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A high temperature nickel-base superalloy (Rene 108) was directionally solidified by imposing various growth rates and thermal gradients using a modified Bridgeman apparatus. The scaling of the solidification structure was recorded as a function of the imposed growth variables. A special Gleeble testing procedure, developed previously where the solidified samples were quickly raised to a predetermined temperature in the semi-solid zone and fractured, was used for the measurement of fracture conditions in the semi-solid region. The effect of the solidification process variables, namely, the temperature gradient and velocity, on the fracture stress in the transverse direction was to increase the fracture stress at a given temperature. The upper hot-tearing temperature was noted to be a function of the solidification variables. The amount of strain accommodation and the hot tearing resistance was found to be influenced by the solidification microstructure. Fracture maps, which include the temperature, transverse fracture stress and temperature gradient during solidification (T-σT-G), for the directionally solidified microstructures are presented. Castability maps are created from the microstructure and the fracture data and display the porosity and semi-solid strength as a function of the casting variables. 相似文献
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《材料科学技术学报》2019,35(6):1044-1052
In this study, the phase field method was used to study the multi-controlling factors of dendrite growth in directional solidification. The effects of temperature gradient, propelling velocity, thermal disturbance and growth orientation angle on the growth morphology of the dendritic growth in the solid/liquid interface were discussed. It is found that the redistribution of solute leads to multilevel cavity and multilevel fusion to form multistage solute segregation, and the increase of temperature gradient and propelling velocity can accelerate the dendrite growth of directional solidification, and also make the second dendrites more developed, which reduces the primary distance and the solute segregation. When the temperature gradient is large, the solid-liquid interface will move forward in a flat interface mode, and the thermal disturbance does not affect the steady state behavior of the directionally solidified dendrite tip. It only promotes the generation and growth of the second dendrites and forms the asymmetric dendrite. Meanwhile, it is found that the inclined dendrite is at a disadvantage in the competitive growth compared to the normal dendrite, and generally it will disappear. When the inclination angle is large, the initial primary dendrite may be eliminated by its secondary or third dendrite. 相似文献
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Mechanical properties of conventionally cast,directionally solidified,and single-crystal superalloys
《Materials Science & Technology》2013,29(5):461-475
AbstractIn this paper the authors compare the creep and low-cycle fatigue properties of conventional, directionally solidified, and single-crystal castings produced from nickel-base superalloys. A brief historical review describes the reasons for the evolution from wrought to cast product through directionally solidified to modern single-crystal (‘monocrystal’) castings. The influence of microstructural variations produced by the casting conditions, such as porosity and grain size, on creep and low-cycle fatigue properties are illustrated. The important aspects of postsolidification heat treatment, hot isostatic pressing, and the damaging effects of impurities are described for conventional castings. The results of controlling the microstructures produced by directional solidification especially by high temperature gradient solidification are demonstrated by comparing the creep properties of directionally solidified materials with those of the conventionally cast alloys in long-term tests. The creep and low-cycle fatigue properties depend on the stress direction relative to the crystallographic directions of the material for both directionally solidified and single-crystal castings. For single crystals, individual alloys show variable dependences of properties on the crystallographic directions. Directionally solidified materials show advantages in thin sections and are less sensitive to the effects of impurities compared to conventional castings.MST/329 相似文献
