This review compiles and analyzes the current state of the art of modified high entropy alloys (MHEAs) processed by laser powder bed fusion (LPBF), establishing composition-processing-microstructure-property relationships that define their printability, structural integrity, and performance. After contextualizing HEA/MHEA concepts and LPBF‑specific solidification phenomena, the review places particular emphasis on the modification strategies that tailor phase stability, melt‑pool behavior, and processability. These include targeted alloying additions, principal‑element ratio adjustments, and microalloying routes to stabilize FCC/BCC/B2 phase composition, mitigate cracking, and enable precipitation strengthening or microstructural refinement under LPBF’s rapid thermal cycles. A second major focus is the correlation between these compositional modifications and the resulting mechanical properties in both the as‑built and post‑processed conditions. The compiled data reveals distinct strength-ductility regimes across Cantor‑type alloys, Al‑containing dual‑phase systems, and refractory BCC‑based MHEAs, demonstrating how specific elemental additions, phase engineering strategies, and post‑processing treatments modulate hardness, tensile behavior, elongation, and failure modes. The comparative analysis highlights the strong dependency of mechanical properties on controlled phase fractions, segregation behavior, precipitates distribution, and defects. Overall, this review shows that the successful deployment of LPBF‑processed MHEAs critically depends on composition‑aware process design, where alloy modification strategies and mechanical property requirements must be jointly optimized.

In this study, the feasibility of depositing boric acid-free Ni-P coatings using electroplating techniques was investigated, with a focus on safety considerations. A comparison of these coatings with conventional boric acid-containing ones was conducted, examining various properties such as structure, morphology, roughness, brightness, wettability, and hardness. Notably, the absence of boric acid led to a decrease in deposition rate and increased surface roughness. However, it also promoted a higher phosphorus content in the coatings. Both conditions showed similar colors and hydrophobic behavior tendency, with the heat treatment promoting no significant change in this behavior for the boric acid-free coating. The same occurred for the mechanical properties (hardness and Young’s modulus) where no significant differences were found for either of the conditions tested. These findings demonstrate that boric acid-free coatings can retain their functional properties while addressing safety concerns associated with hazardous boric acid.

The integration of functional shape memory alloys into metallic matrices produced by additive manufacturing has remained largely unexplored. In this work, a superelastic NiTi wire was embedded within an AlSi10Mg matrix fabricated by Laser Powder Bed Fusion and investigated as an intrinsic strain sensor. Ex-situ tensile tests up to 6 % strain revealed a distinct resistivity response directly associated with the onset and progression of stress-induced martensitic transformation. When embedded, the wire’s in-situ resistivity measurements up to 2.5 % strain reproduced the same transformation signature, confirming that matrix encapsulation preserved the sensing functionality. Real-time synchrotron X-ray diffraction identified the initiation of the B2→B19′ transformation at ∼1.0 % strain and tracked the evolution of the variant under interfacial constraints. Finite element analysis predicted localized stress amplification at the wire–matrix interface, in close agreement with experimentally observed strain thresholds. The combined experimental and computational results demonstrate the feasibility of embedding NiTi wires as strain sensors, offering high sensitivity, extended strain range, and enhanced stability compared to conventional gauges. These findings establish a foundation for multifunctional smart structures in aerospace, biomedical, or advanced manufacturing applications.

Dissimilar joining of advanced engineering alloys is of major importance for several applications to take advantage of the properties of each one of the base materials. Due to the formation of Ti2Ni 2 Ni and to the thermal expansion coefficient mismatch, dissimilar laser welding between Ti6Al4V and NiTi is particularly challenging. Nevertheless, a joint without pores or cracks was obtained using a Nd:YAG laser system with a wavelength of 1064 nm and a spot size of 0.45 mm. Full-penetration occurred and the weld pool is asymmetric with a key-hole shape. Typical dendritic structure is observed throughout the welded zone, although without apparent orientation on the middle. Close to the Ti6Al4V side a zone with a different morphology is observed along the entire thickness with high hardness corresponding to NiTi2 2 . Multiscale microstructure and mechanical characterization encompassing electron microscopy, synchrotron X-ray diffraction, electron probe microanalysis and instrumented nanoindentation were used to reveal the microstructure/properties relationships correlating the extremely high hardness and brittleness of the welded joint to its microstructural constituents

