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采用熔融玻璃净化和循环过热相结合的方法研究Ni-31.44%Pb偏晶合金宽过冷区间凝固组织演化规律;结果表明,过冷偏晶合金在快速凝固阶段首先形成枝晶α骨架,再辉重熔后分布于枝晶间的残余液相按照平衡凝固模式进行后续反应;在0~286K过冷范围内,当ΔΤ<50K时,合金凝固组织为粗大枝晶α+枝晶间Pb相;当70<ΔT<232K时,凝固组织为细密枝晶α+枝晶臂上细小的Pb颗粒+枝晶间Pb相;当ΔT>242K时,凝固组织为过冷粒状晶+均匀细小的Pb颗粒+少量尺寸较大的枝晶间Pb颗粒,过冷粒状晶的粒化机制属于枝晶碎断-再结晶机制. 相似文献
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1 INTRODUCTIONThesolidificationoftheundercooledalloymeltshasbeenthesubjectsofextensivestudyforover30a .Asanimportantwaytostudymode 相似文献
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对熔融玻璃净化后深过冷Ni-21.4%Si(原子分数,下同)共晶合金的凝固特性进行了实验研究,并对其均质形核过冷度进行了理论预测.结果发现,采用熔融玻璃净化可使Ni-21.4%Si共晶合金获得318 K的过冷度.理论计算表明,此过冷度达到了Ni-21.4%Si共晶合金的均质形核过冷度.Ni-21.4%Si共晶合金凝固特性与过冷度△T有关:当过冷度小于250 K时,冷却曲线有2个再辉峰,其中当过冷度小于206 K时,凝固组织由Ni3Si相和规则共晶组成,当过冷度在206 K到250 K之间时,凝固组织由α-Ni相和规则共晶组成;过冷度大于250 K后,冷却曲线只有1个再辉峰,凝固组织为反常共晶.过冷度会影响初生相Ni3Si的生长方式.随着过冷度的增大,初生相Ni3Si的生长会由小平面生长方式转为非小平面生长方式. 相似文献
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采用熔盐净化剂与循环过热相结合的方法,获得了过冷度高达180 K的DZ125高温合金深过冷熔体,研究了合金深过冷凝固的组织演化过程.结果表明,随着过冷度△T的增大,凝固组织经历3次转变过程:当△T<48 K时,合金的凝固组织为普通树枝晶;当48 K≤△T<85 K时,枝晶因再辉发生熟化和重熔,组织转化为第1类粒状晶;当85 K≤△T<160 K时,再辉所产生的重熔效应大大降低,凝固组织为深过冷树枝晶;当△T≥160 K时,发生枝晶破碎及再结晶,凝固组织转变为第Ⅱ类粒状晶. 相似文献
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利用熔融玻璃净化循环过热的方法进行了Ag-Cu/Co-Sn共晶合金的深过冷快速凝固实验,并系统研究了熔体过冷度和微量Nb添加对反常共晶形成的影响。结果表明,快速凝固过程中共晶枝晶内部首先重熔形成反常共晶,随着过冷度的增大,共晶相的形貌从蠕虫状转变为球形颗粒,被重熔形成的固相颗粒将作为剩余液相形核生长的基底,Ag-Cu共晶中共晶两相形核具有非互惠性。Co-Sn共晶合金中添加Nb元素后样品内部反常共晶形成的临界过冷度由23 K降低至15 K,而表面组织中过冷度从45 K降低至30 K。由于样品表面与坩埚壁接触有利于结晶潜热消散,反常共晶形成的临界过冷度较高。Ag-Cu共晶合金温度再辉曲线上慢速凝固阶段持续的时间较Co-Sn共晶合金要长。 相似文献
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The structure evolution driven by recrystallization in the bulk undercooled Ni54.6Pd45.4 alloy was investigated by quenching the sample at different cooling stages. It is found that recrystallization of the solid beyond the critical undercooling for grain refinement starts at the end of rapid solidification, and develops during the slow solidification and the subsequent cooling process. At the initial stage of recrystallization, nuclei successively form in the sample, leading to a decrease in grain size. At the later stage, annexation of grains dominates the recrystallization, due to which the grain size increases. As undercooling prior to solidification increases, the deformation degree in the rapidly solidified dendrite net rises, and the recalescence temperature as well as the duration at high temperature decreases. Consequently, the grain size of the recrystallization structure decreases. 相似文献
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《Acta Materialia》2002,50(4):725-734
The change of the primary solidification mode of undercooled peritectic Fe–Mo melts has been studied by in situ observation of recalescence events during electromagnetic levitation. A maximum melt undercooling up to 380 K has been achieved. Levitated drops of controlled undercooling were quenched onto chill substrates and subjected to phase and microstructure analysis. A transition from the primary bcc-Mo to the peritectic σ-phase solidification mode beyond a critical undercooling of 345 K was revealed for the Fe47Mo53 alloy and in a similar way for other compositions between Fe45Mo55 and Fe54Mo46. The suppression of the properitectic bcc-Mo phase was also achieved for subcritical undercooling in substrate-quenched Fe45Mo55 samples. In Fe61Mo39 a transition from the primary σ- to the peritectic R-phase solidification mode beyond a critical undercooling of 150 K was inferred from recalescence processes and X-ray investigation of as-quenched undercooled samples. 相似文献
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采用熔融玻璃净化与循环过热相结合的方法研究了过冷Ni-2Pb单相偏晶合金的组织粒化机制。在22~280K过冷度范围内,Ni-2Pb合金组织发生两次粒化。当22K<ΔT<66K时,合金组织由普通树枝晶渐变为第一类粒状晶;当ΔT>88K时,合金组织由第一类粒状晶转变为深过冷树枝晶;当ΔT>187K时,合金组织骤然粒化为第二类粒状晶。BCT模型分析表明第一类粒状晶的粒化机制为枝晶熔断再结晶机制;第二类为枝晶碎断再结晶机制。 相似文献
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《Acta Materialia》2002,50(12):3241-3252
