Ultrafine-grained (UFG) materials have caught much attention due to their significantly enhanced mechanical properties. However, local deformation easily occurred during tensile and fatigue processes of the traditional UFG materials produced by severe plastic deformation methods due to their metastable microstructure, resulting in the greatly reduced mechanical properties. This paper introduced a new method of preparing the UFG materials -friction stir processing (FSP), and the microstructure and mechanical properties of FSP UFG materials were summarized and discussed compared with other UFG materials.
Oxygen plasma treatment was used to modify the surface of aramid fiber III. The changes of fiber surface before and after oxygen plasma treatment was investigated in this paper. The surface chemical structure, element composition, surface morphology, surface roughness and surface wettability before and after oxygen plasma treatment were analyzed by FTIR, X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), atomic force microscopy (AFM) and dynamic contact angle analysis (DCAA), respectively. It was found that oxygen plasma treatment introduced some newly polar groups such as (C-O and O-C=O) to fiber surface, the content of which were 20.1% and 8.1%, respectively. After oxygen plasma treatment, the roughness of fiber surface increased and surface grooves and ups and downs were increased obviously. It was also shown that the fiber surface wettability was improved significantly by oxygen plasma treatment. The total surface free energy increased from 49.9 mJ/m2 to 67.1 mJ/m2.
The effect of cooling rate (0.03, 1.08 and 40°C/s) and Al-content on the solidified microstructure and corrosion resistance of Zn-xAl (x=4%, 5%, 7%)-0.06%Nd alloys used for hot-dip galvanizing were examined by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), polarization curves tests and neutral salt spray tests (NSS). The results show that the solidified microstructure of alloys is refined and the eutectic lamellar spacing became smaller as the cooling rate increases, and the corrosion resistance of the alloy increases initially and decreases afterwards with the increase of the cooling rate. Moreover, the addition of Nd can be beneficial to the further reduction of the eutectic lamellar spacing and the improvement of the corrosion resistance of the alloys. Therefore, after air cooling, the Zn-5%Al-0.06%Nd alloy presents the best corrosion resistance. Besides, the variation of Al-content between 4% and 7% caused mainly the change of microstructure, but little effect on the corrosion resistance of the alloys.
The lubricating property of water-based lubricant of konjac glucomannan (KGM) was assessed for the contact surface of quartz to quartz. The molecular structure of konjac glucomannan was analyzed by Fourier transform infrared spectroscopy. The surface topographies of the worn quartz surface after sliding-wear were examined by LEXT OLS4000 3D microscope. The friction performance of the friction-pair of quartz against quartz was evaluated by the CETR Universal Micro-Tribometer (UMT-2). The lubricating property of KGM solutions was then analyzed. The results show that the 0.3% KGM solution possesses the best lubricity, in the presence of which the friction-pair of quartz exhibits a friction coefficient about 0.002. The frictional coefficient of the friction-pair of quartz varied with the KGM concentration of the solution, as well as the relatively rotating speed of the components of the friction-pair. By adding saturated boric acid to the solution, the hydration layer of KGM was promoted due to the coordination compound which was generated by the chemical reaction between the boric acid and the KGM molecules. The lubricating model of KGM solution was composed of hydrationlayers of KGM and water layers, in which the former absorbed on the frictional pairs to form a lubricating film, while the water layer ensures the shear liquidity of lubricant, only the combination of the two can realize the effective lubrication.
The effect of microstructure on tearing fracture behavior for thick plates of X80 pipeline steel was assessed at -25 oC by means of drop-weight tear tester (DWTT),as well as optical microscopy and scan electron microscopy (SEM). The result shows that the volume fraction of acicular ferrite reduced gradually in the thickness direction and reached a minimum level at the center of the plate, whilst more volume fraction of granular bainite (GB), polygonal-like ferrite (PF) and quasi-polygonal-like ferrite (QF) appeared. The higher volume fraction of acicular ferrite of the plate is, the larger tearing share area will be. In addition, the existence of PF and QF, and large size martensite-austenite (MA) could lead to the initiation of cleavage crack, and reduce the fracture toughness of the plate. During the crack propagation process, microstructures near the main crack deformed and elongated seriously, but the hard and brittle MA can hardly deform, resulting in the growth of voids and formation of micro cracks. The secondary crack is always reflected by or arrested on acicular ferrite boundaries, which demonstrates that the acicular ferrite has good toughness, and thereby retards the crack propagation effectively.