Rising demands for miniaturization in industries such as aerospace and electronics have motivated advancements in metal additive manufacturing (AM), resulting in downscaled strategies using direct-energy deposition (DED) processes, now termed micro-DED (µ-DED). Within this context, micro gas metal arc DED (μ-GMA) has demonstrated the ability to deposit layers approximately 1 mm wide with a build rate of 30 cm3/h, positioning this technology between GMA-based DED and other µ-DED processes in terms of regarding dimensional accuracy and build rate. Despite promising initial results, further evaluation of the process impact on the microstructure and mechanical behavior of various alloys is necessary due to the pioneering nature of μ-GMA. The present work focuses on the evaluation of the microstructure (via scanning electron microscopy, energy dispersive spectroscopy, thermodynamic simulations, and electron backscatter diffraction analyses) and mechanical behavior (using nanoindentation maps) of single-layer depositions of low alloy and stainless steels using μ-GMA. In addition, traditional GMA-based DED using larger diameter wires was employed to deposit comparably alloys for further discussion. μ-GMA successively deposited a low-alloy steel with a microstructure composed of ferrite and martensite–austenite constituents, achieving a nanohardness (NH) of 3.1 GPa and an elastic modulus (NE) of 196 GPa. In addition, μ-GMA additively manufactured stainless steel with a microstructure composed of a γ matrix and δ-ferrite, exhibiting an NH of 3.7 GPa and an NE of 188 GPa. These results for both deposited materials are comparable to those reported in the literature for regular GMA-based DED depositions, indicating that this new variant has promising potential as a printing technology for small and detailed parts.

NiTi shape memory alloy films were prepared by magnetron sputtering using a compound NiTi target and varying deposition parameters, such as power density, pressure, and deposition time. To promote crystallization, the films were heat treated at a temperature of 400 °C for 1 h. For the characterization, scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, synchrotron X-ray diffraction, and nanoindentation techniques were used on both as-deposited and heat-treated films. Apart from the morphology and hardness of the as-deposited films that depend on the deposition pressure, the power applied to the target and the deposition pressure did not seem to significantly influence the characteristics of the NiTi films studied. After heat treatment, austenitic (B2) crystalline superelastic films with exceptionally high nickel content (~60 at.%) and vein-line cross-section morphology were produced. The crystallization of the films resulted in an increase in hardness, Young’s modulus, and elastic recovery.

In recent years, efforts have been focused on the development of metal additive manufacturing (AM) processes to address the growing trend of miniaturization in industries such as aerospace and electronics. Thus, new technologies have been developed based on a downscaled approach using direct energy deposition (DED) processes, now referred to as μ-DED. In this context, the development of a downscaled DED prototype based on gas metal arc (GMA) working with micrometric wires (μ-GMA) has the potential to unify the positive characteristics of GMA-based DED, increasing the complexity of the design and resolution of the produced parts. Therefore, this work focuses on developing a μ-GMA prototype and assessing its technical feasibility. This paper describes the development of the μ-GMA prototype, characterizes the metallic transfer mode, and statistically analyzes the effect of deposition parameters on bead width and height. Additionally, microstructural analysis, Vickers microhardness, and reduced Young’s modulus tests were performed. The μ-GMA prototype demonstrated the capability to deposit beads with an approximate width of 1 mm, nearly 5 times thinner than standard GMA-based DED deposition, with a build rate of 30 cm3/h, which is lower than GMA-based DED but higher than other μ-DED processes. Furthermore, the mechanical properties of the μ-GMA depositions are comparable to regular GMA-based DED parts.

