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Electro-chemical machining (ECM) can safely be categorized as being a unique unconventional machining technique, in which the role of thermal defects are not involved. The NiTiCo shape memory alloy has high yield strength coupled with good resistance to aggressive aqueous environments, which makes it a potential candidate for use in several bio-medical applications. This research concentrates on electro-chemical machining of a NiTiCo alloy. Taguchi's Design of Experiment (DOE) containing three-parameters and three-factors was used to conduct the experimental study. The influence of concentration of the sodium chloride electrolyte, voltage, and frequency on output characteristics, such as (i) material removal rate (MRR), (ii) surface roughness (SR), and (iii) over-cut (OC), was analyzed. Experimental outputs revealed the voltage (45.29%) to be the most influential among the three controlling parameter. Grey relational analysis (GRA) was utilized to discover the ideal parametric relation and optimize machining characteristics. [ABSTRACT FROM AUTHOR]

We report unique two-step strain glass transition toward different local strain states in NiTi, i.e. R and B19′ strain glasses. This unique transition is evidenced by dynamic mechanical analysis and in-situ HR-TEM. A comprehensive phase diagram is established to illustrate diverse transition pathways and corresponding tunable superelastic properties. This pathway exploits the integrated transition of different phases, lowering the transition energy barrier, yielding superelasticity with large recoverable strain (6%), ultralow modulus (24 GPa) and robust cyclic and wide-temperature stability. Our investigation provides fresh insights into continuous transition pathways among different strain glass states to achieve exceptional properties in shape memory alloys. [ABSTRACT FROM AUTHOR]

Nitinol alloys are widely utilized across various fields owing to their exceptional elasticity and shape memory characteristics. Their low thermal conductivity, high strength, and high toughness pose significant challenges to conventional machining technologies. To address these challenges, several non-conventional machining processes such as electrical discharge machining have been developed. This study introduces an innovative approach that combines the use of insulated coated electrodes with multi-energy field-assisted electrical discharge machining to improve the application of electrical discharge machining in machining deep microporous. We investigated the effects of the insulated electrode and multi-energy field on surface morphology, taper accuracy, diameter cutting, and the thickness of the recast layer in detail. The findings suggest that the insulated coated electrode combined with multi-energy field-assisted electrical discharge machining achieves better taper accuracy and lower diameter cutting, resulting in a smoother surface and a more uniform, thinner recast layer compared to traditional electrical discharge machining. [ABSTRACT FROM AUTHOR]

Nitinol alloy is widely utilized across various industries due to its special properties. In this paper, the compound effects of two kinds of energy fields on material removal rate (MRR), hole wall quality, machining accuracy, and recast layer in ultrasonic combined magnetic field assisted EDM (UV-MFEDM were studied and analyzed. In addition, the influence of magnetic field intensity on the efficiency and accuracy of micro-hole machining is analyzed systematically. The results show that the surface quality of the micropore is significantly improved, the MRR is increased by 31.6%, the taper of the micropore is reduced by nearly 30%, the overcut diameter is reduced by nearly 23%, the recast layer is more uniform and the thickness of the recast layer is reduced by nearly half. Appropriate magnetic field intensity proves beneficial for improving micro-hole machining efficiency while reducing both taper angle and diameter overcut of micro-holes. [ABSTRACT FROM AUTHOR]

Nowadays, advanced engineering materials are gradually becoming more attractive to the industries because of their high fatigue strength, hardness, thermal shock resistance, attractive strength to weight ratio, etc. Aluminium metal matrix composites (MMCs) have such properties and good electrical conductivity. Therefore, wire electrical discharge machining (WEDM) was found to be a suitable process for machining of such materials. The open gap voltage, pulse-on-time, pulse-off-time, peak current, wire feed rate and wire tension were considered as input process parameters, and experiments were carried out on fabricated hybrid Al/(SiC+ZrO2+ NiTi)-MMC. Taguchi method-based L18 (21x37) mixed orthogonal array was employed for planning of experiments. The process parameters were optimised for material removal rate (MRR) and surface roughness (SR) heights. Confirmation results reveals 61.88%, −28.75% and −20.25% improvement in MRR, Ra and Rt respectively, over initial setting. From analysis of variance (ANOVA), open gap voltage and pulse-on-time were found significant parameters for MRR and SR. The mathematical models for MRR and SR were developed and confirmation test reveals good agreement of it with experimental results. Scanning electron microscopy images reveal that the recast layer thickness was 8.569 µm at optimal MRR setting and 6.113 µm at optimal surface roughness (Ra) setting. [ABSTRACT FROM AUTHOR]

The NiTi alloy has attracted significant interest owing to its notable wear and corrosion resistance, suggesting the significant promise of utilizing additively manufactured NiTi alloys in tribological applications. In this study, dry sliding wear tests with sliding velocity of 0.1 m/s for total distance of 250 m at room temperature, 50 °C, 100 °C, and 200 °C were carried out on samples of NiTi alloy samples fabricated using laser powder and laser wire directed energy deposition (LP-DED and LW-DED) processes. Enhanced friction and wear behavior of LP-DED samples were captured at lower temperatures due to higher hardness and the stable dominating NiTi B2 austenite phase in the sample microstructure as confirmed from x-ray diffraction (XRD) analysis. Accumulated transferred material at lower temperatures played a crucial role in modifying the wear mechanisms. However, at higher temperatures both LP-DED and LW-DED samples presented similar wear mechanisms. [ABSTRACT FROM AUTHOR]

Micro-electrical discharge machining (µ-EDM) is one the most favourable process to machine difficult to cut materials in micro-scale with higher accuracy and precision. In this paper, two multi-response optimisation tools called Taguchi's grey relation analysis (GRA) and response surface methodology (RSM)-based desirability function are used to evaluate optimised micro-machining parameters for minimal overcut and circularity error during µ-EDM of nickel-titanium (NiTi) shape memory alloy (SMA). Taguchi's GRA revealed that electrode material has the strongest influence on both the responses followed by capacitance and discharge voltage. ANOVA analysis established that electrode material has the highest percentage contribution of 40.15% on both the responses. The optimisation result obtained by Taguchi's GRA approach is validated by the RSM-desirability function-based technique. The final optimisation result (capacitance 155 pF, electrode material tungsten, discharge voltage 80 V) is a very close agreement with the literature model (capacitance 355 pF, electrode material tungsten, discharge voltage 80 V), with reference to the overcut and circularity error for the improvement of the dimensional accuracy of the micro-holes. Further, the response surface plots disclosed the variation of overcut and circularity error with the process parameters at various levels in a descriptive manner. [ABSTRACT FROM AUTHOR]

