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Shape memory alloys (SMAs), such as Nitinol (i.e., NiTi), are of great importance in biomedical and engineering applications due to their unique superelasticity and shape memory properties. In recent years, additive manufacturing (AM) processes have been used to produce complex NiTi components, which provide the ability to tailor microstructure and thus the critical properties of the alloys, such as the superelastic behavior and transformation temperatures (TTs), by selection of processing parameters. In biomedical applications, superelasticity in implants play a critical role since it gives the implants bone-like behavior. In this study, a methodology of improving superelasticity in Ni-rich NiTi components without the need for any kind of post-process heat treatments will be revealed. It will be shown that superelasticity with 5.62% strain recovery and 98% recovery ratio can be observed in Ni-rich NiTi after the sample is processed with 250 W laser power, 1250 mm/s scanning speed, and 80 µm hatch spacing without, any post-process heat treatments. This superelasticity in as-fabricated Ni-rich SLM NiTi was not previously possible in the absence of post-process heat treatments. The findings of this study promise the fast, reliable and inexpensive fabrication of complex shaped superelastic NiTi components for many envisioned applications such as patient-specific biomedical implants.

Laser powder bed fusion has been widely investigated for shape memory alloys, primarily NiTi alloys, with the goal of tailoring microstructures and producing complex geometries. However, processing high temperature shape memory alloys (HTSMAs) remains unknown. In our previous study, we showed that it is possible to manufacture NiTiHf HTSMA, as one of the most viable alloys in the aerospace industry, using SLM and investigated the effect of parameters on defect formation. The current study elucidates the effect of process parameters (PPs) on the functionality of this alloy. Shape memory properties and the microstructure of additively manufactured Ni-rich NiTiHf alloys were characterized across a wide range of PPs (laser power, scanning speed, and hatch spacing) and correlated with energy density. The optimum laser parameters for defect-free and functional samples were found to be in the range of approximately 60–100 J/mm3. Below an energy density of 60 J/mm3, porosity formation due to lack-of-fusion is the limiting factor. Samples fabricated with energy densities of 60–100 J/mm3 showed comparable thermomechanical behavior in comparison with the starting as-cast material, and samples fabricated with higher energy densities (>100 J/mm3) showed very high transformation temperatures but poor thermomechanical behavior. Poor properties for samples with higher energies were mainly attributed to the excessive Ni loss and resultant change in the chemical composition of the matrix, as well as the formation of cracks and porosities. Although energy density was found to be an important factor, the outcome of this study suggests that each of the PPs should be selected carefully. A maximum actuation strain of 1.67% at 400 MPa was obtained for the sample with power, scan speed, and hatch space of 100 W, 400 mm/s, and 140 µm, respectively, while 1.5% actuation strain was obtained for the starting as-cast ingot. These results can serve as a guideline for future studies on optimizing PPs for fabricating functional HTSMAs.

Unorthodox material processing technologies create the possibility to produce unique microstructural features at various length scales to bring forward unique material properties. Additive manufacturing (AM) rapidly became integrated within many sectors over the past two decades, with research previously focused on suppressing the nonequilibrium/metastable microstructures. Yet, it is not fully understood whether these unique microstructures, with their inherent defects, could be exploited as templates to enhance the properties of conventional alloys. In this work, functional and structural Ni alloys (Ni-rich NiTi and Inconel 718) have been produced with additive manufacturing (AM), selective laser melting (SLM). Detailed S/TEM based characterization reveals that NiTi produced under high energy density process parameters showed textural evolution leading to unexpected narrowing of the hysteresis during pseudoelastic cycling and reduction in strain accumulation. Nonequilibrium microstructures have previously been produced utilizing radiation to induce unique crystallographic defects. In this study, ion beam implantation is used to induce defects and modulate the local transformation, to produce unique heterogeneous microstructures with the potential to enhance psuedoelastic properties. Results showed Ni ion irradiation amorphized the B2 structure and subsequently suppressed the martensitic transformation. SLM fabricated Inconel 718 has not been understood whether the as-fabricated AM microstructure can be used for creep due to the non-equilibrium solidification structures and their defects. Creep testing at 649° has revealed that the as-fabricated Inconel 718 exhibits exceptional creep resistance. In fact, the creep rate in the as fabricated 718 was observed to be slower than the conventionally processed and aged wrought alloy.

