Tingfei Xi

Effect of extrusion process on microstructure and mechanical properties of Ni3Al-B-Cr alloy during self-propagation high-temperature synthesis

The well-densified Ni3Al-0.5B-5Cr alloy was fabricated by self-propagation high-temperature synthesis and extrusion technique. Microstructure examination shows that the synthesized alloy has fine microstructure and contains Ni3Al, Al2O3, Ni3B and Cr3Ni2 phases. Moreover, the self-propagation high-temperature synthesis and extrusion lead to great deformation and recrystallization in the alloy, which helps to refine the microstructure and weaken the misorientation. In addition, the subsequent extrusion procedure redistributes the Al2O3 particles and eliminates the γ-Ni phase. Compared with the alloy synthesized without extrusion, the Ni3Al-0.5B-5Cr alloy fabricated by self-propagation high-temperature synthesis and extrusion has better room temperature mechanical properties, which should be ascribed to the microstructure evolution.

Microstructure and elevated temperature tensile behaviour of directionally solidified nickel based superalloy

Abstract In this paper, a nickel based superalloy with good corrosion resistance is fabricated by directional solidification, and its microstructure and tensile properties were investigated. Microstructure observations reveal that besides the γ′ precipitates and γ matrix, some MC, Ni5Hf and M3B2 particles precipitate along the grain boundary. Tensile tests exhibit that the alloy has obvious anomalous yield and intermediate temperature brittleness (ITB) behaviour. The tensile properties depend on temperature significantly. Below 650°C, the yield strength decreases slightly but rises rapidly between 650 and 750°C, and after then, it decreases gradually with temperature increasing further. Examination by TEM exhibits that sharing of the γ′ by dislocation is almost the main deformation mechanism at low temperature, but the γ′ bypass dominates the deformation at high temperature and the transition temperature should be ∼800°C. In addition, the carbides and eutectic structure contribute partly to the ITB behaviours.

Cell response of nanographene platelets to human osteoblast‐like MG63 cells

The biologic/cytotoxic effects of dispersed nanographene platelets (NGPs) on human osteosarcoma cells (MG63 cell line) were first studied by examining cell viability, cycle, apoptosis, change in morphology, lactate dehydrogenase (LDH) release, alkaline phosphatase (ALP) activity, and inflammation. The results shown that the cell cytotoxicity of the dispersed NGPs exhibited dose-dependent characters, which had no obvious cytotoxic effects to MG63 cells at the concentration less than 10 μg mL(-1), whereas could postpone cell cycle, promote cell apoptosis, damage cell microstructure, induce serious tumor necrosis factor-α expression and greatly reduce ALP activity of MG63 cells at higher concentration of NGPs (>10 µg mL(-1)). Besides, NGPs had little influence on the LDH leakage. The cytotoxic mechanism of NGPs to MG63 cells was speculated to be intracellular activity with no physical damage of plasma membrane.

TEMPO-mediated oxidation of bacterial cellulose in a bromide-free system

A partially C6-carboxylated bacterial cellulose (BC) with a high carboxylate content was prepared in a bromide-free system by using 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) as a catalyst. ART-FTIR, X-ray diffraction, solid 13C-NMR, TEM analysis, and reaction kinetics measurements were performed to investigate the oxidation reaction of BC. Results show that C6 carboxylate was formed selectively on the microfiber surface without disrupting its highly ordered nanocrystalline structure. Given the extremely low accessibility of hydroxyl groups in d-anhydroglucopyranose units, the reaction can be described by second-order kinetics with very low reaction rate constants. pH exhibited a significant influence on the oxidation of BC and a higher activity at C6 was observed in a neutral medium.

