Microstructure and Microhardness in Current Annealed Fe65.5Cr4Mo4Ga4P12C5B5.5 Bulk Metallic Glass
The rods of Fe-based bulk metallic glasses with the nominal composition Fe65.5Cr4Mo4Ga4P12C5B5.5 were cast by melt injection into 1.5 and 1.8 mm diameter copper molds. The thermal stability, microstructure and crystallization behavior were investigated by differential scanning calorimetry, optical micrography and X-ray diffraction, respectively. The wide supercooled liquid region between crystallization temperature (Tx) and glass transition temperature (Tg) in the as-cast state Tx=Tx-Tg=60 K, as well as the high value of reduced glass transition temperature Trg=Tg/Tl=0.567 (Tl is liquidus temperature) approves enhanced thermal stability of the alloy against crystallization. In the as-cast “XRD-amorphous” state, microhardness HV1=742 was observed. Multistep current annealing thermal treatments were performed for structural relaxation. After applying high enough heating power per square area (PS ≥ 6 W/cm2), intensive crystallization of the samples characterized by appearance of several iron-metalloid compounds (Fe5C2, Fe3Ga4, Fe63Mo37 and Mo12Fe22C10) was observed. The microstructure changes after crystallization bring about differences in the microhardness values. The areas of still present amorphous matrix are with increased value HV1=876, but a remarkable decrease to HV1=323 was observed in precipitated crystallized zone that propagate along inner part of cylinders.
Dragan P. Uskoković, Slobodan K. Milonjić and Dejan I. Raković
N. Mitrović et al., "Microstructure and Microhardness in Current Annealed Fe65.5Cr4Mo4Ga4P12C5B5.5 Bulk Metallic Glass", Materials Science Forum, Vol. 555, pp. 521-526, 2007