Abstract Secondary phases precipitated in diffusion affected zones (DAZs) of a transient liquid phase (TLP) bonded Ni-based superalloy have a large impact on materials properties. Here we report an atomic-scale analysis of the crystal structures and elemental distributions within DAZ precipitates in a TLP-bonded single-crystal superalloy using a range of electron microscopy techniques. The predominant precipitate phases are found to be M3B2- and M5B3-type borides, where M is a mixture of transition metal elements. Atomically-resolved energy-dispersive X-ray spectroscopy in an aberration-corrected scanning transmission electron microscope (STEM) enabled the distributions of metal atoms within the precipitates to be determined. The observation that different metals occupy preferred sites within the crystals indicates that these phases are not uniform solid solutions, but instead are chemically ordered. Both borides contain two distinct metal lattice sites such that the phases can be described as L2SB2 and L4SB3, where L and S are elements with larger (e.g., W, Mo) and smaller (e.g., Cr, Co, Ni) atomic numbers, respectively. Ordering of W and Cr is found to be particularly strong. A systematic search for stable phases within the chemical space of the W-Cr-B ternary system using the crystal structure prediction (CSP) program USPEX provided further insights into the nature of the observed chemical ordering. This combination of STEM and CSP techniques provides a direct and robust way of determining chemical features and local structures of multicomponent phases with atomic resolution even when particle sizes are too small for analysis using conventional methods.

中文翻译：

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M 3 B 2 和M 5 B 3 硼化物中化学排序的原子尺度观察和分析

摘要 在瞬态液相 (TLP) 粘结镍基高温合金的扩散影响区 (DAZ) 中析出的二次相对材料性能有很大影响。在这里，我们报告了使用一系列电子显微镜技术对 TLP 键合单晶高温合金中 DAZ 沉淀物中的晶体结构和元素分布进行的原子级分析。发现主要的沉淀相是 M3B2-和 M5B3-型硼化物，其中 M 是过渡金属元素的混合物。像差校正扫描透射电子显微镜 (STEM) 中的原子分辨能量色散 X 射线光谱能够确定沉淀物中金属原子的分布。观察到不同金属占据晶体内的优选位点，表明这些相不是均匀的固溶体，而是化学有序的。两种硼化物都包含两个不同的金属晶格位点，因此可以将相描述为 L2SB2 和 L4SB3，其中 L 和 S 分别是原子序数较大（例如 W、Mo）和较小（例如 Cr、Co、Ni）的元素. 发现 W 和 Cr 的排序特别强。使用晶体结构预测 (CSP) 程序 USPEX 在 W-Cr-B 三元系统的化学空间内系统搜索稳定相，提供了对观察到的化学排序性质的进一步见解。