Department
of Materials Science and Engineering
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Materials Science
RESEARCH DESCRIPTIONInfluence of stress on coarsening kinetics and microstructure in alloys containing coherent precipitates, Ostwald ripening in liquid metals, fracture toughness from small-specimen tests, high-temperature deformation, transmission electron microscopy, physical metallurgy.The influence of internal and applied stress on the morphology, spatial correlations and kinetics of coarsening of Ni3X-type precipitates in binary Ni-X alloys (X = Al, Ga, Ge, Si or Ti) are currently under investigation. The role of volume fraction is being explored using special "up-quenching" aging treatments to overcome problems with natural fluctuations in concentration attendant to alloy preparation by ingot metallurgy. Experiments using novel tapered specimens will be examined to obtain data for the first time on the kinetics of coarsening under stress. This research program makes heavy use of transmission electron microscopy, to measure precipitate sizes and size distributions, and magnetic analysis to measure solute concentration in the matrix during coarsening. New apparatus is being developed to enable continous monitoring of solute concentration during the coarsening of solid and liquid "droplets" in a liquid metal matrix. Other research involves
grain growth, pore coarsening and fracture toughness of MoSi2. Of special interest is the
effect of grain size on fracture toughness, measured using the
miniaturized disk-bend test apparatus developed in our laboratory. D.M. Kim and A.J. Ardell, " Coarsening of Ni3Ge in Binary Ni-Ge Alloys: Microstructures and Volume Fraction Dependence of Kinetics", Acta Materialia 51 (2003) 4073-4082. S.V. Prikhodko, D.G. Isaak, J.D. Carnes, S. Moser, Y. Ma, and A.J. Ardell "Elastic Constants of FCC and L12 Ni-Si Alloys: Composition and Temperature Dependence", Metallurgical and Materials Transactions A 34A (2003) 1863-1868. S.V. Prikhodko and A.J. Ardell, "Coarsening of g' in Ni-Al Alloys Aged Under Uniaxial Compression: I. Early-Stage Kinetics", Acta Materialia 51 (2003) 5001-5012. A.J. Ardell and S.V. Prikhodko, " Coarsening of g' in Ni-Al Alloys Aged Under Uniaxial Compression: II. Diffusion Under Stress and Retardation of Coarsening Kinetics Acta Materialia 51 (2003) 5013-5019. S.V. Prikhodko and A.J. Ardell, "Coarsening of g' in Ni-Al Alloys Aged Under Uniaxial Compression: III. Characterization of the Morphology", Acta Materialia 51 (2003) 5021-5036. Y. Ma and A.J. Ardell, "The (g + g')/g' phase boundary in the Ni-Al phase diagram from 600 to 1200 °C", Zeitschrift für Metallkunde 94 (2003) 972-975. Y. Ma, J. Joshi and A.J. Ardell, "Coarsening of g (Ni-Al Solid Solution) Precipitates in a g' (Ni3Al) Matrix: Preliminary Results", Materials Science Forum, 442, Eds. H.A. Calderon and J.J. Cabaņas-Moreno, Trans Tech Publications, Switzerland 2003, 1-6. J.Z. Zhu, T. Wang, A.J. Ardell, Z.K. Liu and L.Q. Chen, "Phase-field Modelling of Microstructural Evolution in Ni-Al Binary Alloys", Acta Materialia 52 (2004) 2837-2845.
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