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Antimicrobial potential of bioactive glass (BAG) makes it promising for implant applications, specifically overcoming the toxicity concerns associated with traditional antibacterial nanoparticles. The 58S composition of BAG (with high Ca and absence of Na) has been known to exhibit excellent bioactivity and antibacterial behaviour, but the mechanisms behind have not been investigated in detail. In this pioneering study, we are using Atomic Force Microscopy (AFM) to gain insights into 58S BAG's adhesive interactions with planktonic cells of both gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacteria; along with the impact of crystallinity on antibacterial properties. We have recorded greater bacterial inhibition by amorphous BAG compared to semi-crystalline glass–ceramics and stronger effect against gram-negative bacteria via conventional long-term antibacterial tests. AFM force distance curves has illustrated substantial bonding between bacteria and BAG within the initial one second (observed at a gap of 250 ms) of contact, with multiple binding events. Further, stronger adhesion of BAG with E.coli (~ 6 nN) compared to S. aureus (~ 3 nN) has been found which can be attributed to more adhesive nano-domains (size effect) distributed uniformly on E.coli surface. This study has revealed direct evidence of impact of contact time and 58S BAG's crystalline phase on bacterial adhesion and antimicrobial behaviour. Current study has successfully demonstrated the mode and mechanisms of initial bacterial adhesion with 58S BAG. The outcome can pave the way towards improving the designing of implant surfaces for a range of biomedical applications. [ABSTRACT FROM AUTHOR]

The effect of solid solution and aging treatment on microstructure evaluation and resulting mechanical properties of as-cast Mg-9wt.%Li-5wt.%Al-3wt.%Zn-1wt.%Sn (LATZ9531) light-weight alloys were investigated for the application in automobile, aerospace, and bio-medical field. The hardness of the Mg-rich (α-phase, hardness: 2.13 GPa) and the Li-rich (β-phase, hardness: 1.49 GPa) of the solutionized alloy derived from nanoindentation was increased to ~ 35 and ~ 21%, respectively, as compared to the as-cast condition. The hardness of both α- and β-phase was found to be decreased after aging treatment due to the age softening effect. Also, the resulting microstructures were analyzed using finite element modeling (FEM) to understand the effect of the distribution of precipitates on the mechanical properties. Further, the effective elastic modulus for the different heat-treated LATZ9531 alloy was quantified using stress-strain contour obtained from OOF2 (Object Oriented Finite Element Modeling). Also, the role of precipitates, α- and β-phase that possesses different elastic modulus was shown a different stress-strain contour at the interfaces. [ABSTRACT FROM AUTHOR]

Ultra-high temperature ceramics, especially di-borides, are regarded as potential candidates for thermal protection system in hypersonic vehicles by virtue of their high thermal conductivity. However, studies on thermal conductivity behaviour of ultra-high temperature ceramic di-borides exhibit scattered data at high temperatures. Herein, we report a systematic study of a range of di-boride compositions aiming at multiple aspects including the effect of temperature on thermal conductivity of monolithic di-borides (ZrB2 and HfB2), effect of SiC and carbon nanotubes (CNTs) addition on ZrB2 and HfB2 with increasing temperature till 1200 °C, and effect on thermal conductivity with systematic incorporation of ZrB2 and HfB2 into each another. Highest experimental thermal conductivity (63–83 W m−1 K−1) observed in 20 vol% SiC reinforced ZrB2 composite (in the temperature range of 50–1200 °C) witnessed crossover (and drop) than that of monolithic sample (above 900 °C) due to increased phonon–phonon scattering in SiC with the rise in temperature. Concurrently, agglomerated CNT reinforcement further decreased thermal conductivity due to increased inhomogeneity in solid solutioning and enhanced phonon scattering. [ABSTRACT FROM AUTHOR]

