The Effect of Post-heat Treatment on the Microstructures of Single Crystal DD6 Superalloy

Various thermal cycles at the end of solution heat treatment and their influences on microstructure of single crystal superalloy DD6 were studied by experiments. During various thermal cycles, the qualitative and quantitative microstructure of samples quenched of the transformations is microscopically characterized. This completely includes the large changes in volume fraction, size distribution and morphology of gamma prime precipitate experienced in the upper temperature transformation. Noticeable deviation from the equilibrium volume fraction of γ’ phase is detected in both the dissolution and precipitation processes above 1,120°C for both moderate cooling and heating rate; differences were mainly attributed to the unsteady nature of the turbulent flow. The growth and alignment of the γ’ precipitates are deeply influenced by several factors, e.g. ageing time, cooling rate and quenching temperature. In addition, interesting findings such as “labyrinth” and “cluster” morphologies were observed by scanning electron microscope. During precipitation processes, the complicated microstructure evolution is illustrated by considering the consecutive equilibrium shapes of a coherent precipitate, which grows under the interaction with its neighbors and the coherency of the precipitates improves their potential to resist dissolution.

Elastic Heterophase Domains in Ferroelectric Epitaxial Films

ABSTRACTA heterophase polydomain structure has been recently discovered in BiFeO3 epitaxial ferroelectric films, which provides large electromechanical responses. In this work, the formation of such a microstructure is explained by theory of elastic domains. The thermodynamics of the heterophase polydomain microstructure is analyzed to predict the equilibrium volume fraction of domains at different film-substrate lattice misfits. Extrinsic mechanical and piezoelectric properties are discussed for the heterophase polydomains. It is shown that an applied electric field, which increases electrostatic interaction between domains, may lead to dramatic increase of piezo response. The results of this work are in good agreement with experimental data for BiFeO3.

Estimation, from Swelling, of the Structural Contribution of Chemical Reactions to the Vulcanization of Natural Rubber. Part III. Restricted Method

A method is described whereby the structural contribution of vulcanizing reactions may be estimated graphically from measurements of the equilibrium volume fraction of rubber in a vulcanizate swollen in n-decanc at 25.0°. Use is made of the data of Moore and Watson represented in the form of a relation between (ρMc−1)vulc and υτ. The method is applicable with technically important vulcanizing systems for which no direct method of estimation is available, and is simpler than the previous method (Part I). The method is limited to natural rubber of fixed primary molecular weight, but the limitation avoids a large correction for free ends of chains. Suitable experimental techniques are described.