Surface characteristics and electrochemical corrosion behavior of NiTi alloy coated with IrO2

The aim of this work is to investigate the surface characteristics and corrosion behavior of NiTi (50.6 at.% Ni) shape memory alloy coated by a ceramic-like and highly biocompatible material, iridium oxide (IrO2). IrO2 coatings were prepared by thermal decomposition of H2IrCl6 · 6H2O precursor solution at the temperature of 300 °C, 400 °C and 500 °C, respectively. The surface morphology and microstructure of the coatings were investigated by scanning electron microscope (SEM) and glancing angle X-ray diffraction (GAXRD). X-ray photoelectron spectroscopy (XPS) was employed to determine the surface elemental composition. Corrosion resistance property of the coated samples was studied in a simulated body fluid at 37±1 °C by electrochemical method. It was found that the morphology and microstructure of the coatings were closely related to the oxidizing temperatures. A relatively smooth, intact and amorphous coating was obtained when the H2IrCl6·6H2O precursor solution (0.03 mol/L) was thermally decomposed at 300 °C for 0.5 h. Compared with the bare NiTi alloy, IrO2 coated samples exhibited better corrosion resistance behavior to some extent.

Microstructure and wear behaviour of ceramic particles strengthening NiAl based composite

Abstract In the present paper, the NiAl based composite strengthened by TiC and ZrO2 ceramic particles (NiAl–TiC–ZrO2 for short) was prepared by the hot press aiding exothermic synthesis (HPES) technique to get a material with good wear properties. OM, SEM and TEM were employed to investigate the microstructure of the NiAl–TiC–ZrO2 composite. The mechanical properties and wear behaviour were studied by compression and dry sliding wear tests. The results showed that the NiAl–TiC–ZrO2 composite possesses fine microstructure, but the TiC and ZrO2 particles tended to agglomerate along NiAl phase boundary. Further observations revealed that the ultrafine ZrO2 particles contained stacking faults and microtwins inside and thin amorphous layer was generated along some interfaces of NiAl and TiC phases. Compression tests exhibited that the addition of TiC and ZrO2 particles could increase the strength of the NiAl–TiC–ZrO2 composite significantly. Wear tests results demonstrated that the NiAl–TiC–ZrO2 composite had relative good wear resistance at high temperature. Especially at 973 and 1073 K, the composite exhibited self-lubrication behaviour, which might be attributed to the lubricant film formed on the worn surface. TEM observation on the lubricant film revealed that it was composed of amorphous matrix and nanoparticles. Moreover, TEM observation found the composite near the worn surface contained ultrafine microstructure. When the temperature increased or decreased, the lubricant film would be spalled partly, which led to the increasing of the friction coefficient and wear rate.

Surface modification by natural biopolymer coatings on magnesium alloys for biomedical applications

Abstract Natural biopolymers possess good biocompatibility and exhibit excellent bioactivity due to the components of the extracellular cell matrix, which are abundant in the biomass and are easily accessible from a range of sources, such as forest products, grasses, tunicates, crustacean, and stalks. In this chapter, magnesium alloys modified with a natural biopolymer coating to improve their biocompatibility and degradation properties are introduced. Some natural biopolymers, such as chitosan, phytic acid, collagen, and stearic acid have been studied and coated on the surface of magnesium alloy for biomedical applications. Enhanced corrosion resistance, improved biocompatibility, and a reduced hemolysis ratio of WE43 was achieved after modification with phytic acid solution with different pH values of the conversion coating, especially when the pH value of the modified solution was 5. Various chitosan dip-coated Mg-1Ca alloys also displayed greater corrosion resistance in simulated body fluid. Calcium phosphate/chitosan composite films coated on the surface of micro-arc oxidized (MAO)-AZ91D alloy through electrophoretic deposition or on the surface of AZ31 alloy by aerosol deposition were adopted to enhance the bond strength between the magnesium substrate and hydroxyapatite. Stearic acid coating on hydrothermal-treated Mg samples enhanced the corrosion resistance of Mg. A drug release system on MAO-WE42 was established by a cross-linked gelatin/PLGA particle loaded with paclitaxel. Finally, a comparatively smooth surface of magnesium coated with albumin attached via linker groups was employed for better corrosion property, taking advantage of the presence of an Mg(OH)2-terminated MgO layer via silane coupling chemistry. Although the data and literature are limited in this area, previous works have validated the effectiveness and function of natural polymers on the corrosion resistance and biocompatibility of magnesium alloys, and much more research is expected in the future.

Proteomic profile of mouse fibroblasts exposed to pure magnesium extract.