Nano-SiO2 was firstly modified by (3-glycidoxypropyl)-trimethoxylsilane (GPTMS), and then was grafted with polyaniline (PANI) to form nano-SiO2 (SiO2@PANI) sol with core-shell structure through chemical bonding. Further, the nano-SiO2 (SiO2@PANI) sol was in situ embedded with vinyl trimethoxysilane (VTMS) to prepare the water-born SiO2@PANI/VTMS sol, which can be used as coating material for Mg-Li alloy. The structure and morphology of SiO2@PANI were characterized by Fourier transform infrared spectrum (FT-IR), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) etc. The corrosion resistance of the coating was assessed by potentiodynamic polarization curves and electrochemical impedance spectra (EIS). The effect of aniline- and VTMS-dosage on the particle size, hydrophobic property and corrosion resistance of SiO2@PANI were also examined, and the possible anticorrosion mechanism was proposed. The results show that the SiO2@PANI/VTMS coatings have a high hydrophobic angle, which could reach 145.5° when m(An):m(TEOS)=7:100 and m(VTMS):m(TEOS)=4:4. The composite coatings on Mg-Li alloy present excellent corrosion resistance performance with electrochemical impedance value 7.5×104 Ωcm2 and corrosion current density 4.47×10-8 A/cm2.
The hemodynamic property in physiological saline solution of bioprosthetic heart valve was measured under the physiological considition using a pulse duplicator, accordingly, based on the above measured data, the stress and strain distribution on heart valve leaflets was analized by means of finite element analysis (FEA) at the microscopic level over a cardiac cycle, so that to assess the relationships between the structure and mechanical properties of the bioprosthetic heart valve. The measured parameters of the bioprosthetic heart valve (Edwards #2625) are as follows: the mean transvalvular pressure ~10.8 mmHg, the effective opening area ~2.0 cm2 and the regurgitant fraction ~8.4%, which all meet the requirements of the ISO-5840 standard; The FE simulation results show that the maximum principal stresse was 425 kPa during the systolic phase, the major stress concentration was found on the belly and the suture edge of the leaflet, which underwent severe bending deformation. The maximum principal stresse was 1.46 MPa during the diastolic phase, and the major stress concentration was found on the two sides of the suture of the leaflet; The valvular open areas at different time points were close to those measured during experimental tests, indicating the relibility of the FEA method. Thus, the combination of the simulation test and and the finite element simulation calculation may be considered as an efficient and relible stratigy to evaluate the relationships between the structure and mechanical properties of bioprosthetic heat valve.
Composites of polyaniline (PANI)-coated carbon micro-coils (CMCs) were synthesized by in-situ polymerization and emulsion polymerization methods respectively. The morphology and structure of the composites were characterized by FTIR,SEM and XRD. The results show that after CMCs have been treated with nitric acid (H-CMCs), more carboxyl group appeared on their surface, which is beneficial to the adhesion of PANI to the surface of CMCs. The electrochemical property of the composite was assessed by means of cyclic voltammetry (CV), constant-current charge-discharge and alternating-current impedance measurements. The results proved that the specific capacitance of PANI-coated H-CMCs was obviously higher than that of the H-CMCs themselves, while the in-situ polymerized H-CMCs/PANI-2 had the highest specific capacitance of 109.3 Fg-1, which was much higher than 35.76 Fg-1 of the H-CMCs at a scan rate of 5 mVs-1. The constant-current charge-discharge curves revealed that the composite capacitors contained not only the electronic double-layer capacitance of CMCs but also the faraday pseudo-capacitance of PANI. Electrochemical impedance spectroscopy (EIS) shows that the PANI coated H-CMCs present better conductivity and super capacitor characteristic.
Friction and wear behavior of nitrile butadiene rubber in crude oil with sand was investigated by the reciprocating wear tester, while the movement of sand grains of different shapes during the wear process was also studied. Morphology and chemical composition of the worn surface of rubber were characterized by stereo microscope and field emission scanning electron microscope. The results show that the frictional coefficient and wear loss of the rubber in crude oil increased with the addition of sand. The main movement model of round-shaped sand grains was rolling within the desired range of load, and the grinding abrasive wear was generated on the rubber surface. The movement model of sharp sand grains changed from rolling to sliding when the applied load was above 95 N, and correspondingly the wear mechanism of rubber transformed into cutting abrasive wear. The above observed variation of movement model of different shaped sand grains by varying applied load and its effect on the wear mechanism of rubber was further confirmed by the research result on the mechanical behavior related with translational acceleration and rotational acceleration of sand grains.
Strain induced melt activation (SIMA) based on cold rolling and remelting method is used to prepare the rheological slurry, then with which axle bush parts of Cu alloy ZCuSn10P1 were prepared by rheological squeeze casting process. Whilst the effect of extrusion rate on the microstructure and mechanical property of the prepared copper alloy, and the evolution of solid and liquid phases during the forming process were studied. The results indicate that with the forming specific pressure of 250 MPa and extrusion rate of 15 mm/s, the microstructure of the prepared Cu-alloy ZCuSn10P1 is uniform and the synergy liquidity of solid-liquid is considerable, thereby, the tensile strength of the Cu-alloy reached a peak value of 371.1 MPa and elongation of 8.43%, which are 57.3% and 78.7% respectively higher than those of the Cu-alloy prepared by liquid-phase extrusion casting process. Furthermore, it is noted that liquid-phase segregation phenomenon along not only the vertical direction, but also the horizontal direction could be observed in the microstructure of the prepared axle bush parts by the rheological squeeze casting process.
