A novel HIP processing of mechanically alloyed(MA) amorphous powder is developed, based on the densification via viscous flow mechanism, with which it is possible to obtain a fully dense amorphous compact of large scale. This study describes the evaluation of viscous flow in a thermal mechanical analyzer (TMA) and the optimization of HIP variables, time, temperature, pressure and heating rate for a nearly full densification of MA amorphous Co
79.5Nb
15Zr
5.5 powder.
The pre-compacted compressive sample of amorphous Co
79.5Nb
15Zr
5.5 shows a drastic plastic displacement after thermal shrinkage in a constant heating rate experiment far below the temperature at the onset of crystallization(
Tx). An analysis of the TMA curve for a porous amorphous compact permits us to derive the displacement rate and the viscosity. The temperature dependence of the newtonian viscosity(η) is fairly well expressed by an Arrhenius typed relation of η=η
0 exp (221 kJ·mol
−1/
kT) within the range of the experiment in this study. The well-defined glass temperature(
Tg) shows a constancy for heating rates above 1.7×10
−1 K·s
−1, but a great increase due to structural relaxation below 8.3×10
−2 K·s
−1.
HIP cmpaction of MA amorphous powder in vacuumed can in a temperature range,
Tg<
T<
Tx under a pressure of 196 MPa makes it possible to obtain a high density amorphous product with a diameter of 24 mm at the nearly maximum in our laboratory HIP apparatus. An increase in holding time and/or temperature leads to an increase in relative density of the amorphous HIP compact, approaching to theoretical one. These increases are in good agreement with a HIP map which is constructed based on newtonian viscous flow mechanism with an Arrhenius equation with an increased η
0 for MA amorphous powder subjected to extensive structural relaxation.
The compressive strength(σ
F) for the amorphous HIP compact of Co
79.5Nb
15Zr
5.5 greatly increases with decreasing porosity(
Po). A power law of compressive strength is derived as σ
F=
BP−0.5o.
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