Magnesium and its alloys gain wide attention as degradable biomaterials. In order to reveal the molecular mechanism of the influence of biodegradable magnesium on cells, proteomics analysis was performed in this work. After mouse fibroblasts (L929) were cultured with or without Mg degradation products (Mg-extract) for 8, 24, and 48h, changes in protein expression profiles were obtained using isobaric tags for relative and absolute quantitation (iTRAQ) coupled two dimensional liquid chromatography-tandem mass spectrometry (2D LC MS/MS). A total of 867 proteins were identified (relying on at least two peptides). Compared to the control group, 205, 282, and 217 regulated proteins were identified at 8, 24, and 48h, respectively. 65 common proteins were up or down- regulated within all the three time points, which were involved in various physiological and metabolic activities. Consistent with viability, proliferation, and cell cycle analysis, stimulated energy metabolism as well as protein synthesis pathways were discussed, indicating a possible effect of Mg-extract on L929 proliferation. Furthermore, endocytosis and focal adhesion processes were also discussed. This proteomics study uncovers early cellular mechanisms triggered by Mg degradation products and highlights the cytocompatibility of biodegradable metallic materials for biomedical applications such as stents or orthopaedic implants.

Establishment of a long-term chick forebrain neuronal culture on a microelectrode array platform

The biosensor system formed by culturing primary animal neurons on a microelectrode array (MEA) platform is drawing an increasing research interest for its power as a rapid, sensitive, functional neurotoxicity assessment, as well as for many other electrophysiological related research purposes. In this paper, we established a long-term chick forebrain neuron culture (C-FBN-C) on MEAs with a more than 5 month long lifespan and up to 5 month long stability in morphology and physiological function; characterized the C-FBN-C morphologically, functionally, and developmentally; partially compared its functional features with rodent counterpart; and discussed its pros and cons as a novel biosensor system in comparison to rodent counterpart and human induced pluripotent stem cells (hiPSCs). Our results show that C-FBN-C on MEA platform 1) can be used as a biosensor of its own type in a wide spectrum of basic biomedical research; 2) is of value in comparative physiology in cross-species studies; and 3) may have potential to be used as an alternative, cost-effective approach to rodent counterpart within shared common functional domains (such as specific types of ligand-gated ion channel receptors and subtypes expressed in the cortical tissues of both species) in large-scale environmental neurotoxicant screening that would otherwise require millions of animals.

Investigation on B, Cr Doped Ni3Al Alloy Prepared by Self-Propagation High-Temperature Synthesis and Hot Extrusion

The Ni3Al and Ni3Al-B-Cr alloys were fabricated by the self-propagation high-temperature synthesis with hot extrusion method. Their microstructure and mechanical properties were studied by using combination of X-ray diffraction, optical microscopy, transmission electron microscopy and compression test. Analysis of X-ray spectra exhibited that the elemental powders had been transformed to the Ni3Al phase after the self-propagation high-temperature synthesis processing. Microstructure examination showed that the alloy without extrusion consisted of coarse and fine grains, but the subsequent hot extrusion procedure homogenized the grain size and densified the alloy obviously. Transmission electron microscopy observations on the Ni3Al alloy revealed that Ni3Al, γ-Ni and Al2O3 particles were the main phases. When the boron and chromium were added, besides the β-NiAl phase, α-Cr phase and some Cr7Ni3 particles with stacking faults inside were observed. In addition, a lot of substructure and high-density dislocation arrays were observed in the extruded part, which indicated that the subsequent extrusion had led to great deformation and partly recrystallizing in the alloy. Moreover, the subsequent extrusion procedure redistributed the Al2O3 particles and eliminated the γ-Ni. These changes were helpful to refine the microstructure and weaken the misorientation. The mechanical test showed that the self-propagation high-temperature synthesis with hot extrusion improved the mechanical properties of the Ni3Al alloy significantly. The addition of B and Cr in Ni3Al alloy increased the mechanical properties further, but the compressive strength of the alloy was still lower than that synthesized by combustion. Finally, the self-propagation high-temperature synthesis with hot extrusion was a good method to prepare Ni3Al alloy from powder.