Nancy F. Dean

Inorganic materials synthesis and fabrication

Preface. 1. Crystallographic and Microstructural Considerations. 2. Chemical Energetics and Atomistics of Reactions and Transformations in Solids. 3. Solid - Vapor Reactions. 4. Solid - Liquid Reactions. 5. Solid - Solid Reactions. 6. Nanomaterials Synthesis. 7. Materials Fabrication. Appendix A1: General Mechanical Engineering Terms. Appendix A2: Green Materials Synthesis and Processing. Index.

Steady-state cellular solidification of Al-Cu Reinforced with alumina fibers

The steady-state directional solidification of aluminum-4.5 wt pct copper and aluminum-1.0 wt pct copper alloys reinforced with parallel,continuous, closely spaced alumina fibers is investigated under growth conditions that produce a plane front or cells in corresponding unreinforced alloys. Specimens were designed to have a central reinforced region surrounded by unreinforced metal of the composite matrix composition. Each was produced by pressure infiltration, subsequently remelted, directionally solidified, and quenched to reveal the liquid/solid metal interface. Both unreinforced and composite sections were characterized to determine solidification front morphology and degree of microsegregation. In the unreinforced portion of the samples, the transition from plane-front to cellular solidification was observed to correspond to a coefficient of diffusion of copper in liquid aluminum of 5 − 10−9 m2 − s−1, in agreement with published values. Cell lengths, analyzed using a finite-difference model of microsegregation, are in agreement with the Bower-Brody-Flemings (BBF) model for cell tip undercooling. In the composite portion of the samples, the alloys solidify free of lateral microsegregation for all solidification conditions investigated, in agreement with theory. The shape of the liquid/solid metal interface near the fibers indicates a much lower fiber/liquid metal interfacial energy than fiber/solid metal interfacial energy. In the composite, plane front solidification is therefore not observed even when plane front solidification obtains in the unreinforced alloy. It is shown that geometrical constraint imposed on deep cells by the fibers causes significant increases in cell tip undercoolings, in agreement with current analyses of deep cell solidification.

Microsegregation in cellular solidification

Microsegregation in a binary alloy solidified in the form of deep cells is predicted using a simplified finite difference model. The model accounts for solid state diffusion and for flow of liquid between cells driven by solidification shrinkage. Cell tip undercooling is predicted using the expression originally derived by Boweret al. Cells are assumed to be cylindrical, and solid state diffusion along the cell axis is ignored, simplifying considerably prediction of solid state diffusion and cell shape behind the tip, which are treated as a one-dimensional moving boundary problem. Experiments were conducted on binary Al-4.5 wt pct Cu, solidified in the cellular growth regime using a Bridgman furnace. Microsegregation in the samples was measured and is compared to predictions; good agreement is found, both for cell heights and microsegregation in the fully solidified material. It is found that intercellular fluid flow exerts a small, but discernable, influence on microsegregation and cell shape.