The cuttlebone is known for its ability to possess high specific stiffness, progressive failure and lightweight from the porous chambered structure. Inspired by the microstructural characteristics of cuttlebone and incorporating the wall gradient design, a series of double-asymmetric honeycombs were designed and processed by LPBF. Results indicated that bionic structural units with the junction design can maintain the integrity of the residual parts after local buckling and failure, improving the load-bearing capacity. The double-asymmetric honeycomb with gradation parameter a = 2/3 achieved a maximum specific compressive strength of 70.64 MPa cm3/g. As a decreases, there is an increase in specific energy absorption and a narrowing of the hysteresis loop. The as-build honeycomb had undergone stress-induced martensite transformation during compression. The dissipated mechanical energy (ME) decreased with the increasing cycle number and the decreasing a. The results provide design guidelines and process strategies for developing high-performance honeycombs. [ABSTRACT FROM AUTHOR]

Achieving grain refinement in the wire-arc directed energy deposition (DED) process of NiTi alloy is highly challenging. We have successfully obtained NiTi alloy with a fine microstructure and observed an improvement in superelastic recoverability by introducing an ultrasound-assisted field during the deposition process. The results show that the average grain size of the NiTi alloy samples decreased from 147.3 to 72.2 µm. Additionally, the recoverable strain of the samples increased significantly from 3.7% to 4.4%. This is attributed to the ultrasonic cavitation and acoustic streaming phenomena during the ultrasound-assisted process, which promotes the columnar-to-equiaxed transition (CET) during the solidification process. Fundamentally, the key to the enhancement of recoverable strain after ultrasound-assisted is that the formation of equiaxial grains provides more strain compatibility to the grain boundaries, which reduces the formation of dislocations during deformation. [ABSTRACT FROM AUTHOR]

In this study, we investigate the influence of dislocation strengthening in the metastable parent phase on the deformation-induced martensitic transformation behavior of a face-centered cubic (fcc) Co20Cr20Fe34Mn20Ni6 high-entropy alloy. Annealed and hot-swaged specimens were prepared. In-situ neutron diffraction experiments captured an accelerated transformation kinetics in the hot-swaged specimen due to accumulated dislocations. The phase-specific macrostress development showed that the hexagonal close-packed $ \rvarepsilon $ ε -martensite predominantly accommodated the macroscopic plastic deformation of the annealed counterpart. Conversely, the matrix dislocation strengthening promoted cooperative plasticity of the $ \rgamma $ γ -matrix and the $ \rvarepsilon $ ε -martensitic phase, thus enhancing yield stress while preserving ductility. This paper firstly uncovers the role and significance of matrix dislocation strengthening on the mechanical behavior of metastable high-entropy alloys via in-situ neutron diffraction experiments. [ABSTRACT FROM AUTHOR]

One of the best ways to obtain TiN coatings is through the nitriding process by efficient methods such as dense plasma focus (DPF). The gas composition of the nitrogen environment is a crucial factor affecting the properties of the coating. In this study, three different atmospheres of 100%N2, 50%N2–50%O2, and 75%N2–25%Ar were used to investigate their impact on the mechanical and biological properties of TiN coatings on NiTi substrate. The operating condition that yielded the coating with the highest hardness, as well as the lowest contact angle and Ni ion release, was chosen as the optimum condition. According to the XRD results, TiN was recognized as the dominant phase which causes high hardness and prevents Ni ion release. Moreover, surface analyses determined that the sample coated in 50%N2 composition possessed higher hardness and as a result displayed better mechanical properties. Also, the improved microstructural properties lead to an enhanced coating/substrate adhesion strength. On the other hand, the reaction of TiO2 and TiN lead to the formation of TiN0.6O0.4 ternary compound and for this reason, the 50%N2–50%O2 sample exhibited better performance in preventing the release of the toxic nickel ion compared to the other samples. Finally, due to the presence of TiO2 and TiN0.6O0.4 in the sample surface treated at 50%N2–50%O2, better hydrophilicity was observed compared to other samples. Results confirm that the applied surface modification method is effective in increasing the mechanical and biological properties of the NiTi, where it may open numerous possibilities for efficient use in orthopedic applications. [ABSTRACT FROM AUTHOR]

This paper characterises the dissimilar laser welding of 0.5 mm thick plate of shape memory alloy (NiTi) and copper (Cu) at different welding speeds. Properties of laser welds are characterised by microhardness testing, tensile-shear testing, XRD analysis, differential scanning calorimetry (DSC), and optical microscopy. XRD analysis of welded zone demonstrates the presence of NiTi, Cu, and equiatomic NiTi-Cu phases due to diffusion of NiTi and Cu at the interfacial zone of NiTi-Cu joint. DSC analysis shows the start and finish temperature of austenite phase during heating and martensitic phase during cooling for NiTi and laser welded sample. Microhardness studies reveal that weld zone possesses much higher hardness than NiTi and Cu base alloy. Microhardness value at NiTi-Cu joint interface (fusion zone) increases to 280HV and 150HV because of the presence of brittle and hard IMC phases (i.e. NiTiCu). The welded joints deliver higher joint strength than Cu base alloy but lower strength than NiTi SMA. Maximum joint strength of 335MPa (strain of 13.6%) is achieved at 1400W laser power and 1 m/min welding speed due to improved mixing and material flow. Microstructures of the fusion zone have dendrites grains and show the presence of Cu and NiTi constituents in the weld region. [ABSTRACT FROM AUTHOR]

Shape memory alloys (SMA) made of nickel–titanium (NiTi) have grown in popularity because of their functionality and mechanical qualities. Vanadium (V) was added as an alloying element to the regular binary NiTi shape memory alloy for enhancement of its ability to retain memory at high temperatures. In this research, the machined surface roughness (Ra) and material removal rate (MRR) of fiber-laser cutting of Ni50Ti48V2 SMA were investigated using Box-Behnken design (BBD) experimentation. The surface characteristics in terms of Ra decreased by 57.79% while cutting speed and laser power decreased and the frequency level gradually increased. The microhardness was high due to the resolidified molten layer on the machined surface. A surface morphology study indicated the formation of debris and striations due to the flow of nitrogen gas. DSC analysis reveals a minimal variation in the shape memory property even after laser machining. [ABSTRACT FROM AUTHOR]

