A fracture analysis is developed for crack initiation sequences occurring during sharp indentation of brittle materials. Such indentations, generated by pyramidal or conical loading, generate elastic and plastic deformation. The analysis uses a nonlinear elements-in-series model to describe indentation load–displacement responses, onto which lateral, radial, cone, and median crack initiation points are located. The crack initiation points are determined by extension and application of a contact stress-field model coupled to the indentation load, originally developed by Yoffe, in combination with crack nuclei coupled to the indentation displacement to arrive at an explicit fracture model. Parameters in the analysis are adapted directly from experimental fracture and deformation measurements, and the analysis outputs are directly comparable to experimental observations. After adaptation, crack initiation loads and sequences during indentation loading and unloading of glasses and crystals are predicted by the model from material modulus, hardness, and toughness values to within about 25% of peak contact load. This work is dedicated to George M. Pharr IV on the occasion of his 65th birthday in recognition of his contributions to indentation mechanics.

The measured hardness of a metal crystal depends on a variety of length scales. Microstructural features, such as grain size and precipitate spacing, determine the intrinsic material length scale. Extrinsic (test) length scales, such as the indentation depth, lead to the indentation size effect (ISE), whereby it is typically found that smaller is stronger. Nix and Gao [J. Mech. Phys. Solids46, 411 (1998)] developed a widely used model for interpreting the ISE based on forest hardening in single crystalline pure metals. This work extends that model to consider the hardness of polycrystals and alloys, as well as introducing a finite limit to the hardness at very small extrinsic length scales. The resulting expressions are validated against data from the literature. It is shown that a reasonable estimate of the intrinsic material length scale can be extracted from a suite of hardness tests conducted across a range of indentation depths using spherical indenters of various radii.

A new deep level transient spectroscopy (DLTS) technique is described, called half-width at variable intensity analysis. This method utilizes the width and normalized intensity of a DLTS signal to determine the activation energy and capture cross section of the trap that generated the signal via a variable, kO. This constant relates the carrier emission rates giving rise to the differential capacitance signal associated with a given trap at two different temperatures: the temperature at which the maximum differential capacitance is detected, and an arbitrary temperature at which some nonzero differential capacitance signal is detected. The extracted activation energy of the detected trap center is used along with the position of the peak maximum to extract the capture cross section of the trap center.

Durable antibacterial PAN/Ag NPs nanofiber membrane was prepared by electrospinning. In this study, Ag NPs were composed by applying polyvinyl pyrrolidone as a dispersant and sodium borohydride (NaBH4) as a reductant. The composite nanofiber films and silver nanoparticles were characterized and tested by transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and Brunauer Emmett Teller (BET) and thermogravimetric analysis test. The specific surface area of PAN/Ag NPs (1%) and PAN/Ag NPs (3%) nanofiber membrane were about 25.00 m2/g calculated by the BET equation. It can be seen that the pore sizes of PAN, PAN/Ag NPs (1%), and PAN/Ag NPs (3%) nanofiber membranes were mainly distributed between 30 and 40 nm. The maximum removal rate of PM10, PM2.5, and PM1.0 was about 94%, 89%, and 82%, respectively, indicating it has a good filtering effect. The results also demonstrated that this membrane has bacterial reduction of over 99.9% for E. coli and S. aureus, respectively. In addition, the thermal stability of the fiber membrane with Ag NPs has no clear difference when compared to pure PAN nanofiber membrane and also has better moisture conductivity, indicating it is a potential candidate applied in biopharmaceutical antiseptic protection products.

In this study, a niobium-reinforced hydroxyapatite (HA-Nb) coating was developed on cobalt–chromium (CoCr) alloy by plasma spraying with three varied levels, i.e., 10, 20, and 30% of weight percent (wt%) of Nb content. The corrosion behavior and biocompatibility of the samples were analyzed through electrochemical corrosion testing and cytotoxicity studies, respectively. The results of corrosion testing revealed that the HA coating increased the corrosion resistance of the CoCr alloy, and with the incremental increase of Nb reinforcement in HA, corrosion resistance was further enhanced. The HA-30Nb coating demonstrated the finest corrosion resistance with the highest Ecorr and lowest Icorr values, which were about one order of magnitude lower in comparison to the bare CoCr alloy. The surface hardness increased and the surface roughness decreased with the increase of Nb content in the coating. Wettability analysis revealed that HA and HA-Nb coatings had a hydrophilic nature. HA-Nb coatings demonstrated a significantly better cell proliferation than the CoCr alloy.

