Consolidation of Fe-Co based metallic glassy powder by SPS method

Metallic glasses have been reported to exhibit excellent properties such as high strength, high corrosion resistance, high wear resistance, resulting from their random structure. In addition, metallic glasses usually exhibit a drastic reduction in viscosity in the supercooled liquid region. Therefore, metallic glasses have excellent workability in this temperature range and it has already been reported that large size of bulk metallic glasses are successfully fabricated in several Zr-, Pd-based metallic glasses. In recent years, Fe-based metallic glasses have been intensively studied because of their excellent mechanical performance, excellent magnetic properties and rich resources. However, due to their poor glass forming ability, the size of bulk metallic glasses is limited using a copper mold casting technique. In the present study, [(Fe _0.5Co _0.5) _0.75Si _0.05B _0.2] ₉₆Nb ₄ bulk metallic glasses are fabricated by spark plasma sintering (SPS) of amorphous powders which have been prepared by a gas atomization. To find optimum conditions in the SPS process, Time-Temperature-Transformation diagram (TTT diagram) is also constructed by isothermal differential scanning calorimetry. After consolidation of metallic glassy powders, mechanical properties of consolidated glassy specimens are measured by compressive tests. As a result, the TTT diagram can be constructed and maximum incubation time can be predicted at any holding temperature. Using SPS method, large size and nearly 100% relative dense glassy compacts are obtained with a loading pressure of 75 MPa and 400 MPa, comprising full amorphous in the case within incubation time. Compressive tests indicate that mechanical properties of consolidated specimens are still low, and one of the reasons may be the formation of approximately 50 nanometer crystalline phases between each particle observed by Transmission Electron Microscope (TEM).