A 27.6Cr-3.6Mo-2Ni alloy was solution treated and then aged for a long time to study the effect of grain size on precipitation behaviour by using X-ray diffraction, scanning electron microscopy and transmission electr...A 27.6Cr-3.6Mo-2Ni alloy was solution treated and then aged for a long time to study the effect of grain size on precipitation behaviour by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The experimental results demonstrated that the average grain size increased from 46.3 ± 6.2 to 101.8 ± 13.5 μm and the grain boundary length per unit area decreased from 3.3 × 10^(4) to 1.7 × 10^(4) m/m^(2) with an increasing annealing temperature from 1100 to 1200 ℃. After ageing at 800 ℃, the σ-phase,χ-phase and Laves phase were observed. As the ageing time increased, the σ-phase notably increased, while the χ-phase and Laves phase gradually decreased before finally vanishing after ageing for 400 h. The σ-phase precipitation kinetics curves consisted of two parts, and the grain size had a significant effect on the first stage of the precipitation curves due to the abundance of nucleation sites in the specimens with finer grains. The Laves phase was transformed from Nb(C,N) particles by Nb diffusion. As the ageing time increased, the ferrite phase decreased due to the transformation of the ferrite phase to the σ-phase, and then C was expelled into the untransformed ferrite grains. Moreover, new Nb(C,N) particles were formed by Nb diffusion from the Laves phase, resulting in the absence of the Laves phase.展开更多
The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si com...The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.展开更多
To identify genetic loci controlling grain weight, an elite indica rice variety, Baodali, with large grains was identified and used in this study. Its derived F2, F3 and BC2 F2 with another japonica rice variety Zhong...To identify genetic loci controlling grain weight, an elite indica rice variety, Baodali, with large grains was identified and used in this study. Its derived F2, F3 and BC2 F2 with another japonica rice variety Zhonghua 11 were used as mapping populations. Linkage analyses demonstrated that two genes controlling grain weight, designated as GW3 and GW6, were mapped to chromosome 3 and chromosome 6, respectively. Fine mapping delimited GW3 to a 122 kb physical distance between two sequence tagged site markers （WGWt6 and WGW19） containing 16 open reading frames annotated by The Institute for Genomic Research （http：//www.tigr.org）. GW6 was further mapped between two simple sequence repeat markers （RM7179 and RM3187）. These results are useful for both marker assisted selection of grain weight, and for further cloning of GW genes, which will contribute to the dissection of the molecular mechanism underlying grain weight in rice.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.52075503)the Projects of International Cooperation in Shanxi,China(Grant No.201603D421026)。
文摘A 27.6Cr-3.6Mo-2Ni alloy was solution treated and then aged for a long time to study the effect of grain size on precipitation behaviour by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The experimental results demonstrated that the average grain size increased from 46.3 ± 6.2 to 101.8 ± 13.5 μm and the grain boundary length per unit area decreased from 3.3 × 10^(4) to 1.7 × 10^(4) m/m^(2) with an increasing annealing temperature from 1100 to 1200 ℃. After ageing at 800 ℃, the σ-phase,χ-phase and Laves phase were observed. As the ageing time increased, the σ-phase notably increased, while the χ-phase and Laves phase gradually decreased before finally vanishing after ageing for 400 h. The σ-phase precipitation kinetics curves consisted of two parts, and the grain size had a significant effect on the first stage of the precipitation curves due to the abundance of nucleation sites in the specimens with finer grains. The Laves phase was transformed from Nb(C,N) particles by Nb diffusion. As the ageing time increased, the ferrite phase decreased due to the transformation of the ferrite phase to the σ-phase, and then C was expelled into the untransformed ferrite grains. Moreover, new Nb(C,N) particles were formed by Nb diffusion from the Laves phase, resulting in the absence of the Laves phase.
基金financially supported by the Science and Technology Program of Guangzhou,China(No.2015B090926013)Postdoctoral Science Foundation of China(No.2015M581348)+1 种基金Postdoctoral Science Foundation of Northeastern University(No.20150302)the Doctoral Foundation of Chinese Ministry of Education(No.20130042130001)
文摘The effect of high-speed direct-chill(DC) casting on the microstructure and mechanical properties of Al–Mg_2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al–Mg_2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy(FE-SEM) and transmission electron microscopy(TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg_2Si particles(from 28 to 12 μm), the spacing of eutectic Mg_2Si(from 3 to 0.5 μm), and the grains of AA6061 alloy(from 102 to 22 μm). The morphology of the eutectic Mg_2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg_2Si phase and the grains in the Al–Mg_2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al–Mg_2Si composites and AA6061 alloy billets.
基金Supported by the National Natural Science Foundation of China (30771317)the State Key Basic Research and Development Plan of China(2005CB120807).
文摘To identify genetic loci controlling grain weight, an elite indica rice variety, Baodali, with large grains was identified and used in this study. Its derived F2, F3 and BC2 F2 with another japonica rice variety Zhonghua 11 were used as mapping populations. Linkage analyses demonstrated that two genes controlling grain weight, designated as GW3 and GW6, were mapped to chromosome 3 and chromosome 6, respectively. Fine mapping delimited GW3 to a 122 kb physical distance between two sequence tagged site markers （WGWt6 and WGW19） containing 16 open reading frames annotated by The Institute for Genomic Research （http：//www.tigr.org）. GW6 was further mapped between two simple sequence repeat markers （RM7179 and RM3187）. These results are useful for both marker assisted selection of grain weight, and for further cloning of GW genes, which will contribute to the dissection of the molecular mechanism underlying grain weight in rice.
