镍基单晶高温合金中的位错及其对蠕变行为的影响

Dislocations in Ni-based Single Crystal Superalloys and Their Influence on Creep Behavior

镍基单晶高温合金是一种极为重要的高温结构材料,主要用于制造航空发动机叶片等热端部件。位错是引起材料塑性变形的主要原因,会导致零件失效或断裂。镍基单晶高温合金在实际服役过程中形成的位错类型多样、形态各异,对蠕变性能的影响也各不相同。因此,位错与蠕变机制的关系一直是高温合金性能研究的重点,备受国内外学者关注。单晶高温合金中的位错组态主要包括γ相中的独立位错、形成堆垛层错的位错、界面位错网以及γ′相中的超位错。独立位错、堆垛层错、界面位错网和γ′相中各种类型的超位错均是位错与溶质原子、位错与γ′相以及位错与位错之间复杂交互作用的结果。基体通道中的独立位错形成于蠕变初期,是所有位错之源。堆垛层错是高温合金低温蠕变中最常见的位错组态,既可存在于基体相,也可存在于γ′相,层错形貌与两相层错能大小有关。界面位错网呈四方状或六方状,集中分布于γ/γ′两相界面附近,是高温蠕变的典型组织特征之一。高温蠕变下进入γ′相的超位错有两种,分别是〈110〉型超位错和〈010〉型超位错,两种超位错通过γ′相的机制明显不同,〈110〉型超位错主要以切割方式穿过γ′相,而〈010〉型超位错只能以滑移和攀移相结合的方式通过γ′相。合金的蠕变性能与位错组态密切相关。堆垛层错是合金层错能低的表现,低层错能会增大初始蠕变量,缩短合金的低温蠕变寿命;界面位错网是位错与两相错配应力交互作用的结果,位错网阻碍了位错切割γ′相,对高温蠕变性能非常有利;位错穿过γ′相是高温合金高温蠕变的控制性因素,进入γ′相的超位错因类型不同,对蠕变性能的影响也明显不同。对高温合金中各种位错形貌、结构以及形成过程的认识是高温合金蠕变机理研究的基础,关于位错组态对蠕变性能的影响和位错组态影响因素的分析可以为合金设计提供新思路。本文针对镍基单晶高温合金中的几种主要类型位错,分别从位错形貌与结构、位错形成机理以及位错对蠕变性能的影响三个方面进行了综述,阐明了不同类型位错的形貌特征,分析了位错决定蠕变性能的内在机理,总结了合金元素强化的一般性规律,在此基础上提出了几种提高单晶高温合金蠕变性能的潜在技术途径。

Nickel-based single crystal superalloy is an extremely important high-temperature structural material, mainly used to manufacture the hot end components such as aero-engine blades. Dislocations are the main reason for plasticdeformation of materials and can directly lead parts to failure or fracture. The dislocations in nickel-based single crystal superalloys formed in actual service processes, come in many types and morphologies and have different effects on creep performance. Therefore, the research on the relationship between dislocation and creep mechanism has been the focus of superalloys performance research, and has attracted the attention of researchers at home and abroad. The single crystal sueralloys consists of γ matrix and γ′ precipitate. The dislocations in Ni-based single crystal superalloys mainly include: independent dislocations in γ matrix, stacking fault, dislocation network, and super dislocations in γ′ precipitate, which are the result of interactions between dislocations and solute atoms, dislocations and γ′ precipitate, and dislocations and dislocations. Independent dislocations are formed in matrix channel at primary creep and are the source of all dislocations such as dislocation network and super dislocations. Stacking fault is the most common dislocation configuration in low temperature creep of superalloys. It can exist alone in the γ matrix phase, as well as in the γ′ phase. The stacking fault morphology is related to the fault energy of γ and γ′ phase. The interface dislocation network is mainly tetragonal or hexagonal, and is concentrated in the vicinity of the γ/γ′ two phase interface, which is one of the typical structural features of high temperature creep. There are two kinds of super dislocations entering γ′ precipitate under high temperature creep, which are 〈110〉 type super dislocation and 〈010〉 type super dislocation. The mechanisms of the two super dislocations through γ′ phase are obviously different.〈110〉 type super dislocations mainly pass through the γ′ phase in a cutting manner, while 〈010〉 type super dislocations can only pass through the γ′ phase by a slipping and climbing combination manner. Dislocations determine the properties of superalloys. Stacking fault is the performance of lowfault energy of alloys. Low stacking fault energy will increase primary creep and shorten creep life of low temperature creep of the alloys. The interface dislocation network is the result of interaction between dislocations and two-phase misfit stress, which hinders subsequent dislocation cutting through γ′ phase. It is very beneficial to improve the high temperature creep performance of superalloys. Dislocation through γ′ phase is considered to be the controlling factor for high temperature creep of superalloys. The type of the super dislocation entering the γ′ phase is different, and the creep properties are also significantly different. The understanding of dislocation morphology, structure, and formation processes in superalloys is the basis study of creep mechanism for superalloys. The analysis of the dislocation type influence on creep performance and the influencing factors of dislocation formation can provide new ideas for alloy design. In this paper, several typical dislocations in nickel-based single crystal superalloys are reviewed from three aspects: dislocation morphology and structure, dislocation formation mechanism, and the influence of dislocations on creep properties. The morphological characteristics of different types of dislocations are clarified, and the internal mechanism of dislocationinfluence creep properties is analyzed. The general laws of alloying element strengthening are summarized. On this basis, several potential technical approaches to improve the creep properties of single crystal superalloys are proposed.