共查询到19条相似文献,搜索用时 78 毫秒
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深过冷Ni80.3B19.7合金的再辉和非规则共晶的形成 总被引:3,自引:0,他引:3
采用熔融玻璃净化结合气体保护的方法,使Ni80 3B19 7过共晶合金获得了407 K的大过冷度,研究了其在不同过冷度下快速凝固过程中的再辉行为.结果表明,Ni80 3B19.7过共晶合金在0~112 K过冷度范围内无明显再辉,在112~323 K过冷度范围内,其再辉曲线表现为两个再辉峰,而在323~407 K过冷度范围内,其再辉曲线为一个再辉峰.初生固相含量的随着过冷度的增大而增大,导致一次再辉度随着过冷度的增大而增大.深过冷Ni80 3B19.7合金凝固组织中非规则共晶的形成,归因于共晶两相在快速凝固阶段以自由枝晶的形式进行的非耦合生长和再辉后的慢速凝固阶段两相枝晶所发生的形态上的转变. 相似文献
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为了揭示多元合金中的枝晶生长规律,采用电磁悬浮技术实现了Ni-10%Cu-10%Si三元合金的深过冷与快速凝固,实验中合金熔体获得的最大过冷度为236K。对合金快速凝固过程中初生相-αNi的枝晶生长速度测定结果表明,其与过冷度之间存在幂函数关系:V=1.6×10-13ΔT5.7。当ΔT较小时,随着ΔT的增加V增加缓慢,当ΔT较大时,随着ΔT的增加V迅速增加。对比分析表明,溶质Si对-αNi枝晶的生长影响显著,而溶质Cu则几乎没有影响。随着过冷度的增加,未发现-αNi相的微观形态从枝晶向等轴晶转变,但-αNi晶粒尺寸均随着过冷度的增加而急剧细化。 相似文献
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采用布里奇曼定向凝固技术制备了NiNi3Si亚共晶复合材料,系统地研究了Ni-Ni3Si亚共晶的定向凝固组织特征。在较低的凝固速率R=3μm/s时亚共晶成分的合金为规则的层片共晶组织。随着凝固速率的增大,当R=8μm/s时,平界面失稳,在第二相的旁边出现浅胞状组织。当R=25μm/s时在析出相的旁边出现了突起的胞状组织。当R=40μm/s时由于固液界面前沿的成分过冷逐渐增大,凝固组织生长成为典型的树枝晶组织。并根据"成分过冷"判据,评估了固液界面前沿的"成分过冷"的大小,理论计算与实验结果基本吻合。此外,根据BH模型计算和比较了α-Ni相的界面生长温度和共晶界面生长温度,证明较高速定向凝固下不太可能制备出全耦合生长的共晶组织。随凝固速率的增大,一次枝晶间距减小,组织细化。 相似文献
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目的 研究过冷Ni–0.5%Pb(原子数分数)合金过冷组织的演化行为,阐明其组织演化和晶粒细化的基本机制。方法 采用熔融玻璃净化和循环过热方法制备出过冷度为0~255 K的试样,并结合枝晶生长的动力学–热力学模型,研究其深过冷快速凝固行为机制。结果 在0~255 K过冷度范围内,随着过冷度的增大,Ni–Pb偏晶合金的微观组织发生了2类晶粒细化现象,组织形态由粗大树枝晶向粒状等轴晶转变。结论 第1类粒状晶的形成是由于枝晶熟化和再辉重熔导致发达枝晶破碎,第2类粒状晶的形成是由于在应力和应变能的作用下,枝晶碎变和再结晶引起了晶粒细化。 相似文献
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用熔融玻璃净化与循环过热相结合的方法,研究了亚偏晶Cu-25%Pb合金,Cu-37.4%Pb偏晶合金和过偏晶Cu-40%Pb(质量分数)合金过冷熔体凝固行为和凝固组织的演化规律,以及Cu-37.4%Pb偏晶合金的过冷度对磨损率的影响.研究表明:在过冷亚偏晶Cu 25%Pb合金熔体凝固过程中先形成α(Cu)初生相,随着过冷度的增大,凝固组织经历粗大枝晶重熔形成的细化枝晶向准球状晶粒演化的过程;在过冷Cu-37.4%Pb偏晶合金熔体凝固过程中初生相为L2相,当过冷度在20~150 K区间时,得到第二相S(Pb)弥散在α(Cu)枝晶间的凝固组织,并且在该过冷区间内随着过冷度的增加,材料的磨损率也逐渐降低;在过冷过偏晶Cu-40%Pb合金熔体凝固过程中初生相为L2相,在过冷度区间42~80 K时,得到以偏晶胞形式分布的凝固组织. 相似文献
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目的 探究Co-Si金属间化合物在深过冷条件下产生的再辉现象及对应组织的演化阶段,并分析其形成机理。方法 为获得深过冷,结合了两种热力学方法:循环过热法及熔融玻璃净化法,实现了Co2Si金属间化合物(Co-33at%Si)、CoSi金属间化合物(Co-50at%Si)的深过冷快速凝固,并通过光学显微镜、扫描电子显微镜和XRD进行分析。结果 发现Co-33at%Si金属间化合物凝固过程中存在两次再辉现象,晶粒尺寸随着过冷度的增加而减小,ΔT=190 K时,二次枝晶间距大约为0.5 μm,层片间距为0.289 μm,而Co-50at%Si金属间化合物凝固过程仅有一次再辉现象,且随过冷度增加,晶粒尺寸减小。ΔT<50 K时,微观组织形貌为树枝晶;ΔT>90 K时,微观组织形貌为细小等轴晶。结论 Co-33at%Si中一次再辉对应于初始枝晶形成及细化过程,二次再辉对应于晶粒间残余液相二次凝固,即晶间细小树枝状共晶的形成。而Co-50at%Si中唯一一次再辉现象则对应枝晶向等轴晶的转变。 相似文献
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制备了定向凝固Cu-1.0%Cr亚共晶自生复合材料,研究了初生α相生长对共晶生长的影响机制,探讨了亚共晶合金中共晶的生长规律.研究结果表明,Cu-1.0%Cr合金定向凝固时,在初生α相间生长的共晶受到初生相生长的影响,在热场不定向和生长空间受限的双重作用下,共晶无定向地杂乱生长.初生α相的生长引起枝晶间液相溶质分布的变化,随着凝固速度的增大,初生α枝晶间液相溶质的浓度分布趋于平缓,成分趋近于CE.Cu-1.0%Cr合金在快速凝固条件下,初生α相生长改变了共晶的生长环境,致使形成非平衡凝固组织--离异共晶. 相似文献
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为了研究非稳态凝固过程对共晶合金凝固组织的影响,在Ni-Ni3Nb共晶合金中采用跃迁变速的方法,研究了凝固组织的变化.研究结果表明:凝固速率从1μm/s跃迁到10μm/s时,共晶层片间距因Ni相分叉而发生细化,跃迁前后的层片间距满足λV1/2=18μm3/2s-1/2;从10μm/s跃迁减速到1μm/s时,共晶层片间距因Ni相合并而发生粗化,粗化过程在一个较长的凝固区域内进行;凝固速率从5μm/s跃迁加速到15μm/s时,部分Ni相失稳长大,而Ni3Nb相保持不变,导致合金凝固组织从规则共晶转变为非规则共晶. 相似文献
