A multiphase NiAl-28Cr-5.85Mo-0.15Hf alloy, which was directionally solidified （DS） in an Al2O3-SiO2 mold by standard Bridgman method and then underwent prolonged solution and aging treatment was prepared. The micro...A multiphase NiAl-28Cr-5.85Mo-0.15Hf alloy, which was directionally solidified （DS） in an Al2O3-SiO2 mold by standard Bridgman method and then underwent prolonged solution and aging treatment was prepared. The microstructure, tensile properties as well as tensile creep of the heat-treated alloy at different temperatures were studied. The alloy was composed of NiAI, Cr（Mo） and Hf-rich phase and small amount of fine Heusler phase （Ni2AlHf）. Although the present alloy exhibited high tensile strength at low temperature, it was weaker than that of system with high content Hf but still stronger than that of many NiAl-based alloys at high temperatures. The fracture toughness is lower than that of DS NiAl-28Cr-6Mo alloy. Nevertheless, advantageous effects on the mechanical properties, i.e. the decrease in brittle-to-ductile transition temperature （BDTT） were obtained for the low content of Hf. The obtained creep curves exhibit conventional shape： a short primary creep and long accelerated creep stages. The rupture properties of the heat-treated alloy follow the Monkman-Grant relationship, which exhibits similar creep behavior to that of NiAl/Cr（Mo） system with high Hf content.展开更多
HfV 2, like most Laves phase alloys, is brittle at low temperatures, but when it is alloyed with Nb, substantial deformation is possible—by twinning. These twins are the standard fcc type twins, lying on (111) planes...HfV 2, like most Laves phase alloys, is brittle at low temperatures, but when it is alloyed with Nb, substantial deformation is possible—by twinning. These twins are the standard fcc type twins, lying on (111) planes with shears in the 〈112〉 direction. HREM of the twins shows that they have the same macroscopic shear as twins in fcc crystals, which means that the twinning must be accompanied by atomic shuffles or synchroshear in order to preserve the ordered structure. Given the nature of the material, it was concluded that the mechanism is synchroshear. The HfV 2+Nb alloys have been deformed over a wide temperature range, from 4 K to 1 300 K. An anomaly in the temperature dependence of the flow stress was observed at about 77 K, where there is a precipitous dip in the flow stress. The dip at 77 K has been attributed to an increased ease of twinning (which is taken to be strong evidence against atomic shuffles).展开更多
为了提升电火花线切割(Wire cut Electric Discharge Machining,WEDM)加工后的TC4钛合金表面质量,减少表面重熔层厚度,采用不同浓度配比(1∶4、1∶6和1∶8)的HF-HNO_(3)酸蚀溶液对钛合金试件进行化学抛光处理。实验结果表明,HF-HNO_(3)...为了提升电火花线切割(Wire cut Electric Discharge Machining,WEDM)加工后的TC4钛合金表面质量,减少表面重熔层厚度,采用不同浓度配比(1∶4、1∶6和1∶8)的HF-HNO_(3)酸蚀溶液对钛合金试件进行化学抛光处理。实验结果表明,HF-HNO_(3)酸蚀溶液能使钛合金重熔层得到显著去除,表面微裂纹得到有效控制;当HF-HNO_(3)酸蚀溶液的浓度配比为1:6时,试件能获得最低的表面粗糙度和最大的表面粗糙度下降率,并且抛光前后钛合金表面元素含量发生了不同程度的变化,Ti、Al和V元素质量分数分别提高了21.5%、41.3%和13.2%,而O、C元素质量分数分别降低了82.5%和33.6%;HF-HNO_(3)酸蚀溶液可显著改善TC4钛合金试件电火花线切割加工后的表面缺陷。钛合金重熔层结构的主要成分与化学抛光后氧化膜的主要成分相似,但与氧化膜的结构不同,这对TC4钛合金试件表面质量提升具有重要意义。展开更多
Ti-Hf binary alloys contained 10%,20%,30% and 40%(mass fraction)Hf were manufactured in the vacuum furnace system.And then,specimens were homogenized for 24 h at 1 000 ℃ in argon atmosphere.The formation of oxide nan...Ti-Hf binary alloys contained 10%,20%,30% and 40%(mass fraction)Hf were manufactured in the vacuum furnace system.And then,specimens were homogenized for 24 h at 1 000 ℃ in argon atmosphere.The formation of oxide nanotubes was conducted by anodic oxidation on the Ti-Hf alloy in 1 mol/L H3PO4 electrolytes containing small amounts of NaF at room temperature.The hydroxyapatite(HA) coating made of tooth ash prepared by electron-beam physical vapor deposition(EB-PVD) method.The corrosion behaviors of the specimens were examined through potentiodynamic test in 0.9% NaCl solution by potentiostat.The microstructures of the alloys were examined by field emission scanning electron microscopy(FE-SEM) and x-ray diffractometer(XRD).It was observed that the lamellar structure translated to needle-like structure with Hf contents.Nanotube formed and HA coated Ti-xHf alloys had a good corrosion resistance.展开更多
The NiA1 Cr（Mo） （Hf, Dy） hypoeutectic alloys were prepared by conventional casting and injection casting techniques respectively, and their microstructure and room temperature mechanical properties were investigat...The NiA1 Cr（Mo） （Hf, Dy） hypoeutectic alloys were prepared by conventional casting and injection casting techniques respectively, and their microstructure and room temperature mechanical properties were investigated. The results reveal that with the addition of Hf and Dy, the Ni2AIHf Heusler phase and NisDy phase form along the NiAI/Cr（Mo） phase boundaries in intercellular region. By the injection casting method, some Ni2AIHf Heusler phase and NisDy phase transform into Hf and Dy solid solutions, respectively. Moreover, the microstructure of the alloy gets good optimization, which can be characterized by the fine interlamellar spacing, high proportion of eutectic cell area and homogeneously distributed fine Ni2AIHf, NisDy, Hf solid solution and Dy solid solutions. Compared with conventional-cast alloy, the room temperature mechanical properties of injection-cast alloy are improved obviously.展开更多
文摘A multiphase NiAl-28Cr-5.85Mo-0.15Hf alloy, which was directionally solidified （DS） in an Al2O3-SiO2 mold by standard Bridgman method and then underwent prolonged solution and aging treatment was prepared. The microstructure, tensile properties as well as tensile creep of the heat-treated alloy at different temperatures were studied. The alloy was composed of NiAI, Cr（Mo） and Hf-rich phase and small amount of fine Heusler phase （Ni2AlHf）. Although the present alloy exhibited high tensile strength at low temperature, it was weaker than that of system with high content Hf but still stronger than that of many NiAl-based alloys at high temperatures. The fracture toughness is lower than that of DS NiAl-28Cr-6Mo alloy. Nevertheless, advantageous effects on the mechanical properties, i.e. the decrease in brittle-to-ductile transition temperature （BDTT） were obtained for the low content of Hf. The obtained creep curves exhibit conventional shape： a short primary creep and long accelerated creep stages. The rupture properties of the heat-treated alloy follow the Monkman-Grant relationship, which exhibits similar creep behavior to that of NiAl/Cr（Mo） system with high Hf content.
