To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-AI based high-temperature structural material, the microstruct...To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-AI based high-temperature structural material, the microstructure of Ni-43Ti-4AI-2Nb-2Hf （at.%） alloy ingots prepared by conventional casting （arc-melting） and directional solidification （DS） at various drawing velocities （2 mm.min-＇, 18 mm.min-1, 30 mm-min-＇ and 60 mmmin~, respectively） was investigated by means of electron probe microanalyses. Experimental results reveal that the microstructures are composed of NiTi matrix phase,/3-Nb phase and Ti2Ni phase for samples obtained by both conventional casting and DS. Conventional casting has an equiaxial structure, while DS has a slender and acicular cellular structure which grows along the [001] orientation preferentially. Small amounts of white/3-Nb phase and black Ti2Ni phase co-exist at the grain boundaries or intercellular regions. With an increase in drawing velocity, the NiTi matrix phase is inclined to grow along （100） and （200） crystallographic planes, and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly. The homogeneous dispersion of,8-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties. Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase, and then the divorced eutectic reaction takes place, which produces the light gray matrix phase and/^-Nb phase. Finally, the peritectic reaction happens, which generates the black Ti2Ni phase.展开更多
目的:探讨剖宫产术中剔除子宫肌瘤时应用缩宫素的效果。方法:选取2019年3月—2020年9月期间该院112例妊娠期伴子宫肌瘤患者作为研究对象,采用随机编号法将其分为两组,对照组单纯分娩后再行子宫肌瘤切除术,观察组剖宫产术中行子宫肌瘤切...目的:探讨剖宫产术中剔除子宫肌瘤时应用缩宫素的效果。方法:选取2019年3月—2020年9月期间该院112例妊娠期伴子宫肌瘤患者作为研究对象,采用随机编号法将其分为两组,对照组单纯分娩后再行子宫肌瘤切除术,观察组剖宫产术中行子宫肌瘤切除术,观察两组患者手术指标、并发症发生率及新生儿健康情况。结果:两组患者手术时间、住院时间、术中出血量、术后出血量及缩宫素使用量差异无统计学意义(P>0.05);观察组患者并发症发生率明显低于对照组(3.57%<23.21%),差异有统计学意义(P<0.05);两组新生儿体质量和5 min阿氏评分(Apgar)差异无统计学意义(P>0.05)。结论:观察组妊娠期伴子宫肌瘤患者剖宫产术中实施子宫肌瘤剔除,并未增加缩宫素使用量,对手术时间、术后出血风险及新生儿5 min Apgar评分无影响,还能有效减少患者并发症风险,安全性高。展开更多
In order to satisfy the drastic temperature change and high chemical activity in direc- tional solidification of Nb Si based alloys, Y2O3 crucible is demanded to possess high thermal shock resistance and erosion resis...In order to satisfy the drastic temperature change and high chemical activity in direc- tional solidification of Nb Si based alloys, Y2O3 crucible is demanded to possess high thermal shock resistance and erosion resistance. This paper improved the sintering degree and density of Y2O3 crucible by optimizing the sintering temperature and time, and its practical application per- formance was investigated. Y2O3 grains gathered with the increase of sintering temperature and time, and the contact area enlarged, resulting in the open pores being changed into closed pores. The higher density caused the improvement of erosion resistance of Y2O3 crucibles. However, exces- sive density weakened the thermal shock resistance. Considering high-temperature strength, erosion resistance, thermal shock resistance and costs, optimum sintering temperature and time of Y2O3 directional solidification crucible were 1800 ℃ and 120min, respectively, and the porosity was 20%. Improved Y2O3 crucible has been successfully applied to directional solidification of Nb Si based alloys, and significantly reduced the oxygen contamination. Slight interaction occurred between Hf and Y2O3, but no obvious dissolution, penetration or erosion was found, showing good erosion resistance and thermal shock resistance.展开更多
基金supported by the Natural Science Foundation of China(Grant No.51101003)
文摘To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-AI based high-temperature structural material, the microstructure of Ni-43Ti-4AI-2Nb-2Hf （at.%） alloy ingots prepared by conventional casting （arc-melting） and directional solidification （DS） at various drawing velocities （2 mm.min-＇, 18 mm.min-1, 30 mm-min-＇ and 60 mmmin~, respectively） was investigated by means of electron probe microanalyses. Experimental results reveal that the microstructures are composed of NiTi matrix phase,/3-Nb phase and Ti2Ni phase for samples obtained by both conventional casting and DS. Conventional casting has an equiaxial structure, while DS has a slender and acicular cellular structure which grows along the [001] orientation preferentially. Small amounts of white/3-Nb phase and black Ti2Ni phase co-exist at the grain boundaries or intercellular regions. With an increase in drawing velocity, the NiTi matrix phase is inclined to grow along （100） and （200） crystallographic planes, and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly. The homogeneous dispersion of,8-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties. Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase, and then the divorced eutectic reaction takes place, which produces the light gray matrix phase and/^-Nb phase. Finally, the peritectic reaction happens, which generates the black Ti2Ni phase.
基金Fundamental Research Funds for the Central Universities (FRF-TP-19-083A1)Aviation Science(20181174001)Guangxi Special Funding Program for Innovation-Driven Development (GKAA17202008)。
文摘目的:探讨剖宫产术中剔除子宫肌瘤时应用缩宫素的效果。方法:选取2019年3月—2020年9月期间该院112例妊娠期伴子宫肌瘤患者作为研究对象,采用随机编号法将其分为两组,对照组单纯分娩后再行子宫肌瘤切除术,观察组剖宫产术中行子宫肌瘤切除术,观察两组患者手术指标、并发症发生率及新生儿健康情况。结果:两组患者手术时间、住院时间、术中出血量、术后出血量及缩宫素使用量差异无统计学意义(P>0.05);观察组患者并发症发生率明显低于对照组(3.57%<23.21%),差异有统计学意义(P<0.05);两组新生儿体质量和5 min阿氏评分(Apgar)差异无统计学意义(P>0.05)。结论:观察组妊娠期伴子宫肌瘤患者剖宫产术中实施子宫肌瘤剔除,并未增加缩宫素使用量,对手术时间、术后出血风险及新生儿5 min Apgar评分无影响,还能有效减少患者并发症风险,安全性高。
基金co-supported by the National Science&Technology Pillar Program of China(No.2013BAB11B04)
文摘In order to satisfy the drastic temperature change and high chemical activity in direc- tional solidification of Nb Si based alloys, Y2O3 crucible is demanded to possess high thermal shock resistance and erosion resistance. This paper improved the sintering degree and density of Y2O3 crucible by optimizing the sintering temperature and time, and its practical application per- formance was investigated. Y2O3 grains gathered with the increase of sintering temperature and time, and the contact area enlarged, resulting in the open pores being changed into closed pores. The higher density caused the improvement of erosion resistance of Y2O3 crucibles. However, exces- sive density weakened the thermal shock resistance. Considering high-temperature strength, erosion resistance, thermal shock resistance and costs, optimum sintering temperature and time of Y2O3 directional solidification crucible were 1800 ℃ and 120min, respectively, and the porosity was 20%. Improved Y2O3 crucible has been successfully applied to directional solidification of Nb Si based alloys, and significantly reduced the oxygen contamination. Slight interaction occurred between Hf and Y2O3, but no obvious dissolution, penetration or erosion was found, showing good erosion resistance and thermal shock resistance.
