This proposed research was submitted in response to the Active Nanostructures and Nanosystems initiative, NSF 06-595, category NIRT. Active nanoscale structures and nanosystems capable of actuation and sensing are needed for a wide range of applications in nanomedicine, nanoelectronics, space exploration, homeland security and defense. An integrated team of co-PIs from Texas A&M University and Georgia Tech proposes, as a combined research effort, a comprehensive interdisciplinary program in hierarchical manufacturing and modeling for phase transforming magnetic shape memory alloys (MSMA).
The main goal of the proposal is to establish a hierarchical framework that will combine the fabrication of MSMA nanolayers with the extrusion of nanowires. These monolithic and hybrid nanowires will then be used in the fabrication of fibers, by coaxial electrospinning, to be used as devices that can be activated by temperature, stress, and remotely by magnetic field. The first level of nanomanufacturing will focus on thin films, composed of nano to micron size layers of conventional shape memory alloys (SMA), magnetic materials and MSMA using magnetron sputtering. Thin films will then serve as precursor for nanowire fabrication by using a cost effective hydraulic pressure extrusion technique. The higher level nanomanufacturing will involve the use of a novel coaxial electrospinning whereby nanowires will be aligned in selected matrices such as silica for the purpose of making biosensors, remotely controlled nano/micro actuators, and active mesoporous ductile membranes. To support the nanomanufacturing effort, selective multiscale modeling will involve atomistic simulations to address phase transformation phenomena at nanoscale, and microstructural mechanism-based continuum level constitutive models to address the functionality of the nanostructures and nanodevice behavior.
The proposed research will attempt to develop a multilevel fabrication methodology for nanowires with combined shape memory and magnetic properties. This hierarchical fabrication methodology will be assisted by a parallel multiscale modeling effort, and also by multiscale state-of-the-art characterization techniques. These unique multifunctional nanowires will be utilized in the manufacturing of biosensors using a novel coaxial electrospinning method. The proposed research is scientifically significant because it will reveal the effect of nanoscale phenomena occurring at crystallographic length scales on larger scale functionality through hierarchical nanomanufacturing. The proposed research will also result in well-structured hierarchical fabrication methodologies and architectures for new multifunctional materials and devices to be used as sensors and actuators in engineering applications, facilitating the design of micro-actuators, biosensors, valves and active mesoporous structures. The knowledge generated from these studies could revolutionize the design of active nano and micro-scale systems and components capable of undergoing very fast reversible deformations, and exhibiting high actuation, sensing and promising power generation characteristics. The proposed project activities will include the development of teaching modules in multifunctional materials for incorporation into undergraduate courses; enrichment of graduate and undergraduate research experiences through summer collaborative exchange programs between Texas A&M and Georgia Tech; development of a graduate course in active thin films, nanowires and active nanostructures; involvement of underrepresented groups through participating regional minority serving universities, and injection of laboratory demonstration models in educational material for secondary educational programs, which will be coordinated with the newly established NSF Nanoscale Undergraduate Education (NUE) program at Texas A&M.
