The effect of homogenization treatments on the microstructure and mechanical properties of Thermo-Span alloy

The effect of homogenization treatments on the microstructure and tensile properties at room temperature and 650 °C of Thermo-Span alloy are systematically investigated. Laves phases with different sizes and morphologies have been obtained by using three types of homogenization treatments. The results show that the precipitation of small granular secondary Laves phases and γ' phases are inhibited effectively by large blocky primary Laves phases, resulting in high plasticity and low strength of the alloy. The precipitations of secondary Laves phases and γ' phases increase with the dissolution of primary Laves phases, leading to low plasticity and high strength of the alloy. The secondary Laves phases continue to increase and γ' phases slightly decrease with the almost elimination of primary Laves phases, resulting in high plasticity and strength of the alloy. Hence, fewer large blocky primary Laves phases are more favorable for the best match between strength and ductility. The factors affecting the yield strength at room temperature and 650 °C tensile are discussed in detail. Moreover, it is first found the deformation mechanism of Laves phases i.e. the stacking faults shearing in Thermo-Span alloy. In terms of ductility, small granular secondary Laves phases are more favorable than large blocky primary Laves phases.