Cui, Chengsong
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Cui, Chengsong
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Cui, Chengsong
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Item-typ:Veröffentlichung, Effect of hot gas atomization on spray forming of steel tubes using a close-coupled atomizer (CCA)Hot gas atomization in spray forming has been used for the first time to improve the quality of spray-formed tubular deposits. This technique reduces gas consumption and produces smaller droplets than cold gas atomization. The flight velocity and cooling rate of the atomized droplets increase with increasing gas temperature. These features can further influence the quality of the spray-formed deposits. Until now, spray-formed tubes have not been used on industrial scale due to insufficient deposit quality in terms of porosity and bonding to the substrate. Using a close-coupled atomizer (CCA), qualitative improvements of the as-sprayed deposits have been previously studied. In the present study, a comparative investigation is done to find the influence of hot gas atomization on the spray forming of the bearing steel AISI 52100 (100Cr6) using a close-coupled atomizer. The spray-formed deposit with hot gas atomization (gas temperature about 300 °C) shows lower deposit surface temperature and smaller grain size in comparison to the deposit produced under cold gas atomization condition due to smaller droplet diameter and higher cooling rate of the droplets. Moreover, the as-sprayed deposits under hot gas atomization show a higher relative density at a lower deposit surface temperature, which extends the process window for the flexible production of spray-formed tubes.Wissenschaftlicher ArtikelBand:28228 22 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Porosity and microstructure of steel tubes spray-formed by close-coupled atomizer(Elsevier, 2020-02); ; ; ; Close-coupled atomizers (CCA) can be used to reduce the porosity of spray-formed deposits compared to free fall atomizers (FFA), possibly due to smaller size and higher velocity of the atomized droplets. Previous studies on spray-formed AISI 52100 (100Cr6) tubular deposits show that CCA leads to less porosity in the inner and outer surface regions of the tubular deposits. However, there are very few investigations on the thermal profiles of the spray-formed deposits and on the influences of process conditions during spray forming via CCA. To provide insight into the thermal profile of the deposits, in this study in-situ measurement of the deposit surface temperature is performed by a two color pyrometer and the substrate temperature is measured by means of thermocouples. The porosity and microstructure of the spray-formed deposits under various process conditions are investigated by means of optical microscopy and image analysis. This investigation shows that the deposit thickness has a higher influence on the deposit surface temperature than the gas to melt flow rate ratio (GMR). Higher deposit temperature results in lower porosity and larger grain size. Moreover, the deposition positions on the deposit length has an influence on the porosity. The porosity in the vicinity of the substrate is higher at the deposit end position than the deposit start position. Finally, the present study suggests an optimal deposit surface temperature range for spray forming of highly dense tubular deposit by CCA.Wissenschaftlicher ArtikelBand:27618 11 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, A comparative study of in-situ alloying in laser powder bed fusion for the stainless steel X2CrNiMoN20-10-3(Elsevier Science, 2023-05-22); ; ; ; This paper compares, for the first time, laser powder bed fusion (PBF-LB/M) processing of a powder mixture (PM), also known as in-situ alloying, with that of a pre-alloyed (PA) powder from gas atomization with the same chemical composition, using the example of X2CrNiMoN20–10–3 ferritic-austenitic stainless steel. The focus is on the differences in the microstructure formation mechanisms during PBF-LB/M between PM and PA using different energy inputs, in order to gain new insights into the process transferability of in-situ alloying to the processing of pre-alloyed powders. The microstructure investigations are carried out using electron backscattered diffraction (EBSD), energy dispersive (EDS) as well as wavelength dispersive X-ray spectrometry (WDS), X-ray diffraction (XRD) and magneto-inductive method (Feritscope®). The microstructures of samples produced from PM and PA differ significantly in terms of the resulting ferritic and austenitic phase fractions, so that a ferritic-austenitic microstructure forms for PM, while the PA is predominantly austenitic. The differences are mainly based on the increased chemical inhomogeneities for the PM in comparison to the PA state, which are discussed based on EDS map analysis through spatial statistics. With increasing energy input, the chemical homogeneity of the PM approaches that of the PA, but it cannot reach it even with maximum energy input. The formation of a ferritic-austenitic microstructure in the case of the PM leads to the formation of a finer microstructure compared to single-phase PA steel resulting in higher hardness of PBF-LB/M-built PM.Wissenschaftlicher ArtikelBand:31865 42