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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]

Accumulatively roll bonded (ARB) Mg-LaNi 5 -Soot hybrid has emerged as a promising hydrogen storage material with enhanced hydrogen storage characteristics, which is amenable to scaled-up production. The key to understanding the hydrogen storage behaviour lies in the nanoscale structure of the hybrid and the associated mechanisms. The focus of the current study is on the use of cross-sectional transmission electron microscopy (TEM) to unravel the underlying mechanisms of hydrogen storage, in the Mg-LaNi 5 -Soot hybrid. The role of processing variables (ARB passes and strain) and the concomitant evolution of the microstructure (distribution of second phase particles (LaNi 5 and soot)) are studied, keeping in view the diffusion of hydrogen and the nucleation of the hydride phase. It is established that the interface between Mg and second phase (LaNi 5 and soot) plays a dominant role in the nucleation of the MgH 2 phase. The MgH 2 nucleation mechanism is studied under the ambit of the Johnson-Mehl-Avrami kinetic (JMAK) model. It is concluded that the internal interfaces provides sites for the nucleation of magnesium hydride. • Cross-sectional transmission electron microscope on Mg–LaNi 5 -soot ARB processed hybrid. • Hydrogen absorption mechanism study in Mg based bulk hybrids. • Study of Johnson-Mehl-Avrami kinetic model on Mg–LaNi 5 -soot hybrid. [ABSTRACT FROM AUTHOR]

Processing of ultrahigh temperature TaC ceramic material with sintering additives of B4C and reinforcement of carbon nanotubes (CNTs) gives rise to possible formation of several interfaces (Ta2C-TaC, TaC-CNT, Ta2C-CNT, TaB2-TaC, and TaB2-CNT) that could influence the resultant properties. Current work focuses on interfaces developed during spark plasma sintering of TaC-system and performing ab initio molecular modeling of the interfaces generated during processing of TaC-B4C and TaC-CNT composites. The energy of the various interfaces has been evaluated and compared with TaC-Ta2C interface. The iso-surface electronic contours are extracted from the calculations eliciting the enhanced stability of TaC-CNT interface by 72.2%. CNTs form stable interfaces with Ta2C and TaB2 phases with a reduction in the energy by 35.8% and 40.4%, respectively. The computed Ta-C-B interfaces are also compared with experimentally observed interfaces in high resolution TEM images. [ABSTRACT FROM AUTHOR]

Nanomechanical dynamic analysis has been utilized to evaluate damping behavior of plasma sprayed carbon nanotube (CNT) reinforced Al2O3 ceramic coatings. Addition and dispersion of CNTs in Al2O3 matrix elicited modulus enhancement from 200 to 400 GPa. Tan delta increases from 0.26 for Al2O3 to 0.39 with 8 wt % CNT coating. CNT bending and curling, Al2O3 coating on CNT, interparticle Al2O3 friction, and CNT/splat sliding serve as strong loss mechanisms in imparting enhanced damping to Al2O3 nanocomposites reinforced with CNTs. Damping and fracture toughness of CNT-Al2O3 coating is semiempirically related to the enhancement of storage modulus and tan delta with varying CNT content and degree of dispersion. [ABSTRACT FROM AUTHOR]

Abstract The effect of systematic substitution of Yb 2 O 3 for Sc 2 O 3 is studied on the phase stability and conductivity of 12Sc 2 O 3 -88ZrO 2 (12ScSZ) samples fabricated through solid-state reaction and pressureless sintering methods. Phase analysis via XRD, Raman spectroscopy and TEM confirmed the existence of a single cubic phase in all the tested compositions including 12ScSZ. The absence of β -phase in 12ScSZ at room temperature is ascribed to the homogenous distribution of Sc3+ inside the ZrO 2 lattice. The oxygen-ion conductivity is measured through impedance spectroscopy technique from 650 °C to 350 °C in air. Even though co-doping of Yb 2 O 3 leads to a decrease in the grain conductivity of 12ScSZ, the grain boundaries possess superior conductivity in co-doped compositions. Thus, the 1 mol% Yb 2 O 3 co-doped 12ScSZ shows marginally better total conductivity (~8.2 mS·cm−1 at 650 °C) compared to 12ScSZ. The long-term ageing study performed at 600 °C for 550 h indicates a substantial conductivity loss (25% to 17%) in all the samples without any evidence of new phase formation. The conductivity degradation with time is attributed to the oxygen vacancy ordering around Sc3+ which is partially disturbed by co-doping of Yb 2 O 3. Highlights • 12Sc 2 O 3 -88ZrO 2 exhibits a cubic fluorite structure at room temperature. • A short-range ordering of oxygen vacancy is observed in 12ScSZ. • The total conductivity of 12ScSZ increases on co-doping with Yb 2 O 3. • A significant conductivity loss is observed on ageing at 600 °C for 550 h. • The magnitude of conductivity degradation decreases on Yb 2 O 3 co-doping. [ABSTRACT FROM AUTHOR]

A single-cell force spectroscopy is utilized to characterize the dynamics of the transient interaction (0–10 s) between alive Staphylococcus aureus and ultra-high molecular weight polyethylene (UHMWPE). Adhesion force of bacteria upon addition of antibacterial additives (i.e. silver (Ag) nanoparticles and zinc oxide (ZnO) micro-rods) has been evaluated. Addition of Ag and ZnO reduces the colony forming units (CFUs) from 93 ± 7 (UHMWPE) to 23 ± 5 (U + 3 wt.% Ag + 3 wt.% ZnO) on 10 × 10 mm 2 area of sample surface. Presence of ZnO causes increase in the surface free energy from 29.1 (UHMWPE) to 32.3 mJ/m 2 (UHMWPE + 1 wt.% ZnO) and 32.3 mJ/m 2 for U + 3 wt.% ZnO whereas due to Ag the surface free energy decreased to 28.3 mJ/m 2 and 28.4 mJ/m 2 for UHMWPE + 1 wt.% Ag and U + 3 wt.% Ag respectively. At a contact time of 10 s bacterial adhesion on U + 1 wt.% Ag + 1 wt.% ZnO, U + 3 wt.% Ag and U + 3 wt.% Ag + 3 wt.% ZnO showed lowest adhesion forces, ~ 2.6 nN, ~ 2.9 nN and ~ 3.2 N respectively as compared to neat UHMWPE (~ 4 nN) due to a lower surface free energies, but U + 1 wt.% Ag and U + 1 wt.% ZnO and U + 3 wt.% ZnO show higher adhesion force due their higher surface free energy. Ag nanoparticles reduce the live bacteria count whereas ZnO reduces the bacterial retention and combination of both acts synergistically so the count of live bacteria as well as total bacterial density reduced in U-Ag-ZnO composite samples. [ABSTRACT FROM AUTHOR]

