Effect of Pulsed Nitrogen Plasma and Nitrogen Ion Fluxes on the Structure and Mechanical Properties of Vanadium

Abstract

The effect of powerful pulsed fluxes of nitrogen plasma and nitrogen ions generated in the PF-4 Plasma Focus setup (LPI; energy flux density of plasma pulse was 108–1010 W/cm2) on the modification of vanadium surface is studied. Melting and ultrafast solidification result in a fine cellular structure (cell size of 100–200 nm) in a thin surface layer in samples. There are irradiation regimes causing directional crack growth after solidification and cooling of the surface layer and the formation of a block microstructure with a block size of several tens of micrometers. The thickness of the melted layer in the samples is 2–4 μm. Cracks propagate to a depth of 5–20 μm. It is established that irradiation by pulsed nitrogen plasma and high-energy nitrogen ions changes the microhardness of the vanadium surface layers. The microhardness increases by a factor of three with the number of plasma pulses and the distance between a sample and the anode of the Plasma Focus (PF) setup. The increase in the microhardness is in agreement with the refinement of coherent scattering regions, the increase in lattice microstrain e, and the formation of vanadium nitrides. Pulsed fluxes of nitrogen plasma and nitrogen ions decrease the lattice parameter much greater than cold working (rolling) does. The lattice parameter decreases when the total irradiation power is increased (the number of pulses increases or the distance between a sample and the anode of the PF setup decreases). Such changes seem to be caused by the action of the residual macrostresses induced by pulsed plasma irradiation. In addition, X-ray diffraction analysis showed a change in the texture of the surface layer after ion-plasma treatment of coldworked vanadium samples in the PF setup.