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MATERIALS ENGINEERING

SEMINAR

“Solid-Solution Strengthening in FCC Concentrated Complex Alloys”

By

Chia-Hsiu Chang

Purdue MSE Ph.D. Preliminary Exam

Advisor: Professor Michael S. Titus

ABSTRACT

Concentrated complex alloys (CCAs) were recently proposed as a novel class of new alloys, and they are defined as alloys composed of four or more alloying elements without a majority concentration or “base” element, for example Co₁Fe₁Mn₁Ni₁. Oftentimes, researchers aim to synthesize CCAs exhibiting a single solid-solution phase (e.g. fcc or bcc) because of the significant solid-solution strengthening provided by the high concentration of many solute elements. Early research revealed that, in some case, these alloys exhibit comparable yield strength to precipitation-strengthened alloys over a large temperature range. However, the strengthening mechanisms of CCAs are not clear at present. Despite the significant historical effort to understand solid-solution strengthening in random alloys, conventional theory is unable to quantitatively predict yield strength as a function of temperature and strain rate in multi-solute, non-dilute solid-solution alloys. A new theory for predicting the yield strength of fcc CCAs has recently developed, and comparisons between predicted and experimental results based on the new model will be discussed. Because the model requires complete knowledge of the material properties for each alloying element, we seek to simplify the model in order to understand additions of a single solute to a given CCA composition. The study hypothesizes that CCAs could be treated as pseudo-binary alloys, in which the “solvent” is a given CCA and the solute is the final alloying element. A brief outline of the proposed research plan to validate and improve on the current model for predicting CCA strength will be presented

Date: Thursday, December 7, 2017

Time: 12:00 P.M.

Place: HAMP 2107