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Applications of Diffusion Multiples to Spatially-resolved Properties Measurements and Exploration of Stable Precipitates for High-temperature Steels

Wei, Changdong
http://rave.ohiolink.edu/etdc/view?acc_num=osu1437611418

Abstract Details

2015, Doctor of Philosophy, Ohio State University, Materials Science and Engineering.
This dissertation presents the applications of diffusion multiples to spatially-resolved specific heat capacity and thermal conductivity measurement using ultrafast laser based pump-probe technique – time-domain thermoreflectance (TDTR), and search for stable intermetallic precipitates to aid the design of high-temperature structural steels. Dual-frequency time-domain thermoreflectance (DF-TDTR) was developed for measuring heat capacity with a spatial resolution on the order of 10 microns. The method was validated by measuring several standard materials with known CP. Rapid measurement of composition-phase-property relationships was demonstrated on Ti-TiSi2 and Ni-Zr diffusion couples. Experimental values of CP of the intermetallic compounds in these diffusion couples were compared with literature values and CALPHAD (CALculation of PHAse Diagrams) calculations. The combination of the localized measurement and diffusion multiples provide an efficient way to generate thermodynamic data for CALPHAD modeling and database construction. Composition-dependent thermal conductivity data of several binary metallic alloy systems were collected from high-throughput TDTR measurements on diffusion multiples. The experimental information together with literature data paved the ground to extend Mott’s two-band conductivity model to more generalized scenarios by including the density of states (DOS) values calculated from first principles, which was then employed to describe the composition dependence such that the semi-empirical model can be readily implemented into the CALPHAD framework. Using calculated DOS as input, an extended Mott’s two-band conductivity model was demonstrated to correlate the experimentally measured thermal conductivity with alloy composition, and an overall satisfactory agreement has been reached. Dual-annealed diffusion multiples were used to study the precipitation morphology and kinetics in a few Fe-based ternary systems at intermediate temperatures. Sigma phase in Fe-Cr-Ni system shows massive transformation morphology at 900 °C as revealed in the SEM (scanning electron microscopy) images. Chi phase in Fe-Cr-Mo system and Laves phase in Fe-Mn-Nb system, showed nearly-spherical geometry and they were distributed evenly in the ferritic/austenitic matrix, which indicates the potential to be used as viable strengthening precipitates for high temperature steels. For the steels designed based on the Chi phase strengthening, a gradient temperature heat treatment (GTHT) technique was developed to efficiently study the precipitation morphology as a function of aging temperature. Vicker’s microhardness test and high-resolution SEM were used to determine the optimum aging condition by looking at the highest hardness and related microstructure. This GTHT technique has much higher efficiency than the traditional method of heat treatment on individual samples.
Ji-cheng Zhao (Advisor)
Wolfgang Windl (Committee Member)
Sheikh Akbar (Committee Member)
181 p.
Materials Science
Diffusion multiple; thermoreflectance; precipitation; phase transformation

Recommended Citations

Citations

  • Wei, C. (2015). Applications of Diffusion Multiples to Spatially-resolved Properties Measurements and Exploration of Stable Precipitates for High-temperature Steels [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437611418

    APA Style (7th edition)

  • Wei, Changdong. Applications of Diffusion Multiples to Spatially-resolved Properties Measurements and Exploration of Stable Precipitates for High-temperature Steels. 2015. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1437611418.

    MLA Style (8th edition)

  • Wei, Changdong. "Applications of Diffusion Multiples to Spatially-resolved Properties Measurements and Exploration of Stable Precipitates for High-temperature Steels." Doctoral dissertation, Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437611418

    Chicago Manual of Style (17th edition)

osu1437611418
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This open access ETD is published by The Ohio State University and OhioLINK.