Desirable Mechanical Properties Research Articles

Development of an antibacterial and antioxidative nanofibrous membrane using curcumin-loaded halloysite nanotubes for smart wound healing: In vitro and in vivo studies

Endowing wound dressings with drug delivery capability is a suitable strategy to transfer medicinal compounds locally to damaged skin layers. These dressings are especially useful for accelerating the healing rate in the cases of long-term treatment, and adding more functionalities to the platform. In this study, a wound dressing composed of polyamide 6, hyaluronic acid, and curcumin-loaded halloysite nanotubes (PA6/HA/HNT@Cur) was designed and fabricated for wound healing applications. The physicochemical properties of this platform were investigated through Fourier-transform infrared spectroscopy and field-emission scanning electron microscopy. Moreover, wettability, tensile strength, swelling, and in vitro degradation were assessed. The HNT@Cur was incorporated in the fibers in three concentrations and 1 wt% was found as the optimum concentration yielding desirable structural and mechanical properties. The loading efficiency of Cur on HNT was calculated to be 43 ± 1.8%, and the release profiles and kinetics of nanocomposite were investigated at physiological and acidic pH. In vitro antibacterial and antioxidation studies showed that the PA6/HA/HNT@Cur mat had strong antibacterial and antioxidation activities against gram-positive and -negative pathogens and reactive oxygen species, respectively. Desirable cell compatibility of the mat was found through MTT assay against L292 cells up to 72 h. Finally, the efficacy of the designed wound dressing was evaluated in vivo; after 14 days, the results indicated that the wound size treated with the nanocomposite mat significantly decreased compared to the control sample. This study proposed a swift and straightforward method for developing materials that might be utilized as wound dressings in clinical settings.

Effect of cooling rate on microstructure and mechanical properties of AlCrFe2Ni2 medium entropy alloy fabricated by laser powder bed fusion

The mechanical properties and serviceability of the alloy fabricated by laser powder bed fusion (L-PBF) additive manufacturing (AM) strongly depend on the phase composition and microstructure, which are affected by the thermal condition of the process, such us cooling rate. In this study, AlCrFe2Ni2 medium entropy alloy (MEA) was fabricated by L-PBF under varying cooling rate via changing process parameters. The phase transformation, microstructure and mechanical properties were experimentally investigated using X-ray diffraction (XRD), scanning transmission electron microscopy (TEM), scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The cooling rate was numerically calculated using a well-tested multi-physic thermal fluid model. The results showed that cooling rate had a significant effect on phase composition, microstructure and mechanical properties. The as-built MEA with lower cooling rate showed a nano-size structure composed of BCC and ordered B2 phases and a higher yield strength of 2055 MPa. While for the higher cooling rate, the as-built MEA showed a homogeneous structure consisted of single ordered B2 phase and a lower yield strength of 1544 MPa. The threshold value of cooling rate for phase transformation was between 4.9 × 106 K/s and 6.0 × 106 K/s. Through the strengthening mechanism analysis, it was crucial to achieve the nano-size dual-phase microstructure by manipulating cooling for obtaininng desirable mechanical properties in L-PBF AMed AlCrFe2Ni2 MEA.

Synergistic effect of silica aerogel and titanium dioxide in porous polyurethane composite coating with enhanced passive radiative cooling performance

Passive daytime radiative cooling is a promising technology that can mitigate the increasing issues of global warming and urban heat island effects. In this work, a series of porous polyurethane (PPU) composite coatings containing silica aerogel (SA) and/or titanium dioxide (T) were prepared though a wet phase inversion method. The effects of the filler types on relevant properties of composite coatings, such as pore microstructure, radiative cooling, mechanical, and hydrophobic performances, were systematically investigated. The typical PPU-SA10@T10 composite coating showed an interleaving porous structure, and the incorporated SA and T fillers were uniformly stacked in the pore cavities. Taking advantages of the strong light-back scattering and molecular oscillation functions, the solar reflectance, thermal emittance in the atmospheric transparency window, and the net cooling power of the PPU-SA10@T10 coating reached 0.917, 0.973, and 87.8 W/m2, respectively, which results in a sub-ambient cooling of 7.8 °C at midday under a solar irradiance of ∼640 W/m2. Moreover, the PPU-SA10@T10 coating possessed well balanced mechanical properties and superior hydrophobicity (water contact angle was 121.7°). The present work provides a viable way for developing radiative cooling coating with desirable mechanical properties and water-repellency.

