弹性场下含Nb镍基合金沉淀亚稳相多尺度双向复合模拟

Niobium has high melting point, ductility strength, and the effect of solution strength and precipitation strength, Yet the low room temperature ductility, high temperature creep strength of Nickel based alloys containing Nb limit its application. The main strengthening phases are some metastable precipitates coherent with their matrix. So it is important to study the influence rule of niobium content and elastic distortion field on the metastable precipitation process of nickel alloy for increasing the room-temperature and high-temperature properties. Here, the main modeling method of Micro Phase Field Method-MPFM for four componets alloys system based on atom-phase-microstructure scale will be developed and employed, and some required parametres will be acquired by First Principles Method-FPM based on electronic-atomic scale. The occupied sites, order-disorder, clustering, volume fraction, scaling law etc. of precipitated metastable phases for different niobium content alloy at different degree of elastic field will be calculated, and the project planed to focus on studying the early precipitation sequence, the middle metastable phenomenon, the later coarsening law and the whole course morphology evolution of precipitation phases. Then the results were compounded with thermodynamic and mechanical properties of first-principles calculation to study the macroscopical preperties of each metastable phase, such as thermodynamic stabilities, strength and plasticities, and were verified through experiments. The project will provide direction for component and strengthening design of nickel alloy added by niobium and increase the reliability of phase field simulation, and expect to match a kind of process description approaching the fact well without model and route with the states and properties of first-principles calculation.

铌熔点高、延性好、强度高，兼具固溶强化和沉淀强化作用，含铌镍基合金室温延性低和高温抗蠕变强度低限制了其应用，该类合金主要强化相为与基体共格的沉淀亚稳相。因此，研究铌含量和共格弹性场对镍基合金沉淀亚稳过程的影响在提高其性能方面具有重要意义。本项目主要采用基于原子-相-组织尺度的四元微观离散格点相场方法，从基于电子-原子尺度的第一性原理计算中获取所需参数，计算不同含铌量合金在不同程度弹性场作用下沉淀亚稳相的原子占位、有序-无序、簇聚、体积分数、标度律等，重点研究沉淀相的早期析出序列、中间亚稳现象、后期粗化规律、全程形貌演化；之后再与第一性原理的热力学、力学性质计算相复合，研究各亚稳相的热力学稳定性、强度、塑性等宏观性能，并进行实验验证。本项目实施会为含铌镍基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，同时期待为第一性原理计算配套一种不预设微结构和转变路径的动力学描述方法。

由于镍基合金具有优良的高温特性，以及极佳的耐疲劳、耐氧化和耐腐蚀性能，所以其在航空航天领域得到广泛应用。合金的时效温度，合金的成分以及弹性应变能对合金的沉淀过程以及原子在格点的占位情况都会产生影响。.通过对Ni-Al-Ti合金在不同的温度下、不同的Al原子浓度和不同的弹性应变能下进行研究，研究发现在不同的温度下、不同的Al原子浓度和不同的弹性应变能常数下，合金的沉淀过程都经历了原子的聚簇，L10过渡相的析出，L10过渡相的有序化和L12相的析出同时进行，化学计量比的L12有序相的形成。Ni原子占据α1位和α2位，Al原子和Ti原子共同占据β位，Ti原子优先占据β位，但是Al原子在β位的占位几率始终都大于Ti原子的占位几率。.Al原子浓度的增大促进了Ni75AlxTi25-x（x=12、14、16、18）合金中Ni原子在α1位和α2位的占位几率，抑制了Ni原子在β位的占位几率。对于Al和Ti原子，Al原子浓度的增大促进了Al原子在三种格点的占位几率，抑制了Ti原子在三种格点的占位几率。.通过对Ni75Al14Mo11合金在不同弹性畸变能常数下的沉淀过程进行模拟研究，发现其沉淀过程为：溶质原子簇聚→L10结构相→L12有序相生成，且L10过渡相在析出过程用有两种投影结构，L10(Ⅰ)结构和L10(Ⅱ)结构，随着弹性应变能增加，两种L10 结构相的析出受到影响，弹性应变能明显抑制L10(Ⅰ)的析出。.通过对弹性应变能对镍基合金沉淀过程中无序相的反向析出研究发现，不同弹性应变能下均出现了有序强化相γ′（L12结构）析出无序相（面心立方结构）的现象。并且发现无序相的析出主要在熟化颗粒的边缘部分，这主要由于边缘部分更容易发生原子的迁移。通过占位几率对比发现相同时间步数下，弹性应变能的增加能够促进无序相的析出。.本项目实施会为镍基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，同时期待为第一性原理计算配套一种不预设微结构和转变路径的动力学描述方法。