[en] In the present study the effects of stress-assisted aging of the Ti_4_9_._2Ni_5_0_._8 single crystals oriented along [11] direction on the stress-induced B2-R-B19' thermoelastic martensitic transformations and superelasticity are investigated. It is experimentally established that aging at 823 K for 1h under compression stress of 150 MPa along [11] direction leads to the precipitation of one crystallographic variant of Ti_3Ni_4 particles of 350(±30) nm in size. Precipitation the single variant of Ti_3Ni_4 particle results in an appearance of homogeneous long-range internal stress field |<σ_G>| ≈ 65 MPa, that defines the main features of stress-induced B2-R-B19’ transformation and determines the increase in the characteristic temperatures of martensitic transformation and the existence of two-way shape memory effect. (paper)