Effects of Duplex Nitriding and TiN Coating Treatment on Wear Resistance,Corrosion Resistance and Biocompatibility of Ti6Al4V Alloy

Ti6Al4V alloy substrates were nitrided at 900 °C. TiN coatings were then deposited on the nitrided substrates using a closed-field unbalanced magnetron sputtering system. The microstructure, hardness and adhesion properties of the TiN-N-Ti6Al4V substrates were evaluated and compared with those of an untreated Ti6Al4V sample, a nitrided Ti6Al4V sample and a TiN-coated Ti6Al4V sample, respectively. The tribological properties of the various samples were investigated by means of reciprocating sliding wear tests performed in 0.9 wt.% NaCl solution against 316L, Si₃N₄ and Ti6Al4V balls, respectively. In addition, the corrosion resistance was evaluated using potentiodynamic polarization tests. Finally, the biocompatibility of the samples was investigated by observing the attachment and growth of purified mouse leukemic monocyte/macrophage cells (Raw 264.7) on the sample surface after culturing periods of 24, 72 and 120 h, respectively. Overall, the results showed that the duplex nitriding/TiN coating treatment significantly improved the tribological, anti-corrosion and biocompatibility properties of the original Ti6Al4V alloy.     

Deposition and super liquid repellency of fluorinated ZnO nanoparticles on carbon fabrics

The liquid-repellent behavior of fluorinated zinc oxide (ZnO) nanoparticles deposited onto carbon fabric (CF) by a pulse microwave-assisted (MA) method followed by surface fluorination treatment was investigated. The MA process is performed at 80 °C within 10 min with different pH values of 5.5, 8 and 12. The hexagonal ZnO nanoparticles with an average size of 100 nm exhibit a well-defined wurtzite crystal structure without any heat treatment. The ZnO nanoparticles produced by MA synthesis at pH = 8 display the maximal density over CF substrate. The fluorination coating effectively imparts super water and oil repellencies on the ZnO–CF surface; i.e., the contact angles are 163° (water) and 153° (ethylene glycol, EG). The liquid repellencies toward water and EG droplets show an increasing function of surface density of ZnO nanoparticles. This result can be attributed to the fact that an air layer is confined in the nanoparticles, thereby inducing a rougher gas–vapor–solid contact line, referred to as the Cassie state. Based on the Young–Duprè equation incorporated with the Cassie parameter, the lowest work of adhesion (W_ad) values of the ZnO–CF surface for water and EG repellencies are estimated to be 3.16 and 4.93 mJ/m², respectively. Accordingly, this work sheds some light on the creation of a two-tier texture by an efficient MA route and on how the surface density of ZnO nanoparticles strongly affects the repellent behavior of the resultant ZnO–CF composites.     

Combustion Behavior and Thermochemical Properties of RDX-Based Solid Propellants

The combustion behavior and thermochemical properties of two types of RDX-based composite propellants, XM39 and M43, are studied and compared in order to investigate the effect introduced by an energetic ingredient in the M43 propellant formulation. Due to the enhanced rate of heat release on the burning surface caused by the energetic material of M43 propellants, the burning rate of M43 propellants is found to be higher than that of XM39 propellants. The presence of the energetic material in the M43 propellant formulation also increases the burning surface temperature and thermal diffusivity of M43 propellants; it does not, however, introduce any observed changes in the flame structure and the heat feedback from the gas phase to the condensed phase. Based upon SEM pictures, burning-surface structures of the recovered XM39 and M43 propellant samples are found to be significantly different, indicating the strong effect of the energetic material on the surface reaction. A set of important thermochemical properties of XM39 and M43 propellants is deduced from the experimental data.     

Interpenetrating polymer networks of polyurethane and furfuryl alcohol,IIa. Processability and properties of pultruded fiber-reinforced composites

A feasibility study of pultrusion of fiber-reinforced polyurethane/furfuryl alcohol (PU/FA) interpenetrating polymer/network IPN composites has been made. From the viscosity study, it was found that the pot life of the PU/FA IPN prepolymers increased with PU content and showed high reactivity at elevated temperature. It was confirmed from the morphological study that the wetting of fibers by the PU/FA IPN resins was improved with PU content. The appearance of the tensile failure surfaces of the pultruded glass fiber-reinforced PU/FA IPN composites showed “hackle patterns” for PU contents below 15 phr. The mechanical property study shows that the tensile strength of pultruded PU/FA IPN composites is the highest when the PU content is 5 phr. However, the flexural strength, flexural modulus and HDT decreased with PU content. The mechanical properties of various fiber-reinforced (glass, carbon, and Kevlar 49 aramid fiber) pultruded PU/FA IPN composites increased with fiber volume content.     

