Alessandra Palombi

This study evaluates the thermal and mechanical behavior of innovative copper–nickel–titanium (CuNiTi) rectangular orthodontic wires featuring rounded edges across two different sizes for clinical applications. Differential scanning calorimetry (DSC) was performed from −20 °C to +80 °C to determine phase transformation temperatures according to ASTM F2004. Three-point bending tests were conducted in accordance with ISO 15841 to evaluate unloading forces (at 3, 2, 1, and 0.5 mm deflections) and permanent residual deflection at 23 °C (room temperature) and 37 °C (oral environment). DSC analysis revealed a single-stage phase transformation within the range 10 °C to 27 °C, indicating near-superelastic behavior at room temperature. Mechanical testing demonstrated reproducible force-deflection profiles and low permanent deformation. At body temperature (37 °C), unloading forces in the 2.0–0.5 mm activation range averaged between 1.9 N and 3.2 N depending on wire cross-section. In conclusion, the evaluated CuNiTi wires provide consistent force delivery during unloading at physiological temperature, offering suitable mechanical properties for orthodontic alignment applications.

Additive manufacturing (AM) represents a quite interesting technology for manufacturing components of nuclear reactors. This work investigated the microstructural stability of 316 L steel fabricated via Laser Powder Bed Fusion (L-PBF) from room temperature to 650 °C. Despite the reduced susceptibility of the material to sensitization owing to its low carbon content, temperature variations may induce deleterious effects in nuclear safety-critical components. In as-printed condition, the microstructure is not stable and undergoes significant changes induced by thermal cycling up to 650 °C in Mechanical Spectroscopy (MS) tests: the typical melt-pool pattern disappears, a population of equiaxed grains substitutes the original ones elongated in the build direction, the average size of the cells forming a finer sub-structure inside the grains increases, texture changes, and the excess of vacancies induced by the rapid cooling is recovered. Although the current literature reports that the microstructure is stable up to 500 °C, MS results indicate that the aforesaid irreversible phenomena start at a lower temperature (~230 °C). The present results suggest that the microstructure of the printed material must be stabilized through suitable heat treatments before its application in structural components for nuclear reactors.

Ni-based superalloys, known for their excellent mechanical strength and corrosion resistance at high temperature, are widely used in aeronautic, aerospace, and energy industries. Since both the materials and manufacturing processes required to produce high-performance components made of these alloys are expensive, the welding repair of damaged components plays a crucial role in industrial applications. High energy density welding techniques, such as laser beam welding (LBW) and electron beam welding (EBW), are the most promising to achieve high-quality welds. Nevertheless, welding processes significantly affect the microstructure and mechanical properties of both the melted zone (MZ) and the heat-affected zone (HAZ). This may result in alloying element segregation, precipitation of undesired secondary phases, and the presence of residual stresses that can lead to crack formation. Therefore, a comprehensive investigation of the effects of process parameters on weld seam properties is essential to maintain high performance standards. In this work, LBW was employed to join 2.5 mm thick plates of equiaxed IN625 superalloy. The seams were produced by varying three parameters: the two characteristic parameters of LBW, i.e., laser power (P = 1700, 2000, 2300 W) and welding speed (v = 15, 20, 25 mm/s), alongside power modulation (Γ = P_min/P_max = 0.6, 0.8, 1). The scope of this work is to evaluate the effect of the combined variation of all these welding parameters on the final characteristics of welded seams. The resulting microstructures were characterized by using digital radiography, Light Microscopy (LM), Scanning Electron Microscopy (SEM), and X-ray Diffraction (XRD). Vickers microhardness measurements were performed across the weld seams to evaluate the mechanical properties in the MZ and HAZ. The optimal set of welding parameters, producing defect-free seams without cracks and pores, was identified as P = 2000 W, v = 25 mm/s, and Γ = 0.6.

