THE EFFICIENCY OF TWIST EXTRUSION FOR COMPACTION OF POWDER MATERIALS

Abstract

In the framework of the theory of plasticity for porous bodies, the compaction of titanium powders by twist extrusion and uniaxial pressing in rigid molds is qualitatively analyzed. It is shown that the strain dependence of porosity with twist extrusion reaches the level that is inversely proportional to backpressure. It has been established that much lower pressure is needed to achieve the same residual porosity of powder titanium billets with twist extrusion than with uniaxial pressing. Numerical estimates give the following result for powdered titanium: when a residual porosity is 5%, the twist extrusion backpressure is 20 times lower than the uniaxial pressing pressure. 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 the number of twist extrusion strain cycles, the hardness of powdered titanium increases up to 140 HB, which is quite close to 160 HB of cast commercially pure titanium. It is experimentally shown that the hardness and density of the powder titanium billets after twist extrusion with a backpressure of 200 MPa practically reach their maximum. Therefore, a further increase in backpressure is unreasonable.