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γ—TiAl增压涡轮近净形铸造过程实验研究 总被引:5,自引:0,他引:5
γ-TiAl金属间化合物的成形工艺是材料成形领域的前沿领域和研究热点,本研究采用水冷铜坩埚真空感应凝壳技术和熔模型壳离心浇注的铸造方法制备γ-TiAl增压涡轮,通过改善冒口工艺获得了健全的γ-TiAl涡轮铸件,分析了γ-TiAl增压涡轮的凝固过程和收缩缺陷产生原因,结果表明,增大冒口与然件的模数之差以及冒口与铸件的体积之比有利于减少及消除涡轮铸件的收缩缺陷,为给数值模拟研究提供热物性参数,针对涡轮铸件用钛铝合金,实验测试了合金的热膨胀系数,比热和热导率等物性参数,其与温度的关系分别为:α1=8.10651 0.0073T-2.97619E-6T^2,Cp=668.28158-0.013T 1.11905E-4T^2;λ=19.82252-0.02781T 6.5197E-5T^2-3.21096E-8T^3. 相似文献
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Ti-Al合金精密铸件微观缩松预测 总被引:5,自引:0,他引:5
根据金属液凝固收缩理论和多孔介质中流体流动原理,建立了离心压力下Ti-Al合金精密铸件中微观缩松缺陷预测的数学模型,采用该模型对Ti-Al增压涡轮铸件进行模拟计算,并进行了实验验证。结果表明,数学模型能够合理反映离心转速,离心半径、温度梯度和冷却速度等重要因素对微观缩松的影响规律,数值模拟结果与实验结果相吻合。分析增压涡轮的计算结果表明,在涡轮轴向,温度梯度值是影响微观缩松度如何分布的主要原因;在涡轮径向,温度梯度、冷却速度和离心半径的共同作用决定着微观缩松度的变化规律。提高温度梯度,降低冷却速度,充分利用离心压力对枝晶间补缩的有效作用,有利于减少涡轮内部的微观缩松,保证叶片和涡轮的组织致密性和力学性能。 相似文献
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为解决K418合金用于浇注车用增压涡轮时出现的热裂问题,采用有限元模拟软件ProCAST的热弹塑性模型,对不同浇注工艺下K418合金车用增压涡轮的充型和凝固过程进行模拟,通过对温度场、固相分数和应力场模拟结果的分析,预测热裂缺陷的形成倾向,模拟结果与实际情况基本吻合。分析结果表明,涡轮叶稍处产生热裂的根本原因是凝固过程中产生了拉应力,应力值越大,铸件处于热裂敏感区的时间越长,热裂倾向性越大;采用较高的模壳温度和较低的浇注温度有利于降低铸件的热裂倾向。 相似文献
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TiAl基合金连杆件底漏式真空吸铸数值模拟 总被引:1,自引:0,他引:1
利用ProCAST数值模拟技术对TiAl合金汽车发动机连杆铸件底漏式真空吸铸过程的充型过程、凝固过程、缩孔缩松缺陷形成进行了模拟。研究了底漏式真空吸铸的几个主要参数,如吸口直径、浇注温度、浇注速度,对连杆铸件充型凝固过程和缩孔、缩松缺陷的影响规律,得到了TiAl合金底漏式真空吸铸的优化工艺参数图。 相似文献
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采用数值模拟方法,研究ZTC4合金机匣离心铸造的充型和凝固过程,分析了离心转速、浇注温度和铸型预热温度对熔体充填过程流动场、凝固过程温度场和应力场的影响,并预测了缺陷的分布.结果表明,随离心转速提高,熔体充型速度无明显变化,但柯氏力作用更加明显,铸型中熔体流股变细;熔体过热度低于30℃时,铸件出现明显的浇不足缺陷;铸型预热温度是影响铸件残余应力的主要因素,而离心转速和熔体过热度的影响次之;铸件最后凝固的较厚部位容易出现缩松、缩孔缺陷,且其位置与X射线检测结果较吻合. 相似文献
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离心铸造高速钢轧辊铸造缺陷形成与控制技术研究 总被引:2,自引:1,他引:1
采用离心铸造方法制造高速钢轧辊工艺简单,操作方便,但易出现偏析、裂纹、气孔、缩孔及夹杂等缺陷,影响轧辊的力学性能和使用性能.采用稀土-钛复合变质处理改善合金的组织和性能,同时改进离心铸造工艺参数可以消除高速钢轧辊铸造缺陷,提高力学性能,改善使用效果. 相似文献
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利用均衡凝固理论降低离心铸造气缸套废品率 总被引:2,自引:2,他引:0
采用均衡凝固理论分析气缸套离心铸造的缩孔类缺陷形成原因,并利用该理论,通过改变热节部位离心铸造模具表面结构,调整斜度区的涂料厚度来调节热节根部的冷却速度,充分利用凝固过程自补缩,从而消除热节部位缩孔缺陷,使缸套的缩孔废品率降到了1%以下。 相似文献
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立式离心场下钛合金熔体充填及凝固过程研究 总被引:2,自引:0,他引:2
研究立式离心场下不同铸造工艺参数对钛合金熔体的充填及凝固缺陷形成的影响。结果显示,立式离心场下得到的钛合金铸件质量优于重力场下的铸件。立式离心场下,合金熔体由于受离心力和科氏力的作用,沿着与旋转方向相对的型壁进行充填,且熔体的截面面积随充填长度的增加而逐渐减小,但是在内浇口处由于速度降低导致截面面积有所回升。此外,铸型的旋转方向,旋转半径及旋转速度直接影响铸件缺陷的形成。旋转方向直接影响合金熔体的充填顺序,进而影响合金熔体的凝固顺序及缺陷位置。实验结果显示,旋转半径及旋转速度的增加有利于减少铸件的缺陷体积。 相似文献
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A technique for the high-quality precision casting of titanium alloys has been developed that consists of the instantaneous
dissociation of oxide at the metal-mold interface, followed by the rapid absorption and diffusion of the dissociated oxygen
into the subsurface of the cast parts during solidification and cooling. In centrifugal casting trials using less molten alloy
than required to completely fill the mold, the results suggest that the melt flowing in the mold cavities maintains contact
with the vertical inside walls and directionally solidifies from the far end of the cavity to the gate, corresponding to the
gradient in the centrifugal force on the horizontal plane. This force enhances the removal of defects, such as entrapped gas
