Micromechanical and microtribological properties of BCN thin films near the B4C composition deposited by r.f. magnetron sputtering

Ternary materials with compositions in the B–C–N system offer properties of great interest. In particular, mechanical and tribological properties are expected to be excellent, as they can combine some of the specific properties of BN, B₄C and C₃N₄. In this paper, BCN thin films deposited by r.f. magnetron sputtering are characterized by their micromechanical and microtribological behavior. BCN coatings with different composition were obtained by varying the N₂/Ar proportion in the sputtering gas. Hardness and elastic modulus of the coatings were measured by nanoindentation. The adhesion and friction coefficient against diamond have been evaluated by microscratch and the coatings have been characterized in their wear behavior at the nanometric scale. These mechanical and tribological properties have been related to film composition and structure, which have been studied in a previous work. It is found that the measured wear resistance at the nanometric scale is directly related to the coating microhardness rather than friction behavior or adhesion of the coating to the substrate, which are the determinant factors in the macroscopic scale wear behavior.     

Effect of additional elements Ni and Cr on wetting characteristics of liquid Cu on zirconia ceramics

The effect of additions (Cr, Ni and 80Ni·20Cr) on the wetting characteristics of liquid Cu on ZrO₂ have been studied using a sessile drop method. Analysis of reaction layers at a solidified droplet/ZrO₂ interface have been performed. Additions of 80Ni·20Cr alloy or Cr alone reduce the contact angle of liquid Cu on ZrO₂. The simultaneous addition of Ni and Cr can markedly improve the wettability of liquid Cu on ZrO₂. According to SEM and EPMA observations, dissolution of the additions into liquid Cu droplets occurred. A uniform distribution of Ni throughout the Cu droplet and segregation of Cr at the Cu droplet/ZrO₂ interface were observed in solidified specimens.     

Preparation of Diversified Ultra‐Fine Microstructures in Q345 Steel with Improved Properties

A typical C‐Mn steel (Q345) with warm‐rolled ferrite/pearlite was used for subsequent simple process resulting in ultrafine ferrite grains in size of ～1µm. No remarkable strain hardening was detected and grain boundary motion was also recognized as an important accompanying deformation mechanisms at the beginning of yielding. However, strain‐hardening capability of this C‐Mn steel could be improved by changing the ultrafine ferrite/pearlite into acicular ferrite with increment of strength.     

Challenges and solutions in surface engineering and assembly of boron nitride nanosheets

Atomically thin boron nitride nanosheets (BNNSs) are normally considered to be chemically inert, which makes them difficult to be functionalized. Many applications require new surface functionalities. Significant efforts have been made towards surface engineering and assembly of BNNSs. In this article, we contribute a critical review of the topic on challenges and solutions in surface engineering and assembly of BNNSs. We first outline the mechanistic insights of tunable surface functionalization of BNNSs, and then highlight some new breakthroughs, seminal studies, and trends in the area that have been most recently reported by our groups and others. Recent application researches include but are not limited to: (1) chemical catalysis; (2) biocompatible BN functional nanomaterials for biological and biomedical applications; (3) molecularly engineered BN surfaces for sensing and drug delivery applications; and (4) the construction of thermally conductive and electrically insulating composites. There is also an in-depth discussion on the merits of the processing-structure–property relationships in the functionalized BNNSs. Finally, with this review article, we hope to spark new ideas and inspire new functionalization strategies by fundamentally understanding surface properties and engineering BNNSs with programmable structures and predictable properties.     

