Carbon nanotubes (CNTs) reinforced Ti matrix composites with tailored microstructures and properties were fabricated by direct metal laser sintering (DMLS). A relationship of processing conditions, distribution characteristics of CNTs, and properties was established. The appearance of balling phenomenon and micropores at relatively low laser energy input reduced the densification level of DMLS CNTs/Ti composites. As a η of 700 J/m was properly settled, the composite part with a near-full 96.8% density was obtained. On increasing the laser energy input, the distribution states of CNTs in Ti matrix changed markedly from agglomeration to homodisperse. The optimally prepared fully dense CNTs/Ti composite with uniform distribution of CNTs had significantly enhanced H d of 9.4 GPa and E r of 328 GPa, which showed respectively ∼2.5- and ∼3.4-fold increase upon that of unreinforced Ti, and resultant a relatively low friction coefficient of 0.23 and reduced wear rate of 3.8 × 10−5 mm3/(N m).

Hot-rolled Nb-stabilized ferritic stainless steel samples were produced with and without annealing. The samples were then cold rolled and isothermally annealed at 650–1000 °C for 10–14,400 s. The recrystallized volume fraction was quantified using the Johnson–Mehl–Avrami–Kolmogorov model and by measuring the microhardness of samples annealed for various duration. The texture evolution was analyzed using electron backscatter diffraction. The calculated Avrami exponents were between 0.8 and 1.2. The intensity of the {111}〈121〉 and {111}〈011〉 components of the γ-fiber increased and the deformation texture seen in the α-fiber decreased with increasing annealing time. The intensity of the rotated-cube component decreased with increasing annealing time. The intensity distributions of the early nucleation and full recrystallization textures were noticeably different. The {554}〈225〉 texture component, which was associated with the largest grains, appeared during the late stages of recrystallization. The final annealing led to a grain refinement with a final average grain diameter of 8 µm.

Hot compression tests of a hot isostatically pressed (HIPed) Ni based powder metallurgy (P/M) superalloy were carried out under various combinations of temperatures and strain rates. To bridge the relationship between stresses and strain rates, constitutive equations were established based on a hyperbolic sine Arrhenius equation, which yielded predicted stresses under the test conditions. It was found that the predict values fit the experimental values with good accuracy. Processing maps of the alloy under the test conditions were established; and the corresponding microstructures after test were examined to elaborate the workability of the alloy. It revealed that surface cracks occurred when strain was higher than 0.25, which initiated at the prior powder boundaries (PPBs) and propagated along the boundaries. The optimum hot working parameters for the alloy were proposed to beat the strain rate of 0.014 s−1 and 1075 °C.

A systematic analysis of effect of metallurgical defect and phase transition on geometric accuracy and wear resistance of iron-based parts fabricated by selective laser melting was conducted. By composition optimization of alloying elements, the desirable martensitic structure was directly obtained based on high-speed laser induction and the content of retained austenite was observed to be different under various laser parameters. Using an optimized scan speed of 1600 mm/s could lead to the highest densification level of 99.24% and the lowest content of retained austenite of 3.5%, hence acquiring a considerably high Rockwell hardness of 61.9 HRC, a reduced coefficient of friction of 0.40, and wear rate of 1.8 × 10−5 mm3/N m. A thorough investigation of dimension offset due to martensite transformation in conjunction with theoretical calculation was performed. Lower top surface roughness (5.25 μm) and reduced side roughness (13.84 μm) were achieved at the optimized scan speed of 1600 mm/s.

Double deformation technique is often used to study static recrystallization (SRX) behavior of materials, and SRX volume fraction can be calculated by the analysis of the stress–strain curve from this technique. The suggested methods to analyze the curve are different, which may lead to different results or even large deviation. In the present research, the methods were discussed based on the stress–strain curves from double deformation compression tests. The results showed that 2% offset method agrees well with 5% total strain method and they can give a better evaluation of SRX volume fraction for the tested steel in the absence of precipitates. While the results from 2% offset or 5% total strain method deviate from the ones from area measurement method when precipitation occurs. Therefore, area measurement method is more suitable when precipitates play a role in SRX process. However, the strain should be large enough to perform this method.

Very high cycle bending fatigue behaviors of FV520B steel under fretting wear were studied by the ultrasonic fatigue technique. The specimen system for ultrasonic bending testing was designed and the stress distribution of fatigue specimen was obtained by finite element method. The microstructure of FV520B steel was characterized by means of optical microscope, transmission electron microscope, and energy-dispersive spectroscope. The P–S–N curve was drawn based on fatigue data. The micromorphology characteristics of fretting wear surface and fracture surface for fatigue specimen were observed. The results indicate that the microstructure of FV520B steel is mainly composed of lath martensite, ferrite, and precipitation particles, with some randomly distributed internal inclusions. The P–S–N curve shows that there exists no “conventional fatigue limit” and the fatigue life decreases continuously with the increase of applied stress Smax. Most of fatigue cracks are observed on fractography and initiate from the overlap region of fretting wear zone and stress concentration zone. The fracture failure for tested specimen is ascribed to fretting wear and bending vibration fatigue.