Additive manufacturing (AM) has revolutionized the production of intricate 3D designs, emphasizing sustainable and customized solutions. The prevailing trend prioritizes sustainable devices that optimize the use of raw materials. Among such innovations, the additive manufacturing of prostheses incorporating strain sensors using NiTi shape memory alloys (SMAs) stands out, particularly in hip prostheses. SMAs, renowned for their superelasticity, showcase a consistent relationship between deformation and electrical resistivity. This unique property allows precise movement assessment throughout the lifecycle of a prosthesis. Our research highlights the significance of integrating strain sensors in the AM process of prostheses. While the assembly and testing of the prosthesis and sensor coupling were prototypical and necessitated further development for practical application tests, there is evidence indicating that the device holds significant potential for monitoring the lifespan of the prosthesis and predicting undesired failures in advance. Hence, the correlation between amplitude variation and electrical resistivity in the NiTi wire is emphasized, indicating its potential as a strain gauge for detecting dislocation in prosthetic implants. Moreover, it underscores the necessity for supplementary analysis, with a specific focus on investigating the high-cycle fatigue behavior, to acquire comprehensive insights into the NiTi wire performance as a sensor over extended periods of use.

Magnesium (Mg) alloys are widely used for temporary bone implants due to their favorable biodegradability, cytocompatibility, hemocompatibility, and close mechanical properties to bone. However, rapid degradation and inadequate strength limit their applicability. To overcome this, the direct current magnetron sputtering technique is employed for surface coating in Mg-based alloys using various zirconium (Zr) content. This approach presents a promising strategy for simultaneously improving corrosion resistance, maintaining biocompatibility, and enhancing strength without compromising osseointegration. By leveraging Mg's inherent biodegradability, it has the potential to minimize the need for secondary surgeries, thereby reducing costs and resources.This paper is a systematic study aimed at understanding the corrosion mechanisms of Mg–Zr coatings, denoted Mg-xZr (x = 0–5 at.%). Zr-doped coatings exhibited columnar growth leading to denser and refined structures with increasing Zr content. XRD analysis confirmed the presence of the Mg (00.2) basal plane, shifting towards higher angles (1.15°) with 5 at.% Zr doping due to lattice parameter changes (i.e., decrease and increase of ``c” and ``a” lattice parameters, respectively). Mg–Zr coatings exhibited ``liquidphilic” behavior, while Young's modulus retained a steady value around 80 GPa across all samples. However, the hardness has significantly improved across all samples’ coating, reaching the highest value of (2.2 ± 0.3) GPa for 5 at.% Zr. Electrochemical testing in simulated body fluid (SBF) at 37 °C revealed a significant enhancement in corrosion resistance for Mg–Zr coatings containing 1.0–3.4 at.% Zr. Compared with the 5 at.% Zr coating which exhibited a corrosion rate of 32 mm/year, these coatings displayed lower corrosion rates, ranging from 1 to 12 mm/year. This synergistic enhancement in mechanical properties and corrosion resistance, achieved with 2.0–3.4 at.% Zr, suggests potential ability for reducing stress shielding and controlled degradation performance, and consequently, promising functional biodegradable materials for temporary bone implants.

Abstract The present work aimed at evaluating the microstructures and mechanical properties of spark plasma sintered WC-6 wt% Co ceramic composites doped with boron (0.2 and 0.5 wt%). W-50 at% C (W-6.13 wt% C) powders produced under different milling times (20, 60, 180, and 600 min) were used as starting materials and subsequently mixed with Co (6 wt%) and B (0.2 or 0.5 wt%) powders for 5 min. The resultant WC-Co-B powder mixtures were consolidated by spark plasma sintering at 1450 °C for 10 min at 40 MPa under vacuum in order to obtain the samples with 10 mm diameter and 3 mm thickness. The starting powders and the sintered samples were characterized by laser diffraction particle size analysis, X-ray diffraction with Rietveld refinement, relative density, scanning electron microscopy, energy dispersive spectrometry, Vickers hardness test, and diametral compression test. Supersaturated W solid solution (WSS) with a crystallite size of <50 nm was formed in W-50C (at%) powder mixtures. The relative density of the sintered composites increased with the increasing milling time up to 180 min from 79.7%±0.6% to 86.7%±0.5% for WC-6Co-0.2B and from 86.7%±0.6% to 90.9%±0.4% for WC-6Co-0.5B. Furthermore, the WC phase appeared as the matrix in the sintered samples, and W2CoB2 precipitated homogeneously around WC grain boundaries, mainly to those containing 0.5% B. The Vickers hardness values of the sintered WC-6Co-0.2B and WC-6Co-0.5B ranged from 1790±39 to 2158±25 HV and 1858±31 to 2182±28 HV, respectively. The fracture strength (determined by diametral compression test) varied between 144-353 MPa due to the porosity and precipitates in thin-thickness cylinder samples.

