【作者】 金文中；

【导师】 殷国茂； 李廷举；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2008， 博士

【摘要】 铸造高温合金大多采用双真空熔铸工艺,即将原材料先在真空感应炉内熔炼并铸造成母合金锭,再在真空感应炉内将母合金锭重熔并浇注成铸件。因此,最初的高温合金母合金锭的质量对高温合金铸件的质量有很大影响。目前采用传统的真空熔铸工艺得到的高温合金母合金锭存在晶粒粗大、元素偏析严重和缩孔较多等问题,从而影响了最终铸件的合格率。采用传统真空熔铸工艺得到的高温合金铸件的凝固组织一般都是粗大不均的,这就导致这类铸件在中低温的环境中工作时具有较差的低周疲劳性能和力学性能。晶粒细化是提高中低温工作条件下高温合金铸件低周疲劳寿命和力学性能的有效途径之一。随着电磁场技术的发展,材料的电磁加工技术已经成为材料科学和材料制备领域重要的研究方向。其中,电磁搅拌技术作为细化晶粒、增加等轴晶率、减轻中心缩孔和偏析、减少夹杂物的重要手段,对提高铸坯的质量具有显著作用。为了解决目前高温合金母合金锭存在的质量问题,本文提出了在高温合金母合金锭真空熔铸的凝固过程中施加旋转电磁场的高温合金母合金锭真空电磁铸造新技术。建立了工频单向旋转电磁场作用下高温合金母合金锭真空电磁铸造技术的试验装置,研究了工频单向旋转电磁场对K417高温合金母合金锭质量的影响。结果表明:在高温合金母合金锭真空熔铸的凝固过程中合理施加工频单向旋转电磁场,其在金属熔体中产生的旋转电磁搅拌作用能够使K417高温合金母合金锭的等轴晶组织得到明显细化、等轴晶率有所增加、夹杂物和中心缩孔的大小和分布得到明显改善、枝晶偏析大为减轻,从而使高温合金母合金锭的质量得到大幅提高。为了提高在旋转电磁场作用下容易产生负偏析带缺陷的一些高温合金母合金锭的质量,本文提出了在高温合金母合金锭真空熔铸的凝固过程中施加行波磁场的高温合金母合金锭真空电磁铸造新技术。建立了单侧向上的工频行波磁场作用下高温合金母合金锭真空电磁铸造技术的试验装置,研究了单侧向上的工频行波磁场对K417高温合金母合金锭质量的影响。结果表明:在高温合金母合金锭真空熔铸的凝固过程中合理施加单侧向上的工频行波电磁场,其在金属熔体中产生的线性电磁搅拌作用能够使K417高温合金母合金锭的质量得到大幅提高。为了得到优质高温合金细晶铸件,本文提出了通过将施加双向旋转电磁场和在模壳内壁的面层涂料中添加孕育剂相结合的方法获得高温合金细晶铸件的新技术,建立了工频双向旋转电磁场和孕育剂作用下高温合金细晶铸造技术试验装置,研究了工频双向旋转电磁场和孕育剂对K417高温合金铸件晶粒尺寸和断面等轴晶比例的影响,并系统研究了晶粒细化到95μm对K417高温合金铸件的枝晶组织、枝晶偏析、MC型碳化物、γ′相、(γ+γ′)共晶以及室温和650℃中温条件下拉伸性能和低周疲劳性能的影响。结果表明:(1)通过增加电磁搅拌强度或缩短金属液的静置时间并不能完全消除高温合金铸件表面的粗大柱状晶层。通过将浇注8秒后施加150A的工频双向旋转电磁场和在模壳内壁的面层涂料中添加孕育剂铝酸钴相结合的方法,可以得到晶粒细化至95μm、断面等轴晶比例达到100%的K417高温合金细晶铸件。(2)通过将施加工频双向旋转电磁场和在模壳内壁的面层涂料中添加孕育剂铝酸钴相结合的方法将晶粒细化到95μm,可以大幅减轻K417高温合金铸件的枝晶偏析,并能改善其枝晶、MC型碳化物、(γ+γ′)共晶和γ′相的形态和分布,这均有利于提高高温合金铸件的塑性、韧性和疲劳性能。(3)在室温和650℃的中温条件下,晶粒细化到95μm可以使K417高温合金铸件的强度、塑性和低周疲劳寿命明显提高。当温度从室温20℃升高到中温650℃时,K417高温合金的抗拉强度和屈服强度基本保持不变,但其延伸率和断面收缩率却有所降低。在0.3%的总应变控制量下,当试验温度从室温20℃升高到中温650℃时,K417高温合金粗晶试样和细晶试样的低周疲劳寿命都有较大幅度的降低,这主要是由温度升高导致氧化损伤和疲劳损伤的增加所引起,其中疲劳损伤起着主要作用。更多还原

