Determination of heat treatment parameters by experiments and CALPHAD for precipitate hardening of Cr-Alloys with Si, Ge and Mo

Abstract

Binary Cr–Si alloys as well as ternary Cr–Si-Ge and Cr–Si–Mo-systems on the Cr rich side of the phase diagram are examined at 1050 °C and 1350 °C regarding the maximum solubility in the bcc solid solution matrix and the A15-phase volume fraction. SEM, EDS and image analysis measurements showed, that the addition of 2 at.% Ge has the same effect on the A15-phase formation as Si but leads to a coarser microstructure. The addition of 2 at.% Mo leads to a decreased A15-phase volume fraction but a small-sized precipitate distribution. The maximum solubility of Si in the binary Cr–Si system is still not clear and has to be verified in further examinations. Thermo-Calc calculations showed, that a reduction of Si content and the addition of Ge and Mo is beneficial for an increase in the process window for solution heat treatment and a decrease of the solvus temperature.