Construction and In Vitro Evaluation of Collagen/Bioactive Glass Composite Membranes as a Corneal Implant

Collagen (Col), the major component of native cornea, has been extensively employed for constructing corneal repair materials. However, inflammation impacts the process of corneal repair, even leading to transplant failure. Bioactive glass (BG) exhibits an excellent anti-inflammatory effect and immunomodulatory function in soft tissue repair. Herein, in this study, the potential of incorporating BG into collagen-based membranes for corneal repair was explored. BG was incorporated at 1, 5, and 7 wt %. The physicochemical properties of the membranes were determined, and in vitro cell-based analyses were also conducted. The results revealed that the Col-BG membranes exhibited desirable light transmission properties, mechanical properties, and good biocompatibility, which meet the requirements of a corneal substitute. Furthermore, Col membranes with 5 and 7% ratio of BG effectively induced corneal epithelial cell adhesion and migration. The Col-BG membranes displayed anti-inflammatory effects as confirmed via polymerase chain reaction and enzyme-linked immunosorbent assay (ELISA) analysis. Among the different BG concentrations tested, the Col-BG membrane containing 5 wt % BG displayed the most favorable combination of physical and biological properties in vitro. Thus, this study described a corneal repair material and provides evidence regarding the feasibility of using Col-BG membranes for corneal repair.

Fiber reinforced sulphoaluminate cementitious composites: Mechanical properties and comprehensive evaluation method

The rapid repair of concrete structures is an important research subject, which has attracted the attention of engineers at home and abroad. Here, an early-strength and strain, fast-setting and fast-hardening cementitious composite named as fiber reinforced sulphoaluminate cementitious composites (FRSACC)was developed. The mechanical properties of FRSACC were investigated through a series of experiments, including compressive strength, flexural strength, uniaxial tensile performance, four-point bending performance, three-point bending fracture, and microstructure analysis. The results indicated that these properties were influenced by the curing age, water to binder (W/B) ratio, sand to binder (S/B) ratio, and fly ash (FA) dosage. To be specific, the W/B ratio plays a vital role in achieving desirable mechanical properties at early curing stage, followed by the FA dosage and the S/B ratio. In addition, a facile six-dimensional representation was proposed to assess the overall performance of FRSACC. This comprehensive evaluation method can also be used for other cementitious composites to evaluate and select the better mixture ratio based on mechanical properties, bending toughness and fracture toughness.

Cytotoxic Properties of Polyurethane Foams for Biomedical Applications as a Function of Isocyanate Index.

Polyurethane foams are widely used in biomedical applications due to their desirable mechanical properties and biocompatibility. However, the cytotoxicity of its raw materials can limit their use in certain applications. In this study, a group of open-cell polyurethane foams were investigated for their cytotoxic properties as a function of the isocyanate index, a critical parameter in the synthesis of polyurethanes. The foams were synthesized using a variety of isocyanate indices and characterized for their chemical structure and cytotoxicity. This study indicates that the isocyanate index highly influences the chemical structure of polyurethane foams, also causing changes in cytotoxicity. These findings have important implications for designing and using polyurethane foams as composite matrices in biomedical applications, as careful consideration of the isocyanate index is necessary to ensure biocompatibility.

Effect of O addition on microstructure and mechanical properties of Ti-Nb alloys with various β stability

