GH4169镍基合金双重晶界强化多尺度研究

GH4169 alloys are currently one of the largest consumption of nickel-based superalloys, whereas the strength and service life are greatly diminished since the grain boundary is weak. Rare earths and directional solidification have better effect on grain boundary strengthening, but its mechanism is not clear yet. It has an important scientific significance to ascertain this theory. In this application, the interface of Ni/Ni3Nb and Ni/Ni3Al with rare earths Y, La and Ce are the research object. The stability, bond strength, charge density difference, interfacial tensile fracture process and so on are studied via first-principles method. The interfacial crack extension and rare earths elements segregation, etc, are also predicted. The mechanism of rare earths grain boundary strengthening and interface failure are revealed based on those results from electron-atomic scale. The parameters from first-principles calculations, such as interface energy, anisotropy coefficient, are be used to couple with directional solidification phase-field model. We employ this model to investigate dendrite morphology, growth regularity of GH4169 alloys containing rare earths elements by directional solidification, and determine the boundary position, grain size, grain boundary orientation, etc. The grain boundary strengthening mechanism of rare earths and directional solidification are explained from phase-organization scale based on the results of directional solidification phase-field method. Experimental study are carried out to verify some simulation conclusions. Finally, the comprehensively grain boundary strengthening theory are obtained. It provides the basis for the design of new high strength Ni-based superalloys, and also provide a multi-scale research idea by coupling with first-principles and solidification phase-field method.

GH4169合金是当前用量最大的镍基高温合金，因晶界薄弱使其强度和使用寿命大大减弱。稀土和定向凝固对晶界强化有较好的作用，但其机理尚未明确，探明这一理论具有重要科学意义。本申请以稀土Y、La、Ce加入Ni/Ni3Nb、Ni/Ni3Al界面为研究对象，采用第一性原理研究界面稳定性、粘结强度、电荷差分密度等性质，并模拟界面拉伸断裂过程，从而预测界面裂纹扩展、稀土元素偏析等，从电子-原子尺度揭示稀土晶界强化机理和界面失效机制。将第一性原理计算的界面能、各向异性系数等参数与定向凝固相场模型耦合，研究含稀土元素的GH4169合金定向凝固过程枝晶形貌、生长规律，确定晶界位置、晶粒大小、晶界取向，从相-组织尺度诠释稀土和定向凝固双向晶界强化机制，并对部分模拟进行实验验证。最终得出系统全面地晶界强化理论，为新型高强镍基高温合金设计提供依据，亦可提供一种第一性原理方法与凝固相场法耦合的多尺度研究思路。

由于GH4169合金具有良好的抗疲劳、抗辐射、抗氧化、耐腐蚀性能以及良好的焊接性能，因此可用于宇航、核能、石油工业等领域中各种复杂零部件的制备。但GH4169合金薄弱的晶界致使其强度和使用寿命大大减弱。.在第一性原理计算的基础上，对不同原子堆垛类型的Ni/Ni3Nb(001)、Ni/Ni3Nb(011)、Ni/Ni3Nb(111)、Ni/Ni3Al(001)、Ni/Ni3Al(011)、Ni/Ni3Al(111)界面性质进行了理论研究。hollow、Ni+Al-top和Ni-hollow界面系统的基体相或强化相内，以及Ni-top界面系统的界面处。对于Ni/Ni3Nb界面，裂纹产生在Ni+Nb-hollow和Ni+Nb-top界面系统的基体相或强化相内，以及Ni-top和Ni-hollow界面系统的界面处。Y、La、Ce均能在Ni/Ni3Al、Ni/Ni3Nb界面会发合金化，甚至形成新的界面相。Ni、NiAl和Ni3Al拉伸和剪切理想强度计算表明[100]方向具有最大的理论拉伸强度。.基于第一性原理得出的参数，采用凝固相场法建模。通过研究发现随生长速度的提高，固/液界面的形态将经历从平界面-胞晶-树枝晶-胞晶-带状组织-绝对稳定平界面的转变。在TEM表征中发现超过临界过冷度，显微硬度急剧下降，说明积累的应力超过合金的屈服强度，使组织结构发生了塑性应变，并作为驱动力促使体系发生再结晶。.本项目实施会为GH4169合金的成分设计和强化设计提供指导，并提高相场模拟的可靠性。同时通过模拟与实验相结合的方法可改变了以前实验设计方法成本高、周期长的缺点。

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