There is growing interest in using instrumented indentation to characterize mechanical properties of soft materials, including tissue properties related to damage and disease. However, sample surface detection has been a major challenge. The multi-indent approach (MIA) is a novel method to indirectly detect the surface using data from multiple indents to determine the preload-induced indentation depth. Elastic modulus and shear modulus determined by MIA were equivalent to bulk measurements for 19 and 49 kPa gels. However, the traditional Oliver–Pharr approach significantly overestimated these properties. MIA is also important to accurate characterization of poroelastic properties and allows for much smaller probes and indentation depths to be used for all measurements. This is particularly important for poroelasticity, where the relaxation time scales with the size of the indenter. The novel approach helps to resolve the long-standing challenge of surface detection and has the potential to broaden the use of instrumented indentation for soft materials.

We present a comprehensive nanoscale tribological characterization of single-layer graphene grown by chemical vapor deposition (CVD) and transferred onto silicon oxide (SiO2) substrates. Specifically, the nanotribological properties of graphene samples are studied via atomic force microscopy (AFM) under ambient conditions using calibrated probes, by measuring the evolution of friction force with increasing normal load. The effect of using different probes and post-transfer cleaning procedures on frictional behavior is evaluated. A new method of quantifying lubrication performance based on measured friction coefficient ratios of graphene and SiO2 is introduced. A comparison of lubrication properties with mechanically-exfoliated graphene is performed. Results indicate that CVD-grown graphene constitutes a very good solid lubricant on SiO2, reducing friction coefficients by ∼90% for all investigated samples. Finally, the effect of wrinkles associated with CVD-grown graphene on measured friction values is quantitatively analyzed, with results revealing a substantial increase in friction on these structural defects.

A new technology for preparing and forming ceramic particle-reinforced metal matrix composites, powder thixoforming, has been proposed. The effect of the SiCp volume fraction on the microstructure and tensile properties of thixoforged SiCp/2024 Al-based composites was studied. The results indicated that the volume fraction affected the effective liquid fraction, primary particle size and shape, and microstructure compactness. A composite with 10 vol% SiCp had the best comprehensive tensile properties, an ultimate tensile strength of 388 MPa, a yield strength of 295 MPa, and an elongation of 3.8%, representing increases of 29.3 and 33.5%, and a decrease of 63.5%, respectively, compared with the values for the thixoforged 2024 Al matrix alloy. During tensile testing, cracks were initiated in the secondary solidified structures, the debonded SiC/Al interface, and the cracked SiCp. For composites containing over 10 vol% SiCp, agglomerated SiCp acted as additional zones of crack initiation.

In this paper, the compressive behaviors of Zr-based bulk metallic glass (BMG) were experimentally studied under different testing conditions. To deeply reveal the inherent deformation mechanisms, numerical study was systematically conducted to analyze the shear banding evolution in BMGs, and the effect of testing machine stiffness, contact friction, and sample parallelism on the compressive ductility was therefore elucidated. Among them the effect of contact friction was carefully studied experimentally and the inherent deformation mechanisms was numerically analyzed in terms of the formation of shear bands. Free-volume theory was incorporated into ABAQUS finite element method code as a user material subroutine UMAT. The numerical method was firstly compared with the corresponding experimental results, and then parameter analyses were performed to discuss the impacts of testing conditions on the malleability of the BMG samples. The present work will shed some light on the interpretation of failure mechanisms in BMGs under different loading conditions.

Graphene-covered copper surfaces have been exposed to borazine, (BH)3(NH)3, with the resulting surfaces characterized by low-energy electron microscopy. Although the intent of the experiment was to form hexagonal boron nitride (h-BN) on top of the graphene, such layers were not obtained. Rather, in isolated surface areas, h-BN is found to form μm-size islands that substitute for the graphene. Additionally, over nearly the entire surface, the properties of the layer that was originally graphene is observed to change in a manner that is consistent with the formation of a mixed h-BN/graphene alloy, i.e., h-BNC alloy. Furthermore, following the deposition of the borazine, a small fraction of the surface is found to consist of bare copper, indicating etching of the overlying graphene. The inability to form h-BN layers on top of graphene is discussed in terms of the catalytic behavior of the underlying copper surface and the decomposition of the borazine on top of the graphene.