To study the effect of O on β-Ti alloys with various β phase stability, Ti–xNb–0.4O (x = 30, 32, 34, 36, 38, 40, 42, mass%) alloys were prepared by arc melting followed by homogenization, hot rolling, and solution treatment. To ensure the O content of the alloys, melting and hot rolling were performed under an Ar atmosphere, and homogenization and solution treatment were performed under vacuum conditions. The mass fractions of O in the Ti–Nb–O alloys were finally accurately controlled in the range of 0.4–0.5%. The phase composition of the alloys was determined by analyzing the X-ray diffraction patterns, the microstructure was observed by optical microscopy, and the mechanical properties were measured by tensile tests. The ω phase and α" phase were found in the solution-treated Ti–30Nb–0.4O. Ti–30Nb–0.4O showed the lowest yield strength owing to the existence of the α" phase. O suppressed ω phase and α" phase transformations during quenching, and showed an obvious solution-strengthening effect. Because the O content of the alloys was essentially the same, the Ti–xNb–0.4O alloys showed similar tensile strengths. The Young's moduli of the alloys ranged from 60 to 69 GPa, and the elongations were all higher than 15%. Particularly, Ti–36Nb–0.4O exhibited desirable mechanical properties, including a Young's modulus of 61 GPa, a tensile strength of 760 MPa, and an elongation of approximately 35%.

Correlation of microstructure and tensile properties in in-situ high-entropy bulk metallic glass composites

To investigate the ‘structure-property’ correlation in the high-entropy bulk metallic glass composites (HE-BMGCs), a series of in-situ dendrites-reinforced Zr28Ti19Hf19Nb9.5Co5.5Be19 HE-BMGCs containing different microstructures are fabricated by varying the cooling rate (R). The underlying correlation between microstructure characteristics of dendrites and tensile properties of HE-BMGCs are elucidated by the postmortem microstructure observation and fracture analysis. The critical investigation shows the volume fraction (Vd), size (δ) and arm diameter (d) of dendrite increase with decreasing R, whereas the interdendritic spacing (λ) decreases correspondingly. The larger d is more beneficial to enhance the back-stress-induced hardening effect of HE-BMGCs, while the strengths of all the HE-BMGCs are negative linear correlation with their Vd (56∼70%). Besides, the finer δ matches the size of ‘plastic zone’ associated with larger λ, which results in higher tensile ductility (∼6.4%). Therefore, the combination of finer δ and appropriate Vd at higher R is favorable for HE-BMGCs to obtain better ductility and higher strength. Our findings provide an important implication for the microstructural optimization of HE-BMGCs with desirable mechanical properties.

PDMS‐silica composite gas separation membranes by direct ink writing

AbstractPolydimethylsiloxane (PDMS)‐based membranes containing amine‐functionalized and unfunctionalized silica particles were fabricated via direct ink writing for CO2/N2 gas separation. The printability of the inks was evaluated by rheological measurements, while spectroscopy, microscopy, thermal measurements, and mechanical testing were employed to characterize the printed membranes. The surface morphology of the membranes revealed the absence of voids, demonstrating their suitability for gas separation. The printed membranes also exhibited desirable thermal and mechanical properties (i.e., thermal degradation temperature of 518 °C and tensile strength as high as 1.178 MPa with 529% elongation). The PDMS‐based membranes generally displayed high permeability for CO2 but slightly low selectivity for the CO2/N2 gas pair. The best‐combined permeability‐selectivity performance of 8794 barrer and selectivity of 11.64 was demonstrated by the printed PDMS membrane containing no SiO2 fillers. The inclusion of unfunctionalized SiO2 particles generally increased the membrane's gas permeability but compromised the selectivity. In contrast, membranes with amine‐functionalized silica showed improved selectivity compared to membranes containing unfunctionalized silica. Overall, the performance and characteristics offered by the PDMS/silica composite membranes demonstrated the potential of 3D printing as an economical and sustainable fabrication approach to developing materials for carbon capture applications.

Enhanced interfacial interaction, mechanical properties and thermal stability of basalt fiber/epoxy composites with multi-scale reinforcements

