The present work explores the processability of an advanced aluminum alloy, namely AlCu-TiB2, by selective laser melting (SLM), and the correlation between microstructure and mechanical properties of ...as built specimens. The principal process parameters of the laser emission in pulsed wave (PW) mode, namely laser power and exposure time, were varied to achieve full density parts starting from prealloyed powders. Detailed analysis of defects in the highest relative density conditions was performed thzrough X-ray computed tomography. It was found that the highest relative density, up to 99.5%, was achieved at a laser energy density of 82 J/mm3. Microstructure of as-built specimens was analyzed through scanning electron microscopy, coupled with EDX and EBSD analyses, and transmission electron microscopy. The as-built microstructure was considerably uniform, and characterized by fine equiaxed grains, decorated with micrometric and nanometric second phases and an even distribution of reinforcing TiB2 particles; no epitaxial grain growth was observed. Finally, tensile behaviour of the as-built specimens indicates a yield and ultimate tensile stress of 325 MPa and 395 MPa, respectively, combined with an elongation of 13%. The low work hardening rate and jerky flow characterizing plastic deformation are analyzed and discussed.
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•The selective laser melting processability of an AlCu alloy with in-situ TiB2 nanoparticles was explored and analysed.•Multi-scale microstructural analysis revealed fine equiaxed grains and several micrometric and nanometric secondary phases.•Mechanical behaviour was characterized by low strain hardening and evident jerky flow.
Among functional materials, quasiequiatomic NiTi alloys are one of the most promising and diffused for some sectors, from the biomedical to aerospace ones. Their peculiar performance, namely, shape ...memory effect and pseudoelasticity, is induced via a thermomechanical treatment called shape setting or with the heat treatment of annealing. This heat treatment is carried out in cold-worked conditions. The present work studies the effect of the material conditions of straight annealing and cold working on the functional performance of diamond-shaped NiTi microdevices realised through ultrashort laser cutting. In detail, experiments were carried out aimed at studying the effect of laser power, scanning speed, and number of passes on the kerf width with the focus on defining the most suitable process condition on both straight-annealed and cold-worked sheets of 100 µm in thickness. After the process parameters had been defined, the transformation temperatures and superelastic behaviour were analysed though differential scanning calorimetry and force–displacement testing. The femtosecond cutting of straight-annealed NiTi did not change the characteristic temperatures of the base material, while the same process induced a soft martensitic transformation with respect to the cold-worked material due to a heat accumulation effect.
The structure evolution in the CeO2–Sm2O3 system is revisited by combining high resolution synchrotron powder diffraction with pair distribution function (PDF) to inquire about local, mesoscopic, and ...average structure. The CeO2 fluorite structure undergoes two phase transformations by Sm doping, first to a cubic (C-type) and then to a monoclinic (B-type) phase. Whereas the C to B-phase separation occurs completely and on a long-range scale, no miscibility gap is detected between fluorite and C-type phases. The transformation rather occurs by growth of C-type nanodomains embedded in the fluorite matrix, without any long-range phase separation. A side effect of this mechanism is the ordering of the oxygen vacancies, which is detrimental for the application of doped ceria as an electrolyte in fuel cells. The results are discussed in the framework of other Y and Gd dopants, and the relationship between nanostructuring and the above equilibria is also investigated.
Nowadays, additive manufacturing (AM) permits to realize complex metallic structural parts, and the use of NiTi alloy, known as Nitinol, allows the integration of specific functions to the AM ...products. One of the most promising designs for AM is concerning the use of lattice structures that show lightweight, higher than bulk material deformability, improved damping properties, high exchange surface. Moreover, lattice structures can be realized with struts, having dimensions below 1 mm—this is very attractive for the realization of Nitinol components for biomedical devices. In this light, the present work regarded the experimental characterization of lattice structures, produced by selective laser melting (SLM), by using Ni-rich NiTi alloy. Differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD), and compression testing were carried out for analyzing microstructure, martensitic transformation (MT) evolution, and superelasticity response of the SLMed lattice samples. The lattice microstructures were compared with those of the SLMed bulk material for highlighting differences. Localized martensite was detected in the nodes zones, where the rapid solidification tends to accumulate solidification stresses. An increase of martensitic transformation temperatures was also observed in lattice NiTi.
Ni56Mn(25-x)Ga19Cox (x = 0, 2, 4 at.%) ferromagnetic shape memory alloys were fully annealed and then prepared according to different thermal routes. It was found that a quench process, together with ...a high heating rate, improves the thermal response and stabilizes the thermo-elastic transformation in Co-doped samples; in addition, it was observed that a low-rate thermal cycling is comparable to an austenitic aging.
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•Ni56Mn(25-x) Ga19Cox samples were prepared according to different thermal routes.•A high heating/cooling rate process stabilizes the thermo-elastic transformation.•A low-rate thermal cycling is comparable to an austenitic aging.
