Microporosity of powders produced by centrifugal sputtering

Conclusions

The nature of the liquid-metal film flow about the end of the pulverized billet is defined by its rotational velocity. In the case of a turbulent film flow regime gas is captured and pores are formed in individual powder particles.

The greatest number of porous particles produced in a single pulverization regime is found in a large-fraction powder while the smallest quantity is found in the finely dispersed powder with grain sizes less than 100μn.

Increasing the helium content in the pulverization medium to 100% produces a discontinuous increase in the number of porous particles as a result of the reduced viscosity of the gaseous medium and the high penetration power of the helium. The smallest number of porous particles is formed when pulverization takes place in a medium with a volumetric argon content in excess of 30%.

The pore size in the powder particles is virtually independent of the production regime and usually amounts to about 25–35 % of the particle diameter. The average gas-pore volume is 2–3% of the volume of the powder particle.

To achieve minimum microporosity in compacted billets fabricated by the methods of powder metallurgy, it is expedient to use 100μm powder fractions, produced at a billet rotation velocity of 35–40 m/sec.