HfB2-ZrB2 based ultra-high temperature ceramics (UHTCs) are used as protective tiles for leading edges and nose cones of the hypersonic vehicles that face harsh re-entry conditions. In the present work, the effect of SiC (20 vol.%) and carbon nanotube (CNT, 6 vol.%) incorporation on the room temperature damage initiation and wear damage tolerance of HfB2-ZrB2-based ceramics, consolidated via spark plasma sintering (SPS), is assessed. The wear rate decreased by almost > 90% in CNT-reinforced HfB2-ZrB2–SiC composites (for both scratch and fretting tests), and a significant increase in the Hertzian contact pressure (from ~ 15 GPa, in case of fretting to ~ 21 GPa, in case of scratch wear) and scratch hardness (from ~ 27 GPa to ~ 46 GPa, respectively) was observed with synergistic reinforcements of SiC and CNT. The study examines synergistic interfacial strengthening by SiC and CNT reinforcement in HfB2-ZrB2 ceramic composites as potential materials for aerospace applications where damage initiation and tolerance are issues. [ABSTRACT FROM AUTHOR]

Surface texturing is a process of inducing specific patterns on a surface to enhance the performance of the surface in its working environment. The arrays of patterns can be either micro-scale, nano-scale, or its combination. In general, micro-texturing of a surface regulates the surface energy and contact angle (CA), which can lead to hydrophobicity and improved tribological properties to the surface. Laser surface texturing process (direct write method) is one of the best suitable processes for producing micro-patterns because of its better accuracy, repeatability, and machining rate over the advanced machining processes (electric discharge machining, electrochemical micro-machining, etc.). In the present work, an attempt has been made to produce micro-textures on polymeric as well as metallic surfaces using CO2 laser and solid-state pulsed ytterbium fiber laser respectively. An experimental analysis is executed to understand how CA and coefficient of friction (COF) depend on substrate's surface topography and areal density of the texture. Various polymeric and metal surfaces such as Kapton, Mylar™ (polyethylene terephthalate or PET), cellulose acetate film, titanium alloy (Ti6Al4V), and stainless steel (SS304) are laser textured by producing various micro-patterns such as array of micro-pillars of the square and triangular cross section, and micro-dimples. A novel study of the influence of areal density of textures on the coefficient of friction and wear is performed to signify the applicability of the textured surfaces. Textures of 32, 140, and 670 pillars/mm2 areal densities are machined and tested through fretting wear test. In Ti6Al4V, texture with (30 μm pillar width) areal density 640 pillars/mm2 leads to lowest COF and highest contact angle of 140°. [ABSTRACT FROM AUTHOR]

The grain growth kinetics of 8YSZ ceramics processed using spark plasma sintering (SPS) has been investigated in the temperature ranging from 1100°C to 1500°C. The activation energy during SPS densification was obtained as 332 kJ/mol with grain boundary diffusion as a dominant mechanism. Further, the effect of CeO2 on the densification kinetics of 8YSZ ceramic processed via SPS and conventional sintering (CS) has been delineated. The lower grain boundary mobility of CS-processed composites (an order of magnitude lower than SPS) is attributed to the solute drag and lattice distortion mechanism. However, no significant change in the grain boundary mobility was observed with CeO2 addition (~ 14.7-43.9 × 10−18 m3/N/s for CS and 107.2-116.7 × 10−18 m3/N/s for SPS) revealing that the defect concentration is nearly constant in 8YSZ. The study highlights the effect of sintering techniques (SPS and CS) and reinforcement (CeO2) on engineering the desired microstructure of 8YSZ ceramic. [ABSTRACT FROM AUTHOR]

Electrophoretically deposited (EPD) nickel and its composite coatings are widely used to enhance the life span of continuous ingot casting molds in the steel, aerospace and automotive industries. This article reports the effect of different concentrations of diamond particles (2.5-10 g/L) on the wear mechanism of EPD Ni. The distribution of diamond particles in the Ni matrix was observed using Voronoi tessellation. Variation in COF was observed by a fretting wear test to be 0.51 ± 0.07 for Ni, which decreases to ~0.35 ± 0.03 for the Ni-diamond coatings. The wear volume of the coatings with 7.5 g/L concentration of diamond was observed to be a minimum (0.051 ± 0.02 × 10 mm) compared with other composite coatings. Further, the micro-scratch testing of the coatings also exhibited a reduced COF (0.03-0.12) for 7.5 g/L diamond concentration compared with Ni (0.08-0.13). Higher wear resistance of the diamond-added coatings (optimum 7.5 g/L concentration) is due to the balance between the dispersion strengthening mechanism and the enhancement of the load-bearing capacity due to the incorporation of diamond particles. Thus, these composites can be used for applications in automotive and aerospace industries. [ABSTRACT FROM AUTHOR]

