PHASE TRANSFORMATION AND MICROCHARACTERIZATION

Displacive Transformation in Ceramics

H. H. Chen,* N. Takesue, V. Gosula, H. Kubo
U.S. Department of Energy, DE-FG02-91ER45439
(In cooperation with the Materials Research Laboratory)

This is a comprehensive interdisciplinary program of basic research on displacive transformations in ceramics. The ultimate aim is to raise the level of understanding of these transformations to that comparable with martensitic transformations in metallic systems. The program involves studies concerning precursor phenomena and phonon effects, elasticity properties, transformation crystallography, static displacements, chemical and structure ordering, and kinetics. Systems currently being studied are KNbO₃, PbTiO₃, and BaT:O₃, as well as relaxor ferroelectrics PMN, PST, and PLZT.

Development of Advanced Photon Source Beamlines for Scattering Science

H. H. Chen,* H. Hong, D. Robinson, P. Jemtan, K. Chung, V. Gosula
State of Illinois, IBHE-HECA Grant; U.S. Department of Energy, DE-FG02-91ER45439; UOP Corp. Grant; NIST Grant
(In cooperation with the Materials Research Laboratory)

The Materials Research Laboratory is engaged in a collaborative effort with personnel from the Oak Ridge National Laboratory, National Institute of Standards and Technology, and UOP Research Inc., for the development of two beam lines of the Advanced Photon Source (APS) being constructed at the Argonne National Laboratory. The foci of this effort are to do research and to educate new generations of scientists and engineers at the cutting edge of the science and engineering in various disciplines. Particular efforts presently underway and planned are in surface/interface diffraction, magnetic scattering, inelastic scattering, Mauossbauer effect, diffuse scattering, and macromolecular crystallography. H. Chen is the director of this APS beam-line development project.

Effect of Composition and Lattice Misfit Strain on the Coarsening Kinetics in Ni-based Superalloys

H. H. Chen,* G. Muralidharan, S. Weber, H. C. Lin
U.S. Department of Energy, DE-FG02-91-ER45439; Argonne National Laboratory, ANL 31482402
(In cooperation with the Materials Research Laboratory)

The principal means by which Ni-based superalloys strengthen themselves is precipitation hardening. Recent years have seen a renewed interest in the phenomena of Ostwald ripening. The classical theory has recently been modified to incorporate the effect of finite volume fraction and the coherency stresses due to lattice mismatch. These factors can have profound effect on the precipitates growth kinetics and their final size distribution. There is an acute need for experimental verification, which is the principal goal of this research. We have found for the first time enhanced coarsening rate due to lattice misfit strain via small-angle neutron scattering measurements. Further study is being conducted using TEM.