Fully dense (ZrC-TaC-WC-TiC)-SiC (named as ZTaWT-S) based high entropy carbide (HEC) composites were fabricated using spark plasma sintering (SPS) at 1750 °C. Herein, effect of carbonaceous reinforcements (multi-walled carbon nanotube (CNT), graphite (G) and graphene (GNP) on microstructure and mechanical properties of the composites is assessed. The formation of a cubic rock salt high entropy carbide (HEC) phase is indicated via phase and microstructural characterization. Further, local elemental distribution using energy dispersive spectroscopy, and interplanar spacing calculation using transmission electron microscopy (TEM) confirmed the HEC phase formation in the sintered samples. Refined grains (∼3.9 μm), and high densification (>99%), has elicited an increasing hardness from 23.1 GPa to 30.2 GPa (by 30.7%) and elastic modulus from 372 GPa to 419 GPa (by 12.6%), which is attributed to an effective load transfer between matrix/reinforcement in ZTaWT-SGNP composite. An attempt is made to delineate the strengthening contributions from the porosity, high entropy phase, and other complex oxy-carbide and/or unreacted phases in multiphasic (ZTaWT-S) based HEC. Instrumented indentations (micro-indentation and nanoindentation) have facilitated delineation of contribution from various phases (i.e. HEC, TaC, SiC, and oxide phases). A remarkable enhancement is observed in the flexural strength from 390 MPa for ZTaWT-S composite to 487 MPa (by 24.9%), 519 MPa (by 33.1%) and 576 MPa (by 47.7%) for CNT, graphite, and graphene reinforced ZTaWT-S composites, respectively. The graphene reinforced composite exhibited highest flexural strength due to wrapping of GNP along grain boundaries, enhanced matrix/reinforcement adhesion, grain shearing and crack deflection. In summary, ZTaWT-SGNP composite exhibit superior mechanical properties and, thus, have potential structural applications in extreme environments. • Spark Plasma Sintering of Zr-Ta-W-Ti based High Entropy Carbides (HEC). • Effect of carbonaceous reinforcement (i.e. CNT, Graphite and Graphene) in HECs. • Delineated contribution of hardness, elastic modulus and flexural strength in HEC. • Damage tolerance mechanism in carbonaceous reinforced Zr-Ta-W-Ti-Si based HECs. [ABSTRACT FROM AUTHOR]

Ultrahigh molecular weight polyethylene (UHMWPE) is widely used as bone-replacement material for articulating surfaces due to its excellent wear resistance and low coefficient of friction. But, the wear debris, generated during abrasion between mating surfaces, leads to aseptic loosening of implants. Thus, various reinforcing agents are generally utilized, which may alter the surface and biological properties of UHMWPE. In the current work, the cellular response of compression molded UHMWPE upon reinforcement of bioactive multiwalled carbon nanotubes (MWCNTs) and bioinert aluminum oxide (Al 2 O 3 ) is investigated. The phase retention and stability were observed using X-ray diffraction, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The reinforcement of MWCNTs and Al 2 O 3 has shown to alter the wettability (from contact angle of ~ 88° ± 2° to ~ 118° ± 4°) and surface energy (from ~ 23.20 to ~ 17.75 mN/m) of composites with respect to UHMWPE, without eliciting any adverse effect on cytocompatibility for the L929 mouse fibroblast cell line. Interestingly, the cellular growth of the L929 mouse fibroblast cell line is observed to be dominated by the dispersion fraction of surface free energy (SFE). After 48 h of incubation period, a decrease in metabolic activity of MWCNT–Al 2 O 3 reinforced composites is attributed to apatite formation that reduces the dispersion fraction of surface energy. The mineralized apatite during incubation was confirmed and quantified by energy dispersive spectroscopy and X-ray diffraction respectively. Thus, the dispersion fraction of surface free energy can be engineered to play an important role in achieving enhanced metabolic activity of the MWCNT–Al 2 O 3 reinforced UHMWPE biopolymer composites. [ABSTRACT FROM AUTHOR]

Although HA is highly biocompatible, one of the major disadvantages of HA include the lack of antibacterial property. In an earlier study, we demonstrated the potential role of magnetic field stimulation on bactericidal property in vitro. Following this, it was hypothesized that antibacterial property can be realized if bacteria are grown on magnetic biocomposites in vitro. In addressing this issue, this study demonstrates the development of HA- Fe3 O4-based magnetic substrate with multifunctional properties. For this purpose, HA- x Fe3 O4 ( x: 10, 20 and 40 wt%) powder compositions were sintered using uniquely designed spark plasma sintering conditions (three stage sintering with final holding temperature of 1050°C for 5 min). A saturation magnetization of 24 emu/g is measured with HA-40% Fe3 O4. Importantly, all the HA- Fe3 O4 composites demonstrated bactericidal property by rupturing the membrane of Escherichia coli bacteria, while supporting cell growth of metabolically active human fetal osteoblast cells over 8 d culture. A systematic decrease in bacterial viability with Fe3 O4 addition is consistent with a commensurate increase in reactive oxygen species ( ROS). [ABSTRACT FROM AUTHOR]

An analytical method was used to investigate the effects of thermal residual stresses on the fracture toughness of multiwalled carbon nanotube (MWCNT)/alumina nanocomposites. Computed results showed that thermal residual stresses contribute negligibly to the overall improved toughness due to immovable dislocations around MWCNTs not included, these immovable dislocations, induced by highly hydrostatic compressive stress upon MWCNTs, usually act as nanocrack nuclei and relieve stress concentration ahead of the main crack, which is evidenced by the existence of nanosteps on the fracture surface. [Copyright &y& Elsevier]

Grain-boundary mobility of the plasma sprayed aluminum oxide (AlO)-carbon nanotube (CNT) composites is evaluated in the current work. Grain mobility is evaluated from the grain growth within the spray-dried particles and thermal history experienced during high-temperature plasma processing. CNTs form an interfacial grain boundary layer during thermal exposure, limiting the grain growth of plasma-sprayed coatings. Consequent hot isostatic pressing (HIPing) of CNT-reinforced AlO at 1773 K shows differences in grain growth kinetics, degree of densification, and pore shrinkage. Densification of HIPed coatings is observed to be dictated by CNTs, phase transformation, initial grain size, and time of thermal processing. CNTs have shown to impede the AlO grain growth by serving as grain pinning obstacles. Impediment of grain-boundary mobility with variation of CNT content, and time and temperature of the heat treatment of aluminum oxide (AlO)-CNT nanocomposite is addressed in detail. [ABSTRACT FROM AUTHOR]

Abstract: This study compares the interaction of carbon nanotubes (CNTs) with the flame/energy sources during different thermal spray processes viz. plasma spraying (PS), high-velocity oxy fuel spraying (HVOF), cold spraying (CS), and plasma spraying of liquid precursor (PSLP). CNTs were successfully retained as reinforcement in metal and ceramic composite coatings in all thermal spray processes except PSLP. The retention of CNT structure is attributed to micron size metal/ceramic powder which acts as a carrier and thermal shield against high heat in plasma spraying (PS) and high-velocity oxy fuel spraying (HVOF). However, vaporization of CNTs occurred in PSLP under the intense heat of the plasma which is attributed to phase transformation in unshielded CNTs. [Copyright &y& Elsevier]