This research highlighting the novel properties of pseudo-elastic Ni-Ti bar owing to their ability to reverse macroscopically inelastic deformation during earthquake known as recentering capability and large elastic strain capacity which originated from the reversible austenite to martensite phase transformation. The homogeneity of Ni and Ti are extremely sensitive to the compositional in austenite finish temperature (Af) which led to phase change transformation behavior and the effect of different size of NiTi bar in design have not comprehensively considered in the previous work. Hence, this paper is presented and evaluates the cyclic properties of three different sizes and austenite finish temperature (Af) of pseudoelastic NiTi and reused NiTi to assess their prospective use as reinforcing bar to be exploited as seismic-resistant design and mitigation. The correlation of hysteretic behavior of Ni-Ti alloy in terms of cyclic loading number and history, mechanical properties at ambient temperature, equivalent damping, energy dissipation, and stress recovery were evaluated. The tensile cyclic test obtained demonstrated a rounded loading curve based on a 0.2% offset and increased with the increase of loading rate corresponding with the values of the stress plateau. The as-received bar and reused NiTi bar exhibited superior pseudo-elastic behavior and recentering through repeated cycling without significant degradation or permanent deformation but low energy damping due to narrow hysteresis while the steel rebar shows vice versa. Experimental results show potential for the use of SMAs in seismic applications and provide areas for continued research. It was concluded that the as-received and the reused pseudo elastic Ni-Ti reinforcing bar are suitable to use for seismic mitigation despite their ability to undergo cyclical strains is 6% to a maximum 8% with minimal residual strain, 0.004% to maximum less than 1%. Due to narrow hysteresis and phase transformation behavior, the 12.7 mm NiTi exhibit the perfect superelasticity with the residual strain (εR) was 0.1076% corresponding with strain recovery capacity of 98.21% for the range of cyclic strains up to 6%. The reused NiTi 12.7 mm exhibits the highest energy dissipation residual strains up to 99.95% for their wide hysteresis and successive to cyclic loading at an 8% strain cycle. In comparison, the strain recovery capacity (%) increased with a decrease in bar size. The energy dissipation and damping increasing with the increasing of the bar size, but decreasing with the increasing of the bar size for reused NiTi Af −6.3, hence correlate in a good agreement corresponding with 8 mm and 12 mm diameter of the bar. However, different relationship demonstrated for NiTi 12.7 mm due to different composition ratio that exhibits different phase transformation behavior. [ABSTRACT FROM AUTHOR]

Elastocaloric cooling has no environmental effects during operation, and achieving a compact structure especially the driver is significant for its commercialization. In this article, a compact, standalone crankshaft driven single long NiTi tube compressive elastocaloric cooler is developed. A crankshaft driver was designed and fabricated to drive a compressive elastocaloric regenerator utilizing a single long polycrystalline superelastic NiTi shape memory alloy tube (outer diameter 5 mm, wall thickness 1 mm, and initial length 305 mm). A novel design of ceramic heat insulation plate was applied to the cooler to reduce the conduction heat loss from the NiTi tube to the stainless-steel loading heads. The cooling performance of the cooler was characterized using synchronized thermocouples and infrared thermography, and the specific cooling(heating) power, temperature span, and coefficient of performance of up to 65(125) W·kg−1, 9.1 K, and 5.0, respectively were measured. The progressions of the temperature span, specific cooling(heating) power, and coefficient of performance with the operation cycle and temperature lift were analyzed. An energy analysis revealed that the heat transfer fluid carried out only 14% of the latent heat generated by the NiTi tube, which demonstrated a potential to enhance the cooling performance by the improvement in the regenerator structure. [ABSTRACT FROM AUTHOR]

The drilling of shape-memory alloys based on nickel-titanium (Nitinol) is challenging due to their unique properties, such as high strength, high hardness and strong work hardening, which results in excessive tool wear and damage to the material. In this study, an attempt has been made to characterize the drillability of Nitinol by investigating the process/cooling interaction. Four different combinations of process/cooling have been studied as conventional drilling with flood cooling (CD-Wet) and with minimum quantity lubrication (CD-MQL), ultrasonic-assisted drilling with flood cooling (UAD-Wet) and with MQL (UAD-MQL). The drill bit wear, drilling forces, chip morphology and drilled hole quality are used as the performance measures. The results show that UAD conditions result in lower feed forces than CD conditions, with a 31.2% reduction in wet and a 15.3% reduction in MQL on average. The lowest feed forces are observed in UAD-Wet conditions due to better coolant penetration in the cutting zone. The UAD-Wet yielded the lowest tool wear, while CD-MQL exhibited the most severe. UAD demonstrated a ∼50% lower tool wear in the wet condition than CD and a 38.7% in the MQL condition. UAD is shown to outperform the CD process in terms of drilled-hole accuracy. [ABSTRACT FROM AUTHOR]

Laminated metal-composite structures or fiber metal laminates (FMLs) are advanced engineering materials currently being utilized in several distinct applications, especially in aircraft and automobile manufacturing industries where an improved impact and fatigue resistance are required. Machining of FMLs is an important task in obtaining near-net shapes for joining and assembly of the components. However, the delamination occurs during conventional machining making FMLs as difficult-to-machine materials. Therefore, the present study will look into the abrasive water jet cutting (AWJC) of novel fiber intermetallic laminates (FILs) made of with alternatively stacked carbon/aramid fiber adhesively bonded with r-GO filled epoxy resin matrix and Nitinol shape memory alloy sheet embedded laminates. The AWJC experiments were performed on fabricated FILs to investigate the cut quality features including kerf taper (Kt), surface roughness (Ra) and kerf deviation (KD) by varying addition of r-GO from 0-2 wt% in the laminates, traverse speed (400-600 mm/min), waterjet pressure (200-300MPa) and nozzle height (2-4 mm), respectively. Statistical results obtained through ANOVA reveals that the traverse speed and nozzle height are the utmost significant variables which influencing the cut quality characteristics followed by waterjet pressure. Surface morphology analysis shows the wear and erosion mechanism of FILs at varying AWJC conditions. For an improved cut quality, the optimal AWJC parameters are achieved through a metaheuristic-based Barnacles Mating Optimization Algorithm (BMOA). [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to assess the effects of changing the Nitinol stent's geometrical characteristics on the superelastic behavior of the stent using the finite element method. Four different geometrical parameters were considered and analyzed in sixteen stents. These geometrical parameters consisted of stent length, number of stent's meanders, inside diameter of the stent and wire diameter. Results showed that decreasing either stent length or the number of stent meanders and increasing either the inside diameter of the stent or wire diameter generally result in more sensible superelastic behavior exposure. The effect of changing stent length is independent of the inside diameter and number of the stent's meanders. Effects of changing inside diameter and number of stent's meanders were exactly dependent together. In addition, increasing wire diameter has a great effect on the maximum force. In conclusion, the results of this study may serve as guidelines for future stent design. [ABSTRACT FROM AUTHOR]

