The ongoing collaborative research between Auburn University and Johnson Controls was described. A Ti rich binary NiTi alloy and two ternary alloys having the compositions Ni 49 Ti 51- x Hf x with 1% and 3%(more fract...The ongoing collaborative research between Auburn University and Johnson Controls was described. A Ti rich binary NiTi alloy and two ternary alloys having the compositions Ni 49 Ti 51- x Hf x with 1% and 3%(more fraction) Hf were investigated. The influence of Hf content, cold working(CW) and heat treatment temperature (HT) on the martensitic and R phase transformations was thermally analyzed using differential scanning calorimetry (DSC). The crystal structures of the alloys were examined by X ray diffraction. Results showed that at low HT, the martensitic transformation temperature (TT) decreases with increasing CW for all the alloys studied. In this alloy, for a given CW, the martensite TT increases with increasing HT above 350 ℃. This phenomenon is enhanced by the presence of Hf. Different mechanisms can be responsible for the observed behavior. These mechanisms may involve interaction between phase transformations, dislocations and internal stresses. The effect of Hf substitution is likely due to the atomic size difference between Ti and Hf. A secondary phase,identified as Ti 2Ni in binary NiTi and (TiHf) 2Ni in the two ternary alloys, was observed. The influence of cold work, heat treatment and thermal cycling on the R phase (R) transformation in three alloys was also thermally analyzed. Results showed that such transformation depends on composition as well as CW and HT conditions in a complex manner. Effort was made to identify the microstructure and the factors responsible for the observed behavior in the R phase transformation.展开更多
In ordertoimprovethe dischargecapacity of Ti2 Ni hydrogen storage alloy, the phases and effecton the property for Ti Nialloy with alittle La( La contentisbetween 5 25 wt% and12 62 wt%) were investigated in this pa...In ordertoimprovethe dischargecapacity of Ti2 Ni hydrogen storage alloy, the phases and effecton the property for Ti Nialloy with alittle La( La contentisbetween 5 25 wt% and12 62 wt%) were investigated in this paper. It is found that La exists in the form ofLaNi5 ,thesecond phase,in Ti Nialloy when La> 8 wt% . LaNi5 phasecaneffectivelyim provethe activity property and discharge capacity of Ti Ni alloy. While the soluble Ti inmain phase Ti2 Niisadverseto hydrogen adsorption desorption cycle and itshould be dimin ished .展开更多
The modification of the electron diffraction pattern(EDP) of B2 in an as rapidly quenched then short time aged Ti Ni shape memory alloy(SMA) has been studied systematically using TEM. It was found that the diffusio...The modification of the electron diffraction pattern(EDP) of B2 in an as rapidly quenched then short time aged Ti Ni shape memory alloy(SMA) has been studied systematically using TEM. It was found that the diffusion scattering rings in EDP of an as rapidly quenched Ti-Ni SMA is associated with short range order (SRO) of vancancies in parent B2. After aging at 450℃ for 5 min the diffusion scattering rings are replaced by 1/2 {001} and 1 / 4 {012} extra reflections. It indicates that the SRO of vacancies has transformed into long range order (LRO) of vacancies,moreover,the LRO of vacancies exists in microdomains.展开更多
Electrochemical behaviors of Ti Ni shape memory alloy in fibrinogen solution were studied by electrochemical techniques. The results indicate that the addition of the fibrinogen has no obvious effect on the corrosion ...Electrochemical behaviors of Ti Ni shape memory alloy in fibrinogen solution were studied by electrochemical techniques. The results indicate that the addition of the fibrinogen has no obvious effect on the corrosion potential, but decreases the pitting potential markedly and increases the passive current densities. The analysis of energy dispersive X ray for samples adsorbing fibrinogen exhibits that the elements of O, C and N exist on the surface of Ti Ni alloy. Furthermore, the scanning electron microscope micrographs confirm that the configuration of the adsorbing fibrinogen concentrating on surface defects is like cluster and the fibrinogen adsorption concentration is 96.67 mg/m 2 through ultroviolet ray absorption method. Fibrinogen combined with Ti Ni alloy surface by complex band and its electrochemical transfer accelerated the corrosion of alloy.展开更多
Functional stability of superelasticity is crucial for practical applications of shape memory alloys.It is degraded by a Lüders-like deformation with elevated local stress concentration under tensile load.By incr...Functional stability of superelasticity is crucial for practical applications of shape memory alloys.It is degraded by a Lüders-like deformation with elevated local stress concentration under tensile load.By increasing the degree of solute supersaturation and applying appropriate thermomechanical treatments,a Ti-Ni alloy with nanocrystallinity and dispersed nanoprecipitates is obtained.In contrast to conventional Ti-Ni alloys,the superelasticity in the target alloy is accompanied by homogeneous deformation due to the sluggish stress-induced martensitic transformation.The alloy thus shows a fully recoverable strain of 6%under tensile stress over 1 GPa and a large adiabatic temperature decrease of 13.1 K under tensile strain of 4.5%at room temperature.Moreover,both superelasticity and elastocaloric effect exhibit negligible degradation in response to applied strain of 4%during cycling.We attribute the improved functional stability to low dislocation activity resulting from the suppression of localized deformation and the combined strengthening effect of nanocrystalline structure and nanoprecipitates.Thus,the design of such a microstructure enabling homogeneous deformation provides a recipe for stable superelasticity and elastocaloric effect.展开更多
