J. Phys. IV France
Volume 112, October 2003
Page(s) 1047 - 1050

J. Phys. IV France
112 (2003) 1047
DOI: 10.1051/jp4:20031061

Phonon precursors to the high temperature martensitic transformation in Ti 50Pd 42Cr 8

S.M. Shapiro1, B.L. Winn1, D.L. Schlagel2, T.A. Lograsso2 and R.L. Erwin3

1  Brookhaven National Laboratory, P.O. Box 5000, Upton, NY 11973, U.S.A.
2  Ames Laboratory, Ames, IA 50011, U.S.A.
3  National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, U.S.A.

Inelastic neutron scattering measurements were carried out on the Ti 20Pd $_{50-\rm x}$Cr $_{\rm x}$ alloy, which is a high temperature shape memory material. For $\rm x=0$, the transformation temperature is ~800K and for the composition studied ( $\rm x=8$ at %) M $_{\rm s}\sim 400$K. The majority of the measurements were performed in the parent, B2-phase, up to 873K. Most of the phonons propagating along the three symmetry directions [ $\zeta$00] , [ $\zeta \zeta \zeta$] , and [ $\zeta\zeta$0] were well defined with the exception of the [ $\zeta\zeta$0] transverse acoustic mode with displacements along the [ - $\zeta\zeta$0] corresponding to the $\rm C'=l/2 (C_{11}-C_{12}$) etastic constant in the $\zeta \to 0$ limit. These phonons are well defined for small $\zeta$, but for $\zeta > 0.10$ they are strongly overdamped near the transition temperature and become better defined at higher temperatures. An elastic peak develops in the cubic phase at $\zeta =0.22$ and increases in intensity as M $_{\rm s}$ is approached. However, the dispersion curves show no anomaly at this particular wavevector, in marked contrast to the lattice dynamic studies of other systems exhibiting Martensitic transformations.

© EDP Sciences 2003