Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence...Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.展开更多
Bridgman-type directional solidification experiments were conducted for Ti-46Al-8Nb （mole fraction, %） alloy. The effects of the growth rate and the diameter on the microstructure, phase transition and hardness of t...Bridgman-type directional solidification experiments were conducted for Ti-46Al-8Nb （mole fraction, %） alloy. The effects of the growth rate and the diameter on the microstructure, phase transition and hardness of the alloy were investigated. The results show that with the increase of the growth rate and the decrease of the diameter, the fullyβphase solidification changes to the peritectic solidification, and the final microstructure is composed of theα2/γlamellar structure and a multiphase microstructure （B2 phase,α2/γlamellar structure） respectively, which can be attributed to the solute enrichment resulting from the decreasing diffusion and convection ability. The occurrence of peritectic reaction at high growth rate promotes the solute segregation heavily and the coarse lamellar spacing in Al-and Nb-rich region, which greatly decreases the hardness values and leads to the discontinuity of the hardness curves with the increase of the growth rate. Comparatively, the Ti-46Al-8Nb alloy has lower hardness values than the other applied TiAl-based alloys in previous studies.展开更多
To design an accelerated method to evaluate thymopentin release from PLGA microspheres in vitro. Microspheres were prepared by double emulsion technique, using poly（lactide-co-glycolide） （PLGA） as carrier. At high...To design an accelerated method to evaluate thymopentin release from PLGA microspheres in vitro. Microspheres were prepared by double emulsion technique, using poly（lactide-co-glycolide） （PLGA） as carrier. At higher medium temperature （45℃, 50℃ and 55℃）, an accelerated release testing in short time was studied and correlated with the conventional release （37℃） in vitro. The release in vitro of thymopentin from PLGA microspheres at 45 ℃, 50℃ and 55℃ was significantly accelerated （P 〈 0.05）. In particular, at 50℃, an accelerated release （30 h） of the hydrophilic peptide from the PLGA matrix was achieved and correlated well with the conventional release （30 d）. An accelerated release testing in vitro at higher temperature could be used to monitor thymopentin release from PLGA microspheres.展开更多
基金Project (51071056) supported by the National Natural Science Foundation of ChinaProjects (HEUCFR1132, HEUCF121712) supported by the Fundamental Research Funds for the Central Universities of China
文摘Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.
基金Projects(51071062,51274077,51271068)supported by the National Natural Science Foundation of ChinaProject(2011-P03)supported by Open Fund of State Key Laboratory of Mold and Die Technology of Huazhong University of Science and Technology+1 种基金Project(HIT.NSRIF.2013002)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2011CB605504)supported by the National Basic Research Program of China
文摘Bridgman-type directional solidification experiments were conducted for Ti-46Al-8Nb （mole fraction, %） alloy. The effects of the growth rate and the diameter on the microstructure, phase transition and hardness of the alloy were investigated. The results show that with the increase of the growth rate and the decrease of the diameter, the fullyβphase solidification changes to the peritectic solidification, and the final microstructure is composed of theα2/γlamellar structure and a multiphase microstructure （B2 phase,α2/γlamellar structure） respectively, which can be attributed to the solute enrichment resulting from the decreasing diffusion and convection ability. The occurrence of peritectic reaction at high growth rate promotes the solute segregation heavily and the coarse lamellar spacing in Al-and Nb-rich region, which greatly decreases the hardness values and leads to the discontinuity of the hardness curves with the increase of the growth rate. Comparatively, the Ti-46Al-8Nb alloy has lower hardness values than the other applied TiAl-based alloys in previous studies.
文摘To design an accelerated method to evaluate thymopentin release from PLGA microspheres in vitro. Microspheres were prepared by double emulsion technique, using poly（lactide-co-glycolide） （PLGA） as carrier. At higher medium temperature （45℃, 50℃ and 55℃）, an accelerated release testing in short time was studied and correlated with the conventional release （37℃） in vitro. The release in vitro of thymopentin from PLGA microspheres at 45 ℃, 50℃ and 55℃ was significantly accelerated （P 〈 0.05）. In particular, at 50℃, an accelerated release （30 h） of the hydrophilic peptide from the PLGA matrix was achieved and correlated well with the conventional release （30 d）. An accelerated release testing in vitro at higher temperature could be used to monitor thymopentin release from PLGA microspheres.
