Mechanical anisotropy and segregation in Mo5Si3 studied by EBSD

The cracking behaviour of indented areas in monolithic Mo5Si3 and segregation in Cr-alloyed Mo5Si3 have been studied by electron back-scattering diffraction (EBSD) in a scanning electron microscope (SEM). Vickers indentation of Mo5Si3 indicates preferred cleavage across the [001] direction, resulting in chipping if the indent is normal to the (001) plane. The other two alloyed Mo5Si3-based compounds studied in this work, i.e. Mo3Cr2Si3 and Mo3Ti2Si3, behave differently during heat treatment. Mo3Cr2Si3, on the one hand, shows unexpected additional X-ray reflections together with broadening of reflections after annealing, when compared to its as-cast condition. Observations of increased segregation upon annealing are made, presumably by a separation into Cr-lean and Cr-enriched (Mo,Cr)5Si3, especially in the <100> directions according to EBSD. Segregation of Cr is linked to additional reflections in X-ray diffraction (XRD). Mo3Ti2Si3, on the other, seems to be in chemical equilibrium in the as-cast state according to energy dispersive spectrometry (EDS) measurements, and there is little difference in XRD between as-cast and heat treated alloys.