文摘HfV 2, like most Laves phase alloys, is brittle at low temperatures, but when it is alloyed with Nb, substantial deformation is possible—by twinning. These twins are the standard fcc type twins, lying on (111) planes with shears in the 〈112〉 direction. HREM of the twins shows that they have the same macroscopic shear as twins in fcc crystals, which means that the twinning must be accompanied by atomic shuffles or synchroshear in order to preserve the ordered structure. Given the nature of the material, it was concluded that the mechanism is synchroshear. The HfV 2+Nb alloys have been deformed over a wide temperature range, from 4 K to 1 300 K. An anomaly in the temperature dependence of the flow stress was observed at about 77 K, where there is a precipitous dip in the flow stress. The dip at 77 K has been attributed to an increased ease of twinning (which is taken to be strong evidence against atomic shuffles).
文摘为了提升电火花线切割(Wire cut Electric Discharge Machining,WEDM)加工后的TC4钛合金表面质量,减少表面重熔层厚度,采用不同浓度配比(1∶4、1∶6和1∶8)的HF-HNO_(3)酸蚀溶液对钛合金试件进行化学抛光处理。实验结果表明,HF-HNO_(3)酸蚀溶液能使钛合金重熔层得到显著去除,表面微裂纹得到有效控制;当HF-HNO_(3)酸蚀溶液的浓度配比为1:6时,试件能获得最低的表面粗糙度和最大的表面粗糙度下降率,并且抛光前后钛合金表面元素含量发生了不同程度的变化,Ti、Al和V元素质量分数分别提高了21.5%、41.3%和13.2%,而O、C元素质量分数分别降低了82.5%和33.6%;HF-HNO_(3)酸蚀溶液可显著改善TC4钛合金试件电火花线切割加工后的表面缺陷。钛合金重熔层结构的主要成分与化学抛光后氧化膜的主要成分相似,但与氧化膜的结构不同,这对TC4钛合金试件表面质量提升具有重要意义。
基金supported by National Research Foundation of Korea (2009-0074672)
文摘Ti-Hf binary alloys contained 10%,20%,30% and 40%(mass fraction)Hf were manufactured in the vacuum furnace system.And then,specimens were homogenized for 24 h at 1 000 ℃ in argon atmosphere.The formation of oxide nanotubes was conducted by anodic oxidation on the Ti-Hf alloy in 1 mol/L H3PO4 electrolytes containing small amounts of NaF at room temperature.The hydroxyapatite(HA) coating made of tooth ash prepared by electron-beam physical vapor deposition(EB-PVD) method.The corrosion behaviors of the specimens were examined through potentiodynamic test in 0.9% NaCl solution by potentiostat.The microstructures of the alloys were examined by field emission scanning electron microscopy(FE-SEM) and x-ray diffractometer(XRD).It was observed that the lamellar structure translated to needle-like structure with Hf contents.Nanotube formed and HA coated Ti-xHf alloys had a good corrosion resistance.
基金Project(2012M510271) supported by the China Postdoctoral Science FoundationProject(2012BAI18B05) supported by the Five-Year National Key Technology R&D Program during the 12th Five-year Plan of ChinaProject(2011AA030104) supported by the National High Technology Research and Development Program of China
文摘The NiA1 Cr（Mo） （Hf, Dy） hypoeutectic alloys were prepared by conventional casting and injection casting techniques respectively, and their microstructure and room temperature mechanical properties were investigated. The results reveal that with the addition of Hf and Dy, the Ni2AIHf Heusler phase and NisDy phase form along the NiAI/Cr（Mo） phase boundaries in intercellular region. By the injection casting method, some Ni2AIHf Heusler phase and NisDy phase transform into Hf and Dy solid solutions, respectively. Moreover, the microstructure of the alloy gets good optimization, which can be characterized by the fine interlamellar spacing, high proportion of eutectic cell area and homogeneously distributed fine Ni2AIHf, NisDy, Hf solid solution and Dy solid solutions. Compared with conventional-cast alloy, the room temperature mechanical properties of injection-cast alloy are improved obviously.