Abstract: A multiple length scale wear study of plasma-sprayed Al2O3–carbon nanotube (CNT) nanocomposite coating is described. CNT content and dispersion have been shown to enhance the macro-wear resistance (pin-on-disk) by more than 49 times, and nano-wear (scratch) resistance up to 18 times. CNTs have been shown to reduce the wear of Al2O3 matrix by (i) increasing densification, (ii) CNT bridging and (iii) CNT lubrication. A strong dependence of wear volume loss on the microstructural features is described at different length scales, and the disparity of material loss observed in the macro- and nano-wear tests is explained. A wear model has been established to numerically quantify wear loss dependence in terms of bulk material properties and correlating these with wear parameters from nano-scratch testing. [Copyright &y& Elsevier]

Aluminum oxide nanocomposites reinforced with multiwalled carbon nanotubes (MWNT) were prepared by atmospheric plasma spraying of blended and spray-dried powders. Thermal conductivity was measured using the laser flash technique for temperatures between 25° and 300°C. An aluminum oxide—4 wt% MWNT nanocomposite prepared from the blended powder showed the highest conductivity, followed by aluminum oxide without nanotubes, 8 and 4 wt% MWNT composite prepared from spray-dried powder in that order. The thermal conductivity values obtained are rationalized taking into account the crystallite size, porosity, MWNT content, microstructure, and the interfaces and metastable γ-Al2O3 content present in the nanocomposite. [ABSTRACT FROM AUTHOR]

Abstract: Carbon nanotubes (CNT) possess excellent mechanical properties to play the role as reinforcement for imparting strength and toughness to brittle hydroxyapatite (HA) bioceramic coating. However, lack of processing technique to uniformly distribute multiwalled CNTs in HA coating and limited studies and sparse knowledge evincing toxicity of CNTs has kept researchers in dispute for long. In the current work, we have addressed these issues by (i) successfully distributing multiwalled CNT reinforcement in HA coating using plasma spraying to improve the fracture toughness (by 56%) and enhance crystallinity (by 27%), and (ii) culturing human osteoblast hFOB 1.19 cells onto CNT reinforced HA coating to elicit its biocompatibility with living cells. Unrestricted growth of human osteoblast hFOB 1.19 cells has been observed near CNT regions claiming assistance by CNT surfaces to promote cell growth and proliferation. [Copyright &y& Elsevier]

Tantalum carbide (TaC) is an ultra-high-temperature ceramic for potential applications as protective coating, furnace components, propulsion liners for space shuttles and aircrafts, etc. Microstructural and mechanical behavior of vacuum plasma-sprayed (VPS) TaC has been investigated in the present study. Apart from major TaC phase, microstructural definitions elucidated Ta2C, non-stoichiometric TaC x phases (0.83≤ x≤0.94), partial grain formation, polygonization of grains, and inhomogeneous C/Ta ratios in the sprayed structure. Near-isotropy in the fracture–toughness ratio ( Kaxial/ Ktrans=1.01) is attributed to compact coating, fine-closed porosity, and distribution of non-stoichiometric phases. [ABSTRACT FROM AUTHOR]

Sintering mechanisms are investigated by determining activation energy of densification (in the temperature range of 1650 °C to 1950 °C) during spark plasma sintering of ZrB 2 and SiC-reinforced ZrB 2 ceramic composite. The fractured surfaces of sintered composites reveal completely dense microstructures above 1800 °C, whereas porous microstructure prevailed in ZrB 2 even after sintering at 1950 °C. Activation energy of 80 ± 16 kJ/mol is obtained for ZrB 2 with grain boundary diffusion as governing diffusion mechanism in the temperature range of 1650 to 1950 °C. On the other hand, dominant densification mechanism of grain boundary diffusion (activation energy of 89 ± 19 kJ/mol) estimated in the range of 1650 to 1800 °C changed to lattice diffusion (activation energy of 601 ± 10 kJ/mol) with the addition of 20 vol% SiC in ZrB 2. The change of prominent densification mechanism in ZrB 2 with SiC, in addition to its impact on the mechanical performance with systemic increase of sintering temperature, is unravelled here. • Spark plasma sintering of SiC reinforced ZrB2 at different temperatures (1650–1950 °C). • Grain boundary dominating diffusion densification mechanism at <1950 °C in ZrB2. • Lattice diffusion dominating densification mechanism at >1850 °C in SiC reinforced ZrB2. • Increased densification and grain-growth inhibition in SiC reinforced ZrB2. [ABSTRACT FROM AUTHOR]

Efficiency and structural stability of gas-turbine engines were acheived with compliant thermal barrier coatings (TBCs) on structural components. In TBCs, top ceramic coatings encountered with other structural parts in a relative motion (amplitude of 100–500 μm and frequency of 1–5 Hz) was leading to failure, namely fretting wear. So, a high hardness material, Al 2 O 3 based ceramic matrix composite (CMC) coatings were utilized to improve the tribological properties of the engineered surface. At this juncture, fretting wear behaviour of atmospheric plasma sprayed Al 2 O 3 –3 and 8 mol% Y 2 O 3 stabilized ZrO 2 (3YSZ and 8YSZ)‑carbon nanotube (CNT) based CMC coatings were investigated. The fretting wear rate of Al 2 O 3 based CMC coatings against WC ball was observed as 0.97–1.87 × 10−6 mm3N−1 m−1. The least in wear resistance of Al 2 O 3 -CNT (1.87 × 10−6 mm3N−1 m−1) among the composite coating is attributed to low hardness and high Hertzian contact pressure (1.65 GPa) on the coatings. Among the composite coatings, Al 2 O 3 -3YSZ and Al 2 O 3 -8YSZ-CNT showed an improved wear resistance (~40.1% and ~34.5%, respectively) with wear rate of 0.97 × 10−6 mm3N−1 m−1 and 1.06 × 10−6 mm3N−1 m−1, respectively. It is attributed to improved mechanical properties, altered surface by reciprocating motion and the presence of wear debris, which reduces the wear rate by acting as a third body. So, there is an overestimation of wear rate (4.1–6.6 times) compared to that of experimentally calculated wear rate. Further, the Al 2 O 3 -YSZ-CNT composite showed fatigue crack on the fretting wear surface due to low plasticity index (62.0–109.3 MPa) of the coating. Also, the gradual change of running-in regime to the steady-state regime is achieved in the CNT reinforced composite coatings due to high resistance by the coatings which possess commendable mechanical properties. The frictional force mapping during the reciprocating motion confirms the rapid and gradual transition of two different regimes in the composite coatings. • Synergistic effect of YSZ and CNT improves the wear resistance of the coatings. • Over estimation of wear rate is attributed to altered surface of the wear scar. • Wear debris accumulated in the territory of wear scar was backing in enhancement of frictional force. • Drastic increase in the frictional force at the extreme edge of each fretting wear cycle. • Al2O3-20 vol% 3YSZ coatings is an optimum material among other composite with improved wear resistance (up to 40.1%). [ABSTRACT FROM AUTHOR]