This paper aims to address the impact of jet impingement on nano titanium-based ENi-P composite coatings deposited through electroless deposition on AH36 steel through Taguchi design of experiments. L9 Taguchi DOE was utilised to synthesise nine coatings by varying the four process parameter combinations suggested by the technique. Jet impingement combined with AFS 50/70 quartz sand erosion experimental run was conducted on the acidic, alkaline and nine ENi-P-TiO2 composite coatings administered through a waterjet erosion tester. The influence of C14-SB type Zwitterionic surfactant and nano TiO2 were discussed along with temperature and bath pH to achieve better resistance against the jet impingement on the surface of the coatings. Analysis of variance, the S/N ratio, and interaction plots were used to determine the optimal bath input parameters to deliver the least weight loss from the erosive environment and identify its use in the marine environment. The proposed optimal coating was validated using a confirmation test, and the weight loss was reduced by more than 35% compared to the initial condition parameter (A2B2C2D2). In addition to mechanical properties, the quality of the deposits was analysed through morphological and chemical composition probed through scanning electron microscope, energy dispersive X-Ray analysis and powder X-Ray diffraction methods. As a result, the Composite Modified Resilience (CMR) value of ENi-P-TiO2 optimal coating was improved by over 41.17%, and its corresponding weight loss was reduced to 35% compared to the initial condition. This experiment paves the way for further study on electroless deposits and their characteristics on AH36 steel generally used for shipbuilding in commercial ships, naval, and marine associated defence applications. [ABSTRACT FROM AUTHOR]

Leadless pacemakers have been developed with key advantages over traditional transvenous pacemakers by substantially mitigating the risks of device infection and lead related complications, and providing an alternative pacing strategy in patients with barriers to superior venous access. The Medtronic Micra leadless pacing system is designed for implantation through a femoral venous approach across the tricuspid valve, via Nitinol tine fixation into the trabeculated subpulmonic right ventricle. Patients with surgically corrected dextro-transposition of the great arteries (d-TGA) have an increased risk of pacing requirement. There is limited published experience of implantation of leadless Micra pacemakers in this population, with key challenges relating to trans-baffle access, and deployment of the device into the less trabeculated subpulmonic left ventricle. Here we describe a case report of leadless Micra implantation in a 49 year old male with d-TGA and Senning procedure in childhood, who required pacing for symptomatic sinus node disease, with anatomic barriers to transvenous pacing. Micra implantation was successfully performed following careful consideration of patient anatomy, including the utilisation of 3D modelling to guide the implantation procedure. [ABSTRACT FROM AUTHOR]

Porous NiTi alloys were obtained by self-propagating high-temperature synthesis (SHS) using layer-by-layer combustion in closed and open gas flow reactors under a protective argon atmosphere. The maximum compressive strain of porous NiTi alloys synthesized in the closed reactor was 34% compared to 7% in the open gas flow reactor. X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, energy dispersive spectroscopy, and optical microscopy showed that the reaction products in the two-phase gas zone of peritectic crystallization are in the form of isolated Ti2Ni crystalline clusters in the TiNi matrix. The ductility and strength of the recrystallized Ti2Ni phase hard dendrites increase the effective stiffness of porous NiTi alloys and decrease the maximum compressive strain. A highly porous NiTi alloy with improved mechanical properties was obtained by the SHS method in a closed reactor. [ABSTRACT FROM AUTHOR]

The temperature dependence of the critical stress of R→B19' transformation in NiTi shape memory alloys remains unclear due to the difficulties in precisely identifying the phase constitution and acquiring sole R phase. Here we investigate the thermally- and stress-induced martensitic transformation in a near-equiatomic nanocrystalline NiTi alloy. In situ synchrotron X-ray diffraction is used to identify the phase evolution such that the temperature window for sole R phase is firmly determined. We find that the temperature dependence of R→B19' is negative (−0.2 MPa/K) in our alloy, in sharp contrast to 3–5 MPa/K reported. Possible reasons for the discrepancies are discussed. Negative temperature-dependence of stress-induced R→B19' transformation was discovered for the first time in NiTi alloys, being in sharp contrast to previous reports. This calls for a revisit of such transformation. [ABSTRACT FROM AUTHOR]

In this study, we report an unconventional precipitation and martensitic transformation behaviour of directly aged Ni-rich NiTi alloys fabricated via laser-directed energy deposition (LDED). Ni4Ti3 particles precipitate uniformly under all ageing conditions and no traditional multiple-step martensitic transformations are observed. We conclude this unique behaviour to the intrinsic characteristics of the LDED technique, which are metastable microstructures and high residual stresses. On the one hand, these features make grain boundaries no longer a fevered location for precipitation and, on the other hand, significantly suppress the martensitic transformation when ageing at low temperatures (300°C/400°C). As the aging temperature increase (500°C), residual stresses release significantly, accompanied by the growth of Ni4Ti3 precipitates from several nanometres to 452 ± 181 nm with increased interparticle spacing. At the same time, reverse martensitic transformations change from two-step (B19' →R→B2) to single-step (B19' →B2). [ABSTRACT FROM AUTHOR]

The pursuit of enhancing NiTi superelasticity through laser powder bed fusion (L-PBF) and [001] texture creation poses a challenge due to increased susceptibility to hot cracking in the resulting microstructure with columnar grains. This limitation restricts NiTi's application and contributes to material waste. To overcome this, we introduce a pioneering approach: utilising spark plasma sintering (SPS) to heal directional cracks in [001] textured L-PBF NiTi shape memory alloy. Diffusion bonding and oxygen utilisation for Ti2NiOx formation was found to successfully heal the cracks. SPS enhances mechanical properties, superelasticity at higher temperatures, and two-way shape memory strain during thermomechanical cycling. This work provides an alternative solution for healing cracks in L-PBF parts, enabling the sustainable reuse of cracked materials. By implementing SPS, this approach effectively addresses hot cracking limitations, expanding the application potential of L-PBF NiTi parts while improving their functional and mechanical properties. [ABSTRACT FROM AUTHOR]

