X-RAY-INVESTIGATIONS OF HIGH-ENERGY BALL-MILLED TRANSITION-METAL CARBIDES

Nanostructured NbC, ZrC, TiC and VC were obtained by reactive high ene rgy ball milling of the elemental powders. A milling rate of 250 r.p.m . leads to carbides after 4 to 12 hrs in correlation with the formatio n enthalpy of the compounds. Between II and 36 hrs the nanocrystalline state (less than or equal to 10 nm) is reached and the final value of crystalline size for all carbides is (7 +/- 1) nm. The nanocrystals p ossess a high degree of lattice strains, from about 0.5 to 1%. High te mperature treatment of the nanostructured carbides leads to the increa se of the grain size and continuous reduction of lattice defects. The reduction of lattice strains is caused by the recrystallization proces s.