In the performed study, a novel fabrication of agar-based nanofibers was electrospun in an asymmetric bilayer dressing for biomedical transdermal patches. The optimal parameters for the fabrication of agar-based nanofibers after optimization were a feed rate of 10 μL/min, a 7 cm collector-to-nozzle distance, a 15 kV applied voltage, and a 700-rpm rotating collector speed. Coaxial nanofibers, as a second asymmetric layer, were produced using polyvinyl alcohol (PVA) with cephalexin hydrate, an antibacterial drug, as the core and agar-PCL as the sheath. The morphology of the developed uniaxial and coaxial nanofibrous layers was analysed using a scanning electron microscope and transmission electron microscopy, respectively. For the formation of bilayer asymmetric structures, the agar-PCL uniaxial layer was fabricated over the layer of coaxial PVA and agar-PCL layers for sustained drug release. The agar-based nanofibrous mats exhibited tensile strength of 7 MPa with 40 % elongation failure, 8-fold increased swelling, enhanced wettability (60° contact angle), and a moisture transmission rate of 2174 g/m2/day. The developed coaxial bilayer mats exhibited antimicrobial activity, hemocompatibility, and cytocompatibility. Overall, this novel agar nanofibrous dressing offers promising potential for advanced biomedical applications, particularly as transdermal patches for efficient drug delivery systems. [ABSTRACT FROM AUTHOR]

• Oxidation kinetics of ZrB2 and HfB2 powders and SiC reinforced composites. • Higher heating rates shift the peak oxidation temperatures to higher temperature. • SiC reinforcement increases oxidation initiation temperature and activation energy of oxidation. • Lower mass gain in HfB2 composite powders compared to that of ZrB2 based powders. • Higher oxidation resistance in SiC reinforced ZrB2 composite than HfB2-composite, sintered under similar conditions. Non-isothermal simultaneous thermal analysis technique elicited the peak oxidation and mass gain shifts to higher temperatures with SiC addition prompting enhanced activation energy (323 kJ/mol to 593 kJ/mol in ZrB 2 and 199 kJ/mol to 207 kJ/mol in HfB 2). On one hand where the peak oxidation temperature in ZrB 2 -SiC pellet could not be observed affirming its high oxidation resistance with negligible mass gain, whereas on the other hand the activation energy of HfB 2 -SiC pellet increased to 266 kJ/mol. HfB 2 -SiC powder is observed to follow 3D diffusion dominated (Jander equation) mechanism in which mass gain increased linearly from peak oxidation temperature ∼710−730 °C at 10–20 °C/min heating rates till the maximum programmed temperature of 1200 °C. Though mass gain starts and almost ends within a range of 5 °C at any heating rate in the case of monolithic ZrB 2 and HfB 2 powders and in ZrB 2 -SiC composite powder at peak oxidation temperature, it (mass gain) remains almost negligible in spark plasma sintered ZrB 2 -SiC and HfB 2 -SiC composites. [ABSTRACT FROM AUTHOR]

This study investigates the effect of laser surface treatment on spark plasma sintered (Zr-Ta-W-Ti)C-SiC (ZTaWT-S) based high entropy ceramic (HEC) composites, reinforced with multiwalled carbon nanotubes (CNT) (ZTaWT-SC), graphite (ZTaWT-SG), and graphene nanoplatelets (GNP) (ZTaWT-SGNP). The increased hardness of the laser-treated composites (25–33 GPa) when compared to that of untreated composites (23–28 GPa) is attributed to the high compressive residual stresses, ranging from 1400 to 2900 MPa. The laser-treated ZTaWT-SGNP composite exhibited a minimum scratch wear rate of ∼0.9 × 10−1 mm3/N.m, representing a 57 % and 73 % reduction compared to the untreated ZTaWT-SGNP and the laser-treated ZTaWT-S, respectively. ZTaWT-SGNP composite demonstrated the best resistance to damage accumulation, due to the synergistic effects of laser treatment and GNP reinforcement, enhancing its suitability for extreme environments. [Display omitted] [ABSTRACT FROM AUTHOR]

This research presents an analytical method to investigate the effect of volume fraction and the number of outer walls of multiwalled carbon nanotube (MWNT) reinforcement on load carrying capability in the aluminum oxide matrix. Interfacial shear stress transfer and energy dissipation have been estimated using the Cox model. Critical energy release rate for the debonding of MWNT from the matrix is also estimated based on the crack deflection. The computed results sufficiently manifest that MWNT pullout and crack deflection contributes greatly to improved fracture toughness of carbon nanotube reinforced aluminum oxide nanocomposites. [ABSTRACT FROM AUTHOR]

A modified model using the Eshelby equivalent tensor is developed to evaluate overall elastic properties of carbon nanotube (CNT) reinforced aluminum oxide nanocomposites. This model accounts for the effect of carbon nanotube geometry and porosity on the effective elastic modulus. Experimental results are compared with the computed predictions. Computed results show higher elastic modulus values, which are attributed to the perfect bonding between the reinforcement and the matrix. It is concluded that the modified Eshelby model can predict the elastic property of CNT reinforced ceramic nanocomposites. [ABSTRACT FROM AUTHOR]

ZrB 2 composites reinforced with SiC of two different particle sizes (coarse ~30 μm and fine ~5 μm) were processed using spark plasma sintering. The oxidation behaviour of the synthesised composites was investigated at 1500 °C under two different partial pressures of oxygen. At higher oxygen partial pressure of 0.21 atm, coarse SiC reinforced ZrB 2 composite developed thicker oxide layers as compared to that of fine SiC reinforced ZrB 2 composite. The thicker silica layer provides an enhanced oxidation resistance for extended exposure periods of greater than 3 h. However, at lower oxygen partial pressure of 2 × 10−5 atm, fine SiC reinforced ZrB 2 composite showed better oxidation resistance due to segregation of finer ZrO 2 particles on the surface, which prevented inward transportation of oxygen. [ABSTRACT FROM AUTHOR]

• Prepared environmentally-benign, rare-earth free, double perovskite Ca x Sr 2−x TiCoO 6. • CSTC shows intermediate metallic phase transition between two semiconductors phases. • Positive Seebeck coefficient suggests holes as majority charge carriers in CSTC. • Charge transport mechanism explained by small polaron hopping conduction model. Present work investigates the effect of calcium doping on the structure and thermoelectric properties of Sr 2 TiCoO 6 (STC) double perovskite. Environmentally friendly rare earth free Ca x Sr 2−x TiCoO 6 (0.0 ≤ x ≤ 0.3) (CSTC) ceramics were synthesized using solid state synthesis route. CSTC ceramics were found to possess a cubic crystal structure with Pm 3 ¯ m space group as confirmed by Rietveld refinement of XRD data. Microstructure analysis was carried out by SEM and energy dispersive x-ray spectroscopy. The temperature dependent electrical conductivity and thermopower of these oxides showed the semiconductor to metal transition at around 700 K. X-ray photoelectron spectroscopy (XPS) confirmed the presence of multiples oxidation states of Co and Ti creating defect sites in these oxides. CSTC ceramic samples exhibited positive Seebeck coefficient implying p-type behavior. Charge transport mechanism of all the CSTC samples was found to be governed by small polaron hopping model. [ABSTRACT FROM AUTHOR]

