Papers by Keyword: Surface Processing

Abstract: Low temperature photoluminescence (PL) of high-resistivity detector-grade Cl-compensated CdTe semiconductor crystals subjected to irradiation with nanosecond (τ = 7 ns) laser pulses of the second harmonic (λ = 532 nm) of a YAG:Nd laser is studied. Irradiation of CdTe crystals within the certain range of laser pulse energy densities results in a relative decrease in the emission intensity in both the deep energy level and edge regions and an increase in the exciton band intensity in the PL spectra. The evolution of the PL spectra depending on laser energy density, excitation level and temperature under excitation are analyzed. Laser-stimulated transformation of the point defect structure of the CdTe surface region and mechanisms of laser-induced defect formation are discussed. The optimal regimes of laser processing have been obtained which result in the minimum ratio of the defect and exciton bands that is an evidence of an increase in the structural perfection of the irradiated crystals.

Abstract: The removable partial dentures are made of alloys from CoCrMo system. This survey work paper considers various commercial CoCrMo alloys that were investigated in terms of surface behavior through different processing methods, respectively: sand blasting, grinding, milling, smoothing and polishing, procedures applied in accordance with the necessary standards for prostheses processing in dental labors, regarding their final trimming. Alloys behavior highlighting was performed by macrostructural investigations carried out at stereomicroscope. In the end an alloy hierarchy was achieved according to the method in which the main macrostructural aspects were highlighted.

Abstract: In this paper, surface residual stress in the cold working tool steel (Cr12MoV) by EDM was investigated by X-350 X-ray residual stress analyzer and method of DJP-2 electrolytic polishing instrument to remove layer by layer in the different EDM conditions. The results show that the distribution of surface residual stress generated not only by the peak discharge current and pulse width, but also by pulse interval. The same depth from the surface, residual stress of material after hardening is larger than the residual stress after annealing, With the different combination of tool electrode and work-piece material, the form of the discharge between two electrodes and the proportion of energy put between two electrodes are different, surface residual stress are also different. Different processing liquid for processing, the depth of residual stress generated is much the same, but closer to the surface, the worse the cooling capacity (quench degrees) and surface physical properties of processing fluids, the greater the residual stress. EDM, the generation and control of the surface residual stress depends on the choice such as processing power criteria, work-piece material, electrode materials and processing liquid. Surface residual stress after processing can be used to eliminate high-temperature heat treatment.

Abstract: The paper deals with the application of semi-Friction Stir Processing (s-FSP) to the improvement of surface contact within the flange joints used in casings of high-voltage switchgears which are filled with electroinsulating SF6 gas. The goal of the research was to design the appropriate tool (shape and size) as well as to select parameters for this s-FSP process which results in the removal of casting defects from the surface layer of the final product. The characteristics of the proposed process is the redesign of a tool shape, which is not equipped with an element penetrating and stirring the material (pin). Moreover, the process does not require the usage of sophisticated devices or tilting the tool relative to the treated surface during the process. The elaborated process is useful for repairing the defective castings, and in the case of high-voltage switchgears, it allows to achieve the required tightness of the joints.

Abstract: Fabrication of friction reducing and anti-wear surface with regular micro/nanostructures is a hotspot of surface engineering studies nowadays. We present a simple and easily-controlled method for fabricating stainless steel-based nanostructures surface. First, by strictly controlling the number of femtosecond laser pulses, two kinds of nanostructures are fabricated. Then, forming mechanisms of nanodots and ripple structure are analyzed. Lastly, we obtained uniform large-area nanodots and ripple structures by adjusting the repetition rate of laser focus accurately. Therefore, this technique will provide a good method to investigate the tribological properties of controllable nanotexture surface.

Abstract: This paper introduces a octree search Kinetic Monte Carlo(OS-KMC) that combines the topological requirements for representing an evolving multivalued surface using minimal memory and an efficient search algorithm for the realization of the KMC time evolution. In addition, the data structure for OS-KMC also provides a nature way to generate hexahedral element meshes for the integration between simulator and performance analysis tool. The density of mesh grid and the refinement of the hexahedral element can be controlled in this octree based mesh generation method. In simulating surface morphology during wet etching and micro structure formed by composite MEMS processes, the octree search KMC shows good simulation results with better calculation performance. The octree structure enables the Monte Carlo solutions for large scale problems with complex dynamic surfaces.