The objective of this study was to understand the effects of ceramic polymer composite and pH of the surrounding vicinity on the release kinetics of doxorubicin. Different concentrations of polymers with polycaprolactone (PCL), poly glycolic lactic acid (PLGA), and a blend of PCL–PLGA with hydroxyapatite (HA) were investigated for doxorubicin release at physiological pH of 7.4 and an acidic pH of 5.0 caused by immediate surgery. Burst release of 20% was observed from bare HA at pH 7.4 over a week, whereas all the polymer incorporated discs showed sustained release. The hydrophilic–hydrophobic and hydrophobic–hydrophobic interactions between the polymer and the drug altered by the surrounding pHs were found to be pivotal in controlling the release kinetics of drug. No cytotoxicity of the drug at a concentration of 50 μg per disc was observed at early time points when cultured with osteoblast cells; however, the same drug dosage inhibited osteosarcoma cell viability. This study mainly bases on the comprehension of the effects of chemistry, environment, and polymer–drug interactions, leading to a beneficial understanding towards the design of drug delivery devices.

The effect of cooling rate on the microstructure evolution and the mechanical properties of ingots and rods of 2–5 mm diameter of (Ni0.92Zr0.08)100−xAlx (0 ≤ x ≤ 4 at.%) ultrafine eutectic composites have been investigated. The microstructure of the composites is comprised of micrometer size γ-Ni dendrites embedded in a nano/-ultrafine lamellar fcc γ-Ni and Ni5Zr matrix. The evolution of the microstructure at a wide range of cooling rates (10–104 K/s) has been analyzed in respect of volume fraction of the phases, lamellar spacing, and secondary dendritic arm spacing. All these composites exhibit high hardness up to 4.6 GPa and yield strength up to 1.6 GPa with large compressive plasticity up to 22% at room temperature. The effect of cooling rates on the strength and hardness, and the plasticity of the nanolamellar composites with wide range of alloy composition have been correlated.

The FeMnCoCr high-entropy alloy/TiC/CaF2 self-lubricating coatings were successfully prepared on a Cu–Zr–Cr alloy for continuous casting mold by laser cladding for wear-resistance. The intriguing finding was that the laser-cladded FeMnCoCr is mainly composed of face-centered cubic and hexagonal close-packed solid solution phases. During the cladding process, the FeMnCoCr/TiC or the FeMnCoCr/TiC/CaF2 mixed sufficiently with Cu matrix, while FeMnCoCr exhibited a spherical shape owing to being insoluble in Cu. The average hardness of the FeMnCoCr/TiC/CaF2 self-lubricating high-entropy alloy (HEA) coatings was twice that of the pure FeMnCoCr HEA coating. By addition of TiC, the friction coefficient and wear rate were decreased from 0.35 and 3.68 × 10−15 mm3/m to 0.27 and 3.06 × 10−15 mm3/m, respectively. When CaF2 was added, the friction coefficients and wear rate were decreased to 0.16 and 2.16 × 10−15 mm3/m, respectively, which was 54% lower than the pure FeMnCoCr HEA coating. The main wear mechanism of the FeMnCoCr coating is abrasive wear while that of the FeMnCoCr/TiC coating is abrasive and adhesion wear. But adhesion wear is dominant for the FeMnCoCr/TiC/CaF2 coating.

Coatings with low friction coefficient and excellent anti-wear and anticorrosion performances are of great interest for fundamental research and practical applications. In the present study, Cobalt–nickel–phosphorus/graphene oxide (Co–Ni–P/GO) composite coating is prepared by a pulse electrodeposition method. Effect of the embedded GO sheets on the microstructures, microhardness, and electrochemical and tribological behaviors of the Co–Ni–P/GO composite coating are researched in detail. The results reveal that the co-deposition of GO sheets significantly improves the microhardness of the as-prepared Co–Ni–P/GO composite coating and changes the morphology of the Co–Ni–P coating from hemispheric structure to nodule structure with smaller globular particles for the Co–Ni–P/GO composite coating. In addition, friction and wear tests show that the incorporation of GO sheets endows the Co–Ni–P/GO composite coating with remarkable friction reduction and improved wear resistance. Electrochemical corrosion tests demonstrate that the Co–Ni–P/GO composite coating possesses better corrosion resistance than the Co–Ni–P coating.

