Temperature dependence of misfit in different Co–Al–W ternary alloys measured by synchrotron X-ray diffraction

Abstract

The lattice misfit between the γ matrix and coherently embedded γ′ precipitates in the ternary system Co–9Al-xW-0.1B(x = 8,9,11) was measured in-situ by synchrotron X-ray diffraction between room temperature and 1000 °C. The lattice parameters of both γ′ and γ phases increase with rising temperature. The thermal expansion of both phases is similar before the γ′ precipitates start to dissolve. When the temperature rises above 700 °C, the lattice parameter of the γ phase increases more rapidly due to a redistribution of W atoms from the dissolving γ′ precipitates. Thus, the misfit remains almost constant in the temperature range between 20 °C and 700 °C but decreases drastically above 700 °C. Nevertheless, the misfit in these Co–Al–W alloys remains positive up to the γ′ solvus.