ABSTRACT In this work, epoxy (EP) resin composites with multi-scale reinforcements were prepared by hand lay-up and hot-pressing. The epoxy was reinforced with basalt fibers (BF) modified with a silane coupling agent (KH560). Carboxylated multi-walled carbon nanotubes (CNTs) were also grafted onto the surface of the modified BF using an impregnation method to achieve BF/CNTs multi-scale reinforcement. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) showed that KH560 was successfully grafted onto the BF surface. Scanning electron microscopy (SEM), indicated a better resin adhesion on the BF and thus a stronger interfacial interaction in the BF/CNTs-reinforced composite. It was observed that the mass fraction of KH560 was a significant parameter in achieving desirable CNT immobilization and mechanical properties of the composites. At an optimal mass fraction of KH560 (5%), the tensile, flexural, and interlaminar shear strength (ILSS) of the modified composite (BF-5%KH560-CNT/EP) increased by 12.5%, 20.9%, and 25.5% respectively compared with the BF-washed/EP composite due to more efficient load transfer. In addition, compared with BF-washed/EP, the decomposition onset temperature of BF-5%KH560-CNT/EP increased from 387°C to 396°C, the maximum decomposition rate temperature increased from 400°C to 408°C, and the residual weight increased by 5.8%.

A conductive multifunctional hydrogel dressing with the synergistic effect of ROS-scavenging and electroactivity for the treatment and sensing of chronic diabetic wounds

Chronic diabetic wound with persistent inflammatory responses is still a serious threat to human health and life. Ideal wound dressings can be applied not only for covering the injury area, but also for regulating the inflammation to accelerate the wound healing and long-term monitoring of wound condition. However, there remains a challenge to design a multifunctional wound dressing for simultaneous treatment and monitoring of wound. Herein, an ionic conductive hydrogel with intrinsic reactive oxygen species (ROS)-scavenging properties and good electroactivity was developed for achieving the synergetic treatment and monitoring of diabetic wounds. In this study, we modified dextran methacrylate with phenylboronic acid (PBA) to prepare a ROS-scavenging material (DMP). Then the hydrogel was constructed by phenylboronic ester bonds induced dynamic crosslinking network, photo-crosslinked DMP and choline-based ionic liquid as the second network, and the crystallized polyvinyl alcohol as the third network, realizing good ROS-scavenging performance, high electroactivity, durable mechanical properties, and favorable biocompatibility. In vivo results showed that the hydrogel combined with electrical stimulation (ES) demonstrated good performance in promoting re-epithelization, angiogenesis and collagen deposition in chronic diabetic wound treatment by alleviating inflammation. Notably, with desirable mechanical properties and conductivity, the hydrogel could also precisely monitor movements of human body and possible tensile and compressive stresses of the wound site, providing timely alerts of excessive mechanical stress applied to the wound tissue. Thus, this “all-in-one” hydrogel exhibits great potential in constructing the next generation flexible bioelectronics for wound treatment and monitoring. Statement of significanceChronic diabetic wounds characterized by overexpressed reactive oxygen species (ROS) are still a serious threat to human health and life. However, there remains a challenge to design a multifunctional wound dressing for simultaneous wound treatment and monitoring. Herein, a flexible conductive hydrogel dressing with intrinsic ROS-scavenging properties and electroactivity was developed for the combined treatment and monitoring of the wound. The antioxidant hydrogel combined with electrical stimulation synergistically accelerated chronic diabetic wound healing by regulating oxidative stress, alleviating inflammation, promoting re-epithelization, angiogenesis and collagen deposition. Notably, with desirable mechanical properties and conductivity, the hydrogel also presented great potential in monitoring possible stresses of the wound site. The “all-in-one” bioelectronics integrating the treatment and monitoring functions present great application potential for accelerating chronic wound healing.

Investigation of Pre-Aged Hardening Single-Point Incremental Forming Process and Mechanical Properties of AA6061 Aluminum Alloy.

Currently, the single-point incremental forming process often faces issues such as insufficient formability of the sheet metal and low strength of the formed parts. To address this problem, this study proposes a pre-aged hardening single-point incremental forming (PH-SPIF) process that offers several notable benefits, including shortened procedures, reduced energy consumption, and increased sheet forming limits while maintaining high mechanical properties and geometric accuracy in formed components. To investigate forming limits, an Al-Mg-Si alloy was used to form different wall angles during the PH-SPIF process. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) analyses were conducted to characterize microstructure evolution during the PH-SPIF process. The results demonstrate that the PH-SPIF process can achieve a forming limit angle of up to 62°, with excellent geometric accuracy, and hardened component hardness reaching up to 128.5 HV, surpassing the strength of the AA6061-T6 alloy. The DSC and TEM analyses reveal numerous pre-existing thermostable GP zones in the pre-aged hardening alloys, which undergo transformation into dispersed β" phases during the forming procedure, leading to the entanglement of numerous dislocations. The dual effects of phase transformation and plastic deformation during the PH-SPIF process significantly contribute to the desirable mechanical properties of the formed components.