The aim of this research work was to optimize the coating of tungsten wires with reactive multilayer thin films and promote an exothermic self-propagating reaction. The ultimate goal is to use this heat to liquify low melting temperature materials, and thus block crack propagation in metallic materials. Ni/Me (Me = Al, Ti) multilayers were deposited by a DC (direct current) magnetron sputtering onto tungsten wires with diameters of 0.05 and 0.20 mm. The depositions were carried out to obtain films with near equiatomic average chemical composition and a modulation period (bilayer thickness) between 20 and 50 nm. The cross-section of the films was analyzed using electron microscopy before and after electrical ignition. A new substrate holder was developed to improve the quality of the Al/Ni films, allowing a reduction in the defects previously observed. The Ni/Ti thin films showed no discernible defects, regardless of the substrate holder. However, after ignition, the Ni + Ti reaction occurred in a non-self-propagating mode. Passing an electric current through a wire (ϕ = 0.05 mm) coated with an Al/Ni thin film, promoted a flash of light that was associated with the start of a self-propagating reaction. The reaction product was a B2-AlNi intermetallic phase. W wires coated with reactive multilayers may contribute to crack filling, and have potential to be self-healing actuators.

Diffusion bonding of Ti6Al4V to Al2O3 using Ni/Ti reactive nanomultilayers as interlayer material was investigated. For this purpose, Ni/Ti multilayer thin films with 12, 25, and 60 nm modulation periods (bilayer thickness) were deposited by d.c. magnetron sputtering onto the base materials' surface. The joints were processed at 750 and 800 °C with a dwell time of 60 min and under a pressure of 5 MPa. Microstructural characterization of the interfaces was conducted by scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The mechanical characterization of the joints was performed by nanoindentation, and hardness and reduced Young's modulus distribution maps were obtained across the interfaces. The joints processed at 800 °C using the three modulation periods were successful, showing the feasibility of using these nanolayered films to improve the diffusion bonding of dissimilar materials. Using modulation periods of 25 and 60 nm, it was also possible to reduce the bonding temperature to 750 °C and obtain a sound interface. The interfaces are mainly composed of NiTi and NiTi2 phases. The nanoindentation experiments revealed that the hardness and reduced Young's modulus at the interfaces reflect the observed microstructure.

Shape Memory Alloys (SMAs) can play an essential role in developing novel active sensors for self-healing, including aeronautical systems. However, the NiTi SMAs available in the market are almost limited to wires, small sheets, and coatings. This restriction is mainly due to the difficulty in processing NiTi through conventional processes. Thus, the objective of this study is to evaluate the potential of one of the most promising routes for NiTi additive manufacturing—material extrusion (MEX). Optimizing the different steps during processing is mandatory to avoid brittle secondary phases formation, such as Ni3Ti. The prime NiTi powder is prealloyed, but it also contains NiTi2 and Ni as secondary phases. The present study highlights the role of Ni and NiTi2, with the later having a melting temperature (Tm = 984 °C) lower than the NiTi sintering temperature, thus allowing a welcome liquid phase sintering (LPS). Nevertheless, the reaction of the liquid phase with the Ni phase could contribute to the formation of brittle intermetallic compounds, particularly around NiTi and NiTi2 phases, affecting the final structural properties of the 3D object. The addition of TiH2 to the virgin prealloyed NiTi powder was also studied and revealed the non-formation of Ni3Ti for a specific composition. The balancing addition of extra Ni revealed priority in the Ni3Ti appearance, emphasizing the role of Ni. Feedstocks extruded (filaments) and green strands (layers), before and after debinding & sintering, were used as homothetic of 3D objects for evaluation of defects (microtomography), microstructures, and mechanical properties. The composition of prealloyed powder with 5 wt.% TiH2 addition after sintering showed a homogeneous matrix with the NiTi2 second phase uniformly dispersed.

