Performance characterization of Ni60-WC coating on steel processed with supersonic laser deposition

Ni60-WC particles are used to improve the wear resistance of hard-facing steel due to their high hardness. An emerging technology that combines laser with cold spraying to deposit the hard-facing coatings is known as supersonic laser deposition. In this study, Ni60-WC is deposited on low-carbon steel using SLD. The microstructure and performance of the coatings are investigated through SEM, optical microscopy, EDS, XRD, microhardness and pin-on-disc wear tests. The experimental results of the coating processed with the optimal parameters are compared to those of the coating deposited using laser cladding.

Jacquard image segmentation using Mumford-Shah model

Jacquard image segmentation is one of the primary steps in image analysis for jacquard pattern identification. The main aim is to recognize homogeneous regions within a jacquard image as distinct, which belongs to different patterns. Active contour models have become popular for finding the contours of a pattern with a complex shape. However, the performance of active contour models is often inadequate under noisy environment. In this paper, a robust algorithm based on the Mumford-Shah model is proposed for the segmentation of noisy jacquard images. First, the Mumford-Shah model is discretized on piecewise linear finite element spaces to yield greater stability. Then, an iterative relaxation algorithm for numerically solving the discrete version of the model is presented. In this algorithm, an adaptive triangular mesh is refined to generate Delaunay type triangular mesh defined on structured triangulations, and then a quasi-Newton numerical method is applied to find the absolute minimum of the discrete model. Experimental results on noisy jacquard images demonstrated the efficacy of the proposed algorithm.

Effect of Laser Power on the Cladding Temperature Field and the Heat Affected Zone

H13 powder is cladded on steel P20 （base） by continuous COe laser, and the influence of technological pa rameters such as the laser power is analyzed. The 3-D model of synchronous powder feeding is built under Gauss heat source. The simulative results in the heat affected zone are compared with the experimental ones, and the average er rors of width and depth are 15% and 4.5%, respectively. It is found that the simulative results provide basic data for investigating of laser cladding further.

Hardfacing steel with nanostructured coatings of Stellite-6 by supersonic laser deposition

The ability to manufacture coatings is critical to engineering design. Many components require the application of additional layers toenhance mechanical properties and protect against hostile environments. Supersonic laser deposition (SLD) is a novel coating methodbased on cold spray (CS) principles. In this technique, the deposition velocities can be significantly lower than those required foreffective bonding in CS applications. The addition of laser heat energy permits a change in the thermodynamic experience of impactingparticles, thereby offering a greater opportunity for efficient bonding at lower velocities as compared with the CS process. The workreported in this paper demonstrates the ability of the SLD process to deliver hardfacing materials to engineering surfaces. Stellite-6 hasbeen deposited on low-carbon steel tubes over a range of process parameters to establish the appropriate target power and traversespeeds for the coating formation. The coating properties and parameters were examined to determine the primary characteristics andgrain structure size. Their morphology and performance were studied through optical microscopy, scanning electron microscope(SEM), X-ray diffraction, hardness measurements and wear testing. The results have shown that SLD is capable of depositing layers ofStellite-6, with properties that are superior to those of their conventionally manufactured counterparts.

Characteristics of Stellite 6 Deposited by Supersonic Laser Deposition Under Optimized Parameters

Stellite 6 powders were deposited on low carbon steel using SLD （supersonic laser deposition） under optimized parameters. The structure, line scan of elements and porosity of coating were examined and analyzed using SEM （scanning electron microscope）, OM （optical microscope） and XRD （X-ray diffraction）. The adhesion strength between coating and substrate was tested by PAT-ADHESION/TENSILE and E900STM adhesive. The results showed the deposition characteristics of optimized coating with N2 at a pressure of 3.0 MPa, a temperature of 450 ℃ and a laser power of 1.5 kW were compared with those of Stellite 6 coating deposited by the HVOF （high velocity oxygen fuel）.

Investigation of multiple metal nanoparticles near-field coupling on the surface by discrete dipole approximation method

We use the method of discrete dipole approximation with surface interaction to construct a model in which a plurality of nanoparticles is arranged on the surface of BK7 glass. Nanoparticles are in air medium illuminated by evanescent wave generated from total internal reflection. The effects of the wavelength, the polarization of the incident wave, the number of nanoparticles and the spacing of multiple nanoparticles on the field enhancement and extinction efficiency are calculated by our model. Our work could pave the way to improve the field enhancement of multiple nanoparticles systems.

Deposition Behavior at Different Substrate Temperatures by Using Supersonic Laser Deposition

The supersonic laser deposition （SLD） is a new fabrication process which combines the supersonic powder stream found in cold spray with laser heating of the deposition zone. Because of the instantaneity of particles impact, the deformation behaviors and the adhesion behaviors of particles impacted on the substrate by SI.D cannot be well investigated through experiments. Therefore, a finite elemen! model was developed to solve the problems above. Meanwhile, the heat effect of the substrate heated by laser was discussed. The effective plastic strain and the effec- tive stress between the particle and substrate at different laser preheal temperatures were studied. The results show that laser depositing temperatures of 1 000 and 1 100 ℃ on substrate would be the optimized for the bonding of parti- cles and substrate. In addition, the simulation results conformed to experimental results.

Deploy Efficiency Driven k-Barrier Construction Scheme Based on Target Circle in Directional Sensor Network

With the increasing demand for security,building strong barrier coverage in directional sensor networks is important for effectively detecting un-authorized intrusions.In this paper,we propose an efficient scheme to form the strong barrier coverage by adding the mobile nodes one by one into the barrier.We first present the concept of target circle which determines the appropriate residence region and working direction of any candidate node to be added.Then we select the optimal relay sensor to be added into the current barrier based on its input-output ratio(barrier weight)which reflects the extension of barrier coverage.This strategy looses the demand of minimal required sensor nodes(maximal gain of each sensor)or maximal lifetime of one single barrier,leading to an augmentation of sensors to be used.Numerical simulation results show that,compared with the available schemes,the proposed method significantly reduces the minimal deploy density required to establish k-barrier,and increases the total service lifetime with a high deploy efficiency.