Uniform distribution of diamond grains is difficult to achieve using traditional fabrication of the micro grinding wheel. The design and performance of novel resinous diamond composites (RDCs) fabricated by hot pressing molding were studied to fabricate micro resinous diamond grinding wheels. The physical and mechanical properties of RDCs were analyzed by constructing and simulating five kinds of RDCs, including acrylonitrile butadiene styrene (ABS)/polyvinyl chloride (PVC)/dioctyl phthalate (DOP)/diamond materials with different mass ratios. Diamond grains presented good compatibility with the ABS–PVC–DOP copolymer, which resulted in improved mechanical properties of RDCs. RDC1–RDC5 samples were fabricated, and their hardness, surface roughness, and infrared spectra were analyzed. The optimal mass ratio of ABS/PVC/diamond/DOP for fabricating RDCs was 62.5/18.6/10.6/8.3. The results provide guidance in fabricating novel materials for resinous diamond grinding wheels with desirable performances for precision and ultraprecision machining.

In this report, bulk graphene–reinforced titanium (Ti–Gr) nanocomposite with millimeter thickness was fabricated by selective laser melting process. Demonstrated by the characterizations of scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectra, graphene nanoplatelets were successfully embedded into the titanium matrix with a uniform dispersion due to a fast heating–cooling process. High-resolution transmission electron microscopy was used to investigate the interface between titanium and graphene, where a certain amount of carbide was formed attribute to the chemical reaction between them during multilayer laser melting. A high density of dislocations was observed surrounding the graphene nanoplatelets in titanium matrix. The strength and elastic modulus of the nanocomposites were significantly improved, which has been demonstrated by nano-indentation tests. The hardness of the bulk Ti–Gr nanocomposites was approximately 1.27 times higher than pristine Ti counterpart. The strengthening mechanisms were discussed in detail.

Cast tungsten carbide is widely used to reinforce iron or steel substrate surface composites to meet the demands of harsh wear environments due to its extremely high hardness and excellent wettability with molten steel. Cast tungsten carbide particle/steel matrix surface composites have demonstrated great potential development in applications under the abrasive working condition. The thermal shock test was used to investigate the fatigue behavior of the composites fabricated by vacuum evaporative pattern casting technique at different temperatures. At elevated temperatures, the fatigue behavior of the composites was influenced by the oxidation of tungsten carbide, producing WO3. Thermodynamic calculations showed that the W2C in the tungsten carbide particle was oxidized at an initial temperature of approximately 570 °C. The relationship between oxidation and thermal fatigue crack growth was investigated, and the results suggested that oxidation would become more significant with increasing thermal shock temperature. These findings provide a valuable guide for understanding and designing particle/steel substrate surface composites.

The oxidation behavior of two percentages of TiB + TiC reinforced Ti–6Al–4V composites derived from Ti–B4C–C and Ti–TiB2–TiC systems was investigated at 873–1073 K for 320 h in air. The oxidation weight gain curves of the (TiB + TiC)/Ti–6Al–4V composites at 973 K basically obey parabolic law, while those at 873 and 1073 K mainly follow linear law and parabolic-linear law, respectively. The oxide layers of the composites are predominately found to be rutile TiO2, Al2O3, and the mixture of V2O3 and V2O5. The oxidation layers turn thinner with increasing the nominal volume fraction of reinforcements in the (TiB + TiC)/Ti–6Al–4V composites. Moreover, according to the calculation results of reaction index (n) and effective activation energy (Qeff) and the analyses of cross-sections of the oxidation layers, the oxidation resistance ability of the composites from Ti–TiB2–TiC system is higher than that from Ti–B4C–C system while employing the same sintering temperature and nominal volume fraction of reinforcement.

A bimetallic metal–organic frameworks (MOFs)-templated strategy was developed to fabricate mesoporous CdxZn1−xS polyhedrons with improved photocatalytic hydrogen evolution activity, and the formation mechanism of these mesoporous polyhedrons was discussed in detail. Incorporating Cd atoms, the Brunauer–Emmett–Teller surface areas of mesoporous CdxZn1−xS polyhedrons were significantly increased (271 m2/g), providing more exposed active sites compared with ZnS. In addition, suitable conduction band potential (< −0.55 eV) of the mesoporous CdxZn1−xS polyhedrons was also beneficial for the photocatalysis. Impressively, by the co-effects of mesoporous structure and modified conduction band, the mesoporous CdxZn1−xS polyhedrons exhibited better photocatalytic activity for hydrogen evolution than most reported photocatalysts without noble metals. The maximum hydrogen evolution rate of the CSZ3 reached 4.10 mmol/(h g) under visible-light irradiation and without any cocatalyst condition. This facile strategy for the construction of mesoporous CdxZn1−xS polyhedrons provided a deep insight to fabricate other metal sulfides for a variety of photochemical applications.

