Phonon Precursors to the High Temperature Martensitic Transformation in Ti50Pd42Cr8

Inelastic neutron scattering measurements were carried out on the Ti{sub 50}Pd{sub 50-x}Cr{sub x} alloy, which has the potential for being a high temperature shape memory material. For x = 0, the transformation temperature is {approx}800K and for the composition studied (x = 8 at.%) T{sub M} {approx} 400K. The majority of the measurements were performed in the parent, {beta}-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 C{prime} = 1/2(C{sub 11}-C{sub 12}) elastic constant. These phonons are well defined for small {zeta}, but for {zeta} > 0.15 they are strongly overdamped near the transition temperature, but become better defined at higher temperatures. An elastic peak develop in the cubic phase at {zeta} = 0.22 and increases in intensity as T{sub M} is approached. However, this dispersion curves show no anomaly at this particular wavevector, in marked contrast to the lattice dynamic studies of other systems exhibiting Martensitic transformations.