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Post Info TOPIC: Review: Laser Polished 3D Printed Metal Parts (III) _ Surface


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Review: Laser Polished 3D Printed Metal Parts (III) _ Surface

Original Title: Overview: Laser Polishing 3D Printing Metal Parts (3) Jiangsu Laser Alliance Guide: This review (3) mainly introduces the application status of laser polishing technology in 3D printing of titanium alloys. 2.3 Application of laser polishing in additive manufacturing of titanium alloys Titanium alloy is the most widely used 3D printing material in aviation. Ti6Al4V alloy has excellent properties, such as high specific strength, high hardness, corrosion resistance, oxidation resistance and so on. Titanium alloys are widely used in aerospace and marine engineering because of their high specific strength, and they are also used as biological implant materials because of their biocompatibility. The formation of oxide film on the surface of SLM during fabrication has been observed and found to be mainly enriched in oxygen, while the surface without external scanning is enriched in titanium. The concentration of V was found to be higher at the scanned surface than at the non-scanned surface region. When the scanning pattern is similar to that of the mesh plate, the initial intensity is reduced by 85%. Marimuthu investigated the effect of laser polishing on SLM-fabricated Ti6Al4V using a continuous fiber laser. The part was fabricated with a 45 orientation and had an average surface roughness of 10.2 m. The average surface roughness is 2. 4 m when the laser power is 60 W, the scanning speed is 750 mm/min, and the beam offset is 0. 35 mm. Under the optimized parameters, the minimum surface roughness is obtained.The SEM images reveal that the columnar grain microstructure of Ti6Al4V titanium alloy has no significant change before and after polishing. The developed computational fluid dynamics (CFD) was used to study the bath dynamics and surface morphology. Higher energy is required to avoid an increase in the velocity of the molten pool, which further causes streaks to form on the polished surface. Ma et al. prepared TC4 (Ti6Al4V) and TC11 titanium alloy components by LAM technology and studied them. The fabricated parts were exposed to laser irradiation to study changes in surface morphology, microhardness, and wear resistance. The average surface roughness Sa of TC4 and TC11 before and after polishing decreased from 5. 226 to 0. 375 m and from 7. 21 to 0. 73 m, respectively. The microstructure of the TC4 sample was observed to be martensite 'in the laser polished area and to be 170 m thick. XRD analysis shows that the phase composition of as-deposited TC4 components is and , while after interaction with laser, the surface microstructure changes to 'martensite phase without the formation of phase. The formation of the homogeneous alpha 'phase is due to the instantaneous melting and subsequent rapid cooling upon interaction with the laser. When the as-deposited watch glass is exposed to laser irradiation, the surface temperature increases, and when the temperature exceeds the phase transition temperature of the phase (about 1273K), the + phase is completely transformed into the phase. During cooling,titanium round bar, depending on the cooling rate, the phase converts back to form the secondary phase or 'martensite. A similar martensitic 'phase is observed in TC11, but the polished area is only 90 m. For TC4, the critical cooling rate point is 410 K/S, which is much higher than that of TC11. Based on the analysis of friction tests, it was observed that both TC4 and TC11 were improved compared to as-deposited. This is attributed to the formation of a hard martensite alpha 'phase after laser polishing. Figure 1. Laser polishing. Yeah Influence of TC4 alloy: (a) laser-polished area on the surface of the LAM component; (B) photograph of the interface of the laser-polished area and the as-deposited area observed by SEM; (C) a surface topography of the as-deposited state; (D) Surface topography after laser polishing Expand the full text Figure 2. Laser polishing. Yeah Influence of TC11 alloy: (a) Laser polished area on the surface of the LAM part; (B) Photograph of the interface of the laser polished area and the as-deposited area observed by SEM; (C) a surface topography of the as-deposited state; (D) Surface topography after laser polishing Figure 3. Yes Results of analysis after laser polishing of TC4 titanium alloy: (a) overall plot; (B) microstructure of the laser polished area; (C) the microstructure of the substrate; (D) Results of XRD diffraction analysis Figure 4. Yes Results of analysis after laser polishing of TC11 titanium alloy: (a) overall plot; (B) microstructure of the laser polished area; (C) the microstructure of the substrate; (D) Results of XRD diffraction analysis Similar to Ma's work, Li et al. Also studied the surface morphology,titanium filler rod, microstructure evolution, and mechanical property of Ti6Al4V components fabricated using SLM. When the laser power is 90 W, the overlap ratio is 10%, and the scanning speed is 150 mm/s, the initial roughness of the surface fabricated by SLM is 6. 53 m, and the best average roughness value is 0. 32 m. A 3D fluid model and a heat transfer model were constructed to examine the melt formation and solidification behavior of the molten pool during laser polishing. According to the simulation results, the peak temperature is about 2800 and the depth of the molten pool is 60 m. The + phase on the as-deposited surface is transformed into martensite 'phase, which is very similar to Ma's results, but the cooling rate is 10 exp (6)/s. The XRD analysis, finite element simulation results, substrate microstructure, heat affected zone, and weld pool are shown in Figure 5 below. After laser polishing, the surface hardness reaches 25%, ti6al4v eli ,titanium bar gr7, increasing from 340 HV (as-deposited) to 426 HV (polished surface). The wear rate of the laser polished surface is 39% lower than that of the as-deposited surface. Continuous rapid melting and rapid solidification of the molten pool result in the formation of residual stresses in the range of 300-500 MPa. The as-deposited and laser polished parts were observed to have no more than 1% variation in tensile and yield strength and 5% elongation. After laser polishing, the fatigue strength of the parts will be reduced to a certain extent. This reduction in fatigue strength is attributed to the reduction in defects in the SLM fabricated components. Figure 5. XRD, finite element analysis simulation results and microstructure: (a) XRD analysis results; (B) Temperature field distribution of the cross section; (C) laser polishing the area; (d) HAZ; (E) Microstructure of as-deposited material Researchers have reported the use of laser polishing technology to treat titanium alloy Ti6Al4V components manufactured by electron beam additive manufacturing (EBM), which represents the worst case of surface roughness in powder bed manufacturing. This component was selected as a case study to investigate and evaluate the capabilities of laser surface finishing technology in improving the surface quality of AM-fabricated components. The experimental results show that the surface roughness can be reduced to Sa = 0. 