Neutron Diffraction Study of Strain/Stress States and Subgrain Defects in a Creep-Deformed, Single-Crystal Superalloy

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2014, Vol.45 (1), p.139-146
• Main Authors: Wu, Erdong, Sun, Guangai, Chen, BO, Zhang, Jian, Ji, Vincent, Klosek, Vincent, Mathon, Marie-Helene
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Creep (materials); Crystal defects; Deformation; Diffraction; Lattices; Materials Science; Metallic Materials; Metallurgy; Metals creep; Nanotechnology; Neutron diffraction; Residual stress; Strain; Stresses; Structural Materials; Superalloys; Surfaces and Interfaces; Symposium: Neutron and X-Ray Studies of Advanced Materials VI: Diffraction Centennial and Beyond; Thin Films
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-013-1887-4

A single crystal superalloy with initial sample axis 10 deg deviated from [001] was creep deformed at 1273 K (1000 °C) 235 MPa and its triaxial strain/stress state and subgrain defects were studied by neutron diffraction. Normal internal stresses with their directions close to the loading axis and their scales smaller than those perpendicular to the axis were observed and attributed to a lattice rotation toward [001] pole. The internal stress at a level approaching to the loading stress and mostly in the state of interphase stress was induced during the first stage of creep prior to rafting and associated to lattice rotation, microstrain relaxation and line-up of misoriented γ′-precipitates. The internal stress was diminished and released at final stage of creep associated with a reduction in unit-cell volume and a transition of strain/stress state between the two phases. The observation was explained by development of dislocations and raft structure during creep.