Abstract A precipitation study was carried out during the isothermal aging at 850 °C for Fe-10at.%Ni-15at.%Al, Fe-10at.%Ni-15at.%Al-2.5at.%Cu and Fe-10at.%Ni-15at.%Al-5at.%Cu alloys. The experimental, Calphad, and Kinetic/Precipitation calculated results indicated that the Cu-addition to the ternary alloy promoted a higher volume fraction of β´precipitates, which caused a better aging response for the Cu-containing alloys. The coarsening resistance was the highest for the 2.5 at. % Cu-containing alloy, compared to the ternary alloy because of its lower interfacial free energy, 0.009 Jm-2, between the precipitate and the matrix. The Cu alloying element was located mainly in the β´ precipitate according to its expected thermodynamic behavior, and it caused an atomic relation of Ni to Al close to that of NiAl intermetallic compound for the β´phase. A content of 5 at. % Cu in the ternary alloy promoted higher interfacial energy, 0.04 Jm-2, and thus the fastest coarsening process.

Abstract This work is focused on the failure analysis of a HP40 steel tube used in steam reformer units, which was operated at about 850 °C for 100000 h. The failure analysis was conducted experimentally and numerically using the Thermo-Calc software. The main results indicated that the failed tube presented slightly different contents of Ni and Cr from the nominal ones, which originated the absence of the interdendritic eutectic microconstituent, composed of austenite and M7C3 carbides. This fact was also corroborated by Thermo-Calc results. This absence of eutectic facilitates the crack propagation on the dendritic zones and then the trangranular brittle fracture propagation through the austenite dendritic zones.

The analysis of phase decomposition was carried out using the nonlinear and linear Cahn-Hilliard equations in a hypothetical A-B alloy system with a miscibility gap. These equations were solved by the explicit finite difference method assuming a regular solution model. The supersaturated solid solution and decomposed phases were considered to have an fcc structure. Different aging temperatures and thermodynamic interaction parameters ΩA-B were used to simulate different alloy systems. The numerical simulation results showed that the growth kinetics of phase decomposition in the alloy with 30at.% A was slower than that of 50 at.% A. Additionally, the start time and modulation wavelength of phase decomposition are strongly affected by the thermodynamic interaction parameter ΩA-B value. The numerical simulation results showed that the growth kinetics of phase decomposition with the linear equation is slower than that with the nonlinear one.