An advantage of electron beam melting (EBM) additive manufacturing technology is the ability to process high-melting temperature, refractory, and/or reactive materials. This research focused on the processing of high-purity niobium precursor powder using EBM technology primarily for the freeform design and fabrication of next-generation superconducting radiofrequency (SRF) cavities. SRF accelerating cavities have been used in particle accelerators for over 35 years and are used in today’s leading applications in high-energy and nuclear physics. Procedures were developed and employed in this research to successfully fabricate high-density niobium parts (>99 % relative density) with a thermal conductivity of ~50 W/m-K that were evaluated mechanically (140 ± 14 MPa yield strength and 225 ± 11 MPa ultimate tensile strength) and compared to wrought reactor-grade niobium (135 ± 17 MPa yield strength and 205 ± 17 MPa ultimate tensile strength). Re-engineered SRF cavities were successfully fabricated whose complex design was intended to overcome nonuniform Lorentz forces during operation. The fabrication of niobium using EBM suggests that similar procedures from this research can be applied to successfully fabricate other refractory materials such as niobium alloys as well as highly conductive materials such as copper.

This paper presents results from a failure analysis investigation of a structural I-beam and supporting bolt of a slimes filter press. Metallurgical failure analysis techniques were employed to investigate the sequence of events leading up to final fracture. From analysis of the micrographs, it is concluded that the cyclic loading operating conditions of the filter press caused an initial fatigue crack on the bolt that propagated until the surrounding bolts failed, causing the last bolt to fracture by overload. Once this final bolt failed, a crack initiated at the weld interface where defects were observed and was the cause for final failure of the filter press.

This work explores whether ion beam modification can be used to modulate the austenite to martensite phase transformation in Nickel-Titanium (NiTi), thereby achieving novel or localized transformation properties in near-surface regions. We report this could provide alternatives to laser shot peening or other surface treatment methods and possibly expand applications in biomedical, aerospace, and other fields. Irradiation induces defects and internal stress that can serve as nucleation and/or pinning sites for the phase transformation. Thus, it can augment more convention- al approaches, including alloying, severe mechanical work, grain size reduction, and precipitation of coherent precipitates. A range of outcomes is possible in principle, including a shift of the critical stress or temperature for onset of the transformation, linearization, reduction of hysteresis, stabilization, and extent of transformation strain.

Ni-ion irradiated NiTi is nearly 50% harder, retains 85% recoverable deformation, and has reduced hysteresis. This work explores the feasibility of using ion beam modification to modulate the austenite to martensite phase transformation in NiTi, thereby achieving novel or localized properties in near-surface regions.

The adhesion ability and adaptability of bacteria, coupled with constant use of the same bactericides, have made the increase in the diversity of treatments against infections necessary. Nanotechnology has played an important role in the search for new ways to prevent and treat infections, including the use of metallic nanoparticles with antibacterial properties. In this study, we worked on the design of a composite of silver nanoparticles (AgNPS) embedded in poly-epsilon-caprolactone nanofibers and evaluated its antimicrobial properties against various Gram-positive and Gram-negative microorganisms associated with drug-resistant infections. Polycaprolactone-silver composites (PCL-AgNPs) were prepared in two steps. The first step consisted in the reduction in situ of Ag+ ions using N,N-dimethylformamide (DMF) in tetrahydrofuran (THF) solution, and the second step involved the simple addition of polycaprolactone before electrospinning process. Antibacterial activity of PCL-AgNPs nanofibers against E. coli, S. mutans, K. pneumoniae, S. aureus, P. aeruginosa, and B. subtilis was evaluated. Results showed sensibility of E. coli, K. pneumoniae, S. aureus, and P. aeruginosa, but not for B. subtilis and S. mutans. This antimicrobial activity of PCL-AgNPs showed significant positive correlations associated with the dose-dependent effect. The antibacterial property of the PCL/Ag nanofibers might have high potential medical applications in drug-resistant infections.