Synthesis and crystallisation of Fe61Co7Zr10Mo5W2B15 bulk metallic glasses

This paper focuses on the effects of casting temperature and cooling rate on glass formation of Fe61Co7Zr10Mo5W2B15. The presence of the highly stable ZrB2 crystalline phase in the master alloy allows to obtain a composite (amorphous + ZrB2) directly by casting the liquid phase from a temperature below the liquidus, without preventing glass formation. Incomplete dissolution of ZrB2 causes a reduction of the B content in the amorphous matrix and, consequently, a shift of crystallisation to lower temperatures and a change of the mechanism. The effect of cooling rate on glass formation is clearly visible in a conical bulk sample, where the amorphous fraction decreases as the sample diameter increases from 1 to 3 mm, because of the precipitation of bcc-Fe. Furthermore, nanoindentation experiments show different values of hardness and elastic modulus for the fully amorphous and composite samples.