bubbles and solidification shrinkage. The results have enabled the development of a two-dimensional model to simulate melt
flow during centrifugal casting.
Author’s Note: Unless otherwise indicated, compositions are given in weight percent.
Ken-ichiro Suzuki earned his Ph.D. at Tohoku University, Faculty of Engineering. He is currently a visiting professor at the Graduate School
of Iron and Steel Technology at Pohang University of Science and Technology. 相似文献
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通过射线照相检测对TC4钛合金铸件内部常见缺陷及其在热等静压前后的演变进行分析,结果表明:TC4钛合金铸件内部大部分闭合孔洞类缺陷经热等静压均可消除,内部缺陷底片上显示消失;少量的夹杂类和非闭合孔洞类缺陷未压合,在底片上与热等静压前缺陷显示基本一致;个别缩孔缺陷部分压合或表面压陷,极少量的大尺寸缩孔缺陷压缩变形为线性缺陷,在底片上缺陷显示形态发生变化。由于线性缺陷的结构特征在射线照相检测时易导致影像对比度下降,进而影响缺陷的检出率,因此应在热等静压前对易产生缩孔部位进行射线照相检测并将大尺寸缩孔清除补焊,避免热等静压后缩孔压缩变形造成缺陷漏检。 相似文献
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《Intermetallics》2015
Gravity and centrifugal investment casting processes of low-pressure turbine blades with high Nb–TiAl alloy were simulated by Procast software. Actual blade components were poured by vacuum induction suspended furnace with Ar protection. The experimental verification indicated that the simulation results were in good agreement with the experimental results. Comparative results had shown that the surface of centrifugal casting blade was more complete than that of gravity casting one. In gravity casting process, molten metal filled the thinnest trailing edge at last, resulting in the generation of misrun defects. Furthermore, the shrinkage porosity and crack defects of gravity casting were much more and dispersive. The internal and external quality of centrifugal casting was much better than that of gravity casting. Microstructures from edge to center of gravity casting blade had no significant change. The microstructure for centrifugal casting blade is finer than that for gravity casting blade, however, a large number of dentritic γ segregation appeared in the blade edge of centrifugal casting, which resulted from the fast cooling rate of centrifugal casting surface. 相似文献
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A two-dimensional simulation model for melt flow and solidification in centrifugal precision casting has been developed based
on experimental results on melt flow in a precision casting tree for Ti-6A1-4V alloy castparts. The amount of liquid alloy
is intentionally adjusted to be less than that required for complete filling and is poured under a centrifugal force. The
melt flows into mold cavities keeping contact with the vertical inside walls of the cavity in the anti-rotation side, and
solidifies directionally by accumulating a solidified layer from the far end of the cavity to the gate according to the gradient
of centrifugal force. The model reproduces melt flow observed in casting trials and directional solidification during centrifugal
casting. In addition, it has been confirmed that the centrifugal force imposed on the melt enhances removal of defects caused
by entrapment of gas bubbles or by solidification shrinkage and improves mechanical properties of the castparts.
Formerly Graduate School of Iron and Steel Technology Pohang University of Science and Technology San 31 Hyoja-dong, Namku,
Pohang 790-784, Korea 相似文献