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 longitudin al and shear sound velocities in Ti4AlN3, Ti3Al1.1C1.8, and Ti3SiC2. The ve locities are measured using a phase sensitive pulse-echo ultrasonic techniq ue in the 90-300 K temperature range. At room temperature, Young's, E-RT, a nd 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 decr easing temperature and plateau out at temperatures below approximate to 125 K. A least squares fit of the temperature dependencies of the shear and Yo ung'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 relati onships 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 tempera tures calculated for Ti4AlN3 and Ti3AlC2, as well as Ti3SiC2, are all above 700 K, in agreement with values calculated from low temperature heat capac ity measurements. (C) 2000 American Institute of Physics. [S0021-8979(00)09 503-7].