Optimization of microfibrillated cellulose isolation from cocoa pod husk via mild oxalic acid hydrolysis: A response surface methodology approach

Theobroma cacao L. species, cultivated worldwide for its valuable beans, generates up to 72% weight of the fruit as waste. The lack of reutilization technologies in the cocoa agroindustry has hindered the exploitation of valuable bio-components applicable to the generation of high value added bioproducts. One such bioproduct is microfibrillated cellulose (MFC), a biopolymer that stands out for its desirable mechanical properties and biocompatibility in biomedical, packing, 3D printing, and construction applications. In this study, we isolated microfibrillated cellulose (MFC) from cocoa pod husk (CPH) via oxalic acid hydrolysis combined with a steam explosion. MFC isolation started with the Solid/Liquid extraction via Soxhlet, followed by mild citric acid hydrolysis, diluted alkaline hydrolysis, and bleaching pre-treatments. A Response Surface Methodology (RSM) was used to optimize the hydrolysis reaction at levels between 110 and 125 °C, 30–90 min at 5–10% (w/v) oxalic acid concentration. The cellulose-rich fraction was characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) analyses. Characterization analyses revealed a cellulose-rich polymer with fibers ranging from 6 to 10 μm, a maximum thermal degradation temperature of 350 °C, and a crystallinity index of 63.4% (peak height method) and 29.0% (amorphous subtraction method). The optimized hydrolysis conditions were 125 °C, 30 min, at 5% w/v oxalic acid: with a 75.7% yield. These results compare with MFC obtained through highly concentrated inorganic acid hydrolysis from different biomass sources. Thus, we show a reliable and greener alternative chemical treatment for the obtention of MFC.

“Tai Chi” philosophy driven dual-network ionogel membrane comprised of ionic guests in a multifunctional host for propylene/propane separation

Facilitated transport ionogel membranes have shown great prospects in propylene/propane separation due to the stability of carrier media, no leakage, and promising thermal/physical properties. In the present study, inspired by the Tai Chi philosophy of adjusting inorganic and organic features, a dual-network ionogel was made of multi-functional organosilane, [EMIM][TFSI] ionic liquid, AgBF4, and catalysts. An effective strategy, including solvent-free solvolytic sol-gel and epoxide ring-opening reaction, was proposed to keep the inorganic/organic balance and obtain ionogel films with high IL loading (up to 82%) and self-standing. The ionogels were characterized by a phase diagram, formation mechanism, FTIR, N2 adsorption-desorption isotherms, TGA, SEM, mechanical properties, and transport properties. The Multifunctional host induced the breaking of bondage between the components of IL electrolyte (AgBF4 and IL); thereby more free Ag+ ions become available for facilitating the olefin transport. A computational molecular approach was applied to better understand the possible interactions between the ionic guest and multifunctional host. Results indicate that the optimized ionogel not only has excellent transport properties (C3H6 permeability of 243.1 Barrer and C3H6/C3H8 selectivity of 20.2) but also has desirable mechanical and thermal properties. The synthesis of ionogel based on Tai Chi philosophy opens a new window for facilitated transport of gas separation membranes.

Poly(styrene sulfonic acid)-Grafted Carbon Black Synthesized by Surface-Initiated Atom Transfer Radical Polymerization.

Owing to their excellent electrical conductivity and robust mechanical properties, carbon-based nanocomposites are being used in a wide range of applications and devices, such as electromagnetic wave interference shielding, electronic devices, and fuel cells. While several approaches have been developed for synthesizing carbon nanotubes and carbon-black-based polymer nanocomposites, most studies have focused on the simple blending of the carbon material with a polymer matrix. However, this results in uncontrolled interactions between the carbon filler and the polymer chains, leading to the agglomeration of the carbon filler. Herein, we report a new strategy for synthesizing sulfonated polystyrene (PSS)-grafted carbon black nanoparticles (NPs) via surface-initiated atom-transfer radical polymerization. Treatments with O2 plasma and H2O2 result in the effective attachment of the appropriate initiator to the carbon black NPs, thus allowing for the controlled formation of the PSS brushes. The high polymeric processability and desirable mechanical properties of the PSS-grafted carbon black NPs enable them suitable for use in nonfluorinated-hydrocarbon-based polymer electrolyte membranes for fuel cells, which must exhibit high proton conductivity without interrupting the network of channels consisting of ionic clusters (i.e., sulfonic acid moieties).