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Integrated effects of undercooling and solute drag on recrystallisation mechanism of rapid solidification microstructure were investigated in highly undercooled Ni-Cu alloys. The equiaxed grained microstructures were prepared by fluxing method and subsequent quenching. Annealing the microstructures of the as-quenched alloys, substantial recrystallisation growth was observed. Applying solute trapping model of undercooled melt and solute drag model of solid-state transformation, it can be inferred that the microstructural evolution was dominated by nucleation and growth of recrystallisation process which is strongly dependent on the initial undercooling of the alloy melt and the solute drag force of the solid-state transition process. 相似文献
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Phase-field modeling for facet dendrite growth of silicon 总被引:1,自引:0,他引:1
Hisashi Kasajima Etsuko Nagano Toshio Suzuki Seong Gyoon Kim Won Tae Kim 《Science and Technology of Advanced Materials》2003,4(6):51-557
Dendrite growth of silicon from its undercooled melt was investigated by using the phase-field model for a faceted crystal with anisotropic interfacial energy. The phase-field parameters at the thin interface limit were derived and used in the simulation. The accuracy of the model was estimated from the calculated equilibrium interface shape. The errors in anisotropy and Gibbs-Thomson coefficient were within 1% and 10%, respectively. The growth of a silicon crystal from its undercooled melt has been analyzed and it is shown that the shape of growing crystal changes from square-like to dendritic with increase of undercooling. In a facet dendrite growth the tip grows keeping its shape and the shape is the same regardless of undercooling or growth velocity. It is also shown that there exists the scaling law between the characteristic length of the tip and growth velocity similar to that of a non-facet dendrite. 相似文献
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Qiu Zhong Huidong Li Ye Tao Chengcheng Cao Liping Yang 《Advanced Engineering Materials》2023,25(16):2300008
Induced homogeneous nucleation of undercooling melt is a fundamental challenge with exciting implications for composite ceramic and metal alloy materials. Nucleation can be induced externally, but physical mechanical properties reduce due to the introduction of impurities. Herein, a novel focused nanosecond pulsed laser-induced nucleation approach is demonstrated for oxide ceramic melts at undercooled state. Using a self-made aerodynamic levitation setup, the pulsed laser-induced nucleation is controlled by optimizing the pulse energy density at different undercooled temperatures. Exploiting this approach, nucleation and growth are observed from surface of undercooled alumina (Al2O3) and neodymium yttrium aluminum garnet (Nd:YAG) melts with high-speed camera. The undercooling sample experiences a nucleate–solidify–recalescence–remelting–recalescence–solidify process. The