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A cast Ni-base superalloy K5 wasdirectionally solidified and various solidification in-terfaces including plane front,cellular,cellular-dendritic and dendritic were obtained in awider range of G/R ratio by using improved highwithdrawal device and liquid metal cooling experi-mental sets.The precipitation pattern of some prin-cipal phases of the alloy and correlation of the vari-ous interfaces with microstructure were studied sys-tematically.It was indicated that the morphology ofsolidification interface of superalloy K5 varied withG/R ratio and that the solidification interfacemorphologies have a considerable effect on the fea-tures of phases both precipitated duringsolidification and post-solidification.Plane frontand cellular directional solidification of superalloyK5 lead to a substantial decrease of MC carbideand elimination of γ-γ'eutectic,but makeneedle-shape M_6C carbide precipitate easily duringageing treatment.The finer dendritic structuressolidified under the condition of higher cooling ratehave less dendritic segregation and idealmicrostructure. 相似文献
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基于国外定向凝固氧化物/氧化物自生复合陶瓷的晶体生长动力学行为研究,阐述了其动力学机制,分析动力学因素对微观结构的影响,探讨了晶体生长动力学行为与微观结构之间的关系;同时结合以重力、超重力下燃烧合成、快速凝固技术所制备的新型高强韧Al2O3/YSZ自生复合陶瓷,探讨了自生复合陶瓷在快速凝固条件下的晶体生长动力学行为。结合定向凝固与快速凝固两种晶体生长机制,得出过冷度、凝固界面前沿的温度梯度是影响晶体生长方式的重要因素,且受二者控制的晶体生长速率则决定材料的微观结构与形态。 相似文献
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H.Q. Zhu S.R. Guo H.R. Guan V.X. Zhu Z.Q. Hu V. Murata 《Materials at High Temperatures》2013,30(4):285-291
Th e effect of silicon on the microstructure and solidification segregation of directionally solidified IN738 nickel-based superalloy was studied. Directional solidification at various solidification rates and partial directional solidification plus rapid quenching were applied. Metallographican alysis and an electron microp robe were mainly used to observe and measure the micro structure and elemental segregation of the alloy, respectively. It was found that silicon affected the morphology of the liquid-solid interface of the alloy during solidification and gave the alloy a tendency to form well-developed dendrites. The addition of siliconen larged the solid us-liquidus temperature interval. and the solidification rate also greatly influenced the interval. The interval increased with increasing solidification rate. Silicon promoted the precipitation of the γ/γ' eutectic, and also affected its precipit ation temperature. Silicon segregated mainly in interd endritic regions, and promoted the segregation of other elements. All of the effects of silicon on the alloy related to the solidification rate. 相似文献
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Hongqun Zhu Yajun Tang Yingao Li Yaoxiao Zhu Zhuangqi Hu Changxu Shi 《Materials at High Temperatures》2013,30(1):39-44
The effect of boron and zirconium on the directional solidification behaviour and segregation of IN738 superalloy has been studied. It was found that additions of boron and zirconium enlarge the solidus-liquidus temperature interval and increase the amount of residual melt during solidification. Boron gives the alloy a tendency to form developed dendrites, while zirconium enhances a cellular solidified structure. Both boron and zirconium are shown to be rejected to the residual melt during solidification, and shown to change the segregation of alloying elements by interaction. 相似文献
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线性电磁搅拌对K417高温合金母合金锭质量的影响 总被引:3,自引:2,他引:1
为了提高高温合金母合金锭的质量,本文提出了在高温合金真空熔铸过程中,施加线性电磁搅拌的真空电磁铸造新技术。使用电子探针和光学显微镜,研究了在真空熔铸的凝固过程,施加工频线性电磁搅拌对K417高温合金母合金锭质量的影响。实验结果表明:在K417高温合金真空熔铸的凝固过程中施加140A的工频线性电磁搅拌,能够细化高温合金母合金锭的等轴晶组织、增加高温合金母合金锭的断面等轴晶比例、大幅减轻枝晶偏析的程度并能将高温合金母合金锭的中心缩松缩孔比率从54%降低到35%,从而使高温合金母合金锭的质量得到明显改善。 相似文献
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《材料科学技术学报》2017,(1)
The effects of a pulsed magnetic field(PMF) on the microsegregation of solute elements during directional solidification of a Ni-based single crystal superalloy were experimentally investigated,and the results show that the PMF significantly affects the microsegregation of Al,Ti,Co,Mo and W elements in the alloy.However,the distribution behavior differs for both positive and negative segregation elements.With the PMF,the microsegregation of negative segregation elements,Co and W,was restrained effectively,while that of positive segregation elements,Al,Tiand Mo,was aggravated.A segregation model was established to reveal the distribution mechanism of the elements with PMF.It is considered that,under the action of PMF,the jumping of solute atoms from the liquid phase to solid phase is hindered,but the jumping of solute atoms from the solid phase into liquid phase is promoted during solidification.As a result,the effective distribution coefficient of the solute atoms is reduced,which leads to the reduction of microsegregation of negative segregation elements and aggravation of microsegregation of positive segregation elements. 相似文献
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Influence of directional solidification variables on the microstructure and crystal orientation of AM3 under high thermal gradient 总被引:2,自引:0,他引:2
Xinbao Zhao Lin Liu Zhuhuan Yu Weiguo Zhang Jun Zhang Hengzhi Fu 《Journal of Materials Science》2010,45(22):6101-6107
Solid–liquid interface morphologies of a nickel-base single crystal superalloy AM3 were investigated under high thermal gradient.
