Modification of the titanium nickelide surface using frictional treatment and subsequent heating in air

The effect of a combined treatment including severe plastic deformation under the conditions of dry sliding friction and heating in air to temperatures of 300?C480°C (holding for 1 h) on the structure and wear resistance of the surface layer of the Ti_49.4Ni_50.6 alloy has been investigated. It has been shown that this frictional treatment results in an amorphous-nanocrystalline structure in the surface layer (of thickness to 10 ??m) of the Ti_49.4Ni_50.6 alloy. Heating to 300°C brings about the complete crystallization of the amorphous phase; as a result, the structure of the deformed surface layer of the alloy becomes single-phase, consisting of nanocrystals of the B2 phase. At 400°C, in this deformed surface layer there arises a nanocrystalline oxide (TiO₂) phase whose amount reaches tens of volume percent. The sizes of crystals of the B2 phase and oxide TiO₂ are in the range of 1?C50 nm. The arising two-phase (B2 + TiO₂) nanocrystalline structure is located just below the oxide TiO₂ film, which is less than 1 ??m thick. With an increase in the heating temperature to 480°C, the deformed surface layer under consideration retains the nanocrystalline two-phase (B2 + TiO₂) structure, but an increase in the amount of the oxide phase and a decrease in the microhardness of this structure are observed. In some cases (heating at temperatures of 430 and 450°C), the presence of the two-phase (B2 + TiO₂) nanocrystalline surface layer leads to a noticeable (to ??25%) enhancement in the adhesive wear resistance of the Ti_49.4Ni_50.6 alloy upon sliding friction in pair with steel 40Kh13.