The Hydrostatic Pressure Effect on Elastic Properties of B2-Phase Single Crystals Ti₅₀Ni₄₈Fe₂ and Ti₅₀Ni₄₅Fe₅ Alloys

¹ Institute of Strength Physics and Materials Science SB RAS, 634021 Tomsk, Russia
² Institute of High-Pressure Physics RAS, 142092 Troitsk, Moscow Region, Russia

Abstract

At first, velocities of longitudinal and transverse ultrasonic waves have 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 of Ti50Ni48Fe2 and Ti50Ni45Fe5 alloys, having <100> and <110> orientations in B2-phase state. The pressure dependences of C_11’ C'=(C₁₁-C₁₂)/2, C₄₄ elastic constants, adiabatic and isotermic compression moduli, Grüneisen microscopic parameters γLA’ γTA1’ γTA2 have been calculated on the basis of these data. It was found that unlike the temperature dependences the anomalous pressure dependence has the modulus - C' (dC'/dP < 0) only. The parameter γTA1 < 0 for both alloys even at atmospheric pressure; γTA2 > 0, but decreases with increasing pressure in both of alloys. The data obtained indicates a rising inclination of B2-phase lattice of these alloys to Zener classical instability (instability relative to the shear of (110)[110]) with a pressure increase.