Temperature deformation behavior of nanocrystalline matrix derived from metallic glass

A single phase α-Fe microstructure with equiaxed, randomly oriented, 15 nm grains was produced through the devitrification of Vitroperm (Fe73.5Cu1Nb3Si15.5B7) metallic glass. This microstructure was found to be stable during tensile testing at 600 °C, showing a strain rate exponent that nominally correlates to grain boundary sliding (m=0.5), but with little ductility, and strengths up to 1250 MPa. It is suggested that the lack of dislocation activity at the small grain sizes can cause the observed brittle behavior. During testing at higher temperatures, a Nb-containing phase grows at the triple points of the original microstructure, and considerable grain growth occurs. At 725 °C, elongations as large as 65% at flow stresses of 250 MPa were attained.