Synthesis and mechanical characterisation of Fe-based bulk metallic glasses and mixed amorphous/crystalline phases

Abstract

ABSTRACTFully amorphous and mixed amorphous/crystalline bulky (Fe77+yGa3P9.5-yC4.5B3.5Si2.5)(100-x)/100Fex alloys were prepared varying Fe and Fe-P contents. The effect of the compositional changes on glass forming ability (GFA), stability of the amorphous phase and mechanical properties was studied. When y = 0 and x is enhanced from 0 to 2, the stability of the supercooled liquid region decreases of 10 K. For x = 0 and y = 3.5 the glass forming ability is drastically reduced leading to a mixed structure consisting of bcc-Fe, Fe3(P,C,B) and a small fraction of amorphous phase.During compression test at room temperature the deformation of fully amorphous samples (y = 0) is dominated by the initiation and propagation of shear bands with consequent nil or small plastic deformation (0.2 % at 3000 MPa) for the alloys with x = 2 and x = 0 respectively. Embrittlement of (Fe77Ga3P9.5C4.5B3.5Si2.5)0.98Fe2 was observed after partial and full devitrification.A higher Young modulus and a maximum strength of 3300 MPa were shown by the as cast partially crystalline Fe80.5Ga3P6C4.5B3.5Si2.5 alloy; also in this case, no yielding was detected.Finally, compression tests at high temperature for fully amorphous Fe77Ga3P9.5C4.5B3.5Si2.5 showed inhomogeneous deformation up to 402°C. Homogeneous non-Newtonian plastic deformation was detected at 427°C. Newtonian homogeneous flow at 452°C is limited by the crystallisation of the superliquid and consequent final failure.