Apparent viscosity of W–Cu powder compacts during sintering

The apparent rigidity of W–Cu (35 vol.%) powder compacts during sintering is characterised from the determination of axial viscosity by dilatometry under sequential loading. The study is carried out on composite powders containing submicron size phases, in the temperature range 1020–1100 °C in which a significant shrinkage is evidenced by conventional dilatometry. When the sintering bodies density increases from 0.5 to 0.74dth, the axial viscosity increases from 103 to 13 × 103 MPa s in solid state and from 0.5 × 103 to 4 × 103 MPa s when Cu is liquid. These rather low values do not indicate the formation of a rigid W particle network. From about 1060 to 1100 °C, the rapid shrinkage, the low axial viscosity and the significant microstructure change support a densification process by rearrangement by viscous flow.