Composite materials include various components with different structures, which cooperatively increase their properties and extend their application. In this study, the graphitic carbon nitride (g-C3N4) guest material was assembled into the porous of the SiO2 aerogel, which was prepared during the gel process. By this way, the g-C3N4 could be absolutely encapsulated into the porous of the disordered porous SiO2 aerogel. The prepared g-C3N4/SiO2 composite had a loose porous structure and exhibited the much higher photocatalytic activity to the photodegradation of rhodamine B (RhB) under visible light. The disordered porous structure enhanced photocatalytic activity, and the degradation rate reached to 96.42% in 90 min under the irradiation of visible light, which could be attributed to its high surface area and effective electron–hole separation rate. The catalyst had the much higher stability and could be easily recycled utilization. The prepared composites could be applied to degrade organic pollutants in wastewater.

A photoresponsive double-layer hydrogel has been developed, in which light-sensitive cinnamic moieties are grafted onto a polyacrylamide network to produce a photoresponsive layer and pure polyacrylamide formed the supporting layer. Ag nanoparticles were dispersed using in situ reduction on the photoresponsive layer to act as the catalyst. The as-fabricated hydrogel exhibits a shape memory effect and controllable catalytic behavior under an external light stimulus. When exposed to ultraviolet (UV) light at λ > 260 nm, the resulting cycloaddition of cinnamic moieties not only fix the hydrogel’s temporary shape, but also greatly slow down the catalytic reaction rate. After irradiated with UV light at λ < 260 nm, however, the newly formed crosslinking points are reversibly cleaved. This results in the shape recovery of the hydrogel to its permanent shape. At the same time, the catalytic reaction was greatly accelerated because of the facile diffusion of the reactants into the hydrogel.

A kind of n–p (SnO2)1.3/(α ∼ Bi2O3)x/(β ∼ Bi2O3)1−x nanocomposite (SB-15) was synthesized with polyvinyl alcohol (PVA) as a template by solid state synthesis. XRD and HR-TEM confirmed the formation of n–p (SnO2)1.3/(α ∼ Bi2O3)x/(β ∼ Bi2O3)1−x. Particle size is found to be about 18 nm from HR-TEM images. FE-SEM clearly detected the boundary between SnO2 nanoparticles and Bi2O3 polyhedron particles. The special morphology and coexisting of α-Bi2O3 and β-Bi2O3 in SB-15 make it have a stronger visible light absorption range as far as 725 nm. PL and photocurrent test shows that the SB-15 has the best photocarriers separation capability. About 99% decolorization ratio of Rh.B was achieved in only 5 min. About 70% Cr6+ was degraded within 20 min and it is about 60% for tetracycline in the coexisting system (Te with Cr6+ solution), introducing it as a promising photocatalytic material. This work has addressed the method of phase-selective synthesis of n–p SnO2/α ∼ Bi2O3/β ∼ Bi2O3 by convenient solid state synthesis, which should be useful for the studies of other composites.

Cordierite foams were prepared by thermo-foaming of alumina–microsilica–talc powder dispersions in molten D-glucose anhydrous followed by reaction sintering at 1400 °C, which exhibited an interconnected cellular morphology and three-dimensional porous cell walls. The cordierite foam had a porosity of up to 96%, and its corresponding thermal conductivity was as low as 0.057 W/(m·K). The foam structures showed a great promise for gas filtration and gas catalytic support. The formation of interconnected cellular morphology, the variations of cell wall thickness, and cell size were explained from the perspective of viscosity and weak points in this paper. The linear shrinkage of cordierite foams having a density of 0.102–0.226 g/cm3 was in the range of 13.0–6.9%. And the compressive strength (0.05–0.28 MPa) was determined by the large cell size (1.1–1.3 mm), ultra-high porosity (91–96%), and characteristic of cordierite.