Low temperature dependencies of the elastic properties of Ti4AlN3, Ti3Al1.1C1.8, and Ti3SiC2

In this article we report on the temperature dependencies of the longitudinal and shear sound velocities in Ti4AlN3, Ti3Al1.1C1.8, and Ti3SiC2. The velocities are measured using a phase sensitive pulse-echo ultrasonic technique in the 90-300 K temperature range. At room temperature, Young's, E-RT, and shear, mu(RT), moduli and Poisson's ratio of Ti4AlN3 are 310 +/- 2, 127 +/- 2 GPa, and 0.22, respectively. The corresponding values for Ti3AlC2 are 297.5 +/- 2, 124 +/- 2 GPa, and 0.2. Both moduli increase slowly with decreasing temperature and plateau out at temperatures below approximate to 125 K. A least squares fit of the temperature dependencies of the shear and Young's moduli of Ti4AlN3 yield: mu/mu(RT) = 1 - 1.5 x 10(-4)(T - 298), and E/E-RT = 1 - 0.74 x 10(-4)(T - 298), for T > 125 K. The corresponding relationships for Ti3Al1.1C1.8 are: mu/mu(RT) = 1 - 1.2 x 10(-4)(T - 298), and E/E-RT = 1 - 0.84 x 10(-4)(T - 298) for T > 125 K. The acoustic Debye temperatures calculated for Ti4AlN3 and Ti3AlC2, as well as Ti3SiC2, are all above 700 K, in agreement with values calculated from low temperature heat capacity measurements. (C) 2000 American Institute of Physics. [S0021-8979(00)09503-7].