Ph.D. Thesis Defense - Zhangwei Wang
“MICROSTRUCTURE AND MECHANICAL PROPERTIES OF CARBON AND TITANIUM DOPED Fe40.4Ni11.3Mn34.8Al7.5Cr6 AND Fe36Ni18Mn33Al13 ALLOYS”
Thesis Committee
Ian Baker, Ph.D. (Chair)
Harold J. Frost, Ph.D.
Erland M. Schulson, Ph.D.
Paul R. Munroe, Ph.D.
Abstract
Two alloys, a single f.c.c. Fe40.4Ni11.3Mn34.8Al7.5Cr6 high entropy alloy (HEA) and a f.c.c./B2 two-phase Fe36Ni18Mn33Al13 alloy, were used as base alloys in this research project. The effects of carbon on the mechanical properties and evolution of the dislocation substructure in Fe40.4Ni11.3Mn34.8Al7.5Cr6 HEAs are present. Carbon additions produce a lattice strain of 0.78/at. % and yield strength increase of 184 MPa/at. %. Microband-induced plasticity (MBIP) was found in the C-doped HEAs induced by the carbon.
Thermo-mechanical treatments were performed on undoped and 1.1 at. % C-doped Fe40.4Ni11.3Mn34.8Al7.5Cr6 HEA. The as-cast HEA was coarse-grained and single phase f.c.c., whereas the thermo-mechanical treatment produced both recrystallization and precipitation, resulting in a sharp increase in strength. The effects of temperature on both the yield strength and MBIP of both as-cast and recrystallized C-doped HEAs were also studied. The yield strength of both as-cast and recrystallized C-doped HEAs increased with decreasing testing temperature. Microbands form in the as-cast C-doped HEA at temperatures ranging from 77-673 K.
The microstructures and mechanical properties of both undoped and C-doped (1.26 at. %) Fe36Ni18Mn33Al13 alloys were investigated. A tetragonal martensite is present in the C-doped alloy. B2-structured precipitates form upon annealing in both alloys. Thermo-mechanical treatments decreased the grain size and dispersed the martensite in C-doped alloys, leading to a significant increase in yield. The carbon addition results in a sharp increase in elongation due to the MBIP effect.
The microstructure and mechanical properties of Fe36Ni18Mn33Al13Tix HEAs with x up to 6 at. % Ti were examined. The lamellar spacing decreased significantly with increasing Ti content with an addition of 4 at. % Ti. The yield strengths of alloys decreased significantly at 973 K due to softening of the B2 phase.
