Linguistics

Phase (matter)

Philosophy

Transmission electron microscopy

Metallurgy

Materials science

Stress (linguistics)

Carbide

Precipitation

Creep

Physics

Nanotechnology

Organic chemistry

Alloy

Microstructure

Optical microscope

Austenite

Composite material

Chemistry

Scanning electron microscope

Meteorology

Materials Science and Engineering A

Alloy 709 is an austenitic stainless steel with potential for structural applications in advanced nuclear reactors. In this study, creep tests on Alloy 709 specimens were performed at a temperature of 700 °C under applied stresses in the range of 125–250 MPa. The alloy exhibited a brief primary, insignificant secondary and prolonged tertiary creep stages. A Norton stress exponent (n) of 5.9±0.7 was obtained from the double-logarithmic plot of minimum creep rate versus stress. Microstructural analyses were carried out for both as-received and crept specimens using optical microscopy, electron backscattered diffraction, and transmission electron microscopy. The microstructures of the as-received and crept specimens were compared. The mode of fracture was transgranular as revealed by scanning electron microscopy of the creep-ruptured specimens. Thermodynamic and precipitation modeling was performed in order to obtain information on the phase types and the kinetics of precipitation for the sigma−phase and the M23C6 carbide. Based on the creep data, microstructural observations and relevant modeling, creep deformation and failure mechanisms at the considered temperature are elucidated.

Creep behavior of Alloy 709 at 700 °C