The Effect of Spatial Heterogeneities on the Transformation Kinetics in Amorphous Al Alloys
Abstract
Funds are provided to support research and development to create, verify, and validate models for the nucleation and growth of phase transformations in heterogeneous systems.The main focus of the proposed activity is on amorphous aluminum alloys, with the results having a broader relevance to the nature of primary crystallization as a common devitrification reaction, and the fundamentals underlying the role of spatial heterogeneities on transformation behavior. The investigators have organized their activity in three phases.During the first phase of the project, the investigators plan to complete measurements of the aluminum nanocrystal number density as a function of annealing time at several temperatures. These measurements will provide nucleation rate data for copper substitutions that increase and decrease critical crystallization temperature, and finalize the medium-range-order measurements. The investigators plan to utilize the delay time data for each annealing temperature from flash differential-scanning-calorimetry measurements to incorporate the nucleation measurements into the kinetic model. Separately, they plan to employ commercial real-time dynamics transmission electron microscope sample holder to conduct in-situ observation of aluminum nanocrystal growth behavior.In order to develop an experimental database for kinetics modeling, the investigators plan in the second phase of the project to extend their nucleation rate measurements to aluminum-yttrium-iron alloys with lead and indium dispersions. They will supplement the nucleation measurements with flash differential-scanning-calorimetry determination of the nucleation delay time. This is an essential component of the kinetics model is the analysis of any change in the medium-range-order character due to the presence of the lead and indium dispersions.In the third phase, the investigators plan to couple the nucleation rate measurements and medium-range-order characterization for aluminum-yttrium-iron alloys with lead and indium dispersions to develop a kinetics model. They plan to extend their in-situ growth observation to include aluminum-yttrium-iron alloy samples with copper substitutions. The changes in medium-range-order density and delay time they expect to observe will also influence the aluminum nanocrystal growth behavior. The investigators also plan to initiate a study of the nucleation of iron nanocrystals during primary crystallization of an iron-base amorphous alloy by determining if there is a medium-range-order effect on nucleation, and by measuring the delay time by flash differential-scanning-calorimetry. Throughout the entire project period the investigators plan to refine and extend their nucleation kinetics model for materials with spatial heterogeneities.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 12, 2016
- Source ID
- N000141612401
Entities
People
- John H. Perepezko
Organizations
- Office of Naval Research
- United States Navy
- University of Wisconsin System