The critical velocities of planar–cellular and cellular–dendritic transition were greatly increased by high thermal gradients.
A high thermal gradient was of great benefit to dendrite refinement. Experimental results showed that the primary and secondary
dendrite arm spacings decreased with increasing cooling rate. As expected, the segregation of elements was suppressed and
the size of the gamma prime (γ′) phase decreased significantly with increasing withdrawal rates. The shape of γ′ in interdendritic
region kept cuboidal at higher withdrawal rate. It was found that the withdrawal rates had little influence on the crystallographic
orientation in high thermal gradient directional solidification. 相似文献
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利用带有红外加热炉的共聚焦激光扫描显微镜(CLSM)对GH3625高温合金在不同冷却速率(30℃/min、100℃/min和200℃/min)下的凝固过程进行了动态原位观察,通过差示扫描量热分析仪(DSC)、扫描电镜(SEM)和能谱仪(EDS)研究了凝固后的组织形态及相的析出规律。结果表明,GH3625合金的液相线温度在1 356.5℃,在凝固过程中自由表面液相分数随温度和时间的变化关系满足Avrami方程;凝固过程中主要相的析出顺序依次为γ基体相、碳化物和Laves相;在GH3625合金凝固过程中,随着冷却速率的增大,枝晶细化,枝晶间距减小,成分偏析减轻,Laves相分布更加弥散,且以析出共晶Laves相为主;凝固末期大量的Nb元素富集在枝晶间和晶界,这是形成Laves相的主要原因。 相似文献
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A directionally solidified sample of superalloy CMSX-4 was investigated to show the effect of crystal orientation on the segregation distribution. The solute distribution of alloying elements across a dendritic cell was measured. Due to the preferred crystal growth in <100> orientation the segregation profiles in this direction is much flatter than that in <110> orientation. 相似文献
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《Materials Science & Technology》2013,29(11):1349-1355
AbstractThe microstructure and composition of the interdendritic liquid along the mushy zone of superalloy Inconel 718 that was directionally solidified at various solidification rates between 2 and 100 μm s?1 have been investigated by SEM and EDAX techniques. The interdendritic liquid segregation profiles along the mushy zone are presented. The liquid density difference and Rayleigh number in the interdendritic liquid were calculated and analysed as well. It was found that when the solidification rates increased in the range 10–70 μm s?1, segregation of Nb decreased, but segregation of Mo was most serious at 20 μm s?1. The liquid density difference increased the most for rates from 20 to 40 μm s?1 as temperature decreased. The maximum relative Rayleigh number was highest at 10°C below the liquidus temperature at 20 μm s?1, which indicated the conditions where fluid flow most easily occurred for Inconel 718. The relative Rayleigh number synthetically considers the factors affecting fluid flow and can give a reasonable prediction for fluid flow tendency. 相似文献
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Ningfu SHEN Yali TANG Dongjie ZHANG Longqing CHEN Shaokang GUAN Research Centre for Materials Zhengzhou Institute of Technology Zhengzhou China 《材料科学技术学报》1993,9(6):464-466
The microstructures of rapidly solidified (RS) Al-Fe-Ce-Ti and Al-Fe-V-Si alloys obtained bymeans of rotating blade quenching were studied with optical microscopy,transmission electronmicroscopy (TEM).The featureless zone observed in the two alloys reveals that the new techniqueoffers a higher solidification rate than the inert-gas-atomized method.Under TEM observation thefeatureless zone presents virtually a micropartition or partitionless feature,and the solute contents init are almost the same as the chemical composition of alloys. 相似文献