Graphite is used in high-temperature gas-cooled reactors because of its outstanding irradiation performance and corrosion resistance. To restrict its high-temperature (>873 K) oxidation, atmospheric-plasma-sprayed SiC-ZrB-AlO-carbon nanotube (CNT) dual-layer coating was deposited on graphite substrate in this work. The effect of each layer was isolated by processing each component of the coating via spark plasma sintering followed by isothermal kinetic studies. Based on isothermal analysis and the presence of high residual thermal stress in the oxide scale, degradation appeared to be more severe in composites reinforced with CNTs. To avoid the complexity of analysis of composites, the high-temperature activation energy for oxidation was calculated for the single-phase materials only, yielding values of 11.8, 20.5, 43.5, and 4.5 kJ/mol for graphite, SiC, ZrB, and CNT, respectively, with increased thermal stability for ZrB and SiC. These results were then used to evaluate the oxidation rate for the composites analytically. This study has broad implications for wider use of dual-layer (SiC-ZrB/AlO) coatings for protecting graphite crucibles even at temperatures above 1073 K. [ABSTRACT FROM AUTHOR]

Tantalum carbide (TaC) is an ultrahigh temperature ceramic, where low damage tolerance limits its potential application in propulsion sector. In this respect, current work focuses on enhancing the toughness of TaC based composites via synergistic reinforcement of SiC and carbon nanotubes (CNTs). Spark plasma sintering of TaC, reinforced with 15 vol% SiC and 15 vol% CNT (processed at 1850 °C, 40 MPa, 5 min), has shown enhanced densification from ∼93% (for TaC) to ∼98%. Potential damage of the tubular CNTs to flaky graphite was revealed using transmission electron microscopy, and was supplemented via Raman spectroscopy. SiC addition has enhanced the hardness to ∼19.5 GPa while a decreases to 12.6 GPa was observed with CNT addition when compared to the hardness of TaC (∼15.5 GPa). The increase in the indentation fracture toughness (from 3.1 MPa m1/2 for TaC to 11.4 MPa m1/2) and fracture strength (from ∼23 MPa for TaC to ∼183 MPa) via synergetic reinforcement of SiC and CNT is mainly attributed to energy dissipating mechanisms such as crack branching, CNT bridging, and crack-deflection. In addition, the reduction of interfacial residual tensile-stresses with SiC- and CNT-reinforcement, resulting an overall increase in the fracture energy and toughening, is also established. [ABSTRACT FROM AUTHOR]

High-energy ball milling is utilized in creating microstructural changes (such as change in lattice parameter, lattice strain) within micro-ceria, which were quantified using line profile analysis by X-ray diffraction. Crystallite size significantly decreased from 85 to 11 nm when subjected to 4 h of high-energy ball milling, and then remained same with increase in milling duration (up to 16 h of milling). Three different methods, namely Nelson-Riley function, Cohen's method, and Pawley fitting, were used to calculate the lattice parameter and a lattice expansion from 5.4082 to 5.4147 Å was observed for a duration of 0 up to 12 h. The effect of milling on generation of residual strain and the probability of stacking fault in affecting the lattice parameter are delineated in the current work. Non-monotonic change of lattice parameter with saturation of crystallite size is attributed to the vacancy-induced stresses that generate at inter-crystallite regions and render excessive free volume during high-energy ball milling. [ABSTRACT FROM AUTHOR]