Abstract The demand of a new generation spacecraft component has led to the development of a novel structure, which combines the traits of both functionally graded material (FGM) as well as an ultra-high temperature ceramics (UHTC). Herein, FGM based on the well-established ZrB 2 -20SiC (vol%) UHTC with the reinforcement of carbon nanotubes (CNT) is processed via powder metallurgy and spark plasma sintering (SPS). A densely graded microstructure with a crack-free seamless interface is witnessed along the cross-section of the FGM. The CNT in the optimized FGM is found to be efficaciously embedded in the matrix retaining its structure during sintering (at 1850 °C), shown microstructurally and supplemented by Raman spectroscopy. Enhanced mechanical and wear resistance of the FGM when compared to that of the conventional ZrB 2 UHTC is attributed to the dense, crack-free microstructure and CNT pull-out mechanism. Oxidation test revealed an enhancement in the thermal stability as the onset of oxide formation starts above 886 °C (i.e. > 30% when compared to that of monolithic ZrB 2). The thermo-structural performance of the processed FGM simulated using finite element method (FEM) indicated a reduction in the thermal residual tensile stresses (~ 8.1 times) which mitigates the crack propagation. The FEM analysis complements the high indentation fracture toughness values of the FGM even at the interfaces (similar to that found in each layer), establishing FGM approach superior to that of the conventional UHTC composites. Thus, addition of CNT in ZrB 2 -20SiC based FGM are conducive enough to be engineered as a potential material, poised to shape the future of re-entry vehicles. [ABSTRACT FROM AUTHOR]

Role of carbon nanotubes (CNTs) on solid solutioning in SiC reinforced equi-volume (40:40) composition of HfB 2 + ZrB 2 is investigated. Incomplete solid solutioning occurred under given sintering conditions in presence of 20 vol% SiC. However, CNTs addition resulted in heterogeneous solid solution formation which is evident from SEM and TEM micrographs and confirmed through EDS analysis and peak de-convolution in XRD. TEM investigation revealed the retention of CNTs and presence of defect structures like stacking faults in the SiC phase is ascribed to the compressive stresses generated during cooling after the sintering process. With CNTs reinforcement, micro-hardness and elastic modulus increased from 10.2 GPa to 11.7 GPa and 129 GPa to 141 GPa, respectively. The reduction in peak oxidation temperature (from 751‐773 °C to 725‐746 °C) and weight gain starting temperature (from 731‐750 °C to 684‐707 °C) with CNTs reinforcement elicits a concurrent reduction in the oxidation resistance. [Display omitted] • CNTs addition increase solid solutioning inhomogeneity in HfB 2 - ZrB 2 -SiC composite. • CNTs (and their effect on solid solutioning) improve micro-mechanical properties. • Inhomogeneous solid solutioning decrease peak oxidation temperature. • Compressive stresses generated in SiC phase produce defects like stacking faults. • Compressive stresses in SiC phase remain un-altered with CNTs incorporation. [ABSTRACT FROM AUTHOR]

An environment-friendly phosphate chemical conversion (PCC) coating has been deposited on novel LAT971 (Mg-9 wt%Li-7 wt%Al-1 wt%Sn) and LATZ9531 (Mg-9 wt%Li-5 wt%Al-3 wt%Sn-1 wt%Zn) alloys for improving their corrosion resistance. A dense and homogeneous flower like morphology (∼30 μm thick) was observed on the PCC coated Mg-Li based alloys. The presence of calcium hydrogen phosphate hydrate, tricalcium phosphate and trimagnesium phosphate were confirmed from the X-ray diffraction and X-ray photoelectron spectroscopy analysis. A lower corrosion current density of 6.74 × 10 −7  mA/cm 2 and 5.39 × 10 −7  mA/cm 2 was obtained for PCC coated alloys in 3.5% NaCl aqueous solution than that of uncoated LAT971 (0.82 mA/cm 2 ) and LATZ9531 (0.34 mA/cm 2 ) alloys, respectively, which offers corrosion protection efficiency of >99%. Electrochemical impedance spectroscopy (EIS) has revealed that the inner PCC coating (at coating/substrate interface) delay the direct contact between electrolyte and substrate, which offered higher charge transfer resistance (>4 orders of magnitude) than that of uncoated alloys. Thus, the PCC coating provides an effective corrosion protection to the ultra-lightweight LAT971 and LATZ9531 alloys surface and may be helpful in proving good anchoring with the top organic coatings or paints. [ABSTRACT FROM AUTHOR]

In order to control the inflammatory reaction and bone resorption due to wear debris and obtain a multi-functional composite with superior mechanical and tribological properties, antioxidant ceria (CeO 2 ) and antibacterial silver (Ag) nanoparticles are synergistically reinforced in hydroxyapatite (HA) matrix. Enhanced hardness (5.3–8.6 GPa), elastic modulus (120.8–167.9 GPa) and fracture toughness (0.21–0.90 MPa m 1/2 ) and reduced brittleness index (24.8–9.6 µm −1/2 ) of HA-CeO 2 -Ag composite were achieved, when compared to that of HA. A multi-length scale tribological study (by dissimilar damage mechanisms in fretting and scratch) is presented. Observed herein, that enhanced mechanical properties elicited a wear resistance of 89% (by fretting) and 13% (by scratch), with synergistic CeO 2 and Ag reinforcement. Compression during fretting over a localized length (100 µm) resulted in the closure of pores, whereas micro-scratching exposed a higher number of interfaces (by an order of magnitude), reducing wear resistance at higher length scales. In summary, HA-CeO 2 -Ag composite restricts tribological damage effectively over multi-length scales, thereby serving as an optimal substrate with efficient load-bearing capacity for orthopedic applications. [ABSTRACT FROM AUTHOR]

Sintering kinetics and densification of tantalum carbide (TaC) based ultra-high temperature ceramics (UHTC) processed using spark plasma sintering (SPS) were investigated. Samples sintered in the temperature ranging from 1600 °C to 2300 °C for 15 min under uniaxial pressure of 50 MPa showed increasing densification (~77% to 99% from 1600 °C to 2300 °C) accompanied by substantial grain growth (~0.57 μm to ~4.05 μm). Below 1900 °C, the densification mechanism was grain-boundary sliding with an apparent activation energy of 97.3 ± 10.2 kJ/mol. However above 1900 °C, the activation energy was found to be 232.7 ± 19.6 kJ/mol with grain boundary diffusion to be an active densification mechanism. The flexural strength (from 161.3 ± 10.4 MPa to 326.5 ± 10.5 MPa) and elastic modulus (from 375.7 ± 3.1 GPa 535.4 ± 4.7 GPa) was observed to increase with the increasing sintering temperature. The study explicitly establishes that the dense bulk TaC ceramic can be produced by SPS in a shorter time and lower sintering temperature, while maintaining the compositional stoichiometry. [ABSTRACT FROM AUTHOR]

Electrophoretically deposited Ni-BN composite coating was strengthened with graphene (Ni-BN-Gr), carbon nanotubes (Ni-BN-CNT) and diamond (Ni-BN-D) carbonaceous reinforcements. Highest hardness (2.0 GPa) and elastic modulus (133.5 GPa) of Ni-BN-D coating than Ni-BN-CNT (1.96 GPa and 102.1 GPa, respectively), Ni-BN-Gr (1.94 GPa and 92.0 GPa respectively) and also from Ni-BN (1.89 GPa and 91.5 GPa, respectively) coatings was linked through high compressive stress (−601 MPa), dislocation density (8.9 × 10 15 m −2 ) and yield strength (4.4 GPa). The micro-scratching damage was contributed by ploughing and adhesion components, which were compared with that of experimental frictional values. Addition of graphene, CNT and diamond in Ni-BN composite showed a decrease in wear volume (from 1.66 × 10 −8 m 3 to 0.45 × 10 −8 m 3 ) due to the synergetic lubricating effect of BN and carbonaceous reinforcements. Thus, Ni-BN-D restrict inception of multiscale wear and can be a potential three phase metal-ceramic coating for engineering and industrial applications. [ABSTRACT FROM AUTHOR]

