ELASTIC-CONSTANTS OF TIAL3 AND ZRAL3 SINGLE-CRYSTALS

The elastic stiffness constants, c(ij), were measured from the velocity of ultrasonic waves for TiAl3 and ZrAl3 single crystals with tetragonal D0(22) and D0(23) structures, respectively. The value of c11 for the <100> direction was approximately equal to that of c33 for the <001> direction in both TiAl3 and ZrAl3. Young's modulus for a single crystal was the highest in the <110> direction in which titanium or zirconium atoms and aluminium atoms were arranged in the closest packed manner, although it was not so high in <012> and <014> directions which showed the other closest packed array of the constituent atoms for TiAl3 and ZrAl3, respectively. The elastic constants, such as Young's modulus, shear modulus and Poisson's ratio, were approximately estimated for ideal polycrystalline TiAl3 and ZrAl3 from the stiffness constants and the compliance constants for single crystals. The Poisson's ratio of these materials was about 0.16 and 0.19 for TiAl3 and ZrAl3, respectively, and these values are much lower than those of ordinary metals and alloys. Debye temperatures were estimated at room temperature from the average velocity of ultrasonic waves and were 681 and 577 K for TiAl3 and ZrAl3, respectively.