NiTi-Fe ternary shape memory alloys were produced by laser powder bed fusion (L-PBF) using the pre-alloyed NiTi and elemental Fe powders. A large process window exists to fabricate dense NiTiFe0.3 and NiTiFe0.5 alloys, while severe cracks occur in the NiTiFe2 alloy. The cracking susceptibility is studied through thermodynamic analysis. Fe is mainly dissolved in the NiTi matrix, which is mainly due to the low Fe addition and rapid cooling associated with L-PBF process. The martensite transformation temperatures (MTTs) decrease monotonously with the increase of scanning speed, the decrease of laser power, or the increase of Fe addition, providing a feasible approach to tailoring the MTTs. Due to the decrease of the MTTs, the NiTiFe0.3 and NiTiFe0.5 alloys show good superelasticity, e.g. the NiTiFe0.3 alloy shows a superelastic recoverable strain of 5.2% (pre-strain of 6%). This work suggests that L-PBF is a potential method to in-situ synthesise ternary NiTiFe alloys. [ABSTRACT FROM AUTHOR]

The ability to integrate multiple distinct properties into a single structure is the driving force behind the development of NiTi to Ti6Al4V dissimilar joints. However, differences in thermophysical properties and the subsequent development of brittle Ti2Ni and Ni3Ti intermetallic compounds (IMCs) make fusion welding of these alloys rather challenging. The solidification of brittle IMC causes cracking upon solidification and a significant reduction on the joint mechanical properties. In this study, two strategies were used concurrently to reduce the formation of brittle IMC: zirconium (Zr) interlayer was introduced alongside with the laser beam being offset to the Ti6Al4V side. The influence on microstructural evolution was investigated using various characterization techniques. Scanning electron microscopy aided by energy dispersive spectroscopy and micro-X-ray diffraction supported by Rietveld refinement revealed that the volume fraction of the Ti2Ni brittle phase was drastically reduced from 90 to 9%, leading to improvements on the joint mechanical performance. A joint with a lower hardness of 392 HV was obtained, compared to 515 HV for the conventional NiTi/Ti6Al4V joint. The strength and ductility of the Zr-interlayered joint were improved to 320 MPa and 1.7%, respectively, compared to 148 MPa and 0.8% for the Zr-free joint. [ABSTRACT FROM AUTHOR]

Nickel titanium (NiTi, or Nitinol) alloy is used in several biomedical applications, including cardiac, peripheral vascular, and fallopian tube stents. There are significant biocompatibility issues of metallic implants to nickel ions and nano-/micro-sized alloy particles. Our laboratories have recently shown that microscale CoCr wear particles from metal-on-metal hips crosslink with the innate immune signaling Toll-like receptor 4 (TLR4), prompting downstream signaling that results in interleukin (IL)-1β and IL-8 gene expression. In vivo, NiTi alloy can also generate wear particles on the nanoscale (NP) that have thus far not been studied for their potential to induce inflammation and angiogenesis that can, in turn, contribute to implant (e.g. stent) failure. Earlier studies by others demonstrated that nickel could induce contact hypersensitivity by crosslinking the human, but not the mouse, TLR4. In the present work, it is demonstrated that NiCl2 ions and NiTi nanoparticles induce pro-inflammatory and pro-angiogenic cytokine/chemokine expression in human endothelial and monocyte cell lines in vitro. These observations prompt concerns about potential mechanisms for stent failure. The data here showed a direct correlation between intracellular uptake of Ni2+ and generation of reactive oxygen species. To determine a role for nickel and NiTi nanoparticles in inducing angiogenesis in vivo, 1-cm silicone angioreactors were implanted subcutaneously into athymic (T-cell-deficient) nude mice. The angioreactors contained Matrigel (a gelatinous protein mixture that resembles extracellular matrix) in addition to one of the following: PBS (negative control), VEGF/FGF-2 (positive control), NiCl2, or NiTi NP. The implantation of angioreactors represents a potential tool for quantification of angiogenic potentials of medical device-derived particles and ions in vivo. By this approach, NiTi NP were found to be markedly angiogenic, while Ni2+ was less-so. The angioreactors may provide a powerful tool to examine if debris shed from medical devices may promote untoward biological effects. [ABSTRACT FROM AUTHOR]

Finite element simulation is used to analysis stent designs, extension as well as interaction between a stent and a vessel. In this paper, two different stents with different geometries have been simulated. One is Zilver stent and the other one is Navalis stent. The aim of this study is to determine the effect of stents deployment with various designs that are made of shape memory alloy (SMA) on the distribution of vessel wall stresses by using computational modeling approach. The constitutive model which described the behavior of SMA is based on Microplane model. In addition, SMA stents have been simulated under torsion loading to compare the flexibility of various designs under different conditions. The superelastic behavior and shape memory effect of SMA stents are investigated in this paper. The numerical simulation results show the different geometries of stents have significant effect on the arterial wall. The results show the Navalis stent causes less stress on the arterial wall and it is more flexible than the Zilver stent under the same torsion loading. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is an orderly construction process involving track-by-track melt pools, which can modulate three characteristic zones between two adjacent melt pools: the heat-affected zone, transition zone, and cellular grain zone. These three zones constitute a function domain that determines the properties of AM metallic materials. In this study, we constructed a novel ordered function domain by AM of modified Ni50.6Ti49.4 shape memory alloy powder, which was produced by adding uniform Ni nanoparticles into atomised Ni49.6Ti50.4 powder. Interestingly, the three zones of the function domain had the same B2 austenite matrix but inhomogeneous Ni4Ti3 clusters and Ti2Ni nanoprecipitates, which caused different compressive recovery and residual strains in the three zones. The synergetic effect of the three zones generated a stable recovery strain and small hysteresis area in the AMed Ni50.6Ti49.4. Our results provide a novel strategy for modulating the microstructure of NiTi by AM to yield superior properties. [ABSTRACT FROM AUTHOR]

The number of defects is the key indicator that affects the properties of the NiTi alloy fabricated by SLM and can be adjusted by the energy density. In this study, the NiTi alloy was manufactured by varying the laser power from 50 to 95 W and matching the scanning speed of 200 to 900 mm/s at the hatch spacing of 80 and 110 μm. The results showed that the energy density for manufacturing high relative density (~99.5%) NiTi alloy was related to the laser power and was in the range of 45 to 70 J/mm3. Such 'optimal energy density' gradually decreased with the laser power or hatch spacing increasing. The results of XRD and DSC revealed that when the NiTi alloy was fabricated with low laser power and small hatch spacing induced the shape memory characteristics of heat recovery prominent. Instead, when the NiTi alloy was manufactured with high laser power and large hatch spacing, it would be superelasticity. [ABSTRACT FROM AUTHOR]

