A. James Clark School of Engineering
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Item COMBINATORIAL EXPLORATION OF PHASE TRANSFORMATION IN NiTi-BASED THIN FILM LIBRARIES FOR SHAPE MEMORY ALLOY APPLICATIONS(2020) Al Hasan, Naila; Takeuchi, Ichiro; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ni-Ti based shape memory alloys (SMAs) have found widespread use in the last 70 years but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their shape via a reversible martensitic phase transformation (PT), they are sensitive to compositional variations. Tuning the SMA lattice parameters, transformation temperature and thermal hysteresis (DeltaT) by alloying with ternary and quaternary elements, therefore, is a challenging materials exploration effort. Combinatorial materials science streamlines synthesis, characterization and data management processes from multiple high-throughput techniques. In this dissertation, composition spreads of Ni-Ti-X (X = Co, Hf, Pd, V) and Ni-Ti-Cu-Y (where Y = Co, Fe, Pd, V) thin film libraries were synthesized by magnetron co-sputtering to probe a substantial composition space with different stoichiometries under identical conditions. Composition-dependent PT temperature, microstructure and thermal conductivity were investigated using high-throughput wavelength dispersive spectroscopy (WDS), temperature-dependent resistance R(T), synchrotron x-ray diffraction (XRD) and scanning hot probe (SHP) microscopy measurements. Through case studies of ternary Ni-Ti-Co and quaternary Ni-Ti-Cu-V systems, I discuss phase determination and how functional properties correlate with composition and local microstructure using composition-structure-property maps. In the Ni-Ti-Co library, a new, expanded composition space having PT with small thermal hysteresis and c(Co) >10 at.% was identified. Of the 177 compositions, 31 had stable PT with near-zero DeltaT in four. Elemental range for SMA compositions was 25.8 at.% < c(Ni) < 70.5 at.%, 21.4 at.% < c(Ti) < 64.3 at.%, and 5.5 at.% < c(Co) < 26.4 at.%. Crystallographic evidence points to a cubic Pm3m structure present as single or mixed with hexagonal or orthorhombic structures for all these compositions. In the Ni-Ti-Cu-V library, PT was observed in 32 compositions (21.3 at.% < c(Ni) < 30.9 at.%, 49.4 at.% < c(Ti) < 57.5 at.%, 13.8 at.% < c(Cu) < 21.6 at.% and 4.1 at.% < c(V) < 6.2 at.%), predominantly in the Ti-rich region, with zero or near-zero DeltaT in five. Increasing V up to 6 at.% stabilized the mixture of transforming cubic and tetragonal phases. These newly identified composition regions provide flexibility in and expand the operating temperature window for their application in different technologies. Lastly, a novel application of SMAs as phase change materials is briefly investigated through high-throughput determination of their thermal conductivity using scanning hot probe microscopy. Binary, ternary and quaternary thin film libraries of Ni-Ti, Ni-Ti-V and Ni-Ti-Cu-V were evaluated as a benchmarking exercise.Item DESIGN, DEVELOPMENT, AND EVALUATION OF A DISCRETELY ACTUATED STEERABLE CANNULA(2014) Ayvali, Elif; Desai, Jaydev P; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Needle-based procedures require the guidance of the needle to a target region to deliver therapy or to remove tissue samples for diagnosis. During needle insertion, needle deflection occurs due to needle-tissue interaction which deviates the needle from its insertion direction. Manipulating the needle at the base provides limited control over the needle trajectory after the insertion. Furthermore, some sites are inaccessible using straight-line trajectories due to delicate structures that need to be avoided. The goal of this research is to develop a discretely actuated steerable cannula to enable active trajectory corrections and achieve accurate targeting in needle-based procedures. The cannula is composed of straight segments connected by shape memory alloy (SMA) actuators and has multiple degrees-of-freedom. To control the motion of the cannula two approaches have been explored. One approach is to measure the cannula configuration directly from the imaging modality and to use this information as a feedback to control the joint motion. The second approach is a model-based controller where the strain of the SMA actuator is controlled by controlling the temperature of the SMA actuator. The constitutive model relates the stress, strain and the temperature of the SMA actuator. The uniaxial constitutive model of the SMA that describes the tensile behavior was extended to one-dimensional pure- bending case to model the phase transformation of the arc-shaped SMA wire. An experimental characterization procedure was devised to obtain the parameters of the SMA that are used in the constitutive model. Experimental results demonstrate that temperature feedback can be effectively used to control the strain of the SMA actuator and image feedback can be reliably used to control the joint motion. Using tools from differential geometry and the configuration control approach, motion planning algorithms were developed to create pre-operative plans that steer the cannula to a desired surgical site (nodule or suspicious tissue). Ultrasound-based tracking algorithms were developed to automate the needle insertion procedure using 2D ultrasound guidance. The effectiveness of the proposed in-plane and out-of-plane tracking methods were demonstrated through experiments inside tissue phantom made of gelatin and ex-vivo experiments. An optical coherence tomography probe was integrated into the cannula and in-situ microscale imaging was performed. The results demonstrate the use of the cannula as a delivery mechanism for diagnostic applications. The tools that were developed in this dissertation form the foundations of developing a complete steerable-cannula system. It is anticipated that the cannula could be used as a delivery mechanism in image-guided needle-based interventions to introduce therapeutic and diagnostic tools to a target region.