The current work focuses on enhancing the flexural strength and fracture toughness of zirconium diboride (ZrB 2 ) reinforced with silicon carbide (SiC) and carbon nanotubes (CNT). The flexural strength has shown to increase by ~ 1.2 times from 322.8 MPa (for ZrB 2 ) to 390.7 MPa and fracture toughness up to 3 times from 3.2 MPam 0.5 (for ZrB 2 ) to 9.5 MPam 0.5 with the synergistic addition of both SiC and CNT in ZrB 2 matrix through energy dissipating mechanisms such as deflection, branching and strong interfacial bonding evidenced from the transmission electron microscopy (TEM). A modified fractal model is used to evaluate the fracture toughness and delineate the contribution of residual stresses, and reinforcements (SiC and CNT) in enhancing the fracture toughness. Interfacial bonding, in terms of a debonding factor, was also evaluated by theoretically predicting the elastic modulus and then correlated with the microstructure along with other mechanical properties of ZrB 2 -SiC-CNT composites. [ABSTRACT FROM AUTHOR]

Ultra-high molecular weight polyethylene (UHMWPE) is one of the most promising materials for cartilage replacement as an acetabular cup liner. Implant failure due to infection is a serious issue and ZnO is a well-known antibacterial agent. In the current work, the effect of the morphology of ZnO on the mechanical properties of UHMWPE is studied, where ZnO is incorporated both as nanoparticles (ZnO(NP)) and micro-rods (ZnO(R)) at 5, 10, 15 and 20 wt%. Uniaxial tensile testing of compression-moulded composites elicited a decrease of 8.8% in the Young's modulus in UHMWPE-ZnO(R) (named ZnO(R)-PE), whereas an increase of 21.1% in the Young's modulus was observed for UHMWPE-ZnO(NP) (named ZnO(NP)-PE). This contrasting effect on the Young's modulus arising due to differences in ZnO morphology is discussed and analysed using the rule of mixture and the Halpin–Tsai equation. Even when accounting for inherent porosity, and with similar crystallinity to that of base UHMWPE, these models fail to explain the decrease in the Young's modulus of compression-moulded ZnO-PE composites. Estimation of Young's modulus via a modified geometric factor is followed by proposing an empirical relation to account for interfacial strength and narrow the bounds of the predicted elastic modulus, thus making the Halpin–Tsai estimations reach the actual experimental values. [ABSTRACT FROM AUTHOR]

Current work pursues generating controlled bimodal microstructure by plasma spraying of micrometer-sized Al 2 O 3 and nanostructured spray-dried agglomerate with reinforcement of 20 wt% of 8 mol % yttria stabilized zirconia (8YSZ) and 4 wt% carbon nanotube (CNT) as potential thermal barrier coating (TBC) on the Inconel 718 substrate. Composite coatings exhibit bimodal microstructure of: (i) fully melted and resolidified microstructured region (MR), and (ii) partially melted and solid state sintered nanostructured regions (NR). Reinforcement with 8YSZ has led to an increase in hardness from ∼12.8 GPa (for μ-Al 2 O 3) to ∼13.9 GPa in MR of reinforced Al 2 O 3 -YSZ composite. Further, with the addition of CNT in Al 2 O 3 -8YSZ reinforced composite, hardness of MR has remained similar ∼13.9 GPa (8YSZ reinforced) and ∼13.5 GPa (8YSZ-CNT reinforced), which is attributed to acquiescent nature and non-metallurgical bonding of CNT with MR. Indentation fracture toughness increased from 3.4 MPam0.5 (for μ-Al 2 O 3) to a maximum of 5.4 MPam0.5 (8YSZ- CNT reinforced) showing ∼57.7% improvement, which is due to crack termination at NR, retention of t-ZrO 2 (∼3.3 vol%) crack bridging, and CNT pull-out toughening mechanisms. Modified fractal models affirmed that the introduction of bimodal microstructure (NR) i.e., nanometer-sized- Al 2 O 3 , nanostructured 8YSZ and CNTs in the μ-Al 2 O 3 (MR) contributes ∼44.6% and ∼72% towards fracture toughness enhancement for A8Y and A8YC coatings. An enhanced contribution of nanostructured phases in toughening microstructured Al 2 O 3 matrix (in plasma sprayed A8YC coating) is established via modified fractal model affirming crack deflection and termination for potential TBC applications. [ABSTRACT FROM AUTHOR]

A biocompatible hydroxyapatite (HA) coating has been deposited on novel Mg-9Li-7Al-1Sn (LAT971) and Mg-9Li-5Al-3Sn-1Zn (LATZ9531) alloys to control their corrosion and rapid degradation. HA coating was applied by a simple two-step conversion coating process, where phosphate conversion coating (PCC) is alkali treated to form HA coating. A ~ 34 μm and ~ 26 μm thick coating was observed on LAT971 and LATZ9531 alloys, respectively, and phase analysis confirmed it to be HA via X-ray diffraction technique. Potentiodynamic polarization test reveals that the HA-coated LAT971 alloys showed the protection efficiency of ̴ 96% with the lower corrosion rate of 23 μm/y than the uncoated one (525 μm/y). The HA-coated LATZ9531 alloy showed the protection efficiency of ~ 12% with a relatively lower corrosion rate of 567 μm/y than that of uncoated one (647 μm/y). Moreover, the polarization resistance of HA-coated LAT971 and LATZ9531 was measured to be ~ 113 times and 1.2 times of their uncoated alloys, respectively. Electrochemical impedance spectroscopy (EIS) results showed the lower degradation rate of HA-coated alloys with the higher charge transfer resistance for the coated LAT971 (3.91 MΩ·cm 2 ) and LATZ9531 (1.13 kΩ·cm 2 ) than that of uncoated one (686 Ω·cm 2 and 204 Ω·cm 2 , respectively). Immersion test in simulated body fluid (SBF) revealed rapid degradation of the uncoated alloys whereas HA-coated alloys showed a limited degradation with the biomineralization ability. Thus, the limited degradation and biomineralization ability of the HA-coated alloys meets the specific requirement for the biodegradable implants for load bearing applications. [ABSTRACT FROM AUTHOR]