The increasing number of studies on the behaviour of stent placement in recent decades provides a clear understanding of peripheral artery disease (PAD). The severe mechanical loads (axial tension and compression, bending, radial compression and torsion) deformation of the femoropopliteal artery (FPA) is responsible for the highest failure rate of permanent nickel-titanium (Nitinol) stents. Therefore, the purpose of this article is to review research papers that examined the deformation of the natural load environment of FPA, the properties of Nitinol and mechanical considerations. In conclusion, a better understanding of mechanical behaviour for FPA Nitinol stents contributes to increased mechanical performance and fatigue-life. [ABSTRACT FROM AUTHOR]

The role of damage in the degradation of tensile properties related to a stress-induced martensite transformation in a hydrogen-charged Ni–Ti superelastic alloy has been investigated. By damage, we mean vacancy clusters and dislocation structures induced in advance by a dynamic interplay between hydrogen and the martensite transformation. To homogenise the hydrogen concentration, the specimen was aged at room temperature after charging with a small amount of hydrogen (approximately 30 mass ppm). In this case, no fracture occurs within 2000 cycles during a cyclic tensile deformation test in the stress plateau region generated by stress-induced martensite and reverse transformations. With this hydrogen concentration, cyclic interplay between hydrogen and the martensite transformation scarcely leads to the degradation of tensile properties. Nevertheless, following cyclic martensite transformations before aging that induces pre-damage, fracture occurs after around 1000 cycles under a cyclic tensile deformation test despite the hydrogen concentration being the same. The present results clearly indicate that pre-damage induced by hydrogen affects the subsequent transformations, thereby causing the self-multiplication of damage, which degrades the tensile properties. [ABSTRACT FROM AUTHOR]

Machining of Nitinol alloy is complicated by the traditional process due to severe strain hardening and low thermal conductivity, which prompts high tool wear and indigent surface quality. Wire Electro Discharge Machining (WEDM) has been most commonly used for machining Nitinol alloy. In this paper, the effect of input attributes such as pulse on time (Ton), pulse off time (Toff), peak current (Ipeak) and voltage (V) on metal removal rate (MRR) and surface roughness (SR) during WEDM of Nitinol alloy have been investigated. Experiments were conducted according to central composite design (CCD) of response surface methodology (RSM). Analysis of variance (ANOVA) was used for studying the effect of input attributes and their interactions. It is perceived that at smaller values, Ton and Ipeak are more significant attributes for improving the MRR and surface finish. The optimum conditions are obtained for minimising surface roughness and maximising MRR using RSM and Desirability analysis. Confirmation test was conducted with optimum input attributes where the estimated values of the output attributes were contrasted with the experimental results. It was established that the experimental and the estimated values are in very close agreement. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the effect of the size variation of the mandibular dental arch on the magnitude and direction of orthodontic forces delivered by a variety of commercially available preformed rectangular Ni-Ti archwires. The means and standard deviations (SDs) of intercanine and intermolar widths and the means of dental arch depths at the canines and first molars were established based on our previous studies of subjects with untreated normal occlusions. The mandibular dental arch of a multi-sensor measuring system was adjusted to the mean, enlarged to +1SD and reduced to −1SD sizes of the normal dental arch. Fifty-nine types of 0.019 × 0.025-inch NiTi archwires were selected, and the intercanine and intermolar widths of the archwires were measured. Delivered forces were measured at the central incisors, canines, and first molars for each dental arch condition. Significant correlations were found between archwire width and forces at all examined teeth for all dental arch widths. Significantly greater facial direction forces were delivered at the central incisor for the large dental arch condition than for the small and mean dental arch conditions. Significantly greater facial direction force was delivered at the canines for the small dental arch than for the large dental arch condition. Possible risks of clinically significant magnitudes of orthodontic force in the facial direction at the central incisors and canines were observed when using preformed rectangular NiTi archwires for patients with relatively large and small dental arches, respectively. [ABSTRACT FROM AUTHOR]

In this work, Ni-Ti shape-memory alloy (SMA) plates were laser welded using different laser powers. A systematic trend of decreasing deterioration in nanomechanical properties – including superelastic recovery – from the weld centre, through the interface region and the heat-affected zone to the base–metal regimes has been observed. The extent of the deterioration increases with increasing laser power. The observations are explained in terms of a decreasing cooling rate and increasing austenite finish temperature (Af) with an increase in laser power. [ABSTRACT FROM AUTHOR]

Purpose: To compare surgery's effect with nitinol flex loop (NFL) or forceps on retinal layers and functional outcomes in the primary epiretinal membrane (ERM). Methods: The operations were classified according to the use of the NFL or forceps. Automatic segmentation of the individual inner retinal layers was performed by spectral-domain optical coherence tomography software, and best-corrected visual acuity (BCVA) before surgery and at the last follow-up visit postoperatively were compared. Results: Forty-two eyes of 42 patients were included with a mean age of 66.9 ± 5.7 years. 45.2% of the surgeries were NFL assisted, 54.8% were forceps assisted. The mean follow-up duration was 9.8 ± 1.3 months. The mean BCVA was 0.79 ± 0.42 vs 0.77 ± 0.39 logMAR in the preoperative period and 0.42 ± 0.27 vs. 0.40 ± 0.21 logMAR at last follow-up in the NFL vs forceps group respectively (p=.403). The retinal nerve fiber layer (RNFL)(32.5% vs. 50.1%, p=.009), ganglion cell layer (18.1% vs. 41.4%, p=.021), inner plexiform layer (13.5% vs. 32.7%, p=.031) and inner nuclear layer (15.5% vs. 30.3%, p=.011) thickness decreased significantly more in the forceps group. The mean surgical time was not significantly different (45.2 ± 5.1 vs. 51.1 ± 6.1 minutes) in the NFL vs. forceps groups, respectively (p=.331). Conclusion: Following primary ERM surgery, the inner retinal layers become thinner; RNFL impacted the most, which was found higher in forceps assisted surgeries. This result shows that the NFL can be used safely in macular surgery. [ABSTRACT FROM AUTHOR]