Additive manufacturing (AM) of Nitinol could enable realizing smart 3D metallic structures that combine the functional properties of shape memory alloys with higher geometrical flexibility. However, ...powder feedstocks suffer from issues related to availability, chemical composition stability, and long-term stocking. Therefore, wire-based AM processes are considered promising for reducing the time required for the process development stage and for maintaining quality over time. In this study, micro laser metal wire deposition (μLMWD) was used for manufacturing thin walls with heights of up to 40 mm by using commercial superelastic Nitinol wires of 0.4 mm diameter. The microstructure, martensitic transformation (MT), and mechanical behavior were analyzed. The results showed that μLMWD could be used to produce Nitinol walls with high aspect ratio and sub-millimeter thickness, that were free of cracks and produced with relative density as high as 99%. The as-deposited wall section was characterized by an almost homogenous composition, which was associated with a solubilized condition, owing to the multiple heating cycles during the deposition of advancing layers. Limited amount of Ni loss induced an increase in the characteristic temperatures of the MT, and shape memory behavior was detected with a recoverable strain of 4.4% upon heating up to 120 °C.
Nowadays, additive manufacturing (AM) of NiTi shape memory alloy is a challenging topic for the realization of 3D functional parts. Particularly, Laser Powder Bed Fusion (LPBF) of NiTi powder is one ...of the most challenging processes belonging to AM, thanks to its best performances in terms of productivity and precision of geometrical complexity. The control of the functional performances in NiTi components requires a strong interaction between technological and metallurgical approaches. In fact, a strong correlation among the process conditions, the microstructure, and the final functional performances, beyond the defects associated with the process are needed to be understood and analyzed. In the present work, the correlation between the feasibility map of processability and the obtained microstructure, which can be tailored according to the use of different energy density values, of Ni-rich NiTi powder processed with LPBF is investigated. In detail, discrete energy density values, in the range 60–300 J/mm3, were correlated to microstructure, Ni:Ti ratio, and transformation temperatures of the martensitic transformation, analyzed with SEM, EBSD, EDX, and DSC characterizations, respectively. An increase in laser energy density was found to promote Ni evaporation, which induced a change of the microstructure from austenite to martensite at room temperature. A consequent shift of the transformation temperatures to higher values and a change in microstructural texture was achieved. These achievements can support the identification of the feasibility range for manufacturing functionally graded NiTi SMA, requiring tailored functional properties located in selected positions in the 3D parts.
Ti6Al4V specimens were produced using electron beam melting (EBM) with the goal of studying the effects of the scanning strategies on the surface morphology, microstructure, and mechanical ...properties. As the factory condition consists in the use of different parameters for scanning the hatch and the contour, additional processing conditions were investigated using the hatch and contour strategies separately, oriented from the center to the border, and vice versa. Due to material anisotropy, the samples were fabricated in both the vertical and planar directions. This work demonstrates that the scanning strategies affect several features of EBMed TiAl4V samples, like the relative density of the specimens, the surface morphology, and the microstructure and mechanical properties. In details, pure contour can increase the relative density, due to the use of pulses instead of continuous electron beam emission, while the hatch scanning produces smoother and more uniform surface morphology. As different thermal histories can be associated with the variation of the scanning strategy, the microstructure can be varied in terms of grain growth. Finally, the tensile behavior of the specimens, evaluated in both the principal orientations, can be correlated to the relative density and surface irregularity.
In this work, the effect of the Al content (x = 5, 10, and 15 at. %) on the martensitic transformation (MT) and microstructure and mechanical properties of Cu(50−x)Zr50Alx alloys was studied. The ...microstructure of the alloys was characterized at room temperature by means of scanning electron microscopy and X-ray diffraction. An increase in Al content reduces the amount of transforming CuZr phase, and consequently the secondary phase formation is favored. The evolution of the MT upon thermal cycling was investigated as a function of the Al content by differential scanning calorimetry. MT temperatures and enthalpies were found to be decreased when increasing the Al content. Al addition can induce a sudden, stable MT below 0 °C, while the binary alloy requires ten complete thermal cycles to stabilize. Finally, the mechanical properties were investigated through microhardness and compression testing. No linear dependence was found with composition. Hardness lowering effect was observed for 5–10 at. % of Al content, while the hardness was increased only for 15 at. % Al addition with respect to the binary alloy. Similarly, compressive response of the alloys showed behavior dependent on the Al content. Up to 10 at. % Al addition, the alloys indicate a superelastic response at room temperature, while higher Al content induced untimely failure.
Prosthetic reconstruction can serve as a feasible alternative, delivering both functional and aesthetic benefits to individuals with hand and finger injuries, frequent causes of emergency room ...visits. Implant-related infections pose significant challenges in arthroplasty and osteosynthesis procedures, contributing to surgical failures. As a potential solution to this challenge, this study developed a new class of silver (Ag)-doped chitosan (CS) coatings via electrophoretic deposition (EPD) on osseointegrated prostheses for infection therapy. These coatings were successfully applied to additively manufactured Ti6Al4V ELI samples. In the initial phase, the feasibility of the composite coating was assessed using the Thermogravimetric Analysis (TGA) and Attenuated Total Reflection (ATR) techniques. The optimized structures exhibited impressive water uptake in the range of 300–360%. Codeposition with an antibacterial agent proved effective, and scanning electron microscopy (SEM) was used to examine the coating morphology. Biologically, CS coatings demonstrated cytocompatibility when in direct contact with a fibroblast cell line (L929) after 72 h. When exposed to the Staphylococcus epidermidis strain (ATCC 12228), these coatings inhibited bacterial growth and biofilm formation within 24 h. These findings underscore the significant potential of this approach for various applications, including endoprostheses like hip implants, internal medical devices, and transcutaneous prostheses such as osseointegrated limb prosthetics for upper and lower extremities.
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