Ultra high molecular weight polyethylene (UHMWPE) is widely used as an acetabular cup liner for cartilage replacement in hip arthroplasty. The implant failure mainly occurs due to the wear of polymeric liner. Thus, in order to increase the wear resistance of polymer liner, 20 wt % ZnO is reinforced in compression molded UHMWPE. Herein, the role of various ZnO morphologies, viz. microrods (R), nanoparticles (NP), and microdisks (D) is assessed on the tribological properties (such as wear rate and coefficient of friction) of UHMWPE matrix. Sliding wear (bulk length scale) and fretting wear (micrometer length scale) have shown highest wear resistance of ZnO(D) reinforced UHMWPE. On one hand, ZnO(R) experience pronounced buckling and weak interfacing in matrix and show an increased sliding wear rate of 8.08 × 10 −14 m 3 /Nm (when compared to that of 5.88 × 10 −14 m 3 /Nm for UHMWPE). Contrastingly, ZnO(D) exhibited strong interfacing and demonstrated a reduced wear rate of 1.80 × 10 −14 m 3 /Nm. A similar trend of wear rate was observed at micrometer length scale i.e. least (1.17 × 10 −21 m 3 /Nm) for ZnO(D) and highest (3.19 × 10 −21 m 3 /Nm) for ZnO(R) when compared to that of UHMWPE (2.40 × 10 −21 m 3 /Nm). Damage mechanism in ZnO(NP) is attributed to the formation of tribofilm on counter surafce. Further, wear-resistance rendered by ZnO morphologies is found to be higher (up to 19%) in sliding wear when compared to that of fretting. In summary, enhanced tribological resistance of UHMWPE-ZnO(D) can make it a potential polymeric liner in total joint arthoplasty. [ABSTRACT FROM AUTHOR]

Mesoporous silica‐based materials are currently being explored as a new type of bioscaffold for bone regeneration applications. Zinc(Zn) ion incorporation is shown to play an important role in promoting bone regeneration and also providing antimicrobial activity to the scaffold materials. In this work, the role of pore size, geometry, and ordered structure on the Zn loading and release performance of two different mesoporous silica, SBA‐1 and SBA‐15, are compared. Zn loading is varied from 2.5 to 10 wt% for both samples, and its effect on the antibacterial and osteogenic activity is evaluated. Zn loading up to 10 wt% has a negligible effect on the morphology and textural properties of the mesoporous silica samples. The inductively coupled plasma mass spectrometry (ICP‐MS) analysis reveals that SBA‐15 exhibits significantly higher Zn release in Luria‐Bertani (LB) broth as compared to SBA‐1 that is reflected in the higher antibacterial activity of SBA‐15 against both gram‐positive and gram‐negative bacteria. Various assays show that 5 wt% Zn loading is sufficient to produce both bactericidal and inhibitory effects on bacterial cells. The 5 wt% Zn‐loaded samples induce osteogenic differentiation ofavianized bone marow‐derived stromal cells (TVA‐BMSCs) though SBA‐15 samples show better compatibility compared to SBA‐1, suggesting that Zn incorporation can produce sufficient antibacterial effect and osteogenic differentiation of TVA‐BMSCs. [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]

Difficulties associated with the manufacturing of diboride based large and complex shapes mandate them to be joined for extreme applications. In the present work, spark plasma sintering is utilized to join HfB 2 -ZrB 2 -SiC-B 4 C-CNT (HZSBC) based composites with Ni-interlayer at 1100 °C and without interlayer at 1800 °C. Microstructural analysis has elicited the formation of Ni diffused reaction zone (150–200 μm), and unaffected HZSBC composite for HZSBC-Ni-HZSBC joined composite (at 1100 °C), which gets merged into a homogeneous microstructure (without any distinguishable interface) in the HZSBC-HZSBC joint (without Ni-interlayer). An overall reduction of 18% and 14% is elicited in hardness and elastic modulus, respectively, in the HZSBC-Ni-HZSBC joint, whereas in HZSBC-HZSBC joined composite, uniform hardness and elastic modulus of ∼22 GPa and ~398 GPa, respectively, is observed. Further, the bending and shear strength of the joined composites was obtained to be ∼209 MPa and ∼41 MPa, respectively, for HZSBC-Ni-HZSBC, which increased to ~342 MPa and ∼81 MPa, respectively, for HZSBC-HZSBC. In conjunction, though superior high-temperature (1500 °C) oxidation protection is witnessed in HZSBC-HZSBC joint, with a thinner oxide layer, both display SiO 2 -rich protective glassy layer, making these composites potential candidates for use in atmospheric re-entry conditions. [ABSTRACT FROM AUTHOR]

Bacterial infection of implants can be controlled by selective trapping of bacteria, followed with consequent killing by targeted antibacterial agents. Herein, the role of various ZnO morphologies, viz. micro-rods (R), nanoparticles (NP), and micro-disks (D) on antibacterial efficacy of ZnO via release of Zn 2 + and H 2 O 2 is assessed, both as isolated powders and via incorporating them in cytocompatible ultra high molecular weight polyethylene (UHMWPE). Though ZnO is antibacterial, interestingly, all ZnO morphologies elicited a supportive growth of gram-negative bacteria ( Escherichia coli ) in culture medium (until 28–35 μg/ml). But, all ZnO morphologies did elicit bactericidal effect on gram positive bacteria ( Staphylococcus aureus or Staphylococcus epidermidis ) both in culture medium (for 0–2.5 μg/ml) or when incorporated (5–20 wt.%) into UHMWPE. The bactericidal mechanisms were quantified for various ZnO morphologies via: (i) H 2 O 2 production, (ii) Zn 2 + release, and (iii) the presence of surface oxygen vacancies. On one hand, where only ZnO(NP) elicited release of H 2 O 2 in the absence of light, maximum Zn 2 + release was elicited by ZnO(D). Interestingly, when ZnO is incorporated as reinforcement (5–20 wt.%), its antibacterial action against E. coli was vividly observed due to selective proliferation of bacteria only on friendly UHMWPE matrix. Hence, luring bacteria on affable UHMWPE surface can be complemented with their targeted killing by ZnO present in composite. [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]

[Display omitted] • Progress on joining of (Hf,Zr)B 2 diboride based ultra high temperature ceramics (UHTCs) • Joining of UHTCs for thermal protection, and thermal management. • Interfacial wettability and reactivity of diborides and solid-state diffusion bonding. • Role of Nickel filler on interfacial reactivity, phases, and wettability of diborides. • Molecular dynamics and density function theory to predict wettability of diborides. • Future directions of spark plasma sintering, towards joining of UHTCs. Stringent applications of HfB 2 and ZrB 2 based ultra-high temperature ceramics (UHTCs) for hypersonic and re-entry space vehicles necessitate their joining with ceramics or metallic structural alloys. Brazing is the most used joining method for diborides requiring good wettability; consequently, this article critically reviews the high temperature interfacial wettability of diborides in contact with different metals like Ag, Au, Ni, Cu, etc. Contact angle data of various metals in contact with diboride is summarized in this paper along with the assessment of the underlying wetting mechanisms. Surface oxides, testing atmosphere, and other aspects affecting the wettability are evaluated along with the approaches to improve it. High melting point (∼1450 °C) and lower contact angle (∼20°) of Nickel on diborides makes it a good choice as filler material; thus, a detailed case study considering its wettability, phase diagram etc. is reviewed to elicit interfacial reactivity with HfB 2 and ZrB 2. Molecular dynamic simulation and density function theory predicting the wettability and adhesion of various metals on the surface of diborides are also discussed, which exemplify visualization of the experimentally observed values. Microstructural evolution during different joining methods; i.e. active metal brazing, diffusion bonding, welding etc.; are described in detail providing an insight into the final properties of the joint in terms of interfacial strength (shear and bending strength) and thermal stability (oxidation resistance, plasma exposure etc.). The impact of thermal expansion mismatch, residual stresses, and chemical reactions induced during joining are also highlighted to assist in parameter selection. This article concludes with the summary on the current state of the art in the joining diborides followed by scope for future research directions. [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia (YSZ) is a potential thermal insulating ceramic for high temperature applications (>1000 °C). YSZ reinforced with multi-walled carbon nanotubes (MWNTs) was processed via spark plasma sintering to produce dense, crack-free homogeneous sample and avoid any degradation of MWNTs when sintered using conventional routes. Despite porosity, the addition of MWNT has a profound effect in improving the damage tolerance of YSZ by allowing the retention of tetragonal phase. However, at some instances, the crack lengths in the MWNT reinforced YSZ matrices have been found to be longer than the standalone counterparts. Therefore, it becomes inappropriate to apply Anstis equation to calculate fracture toughness values. In this regard, a combined analytical cum numerical method is used to estimate the theoretical fracture toughness and quantitatively analyze the mechanics of matrix cracking in the reinforced composite matrices incorporating the effects of various factors (such as far-field stresses, volume fraction of MWNTs, change in the modulus and Poisson’s ratio values along with the increase in porosity, and bridging and phase transformation mechanism) affecting the fracture toughness of YSZ-MWNT composites. The results suggest that the incorporation of far-field stresses cannot be ignored in estimating the theoretical fracture toughness of YSZ-MWNT composites. [ABSTRACT FROM AUTHOR]

