The non-ferrous SMAs(shape memory alloys)have,normally,two problems that hinder the use in industrial scale:the natural aging and grain growth.The first degrades the memory effect,while the second,observed during the ...The non-ferrous SMAs(shape memory alloys)have,normally,two problems that hinder the use in industrial scale:the natural aging and grain growth.The first degrades the memory effect,while the second,observed during the alloy’s mechanical processing,modifies the phase transformation temperatures.Thus,the study of recrystallization kinetics is important for enabling the control of hardened state as a function of treatment time without allowing the exaggerated grain growth.The objective of this study is to determine the recrystallization kinetics in different SMAs(Cu-14Al-4Ni,Cu-12Al-0.5Be and Ni-42Ti),based on an empirical law of J-M-A(Johnson-Mehl-Avrami),as well as their activation energies for grain growth process according to the empirical Arrhenius law.Quantitative evaluations of the grain growth kinetics over a wide range of indicated DSC(differential scanning calorimetry)temperatures have been performed.The results show that the alloy less susceptible to aging in temperatures below the recrystallization peak is the Ni-42Ti,because it presented the highest activation energy,followed by the Cu-14Al-4Ni.The equations that describe the recrystallization kinetics follow the empirical law of J-M-A.The recrystallization kinetics accompanied by hardness variation was an important tool,working as an advisor for selection of treatment time as a function of temperature.展开更多
The present research aimed to analyze the influence that different contents of titanium(x=0.5,0.6 and 0.7 wt.%)have on the martensitic transformation temperature of a Cu-14Al-4Ni(wt.%)SMA(shape memory alloy).The Cu-14...The present research aimed to analyze the influence that different contents of titanium(x=0.5,0.6 and 0.7 wt.%)have on the martensitic transformation temperature of a Cu-14Al-4Ni(wt.%)SMA(shape memory alloy).The Cu-14Al-4Ni-xTi samples were casted in an arc-melting furnace and rapidly solidified.All samples underwent heat treatment in a tubular furnace at a temperature of 1,100°C for 30 min and water quenched at 25°C.Subsequently,samples were analyzed by SEM(scanning electron microscopy)with EDS(energy dispersive spectroscopy),XRD(X-ray diffraction)and DSC(differential scanning calorimeter).SEM images and XRD patterns showed that the presence of titanium modified the alloy’s microstructure,induced the formation of three titanium rich phases called“X”phase(CuNi2Ti,Cu3Ti and AlCu2Ti)and reduced the presence of the brittle phaseγ2(Cu9Al4)for samples with 0.6 and 0.7 wt.%Ti.The titanium added to the copper based SMA also functioned as a refiner,reducing GS(grain size)up to approximately 80%with the increase of Ti content.DSC results exhibited low enthalpy levels,hysteresis,as well as low start martensitic transformation temperatures.展开更多
This paper aims to verify the Cu9Al4 phase influence on the nanomechanical behavior of the Cu-14Al-4Ni-xTi alloy obtained by rapid solidification with addition of different amounts of Ti.Using the Scanning Electron Mi...This paper aims to verify the Cu9Al4 phase influence on the nanomechanical behavior of the Cu-14Al-4Ni-xTi alloy obtained by rapid solidification with addition of different amounts of Ti.Using the Scanning Electron Microscopy(SEM),Atomic Force Microscopy(AFM),Energy Dispersion Spectroscopy(EDS)and X-Ray Diffraction(XRD),it was possible to perform the samples’microstructural characterization.In addition,the reduction of the Cu9Al4 phase precipitation and the X-phase appearance were verified according to the increase of the titanium percentage added.The nanomechanical behavior was evaluated by nanoindentation tests,which showed a significant decrease of the elastic modules and an increase of the Poisson coefficient’s according to the titanium amount.This research establishes that the reduction of Cu9Al4 phase implies on the increase of the capacity to dissipate energy.Therefore,the high damping capacity combined with the X-phase presence increases the super elasticity and the alloy ductility.展开更多
DCT(deep cryogenic treatment)is commonly used in industry to improve the wear resistance characteristics of steels,especially.However,there are just a few researches about the effects on non-ferrous metals.The purpose...DCT(deep cryogenic treatment)is commonly used in industry to improve the wear resistance characteristics of steels,especially.However,there are just a few researches about the effects on non-ferrous metals.The purpose of this work was to investigate how DCT affects the properties of Cu-14Al-4Ni alloy treated at different soak time and submitted to thermomechanical cycling.A comparative experimental analysis was performed of the thermal properties of alloys obtained on a vacuum furnace,treated by DCT and thermomechanically cyclized.The results indicates that thermomechanical cycling promoted the appearance and growth of the martensitic phaseγ'1,less ductile than the martensitic phaseβ'1,which together with the induced hardening produced an increase in transformation temperatures and microhardness.The higher the number of cycles,the greater these effects.The DCT promoted an increase in the intensity of the diffraction peaks corresponding to the phaseβ'1 and the maintenance of them during the thermomechanical cycling of the material,which indicates that the DCT stabilizes the martensitic phaseβ'1 and,consequently,caused a reduction and stabilization of the martensitic transformation temperatures and the microhardness,when compared to the untreated material.The longer the soaking time of DCT,the greater these effects.展开更多
文摘The non-ferrous SMAs(shape memory alloys)have,normally,two problems that hinder the use in industrial scale:the natural aging and grain growth.The first degrades the memory effect,while the second,observed during the alloy’s mechanical processing,modifies the phase transformation temperatures.Thus,the study of recrystallization kinetics is important for enabling the control of hardened state as a function of treatment time without allowing the exaggerated grain growth.The objective of this study is to determine the recrystallization kinetics in different SMAs(Cu-14Al-4Ni,Cu-12Al-0.5Be and Ni-42Ti),based on an empirical law of J-M-A(Johnson-Mehl-Avrami),as well as their activation energies for grain growth process according to the empirical Arrhenius law.Quantitative evaluations of the grain growth kinetics over a wide range of indicated DSC(differential scanning calorimetry)temperatures have been performed.The results show that the alloy less susceptible to aging in temperatures below the recrystallization peak is the Ni-42Ti,because it presented the highest activation energy,followed by the Cu-14Al-4Ni.The equations that describe the recrystallization kinetics follow the empirical law of J-M-A.The recrystallization kinetics accompanied by hardness variation was an important tool,working as an advisor for selection of treatment time as a function of temperature.
