W0196

Local and Global Structures of the Martensitic phase of Ni.62Al.38. Despina Louca, T. Darling, A. Migliori, F. Freibert, F. Chu, G. H. Kwei, Los Alamos National Laboratory, MST-10 MS K764, Los Alamos, NM 87545

Although martensitic compounds as in the Ni-Al alloys have been studied for many years, recent data bring to light new insights on the mechanism of the actual transition. Using the Pair Density Function (PDF) analysis of pulsed neutron diffraction and Resonant Ultrasound Spectroscopy (RUS) measurement of the martensitic phase transition in polycrystal and single crystal Ni.62Al.38 samples, we observed the hysteretic behavior of the transition process, both revealed in the softening of the elastic constants and in the diffraction pattern. In cooling, the elastic moduli which reflect an average change over the entire crystal, go through a transition at a temperature range of 80 - 90 K and the process is reversible. From the diffraction pattern which also depicts the average structure, a change from the B2 cubic symmetry is becoming apparent through this temperature range but with no major structural distortions. By 60 K the average structure is still essentially cubic. With further cooling, it transfor

*Work at the Los Alamos National Laboratory is performed under the auspices of the U.S. Department of Energy under contract W-7405-Eng-36.