Corrosion behavior of two multiphase Mg-Li-Al-based alloys in 0.6 M NaCl aqueous solution is investigated by hydrogen gas evolution measurement and electrochemical test. This paper reports, for the first time, the comparison of hydrogen evolution and Tafel extrapolation results of Mg-Li-Al-based alloys. The corrosion rate of Mg-9Li-7Al-1Sn is observed to be reasonably higher when compared to that of Mg-9Li-5Al-3Sn-1Zn, and both the alloys have shown higher corrosion rate than that of Mg-3Al-1Zn alloy (AZ31B). The micro-galvanic corrosion of primary precipitates and hcp α-phase (Mg-rich) is not as severe as was observed in case of the secondary precipitates and bcc β-phase (Li-rich). Corrosion mechanism of multiphase Mg-Li-Al-based alloys in chloride solution, which has not been adequately reported in the literature, is lucidly articulated based on the early stages of corrosion, film morphology, and in situ hydrogen bubble study. [ABSTRACT FROM AUTHOR]

The present research aims to investigate the effect of multi-walled carbon nanotube (MWNT) reinforcement on the mechanism of transformation toughening in zirconia matrix, and consequently, its fracture toughness. Monoclinic zirconia (un-doped ZrO), partially stabilized zirconia (3 mol pct yttria-stabilized zirconia (3 mol pct YSZ)), and fully stabilized cubic zirconia (8 mol pct YSZ) with and without 6 vol pct MWNT-reinforced nanocomposites were processed via multi-stage spark plasma sintering. Phase analysis of powders, and sintered and crushed pellets performed using X-ray diffraction reveals the absence of any phase transformation in monoclinic ZrO, 8 mol pct YSZ and their MWNT-reinforced nanocomposites upon application of stress by means of crushing. However, a significant decrease in the stress-induced phase transformation (81.1 pct metastable tetragonal phase retained with 6 vol pct MWNT reinforcement when compared to that of 68.4 pct tetragonal phase in 3 mol pct YSZ) is observed in the crushed pellet samples of partially stabilized zirconia upon 6 vol pct MWNT reinforcement. Transmission electron microscopy has been utilized for complementary phase analysis. Evaluation of mechanical properties indicates enhancement in fracture toughness (~23.6 to 26.4 pct) with the incorporation of 6 vol pct MWNT. Isolation of the net toughening contribution suggests that MWNT toughening mechanisms are ~3.8 times more effective than transformation toughening in enhancing the fracture toughness of YSZ/MWNT nanocomposites. [ABSTRACT FROM AUTHOR]

The success of the implants used for bone regeneration and repair is highly dependent on the cell material interaction, which is further influenced by interaction of body proteins with the implant materials. In this study, a novel nanostructured Zircaloy-2 has been developed using cold rolling (reduction of 25%, 50%. 75%, and 85%), which resulted in the refinement of grains by several orders of magnitude. Phase analysis was done using x-ray diffraction, and the microstructures of room-temperature rolled Zircaloy-2 were obtained using optical microscopy. The adsorption behavior of bovine serum albumin as a function of protein concentration on Zircaloy-2 was performed, and the wettability before and after protein adsorption on Zircaloy-2 samples was estimated by measuring the contact angle of a water droplet on the processed samples. Nanoindentation studies were performed, which indicated higher hardness (of 2.15 GPa) and reduced elastic modulus (47.4 GPa) when compared with that of as-received Zircaloy-2 (hardness of ~0.12 GPa and reduced elastic modulus of 5.6 GPa). Also, it was found that protein adsorption increases to 0.59 mg/cm for maximum deformed samples when compared with that of 0.38 mg/cm for as-received samples. Contact angle decreased with increasing reduction from 62° (of the as-received sample) to 44° (at a reduction of 85%). But after protein adsorption, a further decrease in the contact angle from 43° (as received) to 26° (for 85% reduction) was observed. Thus, the engineered cold rolling can allow tailoring the nanomechanical properties of Zircaloy-2 while rendering the required protein adsorption as potential implant material. [ABSTRACT FROM AUTHOR]