Employing a high-speed video, in situ recalescence behaviors of Ni–Sn eutectic melts under different undercooling conditions have been investigated. Based on the surface morphologies and cross-sectional microstructures that consist of independent eutectic colonies, copious nucleation is proposed to take place in Ni–Sn eutectic melt regardless of melt undercooling in the unconstrained solidification. The boundary with sharp contrast between the crystallized bright solid and undercooled dark liquid during recalescence is not the solid/liquid interface but the simultaneous thermal release of concentrated crystallizing eutectic colonies. It may not be feasible to measure growth velocities in free solidification of the system due to copious nucleation. The fluctuations in undercooled melts are proposed to activate a chain-like successive nucleation reaction once an effective nucleus is formed. The current observation urges that we should deliberate further the conventional concept that once an effective nucleus is formed in a deeply undercooled melt, the growth will be initiated promptly and the solid/liquid interface will sweep across the entire sample rapidly. The origin of anomalous eutectic formation and the growth have been discussed when the current nucleation phenomenon is taken into account. Based on the copious nucleation theory and the improved driving force for growth, the present recalescence frames and some other experimental phenomena concerning the free growth of the undercooled eutectic system can be well clarified. 相似文献
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基于平均体积方法建立过冷单相固溶体合金的凝固动力学模型并研究反向扩散在凝固动力学过程中的作用。模型在过冷Ni-15%Cu(摩尔分数)合金快速凝固中的应用表明:反向扩散显著影响凝固结束温度但对再辉阶段凝固的固相体积分数影响不明显。与Herlach观点相反,凝固结束温度介于杠杆定律和Scheil方程的预测值之间,且其具体值由反向扩散、初始过冷度和冷却速率决定。 相似文献
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Li Delin Yang Gencang Zhou Yaohe Northwestern Polytechnical University Xi'an China 《中国有色金属学会会刊》1993,(4)
Fluxing of 5 g bulk melt Ni77Si13B10 permits high undercoolings to be attained prior to nu-cleation onset.Investigations of grain refinement in the bulk undercooled alloy as a function ofundercooling,recalescence behavior and cooling rate have been reported.A significant inhomo-geneity of reduction in grain size of a bulk sample is observed,which is caused by the different so-lidification conditions:(1)recalescence process,and(2)the followed plateau in which the heatrelease and extraction rates are equal.It is concluded that the homogeneous refined microstructurecan be achieved if the initial undercooling prior to nucleation,or cooling rate after recalescence isfurther increased. 相似文献
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Microstructures and evolution mechanism of highly undercooled Ni-Pb hypermonotectic alloy 总被引:1,自引:0,他引:1
The microstructures and evolution mechanism of the undercooled Ni-20%Pb(molar fraction) alloy were investigated systematically by high undercooling solidification technique. The experiment results indicate that the morphology of α-Ni phase and the distribution of Pb element in undercooled Ni-20% Pb alloys change with the in-crease of undercooling. The main evolution mechanisms of α-Ni are dendrite remelting and recrystallization. Pb phase in the microstructure of Ni-20% Pb hypermonotectic alloy originates from L2 phase separated from the parent melt during the cooling process through immiscible gap and L2 phase formed at the temperature of monotectic trans-formation. The solubility of Ph element in α-Ni phase under high undercooling condition is up to 5.83% which is ob-viously higher than that under equilibrium solidification condition. The real reason that causes the solubility difference is distinct solute trapping. 相似文献
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1. IntroductionDendrite is the common growth manner of undercooled single-phase alloys, and recentinvestigations['] revealed that there are three critical undercoolings, ATI, ATZ and aT3,during the solidification process of this kind of alloys. Within the undercooling range of aTIand aT2, the solidification structure undergoes the first change from common dendrites, (less than ATI) to the first class granular grains (higher than aTI). When the undercoolingis higher than aT2, the change f… 相似文献
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通过熔融玻璃净化与循环过热相结合的方法研究了过冷Ni-1at%Fe合金的微观组织演化及再结晶。通过再辉后快淬和空冷实验对比,证明大过冷下的细化组织是再结晶的产物。结合无量纲过热度的计算,系统考察了合金凝固组织随过冷度的演化规律。研究发现合金的凝固组织在所获得的过冷度范围内发生了两次晶粒细化,第一次细化归因于枝晶的熟化和重熔导致的高度发达树枝晶碎断,第二次细化归因于应力积累导致的再结晶。 相似文献