Self-heating fiber reinforced polymer composite using meso/macropore carbon nanotube paper and its application in deicing

A meso/macropore carbon nanotube paper (CNP) and a self-heating fiber reinforced polymer composite of CNP/glassfiber/epoxy (CGE) based on the meso/macropore CNP were fabricated in this article. The pore diameters mainly distribute from 30 to 90 nm characterized using nitrogen adsorption isotherms at 77 K. The electric conductivities of the CNP and CGE composite are 77.8 and 64.9 S cm⁻¹. Electric heating performance of CGE was investigated at different heat flux densities, wind speed and ambient temperature. A uniform temperature distributed was observed on the surface of CGE detected by an infrared temperature camera. The electric heating performance was verified by deicing a certain amount of ice at different heat flux densities under two kinds of ambient conditions: −22 °C without wind and −22 °C with 14 m/s of the wind speed. The deicing time under the two conditions were less than 220 and 450 s, respectively. The feasibility of the deicing performance was demonstrated through a series of experiments and the results indicate this material is a promising candidate as an electric heating material for deicing.     

Reinvestigation of the tensile strength and fracture property of Ni(1 1 1)/α-Al2O3(0 0 0 1) interfaces by first-principle calculations

First-principle calculations are performed to reinvestigate the mechanical tensile property and failure characteristic of Ni/Al₂O₃ interfaces, in order to clear the inconsistence existed in the literatures. Four types of interface models without initial lateral stresses are used, i.e., Al-terminated O-site, O-terminated Al-site, Al-terminated Al-site and Al-terminated H-site models. Two kinds of tensile methods, viz., uniaxial extension and uniaxial tension, are adopted to check the mechanical responses of these interface models. It is found that the results under uniaxial extension are generally consistent with those under uniaxial tension, including the overall shapes of stress–strain curves and the values of tensile strengths. Moreover, the initial lateral stresses have an apparent influence on the mechanical properties of the interfaces during the loading process, such as tensile strength, fracture strain and the work of separation. Our simulation results also clarified that, under tensile loading, the most stable O-terminated Al-site interface model tends to fracture in a brittle way along the sublayer between in-plane Ni–Ni atomic bonds, while all of the Al-terminated interface models will fail in a ductile fracture manner with relatively lower stress levels, breaking along the interlayer between the Ni(1) and Al(1) layers.     

Large scale fabrication of porous boron nitride microrods with tunable pore size for superior copper (II) ion adsorption

Herein, large scale fabrication of porous boron nitride (BN) microrods has been achieved via a facile process, which involves the synthesis of melamine diborate precursors and subsequent thermal treatment process. The fabrication can be scaled up to ultra-large scale which is limited by the furnace. The characterization results show that the as-obtained products are porous BN microrods with diameters in the range of ten to tens of micrometers and length of a few millimeters, respectively. The specific surface area and porosity of these porous BN microrods are tunable by adjusting the synthesis processes of precursors. A highest specific surface area of 653.66?m²/g is obtained for the sample of BN-4, corresponding to the differential pore volume of 0.289?cm³/(g?nm) and pore size of about 1.928?nm. Further measurement shows that the as-obtained porous BN microrods possess excellent copper ion adsorption property with a highest adsorption capacity of 365.4?mg/g. This adsorption capacity is superior to those of most copper ion adsorbents reported in recent literature. The high copper ion adsorption capacity combining with the unique properties of hexagonal BN makes them promising candidates for copper ions adsorption in practical wastewater treatment.     

Synthesis and structural characterization of SiBOC ceramic fibers derived from single-source polyborosiloxane

SiBOC ceramic fibers have been successfully prepared from single-source polyborosiloxanes which are synthesized from polymethylethoxysiloxane and B(OH)₃ via a sol-gel route. The morphological change, structural evolution and crystallization behavior of fibers as a function of thermal treatment are studied by several techniques. Polyborosiloxane sols exhibit remarkable spinnability, in which B atoms are homogenously incorporated into the linear Si-O-Si skeleton via Si-O-B bridges. SiBOC ceramic fibers with diameters of about 10 μm are prepared with high ceramic yield ranging from 80.5 to 86%. Although a continuous structural evolution occurs with increasing pyrolysis temperature, the SiBOC ceramic fiber with B/Si atom ratio of 0.14 is thermal stable at 1500 °C. The thermolysis and crystallization behaviors are closely related to the boron content. The tendency toward crystallization of SiC and graphitization of free carbon is strengthened with the increase of boron content and pyrolysis temperature.