SCHOOL OF ENGINEERING
Mechanical Engineering Seminar Series
Dr. Ian Baker
Sherman Fairchild Professor of Engineering
Thayer School of Engineering -- Dartmouth College
Microstructures and Mechanical Properties of FeNiMnAl-Alloys
Three different types of microstructures have been observed in FeNiMnAl alloys: 1) an ultrafine microstructure present in Fe_30 Ni_20 Mn_20 Al_30 ,_Fe_25 Ni_25 Mn_20 Al_30 and Fe_35 Ni_15 Mn_25 Al_25 that consists of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L2_1 -ordered (Heusler) phases aligned along <100>; 2) a fine microstructure present in Fe_30 Ni_20 Mn_30 Al_20 , Fe_25 Ni_25 Mn_30 Al_20 , and Fe_28 Ni_18 Mn_3 _3 Al_2 _1 thatconsists of alternating (Fe, Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered platelets with an orientation relationship close to f.c.c (002) // B2 (002); f.c.c. (011)// B2 (001); and 3) a lamellar microstructure observed in Fe_30 Ni_20 Mn_35 Al_15 that consists of alternating (Fe, Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered phaseswith a Kurdjumov-Sachs orientation relationship between the phases.The microstructure of the alloys coarsened after annealing at 823-1173 K. In addition, an L2_1 -to-B2 transition was observed in the B2/L2_1 alloys at 650-750 K. The hardness of the alloys was studied as a function of annealing time at 823 K. Both the strain rate and temperature dependence of the yield strength of the alloys was alsostudied. The B2/L2_1 alloys underwent a brittle-to-ductile transition, which happened slightly below the L2_1 -to-B2 transition temperature. Hydrogen embrittlement was found in Fe_30 Ni_20 Mn_35 Al_15 tensile tested at a strain rate lower than 3x10^-3 s^-1 .The effect of additions of a few at. % of Cr both on ameliorating the environment embrittlement observed in some of these alloys and on generally increasing the ductility will also be discussed.
Bio: *Ian Baker joined the Faculty of the Thayer School of Engineering at Dartmouth College, in 1982, where he is currently the Sherman Fairchild Professor of Engineering, Senior Associate Dean for Academic Affairs, and Director, Dartmouth Center for Cancer Nanotechnology Excellence.He is a Chartered Engineer (U.K.) and a Fellow of ASM international, The Minerals, Metals and Materials Society, The Institute of Materials, Minerals and Mining (U.K.) and the Materials Research Society.He is Editor-in-Chief of Materials Characterization, has published over 350 papers and has given over 200 presentations at conferences, universities and to industry.His research interests include mechanical behavior particularly of intermetallic compounds and ice; processing; recrystallization phenomena, particularly directional recrystallization; applications of electron microscopy, X-ray diffraction and X - ray topography, particularly /in-situ/ deformation experiments; the structure, chemistry and properties of firn and ice cores; production and properties of nanocrystalline, particularly magnetic materials; nanoparticles for biomedical applications.
Friday, January 17 , 2014
All are welcome