To compare the adhesive interface of eroded dentin formed by a functional dental adhesive and a gold standard strategy, by testing microtensile bond strength (μTBS), hardness/elastic modulus. Permanent sound human molars were randomly allocated to four experimental groups, all subject to artificial erosion (0.05 M citric acid; 3× daily, 5 days). Groups included control Clearfil SE Bond 2 (CFSE), and experimental group Clearfil SE Protect (CFP), at two different time points-immediate (24 h) and long term (3 months–3 M). Samples were sectioned into microspecimens for μTBS (n = 8) and into 2-mm thick slabs for nanoindentation assays (n = 3). Groups CFSE_3M and CFP_3M were stored in artificial saliva. Statistical analysis included two-way ANOVA for μTBS data, while hardness/modulus results were analyzed using Kruskal–Wallis H Test (significance level of 5%; SPSS v.27.0). Although no significant differences were found between mean μTBS values, for different adhesives and time points (p > 0.05), a positive trend, with μTBS rising in the CFP_3M group, was observed. Regarding hardness, no significant differences were seen in the hybrid layer, considering the two variables (p > 0.05), while the reduced elastic modulus rose in CFP_3M when compared to 24 h. Thus, CFP shows similar mechanical and adhesive performance to CFSE in eroded dentin, although it may comprise promising long-term results. This is advantageous in eroded substrates due to their increased enzymatic activity and need for remineralization.

The interaction between the stress-induced martensitic transformation and resistivity behavior of superelastic NiTi shape memory alloy (SMA) was studied. Strain-controlled low-cycle fatigue up to 6% was monitored by in situ electrical resistivity measurements. The experimental results show that a great motion of martensite fronts results in a significant accumulation of defects, as evidenced by transmission electron microscopy (TEM), before and after the tensile cycles. This gives rise to an overall increase of the resistivity values up to the maximum deformation. Therefore, the research suggests that shape memory alloy wire has great potential as a stress sensor inside bulk materials.

This work aims to investigate the joining of Ti6Al4V alloy to alumina by diffusion bonding using titanium interlayers: thin films (1 µm) and commercial titanium foils (5 µm). The Ti thin films were deposited by magnetron sputtering onto alumina. The joints were processed at 900, 950, and 1000 °C, dwell time of 10 and 60 min, under contact pressure. Experiments without interlayer were performed for comparison purposes. Microstructural characterization of the interfaces was conducted by optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The mechanical characterization of the joints was performed by nanoindentation to obtain hardness and reduced Young’s modulus distribution maps and shear strength tests. Joints processed without interlayer have only been achieved at 1000 °C. Conversely, joints processed using Ti thin films as interlayer showed promising results at temperatures of 950 °C for 60 min and 1000 °C for 10 and 60 min, under low pressure. The Ti adhesion to the alumina is a critical aspect of the diffusion bonding process and the joints produced with Ti freestanding foils were unsuccessful. The nanoindentation results revealed that the interfaces show hardness and reduced Young modulus, which reflect the observed microstructure. The average shear strength values are similar for all joints tested (52 ± 14 MPa for the joint processed without interlayer and 49 ± 25 MPa for the joint processed with interlayer), which confirms that the use of the Ti thin film improves the diffusion bonding of the Ti6Al4V alloy to alumina, enabling a decrease in the joining temperature and time.

This paper aims to investigate the diffusion bonding of Ti6Al4V to Al2O3. The potential of the use of reactive nanolayered thin films will also be investigated. For this purpose, Ni/Ti multilayer thin films with a 50 nm modulation period were deposited by magnetron sputtering onto the base materials. Diffusion bonding experiments were performed at 800 °C, under 50 MPa and a dwell time of 60 min, with and without interlayers. Microstructural characterization of the interface was conducted through scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). The joints experiments without interlayer were unsuccessful. The interface is characterized by the presence of a crack close to the Al2O3 base material. The results revealed that the Ni/Ti reactive multilayers improved the diffusion bonding process, allowing for sound joints to be obtained at 800 °C for 60 min. The interface produced is characterized by a thin thickness and is mainly composed of NiTi and NiTi2 reaction layers. Mechanical characterization of the joint was assessed by hardness and reduced Young’s modulus distribution maps that enhance the different phases composing the interface. The hardness maps showed that the interface exhibits a hardness distribution similar to the Al2O3, which can be advantageous to the mechanical behavior of the joints.