【Abstract】 The superalloy casting is usually manufactured by two-ply vacuum casting,i.e.the raw materials are melted and casting into a master alloy ingot in a vacuum induction furnace,then the master alloy ingot is re-melted and casting into foundry goods in a vacuum induction furnace,so the quality of the superalloy cast are greatly affected by the quality of the superalloy master alloy ingots.At the present time,the master alloy ingot made by vacuum casting usually have quality problems of coarse grain,more shrinkage porosity,and more serious segregation,which reduces the percent of pass of superalloy casting.The main disadvantages of the conventional superalloys investment cast are coarseness and non-uniform of grain structures,which reduce the low cycle resistance and high tensile strength of the cast under the medium temperature.It has been demonstrated that the integral grain refinement is the effective method to improve the low cycle resistance and high tensile strength of the cast within the medium temperature ranges.The Electromagnetic Processing of Materials has become the important research field of the materials science.Therein,the electromagnetic stirring has advantages of refining the internal structures of the ingot,reducing the segregation and shrinkage cavity,and minimizing the inclusion.In order to improve the quality of superalloy master alloy ingots,the new technology of superalloy vacuum-electromagnetic casting,i.e.imposing rotating electromagnetic stirring to the solidification process of superalloy vacuum casting was developed,and the effect of rotating electromagnetic stirring on the quality of superalloy ingots was studied.The main conclusions can be listed as follow:Through imposing rational rotating electromagnetic stirring to the solidification process of superalloy vacuum casting,the equi-axed crystals in the superalloy ingots can be effectively refined and increased,and the central shrinkage porosity,the inclusion and the dendritic segregation of superalloy ingots are greatly reduced. The quality of superalloy ingots is obviously improved.In order to improve the quality of some superalloy master alloy ingots,which is easy to generate the negative segregated band under the action of the unidirection rotating electromagnetic stirring,the new technology of superalloy vacuum-electromagnetic casting, i.e.imposing linear electromagnetic stirring to the solidification process of superalloy vacuum casting was developed,and the effect of linear electromagnetic stirring on the quality of superalloy ingots was studied.The results indicate that the quality of superalloy ingots can be obviously improved through imposing rational linear electromagnetic stirring to the solidification process of superalloy vacuum casting.Furthermore,in order to obtain the good superalloy fine-grain casting,a new fine-grain casting technique of superalloy castings by applying reversible rotary magnetic fields and inoculants simultaneously was proposed,and effects of reversible rotary magnetic fields and inoculants on the crystal structure and performances of K417 superalloy cast were investigated.The main conclusions can be listed as follow:1.The coarse columnar grain surface can not be removed by increasing the current intensity or shortening the stewing time.By initiating the 50Hz and 150A reversible rotary electromagnetic stirring as soon as the molten metal was poured into the mould,which was coated with the inoculant CoAl₂O₄,the average equiaxed grain size of K417 superalloy cast can be refined to 95μm and the fraction of equiaxed grains can be increased to 100%.2.On condition that the average equiaxed grain size of K417 superalloy cast were refined to 95μm,the micro-segregation,the dendritic,the MC carbide,the（γ+γ’） eutectic and theγ’ phase in samples can be greatly improved,which is favorable to the increment of the K417 superalloy performances.3.Under 650℃,the strength,the plasticity and the low cycle fatigue lifes of K417 superalloy can be obviously increased by the grain refinement.When the test temperature is increased from 20℃to 650℃,the strength of K417 superalloy can kept invariable.However, the plasticity of K417 superalloy can be reduced.When the test temperature is increased from 20℃to 650℃,the low cycle fatigue lifes of K417 superalloy can be largely reduced.The reasons can be attributed to the increment of oxidized damage and fatigue damage.Therein, the increment of fatigue damage is the main factor.更多还原