Project Outcome Report - NSF NIRT PI: Lagoudas Active nanoscale structures and nanosystems capable of actuation and sensing are needed for a wide range of applications in nanomedicine, nanoelectronics, space exploration, homeland security and defense. In this project the PIs used a comprehensive interdisciplinary approach to achieve hierarchical manufacturing and modelng of phase transforming magnetic shape memory alloys (MSMA), through collaborative effort among Texas A&M University (lead) and Georgia Tech and Los Alamos National Laboratory (DOE-Center for Integrated Nanotechnologies). The main objective of this project is to establish a hierarchcal framework that will combine the fabrication of MSMA nanolayers with the extrusion of nanowires. The major otcome of this project involves the following: (1) Fabrication and characterization of a variety of MSMA thin films prepared by magnetron sputtering technique. The PIs identified reversible phase transformation in sputtered free-standing Ni-Mn-Ga films by using in-situ X-ray diffraction, in situ transmission electron microscopy technique, and revealed the 14M + non-modulate (NM) martensites and austenite with L21 crystal structure. Furthermore they systematically investigated phase segregation of L12 precipitates, a detrimental non-transformation phase, induced during annealing of films, and used an effective strategy to minimize the volume fraction of L12 phase. In Ni50 Co6 Mn38 In6 system, they successfully fabricated 20 micromolar thick free-standing films. By usng DSC and in situ TEM techniques, they investigated the crystallization of amorphous films and revealed reversible martensitic phase transformation at approximately 4500 C, indicating that these MSMA films could be used at high temperatures. Furthermore they revealed that the decrease in martensitic transformation temperatures (during annealing) may be caused by the formation of nickel-rich precipitates which decrease the electron concentration and hence the transformation temperature of the twinned martensite. In NiCoMnAl thin films, they discovered magnetic field-induced reverse phase transformation. A relatively large field induced variation of transformation temperature was identified in comparison to other studies on NiCoMnIn films. The influence of film thickness, chemistry and residual stresses on phase transformations in these films was also investigated. (2) Size Effect in superelastic behavior of NiFeGa and NiMnGa. Testing of Ni54 Fe19 Ga27 (at.%) micro/nano pillars along [110] direction revealed size dependent two-stage martensitic transformation. Superelastic behavior was observed in deformed pillar with diameters of 10 and 1 micromolar respectively. When the size of the pillars decreased to 1 micromolar two-stage martensitic transformation (stage 1: austenite-to-14M, stage 2: 14 M-to-L10 ) was suppressed and only austenite to L10 transformation took place. The suppression of two-state transformation was also observed at elevated temperatures. Size effect in martensite variant reorientation was studied for NiMnGa pillars cut along [100] orientation. Martensite reorientation stress increased with decreasing pillar diameter. Shape recovery of pillars was obtained however required higher magnetic field in comparison to bulk. In bulk, martensite reorientation can be obtained by approximaely 0.5 T wherease 5T field was requried for reorientation in 10 micromolar pillars. (3) Modeling of phase transformations. A magneto-thermo-mechanically coupled model was developed for the magnetic field induced phase transformation in MSMAs. The hysteric behavior of these dissipative materials was taken into account. The ability of the model to capture magneto-thermo-mechanical coupling was demonstrated and a 3-D transformation surface was predicted. Moreover, the finite element analysis of boundary value problems involving reorientation of martensitic variants was considered. These investigations mainly focused on two aspects: first, a nonlinear magneto-static anaysis was utilized to investigate the influence of the demagnetization effect on the interpretation of experimental measurements. An iterative procedure was proposed to deduce the true constitutive behavior of MSMAs from experimental data that typically reflect the shape-dependent system response of a sample. Secondly, the common assumption of a homogeneous Cauchy stress distribution in the MSMA sample was tested. It was found that highly non-uniform Cauchy stress distributions result under the influence of magnetic body forces and couples, with magnitudes of the stress components comparble to externally applied bias stress. Intellectual merit: The project comprises the development of hierarchical fabrication methodologies, for the first time, for conventional MSMA and nanowires, with the help of a multiscale modeling framework, and their characterization using state-of-the-art techniques. The research is scientifically significant because it reveals for the first time that 1) NiCoMnAl films also have magnetic field induced phase transformations, 2) the effect of nanoscale precipiates on chemistry and thus phase transformation temperature of several MSMA systems, 3) significant size effect on field induced phase transformations, and 4) development of magneto-thermo-mechanically coupled model for the magnetic field induced phase transformtaion in MSMAs. Broader impact: The knowledge generated from these studies could revolutionize the design of active nano and micro-scale systems capable of fast and reversible deformation, and exhibiting large actuation output. This project also included development of teaching modules in active materials for incorporation into undergraduate courses; undergraduate students were involved through NSF Nanoscale Undergraduate Education program and Research Experiences for Undergraduates.
