THE EFFICIENCY OF TWIST EXTRUSION FOR COMPACTION OF POWDER MATERIALS

Within the theory of plasticity for porous bodies, the compaction of titanium powders by twist extrusion and uniaxial pressing in rigid dies was qualitatively analyzed. It was shown that the strain dependence of porosity with twist extrusion reached the level that was inversely proportional to backpressure. Much lower pressure was found to be needed to achieve the same residual porosity of powder titanium billets with twist extrusion than with uniaxial pressing. Numerical estimates gave the following result for powdered titanium: when a residual porosity was 5%, the twist extrusion backpressure was one twentieth the pressure required with uniaxial pressing. The experimental studies for PT5 titanium powder confirmed the conclusions of the qualitative analysis carried out within the theory of plasticity for porous bodies. With increase in backpressure and in the number of twist extrusion strain cycles, the hardness of powdered titanium increased up to 140 HB, being quite close to 160 HB of cast commercially pure titanium. The experiment demonstrated that the hardness and density of the powder titanium billets after twist extrusion with a backpressure of 200 MPa practically reached their maximum. Therefore, a further increase in backpressure was unreasonable.