分类： 材料科学 >> 材料科学（综合） 提交时间： 2023-03-19 合作期刊: 《金属学报》
摘要： Nb- Ti- Si base in situ composites which consist of Nb solid solution (Nbss) and silicides (a-Nb5Si3, b-Nb5Si3, g-Nb5Si3 and/or Nb3Si) phases, have shown great potential as alternative materials to Ni-based superalloys due to their high melting points (beyond 1700 ℃ ), good formability, low density (6.6~7.2 g/cm3) and high strength. However, a major hindrance to the applications of these alloys at elevated temperatures is their poor oxidation resistance. Alloying is an effective method to improve the integrated properties of the alloys, especially for the oxidation resistance. Up to now, many beneficial elements such as Ti, Al, Cr and Sn have been employed to ameliorate their oxidation resistance. Nevertheless, there is no systematic and comprehensive investigation on the effect of Zr contents on the microstructure and oxidation behavior of the alloys based on Nb-Ti-Si system. The aim of this work is to clarify the effects of Zr contents on phase selection, microstructure and high temperature oxidation resistance of Nb-Ti-Si based alloys in detail. The constituent phases, microstructure and composition of the alloys under as- cast state and after oxidation were investigated by OM, XRD, SEM and EDS. Thus, six Nb-Ti- Si base ultrahigh-temperature alloys with compositions of Nb-22Ti-15Si-5Cr-3Hf-3Al-xZr (x=0, 0.5, 1, 2, 4, 8, atomic fraction, %) were prepared by vacuum non-consumable arc-melting. The results show that the alloys with different Zr contents are mainly composed of Nbss and g-(Nb, X)5Si3 (X represents Ti, Hf, Cr and Zr). However, the addition of Zr has an obvious affect on the microstructure of Nb-Ti-Si base alloys. Both the sizes and amounts of primary g- (Nb, X)5Si3 increase with increase in Zr contents. Alloys with different Zr contents were oxidized at 1250 ℃ for 1~50 h, respectively. It is found that both adhesion and compactness of the scales are improved effectively by increase in Zr contents. The scales of alloys with higher Zr contents (x=4 and 8) after oxidation for 50 h show an obvious layered structure: the outmost layer is only composed of TiO2, the middle layer mainly consists of ZrO2, TiNb2O7 and TiO2, and the inner layer is mainly comprised of Si-rich oxides. The mass gain per unit area and the thickness of the scale after oxidation decrease with increase in Zr contents in the alloys, indicating that the addition of Zr can improve the oxidation resistance of the alloys significantly.
分类： 生物学 >> 生物工程 提交时间： 2017-11-26 合作期刊: 《中国生物工程杂志》
摘要： 利用高产早籼嘉育253和高产抗稻瘟病早籼品种中组3号为亲本，通过系谱法和产量比较试验，最终选育获得早籼稻新品种中早39。对超级早籼稻品种中早39及其系谱亲本嘉育253和中组3号进行产量相关性状、光合特性、叶面积指数和光合色素含量等测定和比较分析，发现中早39的每穗总粒数和结实率优于其系谱亲本，库容优势明显；中早39在齐穗后保持最高的净光合速率，其叶面积指数和各光合色素含量也一直优于系谱亲本，因此，中早39具有超高产光合生理特性。育种初期选用了高产亲本，且中早39比其系谱亲本具有更优的光合生理特性，说明水稻高产育种中优良性状的整合；中早39超高产优势来自于品种选育过程中源库的优化、株叶形态的改善；本研究为水稻高产育种提供了参考信息。
分类： 生物学 >> 生物工程 提交时间： 2017-11-26 合作期刊: 《中国生物工程杂志》
摘要： 利用高产早籼嘉育253和高产抗稻瘟病早籼品种中组3号为亲本，通过系谱法和产量比较试验，最终选育获得早籼稻新品种中早39。对超级早籼稻品种中早39及其系谱亲本嘉育253和中组3号进行产量相关性状、光合特性、叶面积指数和光合色素含量等测定和比较分析，发现中早39的每穗总粒数和结实率优于其系谱亲本，库容优势明显；中早39在齐穗后保持最高的净光合速率，其叶面积指数和各光合色素含量也一直优于系谱亲本，因此，中早39具有超高产光合生理特性。育种初期选用了高产亲本，且中早39比其系谱亲本具有更优的光合生理特性，说明水稻高产育种中优良性状的整合；中早39超高产优势来自于品种选育过程中源库的优化、株叶形态的改善；本研究为水稻高产育种提供了参考信息。
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