Date: Thursday, Sep 29th
Presenter: Prof. Somayeh Pasebani, OSU Manufacturing Engineering and Materials Science
Oxide dispersion strengthened (ODS) alloys are potential candidate materials to be used as high temperature structural materials for various energy applications because of highly stable microstructure and high creep strength due to dispersion of ultrafine YTiO-enriched particles. The traditional processing method of ODS alloys involves mechanical alloying (MA) of high chromium content powder mixed with up to 0.5 wt.% Y2O3, followed by hot consolidation via hot extrusion or hot isostatic pressing. In this work, Febased ODS alloys were developed by using spark plasma sintering (SPS) as a hot consolidation method. Furthermore, in Fe-based ODS alloys (aka nanostructured ferritic steels); Y2O3 was replaced by equal atomic percent of La2O3. The effects of alloying composition, processing parameters including milling parameters and sintering parameters, on the microstructural characteristics and mechanical properties of the milled powder and consolidated alloys were investigated. Lanthanum oxide (0.5 wt.%) was added to Fe 14Cr leading to improvement in microstructural stability and mechanical properties mainly due to a high number density of LaCrO-enriched nanoclusters (NCs). The combined addition of La, Ti (1 wt.%) and Mo (0.3 wt.%) to the Fe14Cr base composition further enhanced the microstructural stability and mechanical properties. Formation mechanism of these NCs can be explained through the enthalpy of formation, concentrations and diffusion rates of the initial oxide species during milling and sintering process. Significant densification occurred at temperatures above 950 oC with an achieved relative density of 99%. High mechanical strength was achieved at room and high temperatures due to the combined strengthening mechanisms of grain refinement, dispersion strengthening, strain hardening and solid solution strengthening.
Dr. Somayeh Pasebani is an Assistant Professor in the Manufacturing Engineering Program of the School of Mechanical, Industrial and Manufacturing Engineering at Oregon State University (OSU). She received her PhD in Materials Science and Engineering from the University of Idaho in August 2014 and worked in North American Hoganas Inc. as an Innovation/Metallurgical Engineer prior to joining OSU in September 2016. Her research area at Oregon State University is focused on development of high temperature alloys, ceramic-reinforced metal matrix composites, aerospace and energy materials via advanced manufacturing (field assisted sintering, powder metallurgy and laser additive manufacturing). Her research combines both experimental and empirical modeling to understand advanced manufacturing-micro/nano structure-properties correlations. Her former experience includes development of novel Ni-based and Fe-based oxide dispersion strengthened alloys for high temperature applications, development of 17-4 PH stainless steel powder for laser additive manufacturing and optimization of post processing to reduce the cost of manufacturing and enhancing the mechanical properties of additively manufactured alloy. She has published over fifteen peer-reviewed journal articles and made numerous conference presentations and received multiple awards from ANS, TMS and AIME.