The effects of nano-size γ'-phase particles ((FeNiCo)3AlX (X= Ta, Nb, Ti)) on development of thermoelastic FCC(γ )-BCT(α') martensitic transformation on the single crystals of FeNiCoAlX (X= Ta, Nb, Ti) alloys are investigated. It is shown that the particle size, atomic structure, the nature of the interface between lattices "particle-fcc matrix" determine the critical stress of stress-induced martensitic transformation σcr and their dependence on the test temperature, the value of stress and thermal hysteresis. It is established that the change in the particle size from 5 nm to 15 nm leads to variation of superelasticity strain εSE from 14.5% to 5.5% under tensile deformation, of the stress hysteresis value from 500 MPa to 50 MPa and of the thermal hysteresis value from 150 K to 30 K. In the present study, physical reasons of the dependence of the functional properties on the particle size are described. They are associated with the preservation of coherence of particles in the γ-α'-martensitic transformations, hardening of the high-temperature γ-phase. Methods for increasing the temperatures of martensitic transformations are discussed.