PhD Proposal: Derek Tsaknopoulos

Tuesday, October 23, 2018
10:00 am
Floor/Room #: 

Optimization of Coupled Computational Modeling and Experimentation for Metallic Systems

The use of trial-and-error practices in alloy design and processing adds substantial barriers that impede novel alloy qualification and subsequent adoption within the metallurgical market. However, with access to large sets of material properties data (ideally, data that is highly pedigreed and transient) the cost of the trial-and-error method can be sidestepped by way of iteratively coupling computational models with supportive experimental testing; thus, expediting the materials' design process. At present, Thermo-Calc – a computational thermodynamic and kinetic software – is combined with dynamic nanoindentation to establish representative correlations between microstructural features and mechanical properties for metallic systems. Through the developed techniques, comparisons of material properties (hardness, yield strength, fracture toughness, fatigue resistance, creep, etc) for various conditions are enabled. Differences in processing methods, alloy compositions, and post-processing heat treatments exemplify the nature of said conditions. The effectiveness of this work is determined using thermal, optical, and mechanical characterization methods. In a case study of Al-6061, unique observations were made through the combination of modeling and experimentation. It was discovered that the precipitation kinetics were greatly accelerated in powders and therefore typical heat treatment processes used for cast aluminum alloys are not valid. Due to this shift in precipitation sequences, high-temperature treatment must be severely limited to discourage precipitate and grain coarsening. Additionally, when compared to typical cast Al-6061, the main precipitation hardening phase shifts from Mg2Si to Al4Cu2Mg8Si7 when controlling powder microstructure during the aging. This work demonstrates the process in which the models aided in more effective and efficient discovery of new microstructural elements that directly affect the mechanical properties of the powder