TECHNICAL: Computational thermodynamics using the CALPHAD (CALculation of PHAse Diagrams) approach is one of the most important tools used in multicomponent alloy design and optimization. Its applications are, however, severely limited by the lack of accurate thermodynamic databases with wide elemental coverage. The rate-limiting step in the development of high-fidelity thermodynamic databases is to acquire substantial experimental data inputs including: (a) all the key ternary phase diagrams; (b) knowledge of crystal structures and zero-dimensional (0D) defects such as ordering, site occupancy, site preference, and compositional point defects (vacancies, interstitials, and anti-sites) in order to develop best thermodynamic models for intermetallic phases; (c) specific heat capacity (CP), heat of formation, and heat of transition of the phases and phase transformations; and (d) magnetic transition temperature and magnetic moments as a function of composition to take into account the magnetic contribution to the Gibbs free energy. This project aims to develop robust, high-throughput tools that will revolutionize the measurements of (c) and (d). The research will extend an emerging micro-scale CP measurement tool to both low and high temperatures to enable localized measurement of CP as a function of temperature. Integration of CP over a phase transition temperature range can be used to evaluate the heat of transition which is another important thermodynamic quantity. The research will also develop accurate, micro-scale measurement tools for magnetic moments using both the magneto-optical Kerr effect and magnetic resonance force microscopy. By using these tools to perform measurements on solid solutions and intermetallic phases formed in diffusion multiples, valuable data such as temperature- and composition-dependent CP and composition-dependent magnetic moment can be obtained with high efficiency and high accuracy without making individual alloys. These data together with phase diagrams and 0D defect information obtained from diffusion multiples can greatly improve the accuracy and accelerate thermodynamic assessments to extend the elemental coverage of thermodynamic databases. The development of the diffusion-multiple technique and micro-scale property mapping tools will fundamentally change the way essential experimental data are gathered for fast establishment of high-fidelity thermodynamic databases. The tremendous amounts of materials property data generated from such measurements would greatly enhance our ability to augment materials design, materials informatics, and understanding of complex materials behaviors. Moreover, the micro-scale tools with mapping capabilities constitute a new suite of materials property microscopy that may become as widely used as SEM, thus reshaping the way experimental materials research is performed in the future. The program will help to training students to use these tools and disseminate the data via web-based tools. NON-TECHNICAL: High-fidelity thermodynamic databases with wide elemental coverage will have a tremendous impact on alloy design by: 1) cutting down the trial-and-error experiments, 2) providing thermodynamic data for kinetic and property modeling, and 3) reducing the long-term exposure experiments that are usually required to test the propensity of alloys against detrimental phase formation. The timely design and insertion of high-performance materials are critical to the global competitiveness of the U.S. economy.
Performance Period: 07/01/10 – 06/30/11 Objective: The objective of the project is to develop micron-resolution tools for effective measurements of specific heat capacity and magnetic moments. These tools together with the diffusion-multiple approach for phase diagram mapping can greatly impact the most time-consuming part of the CALPHAD approach – reliable experimental data collection, thus significantly accelerating the speed and quality of thermodynamic assessments for effective establishment of reliable thermodynamic databases for accelerated alloy design. Intellectual Merit: 1) developed and benchmarked a high spatial resolution measurement method for specific heat capacity; 2) developed a forward-simulation method to efficiently extract interdiffusion coefficients from binary diffusion profiles (including multi-phase); and 3) developed a promising idea to perform localized measurements of magnetic moments (benchmark of accuracy incomplete) and composition-dependent Curie temperature; 4) developed a promising idea to measure the anisotropic (single crystal) elastic modulus data from large-grained polycrystalline samples using ultrafast laser generated surface acoustic waves (effort incomplete); and 5) Solved the equations and developed computer codes to simulate the entire surface and bulk waves induced by an ultrafast laser on an arbitrary surface of an isotropic crystal which is the theoretical base for ultrasonic measurements of elastic modulus. These results are summarized in the attached figures. Broader Impacts: These micron-scale resolution tools in conjunction with composition-varying and structure / phase-varying samples such as diffusion multiples and combinatorial thin-films would be extremely effective in constructing composition-phase-structure-property relationships. Effective establishment of such relationships will have a significant impact on materials informatics, testing of materials theories and designing new materials. These micron-scale tools with mapping capabilities constitute a new suite of materials property microscopy tools that may become as widely used as SEM, thus reshaping the way experimental materials research is performed in the future. They are important experimental tools that are one of the three Materials Innovation Infrastructure components (computational tools, experimental tools and digital data) in the newly announced Materials Genome Initiative (MGI). Four students (Ms. Siwei Cao, Mr. Changdong Wei, Mr. Qiaofu Zhang, and Mr. Peng Zhao, part of their research was supported by the PI’s startup fund) have been working on developing and benchmarking various high-throughput measurement techniques. They not only learned the basics of materials science and solid-state physics, but also learned mathematics and setting up a new experimental system from scratch. The ultrafast laser system built by the students using the PI’s startup fund for the equipment items is now a workhorse in the PI’s lab and it has been used to perform research for many organizations including national labs and universities. Two students (one female) are writing their dissertations for graduation in 2013. Mr. Peng Zhao has obtained an offer to work for Western Digital after graduation and he is completing his PhD dissertation. The results lead to 7 publications, 12 invited talks/seminars, and 12 contributed presentations at conferences. Two students (Mr. Changdong Wei and Mr. Qiaofu Zhang) have completed their Ph.D. candidacy exams and are perform research under a new NSF project (DMR-1237577). The idea of the new NSF project was generated during the study of the current NSF project under reporting. We did not complete the benchmark study of the accuracy and the key experimental parameters to control to achieve the best accuracy for both the magnetic moment and anisotropic elastic modulus. We were able to set up the measurement system and demonstrate that the ideas work. The PI has actively expanded the application of the diffusion-multiple approach and laser-based measurement tools. The activities include: 1) completed a research project with GE to perform mapping of order-disorder transformations in Ti-based systems using the laser-based measurement system established under the NSF project; 2) designed and made diffusion multiples for Carpenter Technology Corporation (Reading, PA) to study the R phase stability in both Fe-Cr-Mo and Co-Cr-Mo systems; 3) designed and made diffusion multiples for General Motors to study the Al-Mg-Gd & Mg-Gd-Sn systems to expand the approach to both Al and Mg alloys; 4) performed thermal conductivity measurements for Prof. Joseph Heremans’s group at OSU for development of thermoelectric materials; and 5) performed mapping of thermal conductivity of thermoelectric materials for Institut de Chimie de la Matière Condensée de Bordeaux (France).