Ultra-high molecular weight polyethylene (UHMWPE) is the most widely used biopolymer for articulating surfaces, such as an acetabular cup liner interfacing with a metal/ceramic femoral head. However, the formation of wear debris leads to the aseptic loosening of implants. Thus, in order to improve the life span via enhancing the fretting wear resistance, UHMWPE is reinforced with ZnO/Ag nanoparticles. It is envisaged that the ZnO/Ag addition will also exhibit antibacterial properties. In the current study, the synergetic effect of the reinforcement of ZnO/Ag nanoparticles (0-3 wt.% combinations) on the fretting wear behavior of a UHMWPE matrix is assessed. The phase characterization of compression- molded UHMWPE-Ag-ZnO biopolymer nanocomposites has elicited the retention of starting phases. All samples were processed at >98% density using compression molding. Silver and ZnO reinforcement showed enhanced hardness ~20.4% for U3A and 42.0% for U3Z. Fretting wear performance was evaluated at varying loads (5-15 N), keeping in mind the weight at different joints, with constant frequency (5 Hz) as well as amplitude of oscillation (100 µm). Laser surface profilometry showed change of wear volume from 8.6 × 10 mm for neat polymer to 5.8 × 10 mm with 1 wt.% Ag + 1 wt.% ZnO reinforcement (at 15 N load). Consequently, the mechanics of resistance offered by Ag and ZnO is delineated in the UHMWPE matrix. Further, S. aureus viability reduction is ~28.7% in cases with 1 wt.% Ag addition, ~42.5% with 1 wt.% ZnO addition, but synergistically increase to ~58.6% and 47.1% when each of Ag and ZnO is added with 1 wt.% and 3 wt.%, respectively (when compared to that of the UHMWPE control sample). Increased wear resistance and superior bioactivity and enhanced anti-bacterial properties of 1 wt.% Ag + 1 wt.% ZnO and 3 wt.% Ag + 3 wt.% ZnO shows the potential use of ZnO-Ag-UHMWPE biopolymer composites as an articulating surface. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) is a widely used bioceramic known for its chemical similarity with that of bone and teeth (Ca/P ratio of 1.67). But, owing to its extreme brittleness, α-AlO is reinforced with HA and processed as a coating via pulsed laser deposition (PLD). Reinforcement of α-AlO (50 wt.%) in HA via PLD on 316L steel substrate has shown modulus increase by 4% and hardness increase by 78%, and an improved adhesion strength of 14.2 N (improvement by 118%). Micro-scratching has shown an increase in the coefficient-of-friction from 0.05 (pure HA) to 0.17 (with 50 wt.% AlO) with enhancement in the crack propagation resistance (CPR) up to 4.5 times. Strong adherence of PLD HA-AlO coatings (~4.5 times than that of HA coating) is attributed to efficient release of stored tensile strain energy (~17 × 10 J/m) in HA-AlO composites, making it a potential damage-tolerant bone-replacement surface coating. [ABSTRACT FROM AUTHOR]

Solid-oxide fuel cell components were fabricated using an atmospheric plasma spraying method. Lanthanum strontium manganite (LSM), 8 mol% yttria-stabilized zirconia (8YSZ), ceria (CeO), and YSZ-NiO powders were used as feedstock materials for layered deposition of cathode, electrolyte, and anode, respectively, to make a complete cell. In this work, two types of electrolyte materials were investigated, viz., 8YSZ and the one containing 10 wt.% CeO. Because a high densification is expected in the solid oxide electrolyte (as opposed to observed porosity of ~27%), current work focuses only on the nanomechanical evaluation of the same. Scanning electron microscopy (SEM) images show the retention of nanocrystallinity in the plasma-sprayed deposits. Elemental analyses via energy-dispersive spectroscopy revealed chemically distinct identities of the cell components ruling out diffusion or reaction at the boundaries. Porosity values vary between 29.0% and 35.4% in anode and 42.9-48.4% in cathode, indicating appreciable achievement for high performance of electrode materials. The addition of 10 wt.% ceria to 8YSZ has shown enhancement in the elastic modulus and hardness of the electrolyte material by 18.4 GPa and 1.6 GPa, respectively. Theoretical estimation of thermal conductivity of the plasma-sprayed materials has been found to be in the order of 2.27-4.45 W/mK. [ABSTRACT FROM AUTHOR]

