Advanced Materials Research Vols. 189-193

Abstract: This study presented the desirability function based on Taguchi designed experiments to solve multiple responses statistical optimal problems for the tungsten carbide/cobalt (WC-Co) coatings of high-velocity-oxygen-fuel (HVOF) processes. The eight control factors based on L18 arrays were conducted and the multi-responses of wear-resistant coatings such as hardness, deposited thickness and wear rate were evaluated simultaneously in the desirability-based experiments. Based on desirability analysis, the optimal settings have been identified, and the impacts of control factors are determined by analysis of variance on the multi-responses. Further, a confirmation run was conducted to validate the tests. Experimental results have shown that the hardness increased by 16.61% and the deposited thickness improved by 10.50%, while the wear rate decreased by 34.03%. It was clear that confirmation tests are greatly improved by way of the desirability-based multi-responses on HVOF WC-Co experiments, and these findings achieved the desired values on wear-resistant coatings. The proposed procedure was applied at HVOF sprayed WC-Co experiments, and the implementation results demonstrated its feasibility and effectiveness to maximize hardness, make a target of deposited thickness value and minimize wear rate by a HVOF.

Abstract: The paper describes response surface methodology (RSM) based on design of experiments and analysis of variance (ANOVA) as a statistical design while developing a robust plasma transfer arc (PTA)coating process. Based on ANOVA, The relative important parameters with respect to surface at hardness values were identified in the Taguchi design, where they were further used in predictors. In addition, we applied three-dimensional graphs in RSM to develop a robust PTA response surface yielding the desired-better area of a treated layer. In this study, a quadratic polynomial with a Box-Behnken design is utilized. The results reveal that RSM provides the effective methods as compared to the traditional trial-and-error method for exploring the effects of controlled factors on response. A very good agreement was observed, as evidenced by R-squared value, 90%, between the predicted and the experimental data, and its error percent is found to be approximately 3.801% in the PTA-coating process. It is clear that RSM model demonstrated better accuracy in predicting surface hardness for PTA-coating process. Accordingly, RSM based on design of experiments was used as statistical PTA-coating design tools combined with the hardness model. Device zone optimization and yield enhancement have been demonstrated.

Abstract: Amorphous carbon (a:C-H) coatings with high hardness and low friction coefficient are widely applied in die and mold industries. Zirconium-containing a:C-H (a-C:Zr) coatings with double interlayered Zr/ZrC were deposited by unbalanced magnetron sputtering system. A L18 orthogonal array experiment was designed to investigate the effect of process parameter on the friction coefficient of deposited films. Control factors, such as methane flow rate, bias voltage, sputtering frequency, zirconium target current and work distance were schematized for experiments. The experimental results show that zirconium target current exhibits about 45% percent contribution in analysis of variance, and the friction coefficient of a-C:Zr coatings range from 0.13 to 0.31. From effect plots, the optimum parameters are bias voltage at -70V, zirconium target current at 0.6 A, pulse frequency at 90 kHz, methane flow rate at 6 sccm and work distance at 15 cm. The friction coefficient performs as 0.106 in verification experiments. Meanwhile, one-by-one factorial experiments were also carried out and discussed in this study.

Abstract: An 3D mathematical model was established to illustrate weld pool development in the ASHPW (Automated Submerged Horizontal Position Welding) process. This model takes into consideration the spatial position characteristic of ASHPW, and used the heat transfer and mass transfer phenomena during welding process to explain the weld geometry mechanism in order to correctly design the bevel geometry. The final results show that the predicted geometry , such as the weld cross-section, weld width and weld cross section area, are in good agreement with experimental measurements.

Abstract: Based on CT data of the lesion of an orthopedic patient with knee, Mimics13.1, Magics9.5 can be used for the medical image processing. The CT image data were filtered, interpolated, sharpen, the interest region was extracted by the application of threshold segmentation method and was grown. The three dimension model of patient’s skeleton is reconstructed. Based on selective laser sintering, the digit model of patient’s skeleton reconstructed can be accurately transformed into the object model of the individual matching skeleton. The results indicated that the contour of reconstructed knee-joint bone object model were very coincident, and symmetric with knee-joint bone defect.

Abstract: 316L stainless steel parts were manufactured via selective laser melting . This work stu- dies the effects of powder characteristics such as particle size and particle shape composition on the density. It shows that the powder with a broad size distribution and using spherical fine powder can lead to an increase in the density of the loose powder and thus the densification of the laser melted powder. The aerosol powder forms parts of lower oxygen content well, and the density can reach to 90%.

Abstract: Selective Laser Melting (SLM) can produce high-performance metal parts with complex structures. However, it’s difficult to control the processing parameters, because many factors involves. From the perspective of the molten pool, the study focuses on the effects of processing parameters, including scanning speed, laser power, scanning space, layer thickness, and scanning strategies, on the surface quality, the balling effect, the density of SLM parts, by conducting experiments of single track, single layer and block forming. The results show that the quality of the molten pool is affected by laser power and scanning speed. Scanning drove in the strategy of “jumping and turning”，a smooth surface and a less balling effect will be obtained. The thicker the powder layer is, the lower density will be obtained. The optimal parameters from series of experiments are: laser power of 98W; scanning speed of 90mm/s; scanning space of 0.07mm; layer thickness of 0.1mm; and scanning strategy of “jumping and turning”.

Abstract: Pulsed Nd:YAG has been adopted successfully in welding process of thin (0.7 mm) Ti6Al4V. Laser welding of such thin sheet requires a small focal spot, good laser beam quality and fast travel speed, since too much heat generation can cause distortion for thin sheet weld. The microstructures of Ti6Al4V were complex and strongly affected the mechanical properties. These structures include: α´ martensite, metastable β, Widmanstätten, bimodal, lamellar and equiaxed microstructure. Bimodal and Widmanstätten structures exhibit a good-balance between strength and ductility. The microstructure of pulsed Nd:YAG welded Ti6Al4V was primarily α´ martensite, which showed the lowest ductility but not significantly high strength. A heat treatment at 950 followed by furnace cooling can transform the microstructure in the weld from α´ martensite structure into Widmanstätten structure.

Abstract: The surfaces of 45 steel and 1Cr18Ni9Ti are coated with WFCL-11 by l pulsating laser cladding. Microstructure and hardness between substrate interfaces and surfaces of laser cladding coating are investigated. And the variation of their microstructure, mechanical properties and hardness of coating surface are analyzed under shock loading. The results show that the different material ingredients between substrate and laser clad effect their interfaces.

Abstract: Laser beam of high energy density, melting of the workpiece material welded together, can make the heating affected area and change shape minimum, without the use of flux or for dissimilar materials, particularly strong bonding strength. Laser welding is a high energy of the laser beam as heat source a high precision welding. However, the safe application of new technology is the challenge we face. Laser can damage the eyes, skin, respiratory, central nervous and the whole body. It is generally skin safety standards. View of the laser welding process currently used, the possibility of respiratory hazards in the growth of workers with chronic exposure to hazards by the possibility of laser is growing, so the above five aspects of laser hazards should pay attention.