CoCrMo alloys are widely used for the production of such medical devices as orthopedic and dental implants. Of particular relevance is the possibility to customize biomedical implants through additive manufacturing (AM) to better fit the patient's anatomy. Moreover, in the case of Co‐base alloys, AM allows overcoming some manufacturing limits typical of conventional processes. In biomedical applications, the surface of the implant interacts with biological environments; therefore, its properties are of crucial importance to guarantee patient safety. X‐ray photoelectron spectroscopy (XPS) analyses have been carried out on the surface of the Co28Cr6Mo alloy produced by selective laser melting (SLM) in as‐built condition and after a heat treatment consisting of a heating–cooling cycle from room temperature up to 800°C. The as‐built material is in nonequilibrium conditions and undergoes microstructural and surface modifications as a consequence of the heat treatment. Heating promotes the transformation of part of the metastable γ phase into ε phase, a coarsening of microstructure, and surface segregation of Mo and Cr that form an oxide layer. Surface segregation of Mo occurs in all the samples while Cr segregation is only observed after the heat treatment. Segregation is driven by the energy reduction related to the formation of Mo and Cr oxides. In as‐built samples this effect is low because long‐range diffusion is hindered by the high cooling rate and thermal gradient involved in AM processes. During heat treatment long‐range and surface diffusion can take place; therefore, more Mo and Cr atoms reach the surface. The higher amount of Mo and Cr at the surface promotes the formation of Mo and Cr stable oxides that improve surface passivation.

To date, one of the main problems associated with the engineering application of metallic materials is corrosion protection. To increase their durability and reduce damage, a variety of protection methods have been studied and applied. In recent decades, coating techniques have become increasingly important. Among these coatings, Layered Double Hydroxides (LDHs) have shown unique properties, such as ion exchange, high adhesion, and hydrophobicity, particularly useful for biomedical applications. In this review, after a detailed exposition of the LDHs’ synthesis processes, the most recent corrosion protection methods are illustrated. Intercalation of corrosion inhibitors and release kinetics of intercalates are presented. Although this work is mainly focused on laboratory-scale investigations and fundamental research, the problems inherent to large-scale industrial manufacturing and application are outlined and briefly discussed.

The magnesium AZ31 alloy is one of the most studied biodegradable materials for biomedical applications. It exhibits excellent biocompatibility and osseointegration and has an elastic modulus comparable to that of human bone. Furthermore, magnesium is essential for the metabolism in many biological mechanisms, and the Mg ²⁺ ions, which are produced from its degradation, are useful to promote healing and tissue growth. However, the AZ31 alloy has the drawback of quickly degrading in the presence of biological fluids. Corrosion leads to a reduction of the implant's mechanical properties, compromising its functionality. Unlike other surface treatments that provide only a barrier function, the layered double hydroxides (LDHs) also offer the opportunity to release drugs. This work investigated the growth of LDHs on the AZ31 alloy by using three different nutrient solutions with (i) Zn(NO ₃ ) ₂ *6H ₂ O, (ii) Mg(NO ₃ ) ₂ *6H ₂ O, and (iii) FeCl ₃ . The treatments were carried out at 90°C for 12 h. The chemical composition and structure of treated surfaces were examined by scanning electron microscopy (SEM), x‐ray diffraction (XRD), and x‐ray photoelectron spectroscopy (XPS). The results of these analyses are presented and discussed.

IN792 is a Ni‐base superalloy commonly employed for manufacturing blades and rotors of jet engines owing to its excellent mechanical properties and corrosion resistance at high temperature. These components operate in a very hostile environment and are exposed to high temperature and stress which can lead to the formation of cracks compromising their performance. Laser welding is a suitable high‐energy density method to repair the damaged parts; however, if the IN792 superalloy has a structure with equiaxed grains, new cracks may be caused by the welding process. SEM observations highlighted that the fracture surfaces exhibit the typical morphology of a brittle fracture. XPS investigations made on the crack surfaces showed that they are enriched of Co. Co segregation has been explained by considering the migration of alloying elements in the melt during solidification. In the final stage of solidification, the volume contraction of the last liquid, rich in Co and entrapped in the already solidified parts, is not compensated. This results in relevant stresses that can lead to crack nucleation. Crack propagation takes place in brittle mode due to the significant presence of oxides which represent a preferred pathway for crack advancement.