Nanoscale multilayers can be used as highly localized heat sources, making them attractive for several applications, in particular for joining and as igniters. Over the last decades, academia and industry have given particular emphasis to nanoscale multilayers from the Ni–Al system. In this study, Al/Ni (V) multilayer thin films with periods of nominally 25 and 50 nm (bilayer thickness) and near equiatomic average stoichiometry were produced by d.c. magnetron sputtering from Al (99.999% pure) and Ni (93 wt % Ni, 7 wt % V) targets (vanadium was added to the Ni target to make it non-magnetic). Deposition parameters such as the substrate rotation speed and substrate bias were varied in order to evaluate their effect on the reactivity of the multilayers. The influence of in situ ion bombardment of the multilayer thin films was also studied. Phase identification was carried out by X-ray diffraction, while the microstructure was analyzed in detail by transmission electron microscopy, distinguishing alternating layers throughout the entire thickness of the films. Although the films mainly consist of Al- and Ni-rich layers, the presence of the Al3Ni intermetallic phase was detected, except in the multilayers produced with the ion gun switched on during the deposition process. The ion bombardment, as well as the increase of the substrate bias, promote some microstructural disorder and thus affect the multilayers’ reactivity.

Reaction-Assisted Diffusion Bonding (RADB) of NiTi to Ti6Al4V using either magnetron sputtered Ni/Ti nanomultilayers or Ni/Ti commercial microfoils as filler material was studied. The joining process takes advantage of the exothermal reactive character of the Ni-Ti system to provide extra energy during the bonding process. Therefore, sound joints could be achieved at lower thermal conditions. The oven with load capabilities at the High Energy Materials Science beamline (P07) of the Deutsch Synchrotron (DESY) is ideal to follow the structural evolution of the materials involved in the bonding process. Prior to RABD, Ni/Ti multilayers with a 2.5 mu m total thickness and with 12 or 25 nm of modulation period were deposited onto the materials being joined. In alternative, up to 20 alternated thin mu-foils were placed in between the base materials. The materials were heated by induction to the selected temperature during 30 min and quenched to room temperature by blowing helium. During the thermal cycle a 10 MPa pressure was applied. Using thin mu-foils, 650 degrees C was required to promote joining, while using multilayer coated materials sound joints were obtained at 600 degrees C. Such low temperatures are attractive from the application/economic point of view, and are crucial to reduce the formation of undesired intermetallic phases, such as NiTi2. The nanoindentation experiments of the joints processed using Ni/Ti nanomultilayers confirm that the presence of the NiTi2 phase is more pronounced at 650 degrees C than when the joints are processed at 600 degrees C.

The requirements for the divertor components of future fusion reactors are challenging and therefore a stimulus for the development of new materials. In this paper, WC-Cu composites are studied for use as thermal barrier between the plasma facing tungsten tiles and the copper-based heat sink of the divertor. Composite materials with 50% vol. WC were prepared by hot pressing and characterized in terms of microstructure, density, expansion coefficient, elastic modulus, Young's modulus and thermal diffusivity. The produced materials consisted of WC particles homogeneously dispersed in a Cu matrix with densifications between 88% and 98%. The sample with WC particles coated with Cu evidenced the highest densification. The thermal diffusivity was significantly lower than that of pure copper or tungsten. The sample with higher densification exhibits a low value of Young's modulus (however, it is higher compared to pure copper), and an average linear thermal expansion coefficient of 13.6 x 10(-6) degrees C-1 in a temperature range between 100 degrees C and 550 degrees C. To estimate the behaviour of this composite in actual conditions, a monoblock of the divertor in extreme conditions was modelled. The results predict that while the use of WC-Cu interlayer leads to an increase of 190 degrees C on the temperature of the upper part of the monoblock when compared to a pure Cu interlayer, the composite will improve and reduce significantly the cold-state stress between this interlayer and the tungsten. (c) 2019 Published by Elsevier B.V.