DEVITRIFIED NANOCOMPOSITE STEEL POWDER

摘要

Using basic principles of metallic glass formation, multicomponent steel alloy compositions were developed with low critical cooling rates (≈10~4 K/s) for metallic glass formation. This approach toward alloy design enabled the production of spherical, micron sized, metallic glass powder by inert gas atomization. The metallic glass precursors, depending on the composition, were found to devitrify from 550 to 625℃ with enthalpies of transformation from -75 to -150 J/g. Due to the characteristic uniform nucleation from a metallic glass precursor and high nucleation frequency, multiphase nanoscale microstructures develop after devitrification with phase sizes from 2 to 75 nm. The extremely large fraction of two dimensional defect interfaces/boundaries which exist in the nanoscale structure interact with and prevent dislocation motion. Additionally, hard second phase particles pin the grain boundaries and stabilize the microstructure to high temperatures (850℃). Hardness measurements using nanoindentor and Vickers tests show that the devitrified nanocomposite steel is very hard reaching a maximum hardness of 16.0 GPa. The low-cost and high hardness of the devitrified steel alloys makes them excellent candidates for a wide variety of wear resistant applications.