In situ TEM investigation on the precipitation behavior of μ phase in Ni-base single crystal superalloys

• Published in: Acta materialia 2016-05, Vol.110, p.268-275
• Main Authors: Gao, Shuang, Liu, Zhi-Quan, Li, Cai-Fu, Zhou, Yizhou, Jin, Tao
• Format: Article
• Language: English
• Subjects: Coherence; Crystal defects; In situ TEM; Ni-base single crystal superalloy; Nickel; Nucleation; Planar defects; Precipitation behavior; Single crystals; Stacking; Superalloys; Topologically close-packed phase; Transmission electron microscopy
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2016.03.046

The precipitation behavior of μ phase in Ni-base single crystal superalloys was investigated by in situ transmission electron microscopy (TEM). A layer-by-layer growth process with a ledge propagation mechanism was first observed during in situ precipitation. Three types of μ phase with different morphologies were found, which grow along [001]μ with (001)μ planar defects, [-111]μ with (1–12)μ planar defects, as well as both directions with mixed planar defects. High-resolution TEM image and established atomic models reveal a basic growth mechanism of μ phase by stacking on (001)μ plane and randomly forming coherent planar defects, while the nucleation of incoherent (1–12)μ planar defects at the early stage of precipitation plays an important role in affecting the basic growth mechanism. The frequent faults during the stacking process of the sub-unit layers within μ lattice should be responsible for the defect formation. In situ transmission electron microscopy (TEM) investigations reveal the layer-by-layer growth mechanism of μ phase precipitated in Ni-base single crystal superalloys. Three types of μ phase with different morphologies were formed at 1050 °C, which grows along [001]μ with (001)μ planar defects, [-111]μ with (1–12)μ planar defects, as well as both directions with mixed planar defects respectively. Formation of (001)μ micro-twin and stacking fault is the essential feature for precipitated μ phase, while nucleation of incoherent (1–12)μ planar defects plays an important role in changing growth method. [Display omitted]