Nature of Interactions between Boron Clusters: Extended Delocalization and Retention of Aromaticity Post-Oxidation

Polyhedral boron clusters are lauded as 3D aromatics that frequently form interconnected periodic networks resulting in boron-rich borides with metal and non-metals having high thermodynamic stability and hardness. This leads to the question of whether the spherical delocalization of electrons in these clusters is extended across the network as in organic aromatic networks. These borides also frequently show partial oxidation, having fewer electrons than what is mandated by electron counting rules, whose impact on their aromatic stability and geometry remains mysterious. Understanding of the nature of electronic communication between polyhedra in polyhedral borides is largely unknown, though it is crucial for the rational design of advanced materials with desirable mechanical, electronic, and optical properties. Here, we show that electronic delocalization across polyhedral clusters has a significant impact on their structure and stability. Our computational inquiry of closo borane dimers shows substantial variation in conjugation with the ideal electron count. Upon two-electron oxidation, instead of forming exohedral multiple bonding that disrupts the aromaticity, it undergoes subtle geometric transformations that conserve aromaticity. The nature of geometric transformation depends on the highest occupied molecular orbital (HOMO) that is decided locally on the polyhedral degree of the interacting vertices. The prevalence of π-type interactions as the HOMO in tetravalent vertices encourages conjugation across clusters and turns into a macropolyhedral system hosting a rhombic linkage between clusters upon oxidation. In contrast, the σ-type interactions dominate the HOMO of pentavalent vertices that prefer to confine aromaticity within the polyhedra by separating them with localized 3c-2e bonds. Our findings expose the fundamental bonding principles that govern the interaction between boron clusters and will provide the chemical guidance for the design and analysis of polyhedral boride networks with desired properties.

Development of biodegradable and vermicompostable films based on alginate and waste eggshells

The development of biofilms to replace plastics is urgent, due to the high environmental pollution caused by the non-biodegradable packaging. The objective of this study was to develop and understand the behavior and properties of biodegradable films based on an alginate/glycerol matrix with eggshell waste. Eggshells were transformed to eggshell powder (EP) and this ingredient used to obtain EP biodegradable films (EPBFs) using the casting method. EP contributed opacity and whitish coloration to the EPBFs. Stress-strain curves show that EP content significantly influences mechanical properties; resulting in harder, firmer and less elastic EPBFs with increasing EP content. The EPBFs had heterogeneous and rough surfaces with crystalline forms provided by EP with a particle size distribution ranged from 20.7 to 26.6 μm, arranged as a monolithic pattern with very low porosity. EPBFs were amorphous materials and WAXS analysis indicated that CaCO3 content ranged 18–50% in the EPBFs. Thermal decomposition processes of the EPBFs, was not affected by the EP addition at concentrations below 6%. The addition of EP increased the hydrophobicity of EPBFs, slowing solubilization in water; however, the water solubility percentage was high (82.9% for EPBF-2%–75.2% for EPBF-6%). EPBFs completely biodegrade in vermicomposting in short periods of time (between 14 and 21 days). In conclusion, EPBFs, derived from waste, constitute an interesting new material with desirable mechanical properties for potential use as food coatings or packaging. The biodegradable properties of EPBFs allow easy disposal by dissolving in water or by vermicomposting.

고속 금속 3D프린터용 적응형 5축 경로생성 CAM S/W 개발에 관한 연구

This research developed a CAM S/W, which generates an adaptive 5-axis tool path, to optimize the quality of Direct Energy Deposition (DED) 3D printing. After reconstructing part shapes and generating printing paths in each shape, the path simulation including automatic collision detection was implemented. Productivity and printing quality were improved through equipment improvement and process optimization. In addition, high-quality parts with desirable physical and mechanical properties were produced by generating an adaptive 5-axis path specialized in the printing process that reflects various physical phenomena and monitoring results. Finally, the performance of CAM S/W was verified through the production of prototypes for industrial components.

