Strengthened Cr-Si-base alloys for high temperature applications

The microstructural development of CrSi alloys with Cr ≥ 89 at.% has been studied. As well as silicon, up to 2 at.% germanium, molybdenum, and platinum were used as alloying elements. All alloys consist of only two phases, Crss and A15. The phase fraction of primary A15 precipitates present in the arc melted condition and fine secondary A15 precipitates formed after a heat treatment (100 h at 1200 °C) were determined. EPMA and SEM measurements show that the alloying elements partition in different ways: Molybdenum is homogeneously dissolved in both phases, while platinum, germanium, and silicon predominantly act as A15 phase formers. Additionally, molybdenum refines the A15 precipitates, germanium increases the amount of secondary precipitates, and platinum coarsens the microstructure. The lattice parameters of both phases were determined using XRD. The results were found to be in accordance to the elemental partitioning behavior of the constituent phases and can be correlated to the respective covalent atomic radii of the respective alloying element. Microhardness measurements confirmed the alloy's ability of precipitation hardening. Using nanohardness measurements the A15 phase was found to be around 18GPa harder compared to Crss offering a way to design mechanical properties depending on alloying element additions, A15 phase fraction, and distribution.