerable refinement of grain structure.Ce addition can also lead to a significant rise in electric conductivity.The maximum conductivity of the as-cast CP-AI is 59.7%IACS with an addition of 0.2wt.%Ce.The T7 heat treatment can further improves the conductivity to 60.7%IACS.The Ce-induced evolution of the secondary phases is believed to be the mechanism for it.
文摘Multi-pass ultrasonic impact treatment(UIT)was applied to modify the microstructure and improve the mechanical and tribological characteristics at the near-surface region of commercially pure Ti(CP-Ti)specimens produced by the laser powder bed fusion(L-PBF)method.UIT considerably refined the L-PBF process-related acicular martensites(α′-M)and produced a well-homogenized and dense surface microstructure,where the porosity content of 1-,3-,and 5-pass UITed samples was reduced by 43,60,and 67%,respectively.The UITed samples showed an enhancement in their near-surface mechanical properties up to a depth of about 300μm.The nanoindentation results for the 3-pass UITed sample revealed an increase of about 53,45,and 220%in its nanohardness,H/E_(r),and H_(3)/E_(r)^(2)indices,respectively.The stylus profilometry results showed that performing the UIT removed the L-PBF-related features/defects and offered a smooth surface.The roughness average(R_(a))and the skewness(R_(sk))of the 3-pass UITed sample were found to be lower than those of the L-PBFed sample by 95 and 223%,respectively.Applying the UIT also enhanced the material ratio,where the maximum load-bearing capacity(~100%)in as-L-PBFed(as-built)and 3-pass UITed samples was obtained at 60-and 10-µm depths,respectively.The tribological investigations showed that applying the UIT resulted in a significant reduction of wear rate and average coefficient of friction(COF)of CP-Ti.For instance,under the normal pressures of 0.05 and 0.2 MPa,the wear rate and COF of the 3-pass UITed sample were lower than those of the L-PBFed sample by 65 and 58%,and 20 and 17%,respectively.