We have developed a new synthesis method that includes a chemical vapor deposition process in a chamber settled in organic liquid, and applied its nonequilibrium reaction field to the development of novel carbon nanomaterials. In the synthesis at 1110–1120 K, using graphene oxide as a catalyst support, iron acetate and cobalt acetate as catalyst precursors, and 2-propanol as a carbon source as well as the organic liquid, we succeeded to create carbon nanofiber composed of novel pot-shaped units, named carbon nanopot. A carbon nanopot has a complex and regular nanostructure consisting of several parts made of different layer numbers of graphene and a deep hollow space. Dense graphene edges, hydroxylated presumably, are localized around its closed end. The typical size of a carbon nanopot was 20–40 nm in outer diameter, 5–30 nm in inner diameter, and 100–200 nm in length. A growth model of carbon nanopot and its applications are proposed.

Isothermal homogenization heat treatments for a GCr15 bearing steel cast billet were performed at temperatures of 1000–1250 °C and holding times of 30–180 min. The grain size of austenite was measured with a metallographic microscope through the linear intercept method. Experimental results show that the grain size of austenite increases with the increase in heating temperature and holding time. The relationship between grain size and homogenization cycles was established. The homogeneity of the cast billet has an obvious effect on the austenite grain size distributions. Small and large grains were observed in the high- and low-concentration regions, respectively. The log-normal function can describe the grain size distributions more accurately than other functions after heating at low temperatures for short times. However, the Weibull function fits the grain size data well when the heating temperatures and holding times are improved.

Simple shear deformation via hybrid cutting-extrusion is used to produce continuous electrical steel sheet from a commercial high-silicon (nominal 4 wt%) iron alloy of poor workability in a single deformation step, a fundamentally different route from the multi-step processing of rolling and annealing currently in use. The shear texture created in the sheet is found to be quite different from that produced by rolling. The magnetic properties of the shear-textured Fe–Si sheet are measured using closed-circuit permeametry and compared with those from sheet produced by rolling of the same alloy and a commercial non-grain-oriented sheet of similar composition. Properties compared include maximum relative permeability, induction, coercivity, and hysteresis loss. The results are interpreted in terms of microstructure, texture, and composition. A unit cell representation of the shear texture components is introduced that relates the expected orientation of easy magnetization directions with the sheet axes.

The effect of Ta concentration on the fundamental mechanical properties of W–Ta alloys has been studied from first principles study. The lattice constants, the cell volumes, and the formation energies of the W1−x Ta x (x = 0.0625, 0.125, 0.1875, 0.25, 0.3125, 0.5, 0.5625, 0.625, 0.75) alloys were calculated. It is shown that Ta alloying in bcc W lattice is an infinite solid solution and the W0.5Ta0.5 have the lowest formation energy. With the optimized geometry and lattice, the elastic constants are calculated and then the elastic moduli and other mechanical parameters are derived. Results show that although the mechanical strength of the W–Ta alloys is lower than that of pure W metal, it is much higher than that of pure Ta metal. On the other hand, the B/G ratio and the Poisson's ratio of the W–Ta alloys is much higher than that of pure W, and even higher than that of pure Ta, indicating that Ta alloying can improve the ductility of bcc W substantially.

By using high purity aluminum powders and multi-walled carbon nanotubes (MWCNTs) as raw materials, MWCNTs/Al composites were fabricated with ball milling, followed by cold pressing, vacuum sintering, and hot extrusion. It was found that when the sintering temperature was 863 K, MWCNTs/Al composite sintered for 4 h showed good comprehensive properties, and its tensile strength and elongation reached to 156 MPa and 21%, respectively. The comprehensive mechanical properties of the composites became better with raising sintering temperature when the sintering time was 4 h. When the sintering temperature raised to 923 K, the tensile strength of the composite reached to 167 MPa which is three times more than that of annealed high purity aluminum, mainly due to the higher density and better interface bonding resulted from higher sintering temperature. CNTs' pulling out were observed obviously in the fractured surfaces, and load transfer may be the main strengthening mechanism.

In this paper we have reported analysis on activation energy and humidity sensing studies of Cu-doped ZnO thin films. Thin Films of undoped and Cu-doped ZnO nanomaterials were prepared. Undoped and Cu-doped ZnO thin films annealed at 600 °C showed the best results with sensitivity of 20.63 MΩ/%RH and 39.14 MΩ/%RH respectively in the 15–95% RH range. Low value of activation energy indicated that this sensing element had low operating temperature and could be used at room temperature. Other parameters like response time, recovery time, hysteresis, and aging effects were also studied. The crystallite size for the sensing element of pure ZnO annealed at 600 °C calculated from Scherrer's formula is in the 24–38 nm range. For the sensing element of 7% Cu doped ZnO the range of crystallite size is 25–41 nm. The average grain size as measured from SEM micrograph for 7% Cu doped ZnO and pure ZnO sensing elements were 36 and 42 nm, respectively.