Download or read book Thermal Analysis for Characterizing Effects of Metallurgical Conditions in Nickel Titanium Based Shape Memory Alloys written by Blake Miller and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shape memory alloys (SMAs) undergo a diffusionless solid state transformation (referred as the martensitic transformation) from the high temperature, parent phase austenite to the low temperature, product phase martensite. SMAs recover deformation due to heating, referred to as the shape memory effect (SME). They recover deformation elastic limits beyond typical via unloading, referred as the superelastic effect (SE). Binary NiTi is a specific SMA having properties determined by its Ni composition. Additive manufacturing is important as the layer-by-layer deposition process under desired parameter development allows for microstructure development of NiTi SMAs. Additive manufactured SMAs utilizing Ni-rich compositions (greater than 50.5 at. % / 55.57 wt. % Ni) have been utilized in characterization of the superelastic response. To a lesser extent, research has also used Ti-rich (less than 49.5 at. % / 54.6 wt. % Ni) and near equiatomic (between 49.5 at. %/ 54.6 wt. % and 50.5 at. % / 55.57 wt. % Ni) for studying the SME and SE in NiTi. Primarily research has utilized powder bed fusion (PBF) additive manufacturing while this work looks towards laser directed energy deposition (LDED). This thesis covers Ti-rich LDED NiTi alloys and is one of few to date to report on it. Characterization of the martensitic transformation/shape memory response and subsequent optimization of the thermoelastic properties begins with assessing the thermal-induced shape memory behavior using differential scanning calorimetry (DSC). DSC allows for the ability to determine the temperature ranges for the SME and SE of AM NiTi. DSC uses temperature cycling to measure changing heat flow and endothermic/exothermic events. Endothermic events occur during heating from martensite to austenite (the forward transformation) while exothermic events occur during cooling from austenite to martensite (the reverse transformation). Standard DSC characterization records measurements such as the start, peak, and end temperatures of the forward and reverse transformations. Laser-directed energy deposition (LDED) was used for fabricating Ti-rich AM build coupons which utilized elementally blended Ti and Ni powder feedstock. The layer-by-layer depositions vary in build sizes and thus produce builds with different thermal histories and metallurgical conditions. The first series of build coupons were fabricated as oversized build preforms from which tensile and compression specimens were micromachined. The oversized build preforms have volumes varying between 1500-3950mm3 (XYZ, XZYA, XZYB) and referred to as G0. The second series of build coupons were fabricated as near-net builds with dimensioning close to the designated tension and compression specimens. The near-net builds, referred to as G2, have as-deposited volumes of 2231.4 mm3 for the XYZ build and 3296.5 mm3 for the XZYA build. Specimens were extracted from the fabricated builds with precision wire EDM. DSC is used to study the stress free thermal induced martensitic transformation (TIMT). Standard DSC is performed and its metrics recorded for insight of the TIMT for the AM builds. Standard DSC characterization is augmented to provide advanced metrics for insight into the thermoelastic nature of the AM NiTi builds. Characterization by DSC provides a comparative analysis for the investigating dependence of build, size, and spatial location of elementally blended Ti-rich AM parts on its TIMT. The advanced characterization is used for investigating any dependence of build, size, and spatial location on the thermoelastic nature of the AM builds. We look towards these observations to further advance the research on NiTi additive manufacturing, specifically on Ti-rich materials. An understanding of the TIMT behind Ti-rich NiTi SMAs can allow for production of AM builds having optimal SME properties for applications such as microactuators. Knowledge of the thermoelastic nature in Ti-rich AM NiTi SMAs allows for selection of AM builds with the narrowest hysteresis for pseudo elasticity-based applications.