Re元素对镍基单晶合金长时蠕变损伤与寿命的影响机理及描述模型研究

Rhenium (Re) is widely used as the key element to improve the bearing temperature of nickel-based single crystal superalloys. Higher content of Re significantly improves the creep strength of the alloy, however it can result in precipitations of brittle inclusion which is also known as topology close phase (TCP) under long creep condition. The creep lifetime decreases rapidly. So far, the recorded performance is limited in 2000h, the mechanism of Re element in long-term creep (15000h) has not been studied systematically. The shortages have a strong adverse impact on the safety of single crystal turbine blades during long-term service. .This project makes use of domestic third generation nickel-based single crystal superalloys with high Re as the standard alloy. Nickel-based single crystal superalloys with different content of Re will be prepared and used in the long-term creep tests. The distribution and morphological characteristics of Re elements will be analyzed. It will be studied that the coupling effects of Re and other factors such as temperature, stress and crystal orientation, as well as the effect law of Re on creep life. Combined with the first principle theory, molecular dynamics and crystal plasticity, the project will study the mechanism of the influence of Re elements on the evolution of microstructure. To illuminate the precipitation mechanism of TCP phase induced by Re during the long-term creep, the project will analyze the influence of Re on the pattern, formation and growth of TCP phase. Based on creep crack nucleation and propagation rules, this project will extract the state variables of the dislocation, γ’ rafting and TCP phase evolution to establish the long-term creep constitutive and life models of nickel-based single crystal superalloy with higher Re.

铼（Re）是提高镍基单晶合金承温能力的关键性元素，更高含量的Re能够显著提高合金的蠕变强度；然而，在长时蠕变过程中也易使硬质脆性“拓扑密排（TCP）相”析出，导致蠕变寿命加速衰减。目前的研究均集中在2000h以内，对长时（~15000h）蠕变条件下的Re元素作用机理缺乏系统研究，严重影响了长寿命航发单晶叶片的安全服役。.针对我国在研第三代高Re含量镍基单晶合金，铸造不同Re含量镍基单晶并开展长时蠕变试验，表征Re元素的分布规律及形态特征，研究Re与温度、应力及晶体取向等因素的耦合效应及其对蠕变寿命的影响规律；结合第一性原理、分子动力学、晶体塑性等理论研究，揭示Re元素对微观组织结构演化规律的影响机理，阐明Re元素对TCP相结构形态、形成及演化的影响机制；基于蠕变裂纹形核与扩展规律，提取位错、γ′相筏化、TCP相的演化状态量，结合晶体塑性理论，建立含Re镍基单晶合金长时蠕变本构和寿命模型。

随着航空发动机涡轮前燃气进口温度的进一步提高，需要采用承温能力更高的新一代镍基单晶高温合金涡轮叶片。铼（Re）是提高镍基单晶合金承温能力的关键性元素，决定了镍基单晶合金的代次，更高含量的Re能够显著提高合金的蠕变强度。然而，在长时蠕变过程中也易使硬质脆性“拓扑密排相（TCP）”析出，导致蠕变寿命加速衰减。.本项目针对我国在研第三代高Re含量镍基单晶合金，铸造了不同Re含量镍基单晶并开展长时蠕变试验，表征了Re元素的分布规律及形态特征，研究了Re与温度、应力及晶体取向等因素的耦合效应及其对蠕变寿命的影响规律；结合晶体塑性等理论研究，揭示了Re元素对微观组织结构演化规律的影响机理，阐明Re元素对TCP相结构形态、形成了及演化的影响机制；基于蠕变裂纹形核与扩展规律，提取了位错、γ′相筏化、TCP相的演化状态量，结合晶体塑性理论，建立了含Re镍基单晶合金长时蠕变本构和寿命模型。.研究结果表明：随Re元素含量的提高，合金铸态组织中共晶相体积分数增加，组织不均匀性和成分不均匀性增加，枝晶干与枝晶间元素偏析程度均提高。DSC法与金相法测得到随着Re元素含量增加，合金的初熔点降低。设计了分步固溶热处理制度，成功避免了合金的初熔。Re元素对合金固溶微孔的尺寸与体积分数的增加具有促进作用。随Re元素含量增加，合金蠕变寿命增加，加入Re元素而产生的长程弹性应力场与其低扩散速率均能显著阻碍位错在基体通道中的运动，从而降低合金稳态蠕变阶段的应变率，并对合金筏化具有抑制作用。提取TCP相体积分数用以反映材质劣化，建立了考虑TCP相影响的镍基单晶合金蠕变持久寿命模型，模拟得到的蠕变曲线与试验曲线的寿命误差均小于10%。