Cold Sintering of Rapidly Solidified Iron and Nickel Base Alloys

Rapidly solidified high-speed steel powders (T15, M2, M35) were successfully consolidated to full density via cold sintering with retention of very fine microstructure (Ref 4, 30, 37, 38). Two processing routes can be used for full density consolidation of high speed steels: (a) high pressure consolidation at P = 3 GPa and temperature from 300 to 350 °C; and (b) cold sintering at ambient temperature at P = 3 GPa, followed by annealing at 900 to 1000 °C and repressing/cold sintering at room temperature. Both routes result in finer carbide dispersions compared to similar high speed steels prepared by HIP (Ref 4).

Rapidly solidified high-speed tool steel powders are characterized by a fine cellular structure of carbides (Ref 4), as shown in Fig. 13. Such structure of carbides results in high microhardness and should result in a high elastic modulus, which can be advantageous for some applications. However, exposure to the high processing temperatures (>1200 °C) during consolidation or/and austenizing treatment results in the breaking up of the cell structure and in the partial coarsening of carbides. High pressure consolidation at 400 °C provides full density without destruction of the fine cellular structure. Rapidly solidified nickel-base superalloys can be successfully consolidated to full density using the same cold sintering routes (Ref 4, 29).

Fig. 13 A representative cell structure of carbides in a water-atomized high-speed steel powder cold sintered at 400 °C (SEM)

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