TITANIUM POWDER NITRIDATION BY REACTIVE PLASMA SPRAYING

Titanium powder has been sprayed with nitrogen or Ar/H₂ d.c. plasma jets flowing in air. Particles have been collected at several distances downstream of the nozzle exit. In the first 40-50 mm, convective movements created within the droplets entrain homogeneously nitrogen and oxygen in the particle cores. Farther downstream, convection is less important and absorption of nitrogen and oxygen is controlled by diffusion from the particles surface. After solidification induced by high quenching rates (in the order of 10⁵ K/s) due to different cooling means, particles are composed by a superficial layer which is an oxi-nitride of titanium and in their core by a solid solution α-Ti containing both nitrogen and oxygen.