51 m, which is almost equivalent to the surface machined by CNC. Defects present at the time of AM fabrication were also eliminated after laser polishing. However, the remelted layer undergoes a change in texture, grain size, and martensitic transformation due to in situ tempering caused by repeated back and forth scanning of the laser beam, resulting in an increase in hardness of the subsurface. In addition, high levels of near-surface residual stress are also generated during laser polishing, although this stress is relieved during subsequent stress relief heat treatments. Figure 6. Laser polishing. Yeah Overall view of the results obtained after polishing of titanium alloy parts manufactured by EBM Figure 7. In use Height direction roughness and typical substrate subsurface defects observed in the vertical direction of the Ti6Al4 Ti6Al4V sample prepared by the EBM powder bed method: (a) SEM image of the as-deposited surface; (B) and (C) Analysis results of high-resolution X-ray CT scan (XCT) indicating invasive defects on the surface (see arrows); (d) Physical image of the dental implant surface after electrochemical polishing Figure 8. Test area without polishing and with laser polishing ? All experiments were carried out under optimized parameters, at the vertical edge of the EBM sample. (A) a surface of an EBM-produced titanium alloy component that has not been subjected to laser polishing, (B) a surface resulting from laser polishing of the EBM-produced component surface, (C) results observed at macroscopic magnification for the laser polished area and the area that has not been polished, (D) Magnified area after laser polishing (from the wireframe area in panel (B)); where the arrow area is in the Defect of local surface intrusion with depth in (a) Figure 9. The change of surface roughness measured by surface profile measuring equipment in different dimensions after laser surface polishing : (a) SEM photograph show a comparison of an original surface and a polished surface; (B) Equivalent transition zone results (laser polished zone and non-polished zone) measured with a laser profilometer over an area of 22 mm 6 mm, (C) Laser polished surface, The measured area is 0.6565 mm 0.8686 mm. (D) The result of 0.1313 mm 0.1717 mm area measured by white light interferometer Figure 10. Results for the samples measured by XCT: (a) laser polished area and (B) results for the AM substrate The results show that the laser polishing technology can be significantly and successfully applied to the surface treatment of Ti6Al4 Ti6Al4V parts manufactured by EBM, and the surface roughness is greatly reduced. However, the laser polishing process can significantly change the microstructure and residual stress of the component. Laser polishing reduces the surface roughness of titanium alloy parts manufactured by EBM by 75% when measured in the mm range, but when measured in the micron range, the surface roughness level can reach Sa Sa = 0.5151 m. This level of improvement is almost equivalent to a mechanically polished or machined surface. In addition, laser polishing also removes stress from the surface without loss of material. The surface layer (200 200 m depth) after remelting during laser polishing exhibited a different grain refinement structure and a reoriented texture relative to the AM-fabricated substrate. The columnar crystals in the remelted layer are epitaxially grown again from the substrate toward the melted surface, with different preferred growth directions. This is related to the change in orientation of the melted surface and the relative scan direction with respect to the original MA fabrication. There is a heat affected zone at the surface of the material at a depth of approximately 450 450 m. In this heat affected zone, there is a subsurface with a depth of about 300 300 m, which is almost completely annealed phase, and at the same time, there is a part of transitional phase transformed into. This fully transformed region undergoes approximately one cooling of the martensitic transformation, followed by in situ decomposition into a very fine + lamellar structure, which occurs in the subsequent beam scan. The partially transformed transition layer consists of a secondary phase with decreasing volume and a coarse as-grown lath phase with increasing volume and has a certain depth. As a result, the presence of a very fine microstructure in the subsurface results in a small increase in microhardness at the same depth where the heat-affected zone also occurs after laser polishing. Under the parameters used in this experiment, a certain degree of residual tensile stress (up to 580 MPa) is induced on the surface of the component after polishing, which decreases rapidly with increasing depth. However, residual stresses can be almost completely relieved by a standard stress relief heat treatment. Under optimized parameters, laser polishing was found to be free of cracks, or other defects, but with a similar low degree of porosity. Article Source: Laser polishing of 3D printed metallic components: A review on surface integrity Proceedings,Volume 26, Part 2, 2020, Pages 2047-2054 Reference: Optics and Lasers in Engineering, Volume 93, June 2017, Pages 171-177, Laser polishing of additive manufactured Ti alloys, back to Sohu,titanium sheet grade 5, see more Additive ManufacturingVolume 20, March 2018, Pages 11-22 Material interactions in laser polishing powder bed additive manufactured Ti6Al4V components Responsible Editor:.

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