Static error budget analysis for a land-based dual-camera mobile mapping system

A mobile mapping system (MMS) is developed based on a direct sensor orientation technique that integrates GPS/inertial measurement unit (IMU) and digital cameras. This system is capable of directly mapping geospatial information without the requirement of ground control. In this article, an MMS composed of two digital single-lens reflex cameras and an Applanix POS AV-510^© is described. There are several systematic errors that need to be calibrated before achieving the goal of direct georeferencing. These are related to lens distortion, the lever-arm between the GPS and the camera's perspective center, and the boresight misalignment angles between the IMU and the camera frame. Experimental results show that the calibration field is the major error source. However, with the designed system, we can achieve a maximum three-dimensional positioning error of less than 18.27 and 7.74?cm at distances 20?m using a single camera with parallel imaging and dual-cameras with convergent imaging, respectively. The results demonstrate that the potential of high-accuracy land-based MMS applications is promising.     

Inverse problems of linear feedback control systems: Stabilization,tracking and disturbance rejection

Abstract

Recent developments in the fractional representation approach of linear feedback control systems give some promise for a comprehensive unification of various design methodology. This paper presents some results of the fractional representation theory in terms of mapping of simple algebraic functions defined on appropriate domains of free design parameters. We emphasize that the symmetry of the closed‐loop feedback system could provide us some informations which are useful for the robustness analysis of the closed‐loop system.     

Analysis and design of frequency‐controlled oscillator for frequency‐locked stepping position control system

Abstract

A frequency‐locked stepping position servo system (FLSPS) is presented. The proposed microprocessor‐based sloped‐varied frequency‐controlled oscillator (SVFCO) is designed to achieve nearly the same acquisition times for different position commands. The slope‐varied technique is to quickly position for long distance servo during the wide‐range control. The motion profiles for position locking are adaptively built according to the periodically sampled frequency error. No motion profiles are required to be pre‐installed in the controller. The system model is built for stability investigation and simulation. A design example is realized to verify the theoretical predictions. System simulation and experimentation confirm that the system acquisition times for short, middle, and long distance servos are very close to each other. In comparison with the corresponding traditional stepping position system, the acquisition times of the FLSPS are improved by 53% and 73%.     

A wide-locking range ÷3 injection-locked frequency divider using concurrent injection mechanisms

A new wide locking range divide-by-3 injection-locked frequency divider (ILFD) using a standard 0.18 μm CMOS process is presented. The ILFD uses two concurrent injection mechanisms with two independent push–push circuits to extend the locking range. It is realized with a cross-coupled n-core MOS LC-tank oscillator. The core power consumption of the ILFD core is 11.496 mW. The divider’s free-running oscillation frequency is tunable from 4.32 to 3.78 GHz by tuning the varactor’s control bias, and at the incident power of 0 dBm the maximum locking range is 3 GHz (25 %), from the incident frequency 10.5 to 13.5 GHz. The operation range is 3.6 GHz (30.76 %), from 9.9 to 13.5 GHz.     

A Ni-free Zr-based bulk metallic glass with remarkable plasticity

The effect of Nb and Pd combination on the glass forming ability (GFA) and mechanical properties of Zr₅₃Cu₃₀Nb_xPd_9?xAl₈ (x = 3.5–6.0) bulk metallic glasses (BMGs) were systematically investigated by X-ray diffractometry (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and compression test. TEM observation revealed that a nanocrystalline phase embeds in the amorphous matrix of the as-cast Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ alloy. A tiny nano-crystalline phase (with size about 5–20 nm) embedded uniformly in the amorphous matrix of the Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ alloy was observed and identified to be the tetragonal structured NbPd₃ phase based on the analyses of nano beam electron diffraction. According to the results of thermal analyses, the composition of Zr₅₃Cu₃₀Nb₅Pd₄Al₈ and Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ present the optimum GFA as well as thermal stability in the Zr₅₃Cu₃₀Nb_xPd_9?xAl₈ (x = 3.5–6.0) alloy system. In addition, the result of compression test shows that the yield strength significantly increases from 1700 MPa (Zr₅₃Cu₃₀Nb₅Pd₄Al₈) to 1900 MPa (Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈). A remarkable compression plastic strain (11.2%) occurs at Zr₅₃Cu₃₀Nb_4.5Pd_4.5Al₈ BMG rod with 2 mm in diameter. This significant increase in plasticity is presumably due to the restriction on shear banding by the nano-size second phase.