文摘制备了添加不同含量合金元素Sc、Y的V3Ti Ni0.56系钒基固溶体储氢合金,通过显微组织观察,以及电化学腐蚀性能、充放电循环稳定性的测试与分析发现:合金元素Sc或Y的添加,有利于提高合金的电化学腐蚀性能、充放电循环稳定性,复合添加合金元素Sc和Y的效果较单一添加好。与V3Ti Ni0.56合金相比,复合添加合金元素Sc和Y可以使合金腐蚀电位正移193 m V,充放电循环20次后合金的放电容量衰减率从95%减小至21%。
文摘The ongoing collaborative research between Auburn University and Johnson Controls was described. A Ti rich binary NiTi alloy and two ternary alloys having the compositions Ni 49 Ti 51- x Hf x with 1% and 3%(more fraction) Hf were investigated. The influence of Hf content, cold working(CW) and heat treatment temperature (HT) on the martensitic and R phase transformations was thermally analyzed using differential scanning calorimetry (DSC). The crystal structures of the alloys were examined by X ray diffraction. Results showed that at low HT, the martensitic transformation temperature (TT) decreases with increasing CW for all the alloys studied. In this alloy, for a given CW, the martensite TT increases with increasing HT above 350 ℃. This phenomenon is enhanced by the presence of Hf. Different mechanisms can be responsible for the observed behavior. These mechanisms may involve interaction between phase transformations, dislocations and internal stresses. The effect of Hf substitution is likely due to the atomic size difference between Ti and Hf. A secondary phase,identified as Ti 2Ni in binary NiTi and (TiHf) 2Ni in the two ternary alloys, was observed. The influence of cold work, heat treatment and thermal cycling on the R phase (R) transformation in three alloys was also thermally analyzed. Results showed that such transformation depends on composition as well as CW and HT conditions in a complex manner. Effort was made to identify the microstructure and the factors responsible for the observed behavior in the R phase transformation.
文摘In ordertoimprovethe dischargecapacity of Ti2 Ni hydrogen storage alloy, the phases and effecton the property for Ti Nialloy with alittle La( La contentisbetween 5 25 wt% and12 62 wt%) were investigated in this paper. It is found that La exists in the form ofLaNi5 ,thesecond phase,in Ti Nialloy when La> 8 wt% . LaNi5 phasecaneffectivelyim provethe activity property and discharge capacity of Ti Ni alloy. While the soluble Ti inmain phase Ti2 Niisadverseto hydrogen adsorption desorption cycle and itshould be dimin ished .
文摘The modification of the electron diffraction pattern(EDP) of B2 in an as rapidly quenched then short time aged Ti Ni shape memory alloy(SMA) has been studied systematically using TEM. It was found that the diffusion scattering rings in EDP of an as rapidly quenched Ti-Ni SMA is associated with short range order (SRO) of vancancies in parent B2. After aging at 450℃ for 5 min the diffusion scattering rings are replaced by 1/2 {001} and 1 / 4 {012} extra reflections. It indicates that the SRO of vacancies has transformed into long range order (LRO) of vacancies,moreover,the LRO of vacancies exists in microdomains.
文摘Electrochemical behaviors of Ti Ni shape memory alloy in fibrinogen solution were studied by electrochemical techniques. The results indicate that the addition of the fibrinogen has no obvious effect on the corrosion potential, but decreases the pitting potential markedly and increases the passive current densities. The analysis of energy dispersive X ray for samples adsorbing fibrinogen exhibits that the elements of O, C and N exist on the surface of Ti Ni alloy. Furthermore, the scanning electron microscope micrographs confirm that the configuration of the adsorbing fibrinogen concentrating on surface defects is like cluster and the fibrinogen adsorption concentration is 96.67 mg/m 2 through ultroviolet ray absorption method. Fibrinogen combined with Ti Ni alloy surface by complex band and its electrochemical transfer accelerated the corrosion of alloy.
基金the support of National Key Research and Development Program of China(2021YFB3802104)National Natural Science Foundation of China(Grant Nos.51931004,52173228,52271190 and 51571156)the 111 project 2.0(BP2018008)。
文摘Functional stability of superelasticity is crucial for practical applications of shape memory alloys.It is degraded by a Lüders-like deformation with elevated local stress concentration under tensile load.By increasing the degree of solute supersaturation and applying appropriate thermomechanical treatments,a Ti-Ni alloy with nanocrystallinity and dispersed nanoprecipitates is obtained.In contrast to conventional Ti-Ni alloys,the superelasticity in the target alloy is accompanied by homogeneous deformation due to the sluggish stress-induced martensitic transformation.The alloy thus shows a fully recoverable strain of 6%under tensile stress over 1 GPa and a large adiabatic temperature decrease of 13.1 K under tensile strain of 4.5%at room temperature.Moreover,both superelasticity and elastocaloric effect exhibit negligible degradation in response to applied strain of 4%during cycling.We attribute the improved functional stability to low dislocation activity resulting from the suppression of localized deformation and the combined strengthening effect of nanocrystalline structure and nanoprecipitates.Thus,the design of such a microstructure enabling homogeneous deformation provides a recipe for stable superelasticity and elastocaloric effect.