Hydroxyapatite is a bioactive material that is the main inorganic constituent of human hard tissue (Ca/P ratio of 1.67) whose coatings provide requisite surface bioactivity to the bone implants. In the current work, the characteristics of nanocrystalline hydroxyapatite (HA) coatings, electrophoretically deposited on Ti6Al4V substrate, have been investigated. To enhance the coating's compatibility, a 0.75 μm thick TiO layer was thermally grown as a diffusion barrier prior to electrophoretic deposition of HA. Subsequently, HA was electrophoretically deposited (EPD) at different deposition voltages (100-250 V) while keeping the deposition time as 10 s. Both anodic oxidation during EPD for 10 s and thermal oxidation during sintering at 1000°C for 2 h resulted in the growth of a TiO layer thickness of more than 25 μm. Enhancement of voltage also has shown significant influence on the mechanism of the evolution of biphasic microstructures, attributed to the simultaneous growth of TiO and HA phases. Optimized distribution of HA and TiO phases was evidenced at 200 V, with explicit HA retention as observed via transmission electron microscopy. An empirical relationship is developed to relate the voltage with the suppression of cracking in the deposited coatings. [ABSTRACT FROM AUTHOR]

Ultrahigh-molecular-weight polyethylene (UHMWPE) is used as an articulating surface in total hip and knee joint replacement. In order to enhance long-term durability/wear resistance properties, UHMWPE-based polymer-ceramic hybrid composites are being developed. Surface properties such as wettability and protein adsorption alter with reinforcement or with change in surface chemistry. From this perspective, the wettability and protein adsorption behavior of compression-molded UHMWPE-hydroxyapatite (HA)-aluminum oxide (AlO)-carbon nanotube (CNT) composites were analyzed in conjunction with surface roughness. The combined effect of AlO and CNT shows enhancement of the contact angle by ~37° compared with the surface of the UHMWPE matrix reinforced with HA. In reference to unreinforced UHMWPE, protein adsorption density also increased by ~230% for 2 wt.%HA-5 wt.%AlO-2 wt.%CNT addition to UHMWPE. An important conclusion is that the polar and dispersion components of the surface free energy play a significant role in wetting and protein adsorption than do the total free energy or chemistry of the surface. The results of this study have major implications for the biocompatibility of these newly developed biocomposites. [ABSTRACT FROM AUTHOR]

Nanocrystalline coatings have become an essential component of single and multilayer electronic packaging, ship building, mining, magnetorestrictive applications, etc. In the current work, nanocrystalline Ni-Cu films were synthesized by pulsed electrode-position using a citrate bath. Cathodic polarization experiments were carried out for optimization of bath composition to co-deposit nanocrystalline Ni-Cu films. Depositions were optimized between the current density range of 0.05–0.25 A·cm−2 to achieve a uniform equiaxed coating with a target Ni content of greater than 70% owing to their superior corrosion resistance and enhanced hardness. [ABSTRACT FROM AUTHOR]

Hydroxyapatite (HA) reinforced with sub-micrometer Al2O3 and carbon nanotubes (CNTs) has been synthesized as a coating on the Ti-6Al-4V substrate via plasma spraying. The addition of Al2O3 and CNTs to HA has shown improvement in the hardness and elastic modulus by 65% and 50%, respectively, when compared to HA. Consequently, HA-Al2O3-CNT coatings have been nano-scratched to understand their wear performance. Reinforcement of HA by Al2O3 shows a decrease in the wear volume by more than 13 times, whereas HA-Al2O3-CNT coating demonstrated further wear volume reduction of five times compared to that of HA-Al2O3 coating. [ABSTRACT FROM AUTHOR]

The effect of laser melting on the microstructure and mechanical properties of plasma-sprayed aluminum oxide composite coating reinforced with 4 wt% multi-walled carbon nanotubes (CNTs) is reported. Laser-melted layer consists of dense, coarse columnar microstructure which is significantly different from plasma-sprayed coating that consists of splats and porosity. CNTs retained their original cylindrical graphitic structure after undergoing laser irradiation. Three dimensional heat flow model has been developed to estimate temperature variation in the laser-melted composite layer. Laser-melted layers show an increase in the microhardness at the expanse of degradation of fracture toughness. Nanoindentation study indicates an increase in the elastic modulus and yield strength of the laser-melted layer which is attributed to dense microstructure with absence of weak-bonding splats and porosity. [ABSTRACT FROM AUTHOR]