基金The authors would like to thank the Federal Institute of Science and Technology of Bahia,the University of São Paulo,the University of Brasilia and the PRPGI for all the support to carry out this research.
文摘The present research aimed to analyze the influence that different contents of titanium(x=0.5,0.6 and 0.7 wt.%)have on the martensitic transformation temperature of a Cu-14Al-4Ni(wt.%)SMA(shape memory alloy).The Cu-14Al-4Ni-xTi samples were casted in an arc-melting furnace and rapidly solidified.All samples underwent heat treatment in a tubular furnace at a temperature of 1,100°C for 30 min and water quenched at 25°C.Subsequently,samples were analyzed by SEM(scanning electron microscopy)with EDS(energy dispersive spectroscopy),XRD(X-ray diffraction)and DSC(differential scanning calorimeter).SEM images and XRD patterns showed that the presence of titanium modified the alloy’s microstructure,induced the formation of three titanium rich phases called“X”phase(CuNi2Ti,Cu3Ti and AlCu2Ti)and reduced the presence of the brittle phaseγ2(Cu9Al4)for samples with 0.6 and 0.7 wt.%Ti.The titanium added to the copper based SMA also functioned as a refiner,reducing GS(grain size)up to approximately 80%with the increase of Ti content.DSC results exhibited low enthalpy levels,hysteresis,as well as low start martensitic transformation temperatures.
基金The authorswould like to thankthe Federal Institute of Science and Technology of Bahia,the University of Sao Paulo and the University of Brasilia for all the support to carry out this research.
文摘This paper aims to verify the Cu9Al4 phase influence on the nanomechanical behavior of the Cu-14Al-4Ni-xTi alloy obtained by rapid solidification with addition of different amounts of Ti.Using the Scanning Electron Microscopy(SEM),Atomic Force Microscopy(AFM),Energy Dispersion Spectroscopy(EDS)and X-Ray Diffraction(XRD),it was possible to perform the samples’microstructural characterization.In addition,the reduction of the Cu9Al4 phase precipitation and the X-phase appearance were verified according to the increase of the titanium percentage added.The nanomechanical behavior was evaluated by nanoindentation tests,which showed a significant decrease of the elastic modules and an increase of the Poisson coefficient’s according to the titanium amount.This research establishes that the reduction of Cu9Al4 phase implies on the increase of the capacity to dissipate energy.Therefore,the high damping capacity combined with the X-phase presence increases the super elasticity and the alloy ductility.
文摘DCT(deep cryogenic treatment)is commonly used in industry to improve the wear resistance characteristics of steels,especially.However,there are just a few researches about the effects on non-ferrous metals.The purpose of this work was to investigate how DCT affects the properties of Cu-14Al-4Ni alloy treated at different soak time and submitted to thermomechanical cycling.A comparative experimental analysis was performed of the thermal properties of alloys obtained on a vacuum furnace,treated by DCT and thermomechanically cyclized.The results indicates that thermomechanical cycling promoted the appearance and growth of the martensitic phaseγ'1,less ductile than the martensitic phaseβ'1,which together with the induced hardening produced an increase in transformation temperatures and microhardness.The higher the number of cycles,the greater these effects.The DCT promoted an increase in the intensity of the diffraction peaks corresponding to the phaseβ'1 and the maintenance of them during the thermomechanical cycling of the material,which indicates that the DCT stabilizes the martensitic phaseβ'1 and,consequently,caused a reduction and stabilization of the martensitic transformation temperatures and the microhardness,when compared to the untreated material.The longer the soaking time of DCT,the greater these effects.
