THE HYDROSTATIC-PRESSURE EFFECT ON ELASTIC PROPERTIES OF B2-PHASE SINGLE-CRYSTALS TI(50)NI(48)PE(2) AND TI50NI45FE5 ALLOYS

At first, velocities of longitudinal and transverse ultrasonic waves h ave been measured by a pulse echo overlap method at 3-5 MHz frequency under hydrostatic pressure in the 0-0,6 GPa range in single-crystals o f Ti50Ni48Fe2 and Ti50Ni45Fe5 alloys, having < 100 > and < 110 > orien tations in B2-phase state. The pressure dependences of C-11, C'=(C-11- C-12)/2, C-44 elastic constants, adiabatic and isotermic compression m oduli, Gruneisen microscopic parameters (gamma LA, gamma TA1, gamma TA 2) have been calculated on the basis of these data. It was found that unlike the temperature dependences the anomalous pressure dependence h as the modulus - C' (dC'/dP < 0) only. The parameter (gamma TA1) < 0 f or both alloys even at atmospheric pressure; (gamma TA2) > 0, but decr eases with increasing pressure in both of alloys. The data obtained in dicates a rising inclination of B2-phase lattice of these alloys to Ze ner classical instability (instability relative to the shear of(110)[1 (1) over bar0$]) with a pressure increase.