correlation between nucleation time and undercooling temperature confirms that the undercooled melt is nucleated homogeneously by the pulsed laser. The special microstructural of samples agrees well with the prediction of two-step nucleation theory. Therefore, an assumption for the nucleation mechanism with the high-speed images and the microstructure analysis is proposed. This proposed method may provide a different perspective for the classical nucleation theory of homogeneous nucleation. 相似文献
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Hisashii Kasajima Seong Gyoon Kim Won Tae Kim 《Science and Technology of Advanced Materials》2013,14(6):553-557
Dendrite growth of silicon from its undercooled melt was investigated by using the phase-field model for a faceted crystal with anisotropic interfacial energy. The phase-field parameters at the thin interface limit were derived and used in the simulation. The accuracy of the model was estimated from the calculated equilibrium interface shape. The errors in anisotropy and Gibbs-Thomson coefficient were within 1% and 10%, respectively. The growth of a silicon crystal from its undercooled melt has been analyzed and it is shown that the shape of growing crystal changes from square-like to dendritic with increase of undercooling. In a facet dendrite growth the tip grows keeping its shape and the shape is the same regardless of undercooling or growth velocity. It is also shown that there exists the scaling law between the characteristic length of the tip and growth velocity similar to that of a non-facet dendrite. 相似文献
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Bulk Ni-32.5 wt % Sn alloy was undercooled by purification. The solidification characteristics at different undercoolings and the various microstructures were studied. It was found that the two eutectic phases can grow in a matching form, to produce regular eutectic structures if the melt was undercooled by less than 10 K. If the melt was highly undercooled, the dendrite tip velocity of the Ni3Sn phase was very much larger than that of Ni() phase during recalescence; as a result, the melt did not solidify in the regular eutectic morphology but in the dendrite cluster morphology with Ni3Sn phase acting as the leading phase in the recalescence stage. The dendrite clusters subsequently developed into anomalous eutectic microstructures by ripening of Ni3Sn dendrites and growth of Ni() phase between the Ni3Sn arms. If the undercooling before nucleation was below 130 K, bulk melt of the original composition Ni-32.5 wt % Sn existed between the dendrite clusters after recalescence, which then solidified into regular eutectic microstructures. As a result, the structure of the sample consisted of regular eutectic zones and anomalous eutectic zones. If the undercooling before nucleation was above about 130 K, no bulk melts existed after recalescence, so the structures of the samples were completely anomalous eutectic. 相似文献
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