Novel Electroformed Ni-Au Alloy for High Temperature Semiconductor Test Structures

The ongoing reduction in semiconductor and package pitch leads to challenges for engineering suitable miniaturized test and measurement contact vehicles. Traditional probe card approaches for miniaturization may reach fundamental limits for reduction in scale and pitch. Direct electroforming of conductive electrical contacts at pitch using LIGA technology can allow for direct registration to the test points, the simultaneous formation of all contacts and an opportunity to extend the roadmap for miniaturization. We report here on a new and novel nickel-gold alloy (one to three percent gold by weight) that can be produced by electroforming. This new material was computationally designed to optimize the thermodynamics of the two alloy components such that the alloy has a temperature stable nanocrystalline grain structure which produces highly desirable mechanical and physical properties. Specifically, the alloy is highly electrically and thermally conductive with a resistivity of 10 micro-ohm-cm, while also having a yield strength in excess of 1.5 GPa and an elastic modulus of 130 GPa. This combination of high strength and moderate elastic modulus creates and optimum for mechanical elastic stored energy in a formed contact beam. That is to say, contacts engineered from this material are flexible and strong enough to remain in the elastic regime and have sufficient normal force to maintain low and stable contact resistance, which boosts their long term service life. Further, the alloy shows a fixed cantilever beam bending fatigue limit of more than 1 GPa, further enhancing its viability for long term service. For applications requiring even more strength a 2 GPa yield strength version has also been produced, however this version leads to minor trade-offs in terms of ductility and electrical resistivity and cost. Since these contacts will be used at elevated temperature, the alloy has been designed to be nearly as electrically conductive as plated unalloyed nickel and thermodynamically stable under long term high temperature storage conditions of 400 C. Characterization of the microstructure shows that it is a supersaturated solid solution of Au in a Ni host matrix with evidence of preferential Au segregation to the Ni grain boundaries. Xray diffraction analysis confirms a nanocrystalline grain structure whose size varies as a function of the alloying content. By segregating the Au to the grain boundaries, we extend the electron mean free path and boost electrical conductivity. We also reduce the grain size of the metal leading to improvements in mechanical properties such as yield and fatigue. The electroplating solution is environmentally friendly with no significantly hazardous materials and is REACH compliant. We have shown chemical compatibility with a limited test set of standard photo-resists and masks used for the LIGA process. The plating process is reasonably fast and has shown the ability to plate layers as thick as 400 um without cracks, defects or voids. For some applications it may be desirable to add more plated layers to engineer the contact surface. Gold and other precious metals can be plated on top of the Ni-Au layer with good adhesion and lead to improvements in long term low level contact resistance.

Temperature dependence of the deformation behavior and mechanical response of CoCrNi medium-entropy alloy: Experiment and simulation

Tailoring the microstructure of metallic materials by controlling the fabrication process is crucial to achieving superior mechanical properties. Herein, the mechanism of modifying the microstructure and mechanical properties of medium-entropy CoCrNi alloys was investigated by equal-channel angular pressing (ECAP) at room temperature (RT) and cryogenic temperature (CT) and post-deformation annealing (PDA) and was analyzed by molecular dynamics simulations. It was found that temperature influences the deformation mechanism of the alloy, dislocations, stacking faults, deformation twins, and FCC-HCP phase transitions, which assume different roles at different temperatures. The dislocation density of the ECAP-CT sample is significantly higher than that of the ECAP-RT sample; however, the ECAP-RT sample exhibits unique deformation features of kink bands and hierarchical twin structure, resulting in dynamic grain refinement effects. In addition, the HCP phase strength increment caused by annealing-induced HCP phase transformation is higher in the ECAP-RT sample than in the ECAP-CT sample, thus leading to a substantial increase in strength after PDA. The present study exhibits the strengthening mechanisms and provides a generic approach to obtaining desirable mechanical properties of alloys.