Shape memory alloy (SMA), also called memory metal, is a smart material that exhibits unique shape memory effect and superelasticity properties. NiTi alloys attract researchers because of their myriad applications in areas such as aerospace, medicine, and robotics. In the present NiTi SMA fabrication, the Cu and Zr elements were added to increase the martensitic transformation temperatures. The current study focuses on the machining of high-temperature Ni44Ti50Cu4Zr2 SMA by coated wire electric discharge machining (W-EDM). Machining quality features like surface undulation and material removal were studied by considering current (I), servo voltage (SV), pulse on time (Ton), angle of cut (AC), and pulse off time (Toff). Parametric analysis of machining characteristics has been investigated by conducting experiments following the response surface approach based central composite design (RSM-CCD). It was found that MRR has increased by 57% and Ra by 58% with a gradual increase in pulse on time and applied current and decreases gradually on increasing servo voltage and pulse off time. XRD analysis reveals the presence of an oxide layer on the wire-EDMed surface. The study of SEM confirms the formation of the melted layer, micro-voids, and micro-cracks, resulting in surface irregularities. [ABSTRACT FROM AUTHOR]

NiTi thin sheets were ultrasonic spot welded with a Cu interlayer, where different welding vibration amplitudes were applied to study the influence on the surface and interface microstructural characteristics, phase transformation behavior and mechanical response of the joints, which aimed to enhance the joint performance by proper optimization of the process parameters. An excellent bonding interface was achieved when an optimized vibration amplitude was applied, with a recrystallized microstructure formed in the Cu foil side near the bonding interface, which helped to improve the mechanical performance of the joints. Joints made with vibration amplitude of 55 μm had an improved strength compared to the NiTi base material. [ABSTRACT FROM AUTHOR]

A hierarchical microstructure was obtained, including the unique interlaced dual-phase structure, the solidified molten pool, the coarse columnar B2 grains and fine equiaxed B19' grains, and a great many nanoparticles, during laser powder bed fusion (LPBF) of NiTi alloys. The effect of laser processing parameter on the growth of nanoparticles was assessed. A combination of low laser power and high scanning speed was conducive to the formation of fine granular nanoparticles with a more uniform distribution. Subsequently, effects of rotation angle between adjacent layers on the compressive deformation behaviour of LPBF-processed NiTi alloys were studied. At a small rotation angle (6–36°), the samples could exhibit an excellent combination of high compressive fracture strength and ductility (e.g. 3094 MPa/39.85%). Meanwhile, samples with small rotation angle tended to get a large strain span for the martensite transformation stage and a large deformation capacity (e.g. 4.64% and 9.25% for θ = 6° and σmax = 800 MPa). [ABSTRACT FROM AUTHOR]

The difference in wear behavior of superelastic NiTi and conventional Ti6Al4V alloys with similar elastic limits was investigated. Reciprocating dry sliding wear tests were performed with a ball-on-plate tribometer at different normal loads and sliding times. Mechanical properties were also examined using different microindentation tests, and wear track morphologies and chemical compositions in the scar area were characterized by scanning electron microscopy (SEM) and energy-dispersive spectrometry. Superelasticity of the NiTi alloy was significantly beneficial to its tribological properties, and the wear resistance of the NiTi alloy was up to 40 times higher than that of the Ti6Al4V alloy. Such a significant difference cannot be attributed only to the relatively small difference in hardness (H) or H/E ratios (E = elastic modulus) of the materials but, rather, to a difference in strain energy, which dissipates in the material and results from normal load of the sliding ball. To estimate this energy, spherical microindentation tests in the wear scar were carried out. Understanding the difference between the tribological behavior of the NiTi shape memory alloy and conventional Ti6Al4V material provides insight into wear progression, and an investigation of its mechanisms can effectively prevent the destruction of components, prolonging their safe service life. [ABSTRACT FROM AUTHOR]

Dynamic environmental loads, such as winds and waves, make the stability of offshore structures at high risk, requiring reliable yet efficient control elements to ensure the stability of such structures under lateral loads. Among the variety of control elements that have been developed to enhance the stability of a structure, shape memory alloy (SMA)-based control elements are promising as they are low-cost, easy to embed into the main control element, and do not need an external power supply. However, cyclic loads may highly influence the performance and functionality of SMA-based elements. The present work investigates the effects of pre-straining SMA components in energy dissipation capacity and its force-displacement behaviour under cyclic loads. The results of experimental tests show that pre-straining SMA by 1.7% significantly reduces the residual deformation and increases the energy dissipation capacity of structures under the short and long-term cyclic loads. [ABSTRACT FROM AUTHOR]

In this manuscript, Electrochemical Micromachining (ECM) is well designed with the important concept called scale effect. The main objective is to evaluate the scale effects that occur when the machining parameters is transferred from micro ECM to macro ECM. Similarity theory is used to evaluate the scale effects quantitatively. Input process parameters such as feed rate, duty ratio and voltage are taken and designed as single factor orthogonal experiments to evaluate the scale effect occurred by response parameters such as Material removal rate (MRR) and geometrical features. Utilization of this concept provides improvement in the machining performances, reduction in the energy involved and also useful in optimizing the processing parameters. The similarity precision of the micro and macro systems is calculated. A positive scale effect is observed when the output values of MRR and geometrical features are normalized. No negative scale effect is observed in experimental results. [ABSTRACT FROM AUTHOR]

Isothermal compression tests of NiTi shape-memory alloy (NiTi SMA) were carried out on a Gleeble-3800 thermal simulating tester in the temperature range 750–1050°C and strain rates of 0.005–10 s−1 with a deformation of 0.7. The mechanical behaviour characteristics and microstructure evolution during the hot compression process are the main items of study. The hot-processing maps under five different instability criteria (Prasad, Gegel, Malas, Murty, and Semiatin instability criteria) were constructed based on hot-compression experimental data and dynamic material model (DMM) theory. Suitable forming processing regions and flow instability regions of the NiTi SMA are predicted by the processing maps in the process of hot deformation. The results indicate that: the prediction for the alloy intersect and supplement each other because of the different theoretical basis of the above instability criteria. The prediction range of the above five instability criteria is verified by combining variation of strain-rate sensitivity exponent, microstructure characterisation and actual hot-deformation results in the process of hot deformation. The result predicted by the Prasad instability criteria is the most accurate for the alloy. Plastic flow bands and adiabatic shear cracks mainly occur in the flow-instability regions, while dynamic recovery (DRV) and dynamic recrystallisation (DRX) mainly occur in the processing regions. [ABSTRACT FROM AUTHOR]

