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Cr-containing diamond-like carbon (Cr-DLC) nanocomposite coatings were synthesized by ion beam-assisted arc ion plating with varying hollow cathode ion source (HCIS) currents. The morphologies, compositions and microstructures were characterized by scanning electronic microscopy (SEM), atomic force microscopy (AFM), X-Ray photoelectron spectrometer (XPS), Raman spectroscopy, grazing incidence X-ray diffraction (GIXRD) and high-resolution transmission electron microscopy (HRTEM). Hardness and friction coefficient were investigated by using nanoindentation and ball-on-disc tribometer, respectively. With no HCIS current, the coating exhibits the maximal growth rate and a rough surface, as well as lower hardness and elastic modulus. With the increasing HCIS current from 40A to 80A, the growth rate and the content of chromium carbide decrease obviously, the / ratio increases initially to the maximum at the HCIS current of 60A, the highest hardness and elastic modulus are obtained at the HCIS current of 50A. It is also revealed that moderate HCIS current can reduce surface roughness obviously and promote tribological properties. The correlation of the HCIS current with the microstructure and performance of Cr-DLC coating has been established. Cr-DLC nanocomposite coatings were fabricated by an ion beam-assisted arc ion plating system, with an attempt to offset the shortcomings of arc ion plating deposition by introducing an assistant ion beam. The ion source current had an important effect on the morphologies, microstructures and properties of Cr-DLC coatings. The optimal current can effectively smoothen surfaces, increase sp3 fraction and modify microstructure, thus enhance the mechanical and tribological performance of Cr-DLC coatings. [ABSTRACT FROM AUTHOR]

Pure copper was subjected to high-pressure surface rolling (HPSR) to obtain a surface gradient layer. Effects of HPSR parameters on the surface microstructure and microhardness of Cu were investigated by using optical microscopy, transmission electronic microscopy, X-ray diffraction, and the microhardness test. The HPSR surface layer has a gradient microstructure consisting of increasingly refined grains with decreasing depth from the treated surface (DFS). The thicknesses of the refined surface layer can be up to ~1.8 mm, and the grain size of the topmost surface is down to ~88 nm, depending on the HPSR parameters including pressure, time, and temperature. Microhardness of HPSR samples increases with decreasing DFS, with a maximum of ~2.4 times that of the undeformed matrix. The present results indicated that HPSR could be an effective method for the production of a mm-thick surface layer on Cu with gradient microstructure and property. [ABSTRACT FROM AUTHOR]

Abstract Co-Cr-based alloys have been widely used as mechanical components where high wear-resistance is required. However, conventional Co-Cr alloys usually have coarse-grained microstructures with phase coexistence of both hexagonal close packed (hcp) ε-Co and face-centered cubic (fcc) γ-Co. The wear resistance of the Co-Cr alloys could be further enhanced by grain refinement and exclusion of γ-phase. Here, a Co-30Cr (at%) bulk alloy consisting of ultrafine-grained matrix of ε-phase and uniformly dispersed nanoscale precipitates of σ-phase was fabricated by high energy ball milling and spark plasma sintering. Microstructure and dry sliding wear performance against alumina at room temperature and 600 °C were then investigated. The matrix and the precipitates have the average grain size of 227 nm and 16 nm, respectively. Hardness was determined to be 707 HV. The ε-Co matrix, ultrafine-grained microstructure and the uniformly dispersed nanoprecipitates enable the alloy with excellent wear resistance. Grain growth of the matrix grain was found as the key factor to be responsible for the increase of wear rate at 600 °C. Subsurface microstructures of the alloy show no significant plastic deformation after wear tests, which is attributed to high hardness of the alloy and very limited slip in hcp system. Graphical abstract Image 1 Highlights • An ultrafine-grained Co-30 at% Cr alloy of ε-phase was fabricated. • Nanoscale precipitates of σ-phase are uniformly dispersed in the matrix. • The alloy shows superior wear resistance. • The alloy shows good thermal stability at 600 °C. • The alloy does not form gradient layered nanostructures after wear. [ABSTRACT FROM AUTHOR]

Abstract: Molecularly imprinted polypyrrole (PPy) nanonecklaces were facilely synthesized through a two-step oxidative polymerization route for the amperometric detection of non-electrochemically active herbicide. It has been demonstrated that dissolved oxygen can preoxidize pyrrole to form PPy oligomer bundles, which further self-assemble into necklace-like micelles in the presence of cetyltrimethylammonium bromide. Subsequently, these microstructures were immediately gelled through quick polymerization of residual pyrrole monomers, leading to the formation of PPy nanonecklaces. Meanwhile, herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was synchronously imprinted into the formed PPy and highly dense imprinted sites were generated in PPy nanonecklaces because the necklace-like structure with microgaps/pores provides the facile and complete removal of templates. The imprinted nanonecklaces exhibit the high capacity and fast kinetics to uptake 2,4-D molecules, and produce a imprinting factor of ∼4.2. Importantly, the recognition and binding to 2,4-D significantly amplify the current response by a factor of 8 times in amperometric measurements, providing a sensitive detection of 2,4-D. The molecular imprinting strategy opens a novel avenue to the direct detection of non-electrochemically active species in a more convenient, simpler and cheaper way than the traditional competition-displacing approaches. [Copyright &y& Elsevier]

The present work investigates the microstructural evolution of a biomedical Co-20Cr-15W-10Ni alloy during multi-pass thermomechanical processing (TMP) and clarifies its effect on the tensile properties. The results indicate that multi-pass TMP consisting of repetitive cold groove-rolling followed by annealing is attractive for fabricating the alloy rod for fine wire and mini-tube making. The multi-pass TMP provided significant grain refinement from 100 to 4 μm via five repetition and, can create bimodal grain structures consisting of fine (≈3 μm) and coarse grains (4−16 μm). The bimodal grain structure provided a superior strength-ductility combination, a yield strength of 593−738 MPa and ultimate strength of 1197−1304 MPa with a uniform elongation of 54.7−61.1%. Changing the annealing condition in the final TMP step enables to further refine the grains to 2 μm and also modify the grain size distribution and, the dispersion and fraction of nano-carbides. Thus, the mechanical properties of the Co-20Cr-15W-10Ni alloy can be further optimized, leading to a yield strength of 795−890 MPa and ultimate strength of 1328−1363 MPa with a uniform elongation of 49.4−64.0%. [ABSTRACT FROM AUTHOR]