Ultra-high temperature ceramics (UHTCs) have played a significant role in fulfilling demands for the thermal protection system (TPS) in the aerospace sector, however, a promising candidate has not emerged yet. This critical review provides typical inconsistencies and new perspectives related to UHTCs in terms of: (i) material and processing: i.e., sinterability, reinforcements, microstructural evolution, (ii) properties and performance correlation with the processing conditions and resulting microstructure, and (iii) outlook on the most promising ZrB 2 -HfB 2 -SiC-based composites as potential candidates for hypersonic leading edge and re-entry structures. An optimal selection of the content, size and reinforcing phase (such as silicides, refractory carbides, and carbon-based, etc.) is mandated in upgrading the thermo-mechanical performance of UHTCs to sustain elevated temperature (1700 °C), exhibiting flexural/fracture strength of >300 MPa, high thermal conductivity >14.5 Wm−1K−1, and high oxidation resistance (<80 gm−2 over 2 h at 1400 °C). From emphasis on the powder purity, and sintering additives on affecting the densification, mechanical properties and high temperature oxidation, improvements in the functional performance of UHTCs are carried forward with emphasis mainly on borides and carbides. Emergence of SiC as most promising sintering additive with optimal content of ∼20 vol%, and with supplemented HfB 2 addition in ZrB 2 -HfB 2 -SiC based UHTCs have exhibited higher oxidation resistance and may serve as conceivable entrants for hypersonic vehicles. Further, the review leads the reader to developing new materials (including silicides, MAX phases, and high entropy UHTCs), incorporating novel strategies like designing layered structures or functionally graded materials (FGM), and effective joining to allow the integration of smaller components into scaled up structures. On one hand, where plasma arc-jet exposure mimics high heat-flux exposures, the utilization of multi-length-scale computational modeling (such as finite element methods, density functional theory, ab initio etc.) allows assessing the material performance under dynamic changes (of variable partial pressure, temperatures, gradation, etc.) towards perceiving new insights into the structural stability and thermo-mechanical properties of UHTCs. This review critically underlines the present state of the art and guides the reader towards the futuristic development of new class of high-temperature materials for TPSs. [ABSTRACT FROM AUTHOR]

This work reports the processing-microstructure-property correlation of novel HA- BaTiO3-based piezobiocomposites, which demonstrated the bone-mimicking functional properties. A series of composites of hydroxyapatite ( HA) with varying amounts of piezoelectric BaTiO3 ( BT) were optimally processed using uniquely designed multistage spark plasma sintering ( SPS) route. Transmission electron microscopy imaging during in situ heating provides complementary information on the real-time observation of sintering behavior. Ultrafine grains (≤0.50 μm) of HA and BT phases were predominantly retained in the SPSed samples. The experimental results revealed that dielectric constant, AC conductivity, piezoelectric strain coefficient, compressive strength, and modulus values of HA-40 wt% BT closely resembles with that of the natural bone. The addition of 40 wt% BT enhances the long-crack fracture toughness, compressive strength, and modulus by 132%, 200%, and 165%, respectively, with respect to HA. The above-mentioned exceptional combination of functional properties potentially establishes HA-40 wt% BT piezocomposite as a new-generation composite for orthopedic implant applications. [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]

Abstract: Chromium carbide is widely used as a tribological coating material in high-temperature applications requiring high wear resistance and hardness. Herein, an attempt has been made to further enhance the mechanical and wear properties of chromium carbide coatings by reinforcing carbon nanotubes (CNTs) as a potential replacement of soft binder matrix using plasma spraying. The microstructures of the sprayed CNT-reinforced Cr3C2 coatings were characterized using transmission electron microscopy and scanning electron microscopy. The mechanical properties were assessed using micro-Vickers hardness, nanoindentation and wear measurements. CNT reinforcement improved the hardness of the coating by 40% and decreased the wear rate of the coating by almost 45–50%. Cr3C2 reinforced with 2wt.% CNT had an elastic modulus 304.5±29.2GPa, hardness of 1175±60 VH0.300 and a coefficient of friction of 0.654. It was concluded that the CNT reinforcement increased the wear resistance by forming intersplat bridges while the improvement in the hardness was attributed to the deformation resistance of CNTs under indentation. [Copyright &y& Elsevier]

Abstract: Multiwalled carbon nanotube (CNT) reinforced aluminum nanocomposite coatings were prepared using cold gas kinetic spraying. Spray drying was used to obtain a good dispersion of the nanotubes in micron-sized gas atomized Al–Si eutectic powders. Spray dried powders containing 5 wt.% CNT were blended with pure aluminum powder to give overall nominal CNT compositions of 0.5 wt.% and 1 wt.% respectively. Cold spraying resulted in coatings of the order of 500 μm in thickness. Fracture surfaces of deposits show that the nanotubes were uniformly distributed in the matrix. Nanotubes were shorter in length as they fractured due to impact and shearing between Al–Si particles and the Al matrix during the deposition process. Nanoindentation shows a distribution in the elastic modulus values from 40–229 GPa which is attributed to microstructural heterogeneity of the coatings that comprise the following: pure Al, Al–Si eutectic, porosity and CNTs. [Copyright &y& Elsevier]

Nanomechanical properties of plasma-sprayed HfN coating with and without hot isostatic pressing (HIP) treatment were evaluated using nanoindentation. For HIPed HfN coating, the elastic modulus (E) and yield strength increase whereas the hardness (H), H/E ratio and fraction of the elastic work decrease. HIPed HfN coating shows a larger pile-up around the indent as compared to as-sprayed HfN. HIPing causes densification and improvement in inter-splat bonding which subsequently lead to increase in nanomechanical properties. [Copyright &y& Elsevier]