GH4151镍基高温合金μ相中的基面层错

Basal Stacking Faults ofμPhase in Ni-Based Superalloy GH4151

晶界析出相对变形高温合金的力学性能有重要影响。本工作采用像差校正透射电镜观察发现,μ相中存在大量基面层错,依据层错结构单元排列的不同将基面层错分为4类。与μ相结构相比,I型基面层错相当于一层平行四边形结构单元反向;Ⅱ型基面层错相当于在I型基面层错的基础上缺失一层矩形结构单元,形成C14结构;μ相内单独缺失一层平行四边形结构单元或矩形结构单元后相应地会形成Ⅲ型和Ⅳ型基面层错,分别形成完整Zr_(4)Al_(3)相和C15结构。其中,Ⅱ型和Ⅳ型基面层错都会形成Laves相,统计发现前者的数量多于后者。第一性原理计算表明,这与Ⅱ型基面层错(C14结构)的稳定性高于Ⅳ型基面层错(C15结构)有关。

Wrought Ni-based superalloys are widely used in aviation and energy fields because of their excellent creep resistance,thermal stability,heat corrosion resistance,and oxidation resistance at high temperatures.The mechanical properties of wrought Ni-based superalloys are significantly affected by grain boundary precipitation.Among the grain boundary second phases,the topologically closepacked(TCP)phase is usually discovered in wrought superalloys with the addition of refractory metal elements.As a complex intermetallic compound with only tetrahedral interstices,the TCP phase is stacked with a high packing density of atoms,embodying low plasticity and high brittleness.Given these characteristics,the TCP phase tends to promote crack initiation and propagation during creep,thereby reducing the alloy's creep strength.Additionally,the formation of the TCP phase requires several refractory elements,thereby weakening the effect of the solid solution strengthening of the matrix.As a ubiquitous TCP phase in wrought superalloys,μphases are represented by rectangular and parallelogram structural subunits,which are parallel to the basal plane ofμphases.Basal stacking faults(SFs)are the most common defects in theμphase,and SFs with different stacking sequences will form different phases with corresponding structures and mechanical properties.Theμphases and their basal SFs in wrought Ni-based superalloy GH4151 were systematically studied by multifarious electron microscopy techniques,such as EDS and atomic-resolution high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)of aberration-corrected TEM,revealing the structure and composition of theμphase and the structure and distribution of numerous basal SFs in theμphase.Based on the different arrangements of structural subunits,the basal SFs were divided into four types.Type I basal SF is equivalent to theμphase with a layer of parallelogram structural subunit reversing to form two layers of microsymmetric structures,the reversed parallelogram structural subunit is symmetrical to the rectangular one;type II basal SF is equivalent to type I basal SF in the absence of a layer of the rectangular structural subunit,forming a C14 structure and microsymmetric structure;type III basal SF results from the absence of a layer of the parallelogram structural subunit in theμphase,forming a complete Zr_(4)Al_(3)phase;and type IV basal SF results from the absence of a layer of the rectangular structural subunit in theμphase,forming a C15 structure.Among the four types of basal SFs,type II and type IV basal SFs form Laves phases,but the occurrence of the former is more than that of the latter.This finding is related to the stability of type II basal SF(C14 structure)over type IV basal SF(C15 structure)revealed by the firstprinciple calculations.