To date, numerous attempts have been made to modify the surface condition of NiTi shape memory alloy to fully benefit from its desirable characteristics, and develop its potential clinical applications. In this survey, the Fenton oxidation process as a newly presented technique for surface modification of NiTi, was employed to address two major priorities in biomedical applications of NiTi, i.e. corrosion improvement and suppression of Ni ion release. To meet these priorities, two important variables involved in the Fenton oxidation process, namely immersion time and electrolyte temperature, were controlled. Results suggested that the application of such an oxidation process may considerably improve the corrosion behaviour of NiTi. The Fenton oxidation process carried out at 65°C for 24 h yields the lowest corrosion current density, 74% lower than bare NiTi. Additionally, Ni ion releases from the surface of NiTi after Fenton's oxidation decreases by ∼97%. [ABSTRACT FROM AUTHOR]

The isothermal bainite transformation in low-carbon low-alloy steel under direct and step-quenching conditions have been investigated in the present work. Varying quantities of prior bainite and prior martensite were formed separately by quenching above and below M s temperature to understand their effects on the extent and kinetics of subsequent bainite transformation in B s − M s regime. Formation of prior bainite at higher temperature has been found to stabilise part of remaining austenite against subsequent bainite transformation at lower temperature showing thermal stabilisation of austenite. Hence, the total amount of bainite in two-step treatment is less than that obtained in single-step isothermal bainite transformation at the latter temperature, indicating the inapplicability of 'additivity rule' for continuously cooled bainite. A decrease in the bainitic ferrite plate volume due to higher strength of parent austenite and higher nucleation rate, together with limited number of bainite nucleation sites at the latter temperature are believed to be responsible for the thermal stabilisation of austenite. Prior martensite also stabilises part of remaining austenite against further bainite transformation through fragmentation of austenite grains and increased defect density in austenite. The kinetics of bainite transformation in each of the above-mentioned conditions have been analysed quantitatively using an established model and the results are correlated with the microstructures. [ABSTRACT FROM AUTHOR]

Thermal switches control thermal circuits and are widely used in electronics and engineering. Shape-memory alloys can be deformed by heating, which is widely used as a driving part for thermal switches by many research groups. Shape-memory alloys are inappropriately used in thermal switches as the heat transfer components because of their lower thermal conductivity. Components responsible for the heat transfer and driving are usually separated from each other inside the device. Such design increases the complexity of the device and its production cost. By combining high thermal conductivity and self-driving properties of the shape-memory alloys, the structure of the thermal switch can significantly not only simplify its design but also can improve its performance. In this paper, we implemented two-way memory alloy as the drive device. Graphene paper was used to cover the surface of the memory alloy. Self-actuation of the shape-memory alloy and high thermal conductivity of graphene enhance heat conduction of the switch. The resulting device has a simple structure, is flexible, stable and easy to operate. We thoroughly studied structure and working principle of this thermal switch. Both simulations and experimental tests were performed to analyze thermal conductivity of the switch. We obtained a switch ratio equal to 54.0 ± 24.3. Our thermal switch is very promising for the advanced thermal management of the electronic devices. [ABSTRACT FROM AUTHOR]

In the present work, the results of the research gas discharge lamp constructive elements those made from niobium and zirconium alloy, sealing by means of melting titanium with its alloy with nickel are presented. It is performed construction peculiarities analysis of gas discharge lamp with sapphire shell. The requirements to sealing materials are formed. It is studied physical and chemical processes occurring in materials during lamp sealing and lifetime. [ABSTRACT FROM AUTHOR]

Sustainability is a concept which is widely considered nowadays, including in factories where machining operations are present. The search for methods able to improve the performance of industrial processes without damaging the environment or the worker's health has been the main goal of several investigations. In this context, cryogenic machining is a technique that has been studied as an alternative to the use of mineral oil-based cutting fluids, mainly in the machining of titanium and nickel alloys. Investigations on the cryogenic machining of hard tool steels are still scarce in the literature. This article presents results from a series of turning trials under dry and cryogenic conditions using a hardened AISI D6 tool steel bar (57 HRC) as the workpiece. For the cryogenic machining tests, liquid nitrogen was delivered to the flank face, rake face and on both faces of PCBN inserts. The main cutting parameters (cutting speed, feed rate, and depth of cut) were kept constant during the trials. Tool wear and chip morphology were the output variables studied. The results show that the liquid nitrogen was able to reduce the cutting tool wear, providing a tool lifetime around 50% longer compared with the dry process. Moreover, the frequency of chip segmentation was diminished under cryogenic conditions in comparison with the dry process. [ABSTRACT FROM AUTHOR]

Sustainability is a concept which is widely considered nowadays, including in factories where machining operations are present. The search for methods able to improve the performance of industrial processes without damaging the environment or the worker's health has been the main goal of several investigations. In this context, cryogenic machining is a technique that has been studied as an alternative to the use of mineral oil-based cutting fluids, mainly in the machining of titanium and nickel alloys. Investigations on the cryogenic machining of hard tool steels are still scarce in the literature. This article presents results from a series of turning trials under dry and cryogenic conditions using a hardened AISI D6 tool steel bar (57 HRC) as the workpiece. For the cryogenic machining tests, liquid nitrogen was delivered to the flank face, rake face and on both faces of PCBN inserts. The main cutting parameters (cutting speed, feed rate, and depth of cut) were kept constant during the trials. Tool wear and chip morphology were the output variables studied. The results show that the liquid nitrogen was able to reduce the cutting tool wear, providing a tool lifetime around 50% longer compared with the dry process. Moreover, the frequency of chip segmentation was diminished under cryogenic conditions in comparison with the dry process. [ABSTRACT FROM AUTHOR]

An interstitial solute strengthened high entropy alloy (iHEA), Fe49.5Mn30Co10Cr10C0.5 (at.%), was successfully additively manufactured via selective laser melting. The as-built iHEA exhibits a hierarchically heterogeneous microstructure with length scales across several orders of magnitude, which engenders an enhanced strength–ductility combination relative to those fabricated by conventional processing routes. The high yield strength mainly stemmed from the dislocation strengthening besides the friction stress and grain boundary strengthening. The joint activation of multiple deformation mechanisms involving dislocation slip, deformation twinning and phase transformation can maintain the steady work-hardening behavior at high stress levels, leading to a high ductility. A hierarchical interstitial high entropy alloy, Fe49.5Mn30Co10Cr10C0.5 (at.%), was successfully additively manufactured via selective laser melting. Its exceptional strength–ductility synergy surpasses that of the most SLM processed conventional alloys. [ABSTRACT FROM AUTHOR]