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•Fatigue properties of additively manufactured (AM) AlSi10Mg are similar to castings.•Oxide-driven porosity is the most common internal defect in the AM parts.•Pores and oxide ...particle size at the part surface control fatigue life.
It is well-known that the fatigue behavior of cast aluminum alloy parts is largely determined by internal defects, particularly pores and inclusions. In this work, it is shown that such imperfections are also present in AlSi10Mg parts produced by selective laser melting, and serve as sites to initiate fatigue cracks. The effect of hatch spacing and building orientation on tensile and fatigue properties was tested. Oxide-driven pores dominate the fatigue resistance of the samples in this work. The larger oxide particles which are associated with crack initiation likely form by oxidation of metal vapor during part manufacture.
Rapid movement of the melt pool (at a speed around 1 m/s) in selective laser melting of metal powder directly implies rapid solidification. In this work, the length scale of the as-built ...microstructure of parts built with the alloy AlSi10Mg was measured and compared with the well-known relationship between cell size and cooling rate. Cooling rates during solidification were estimated using the Rosenthal equation. It was found that the solidification structure is the expected cellular combination of silicon with α-aluminum. The dependence of measured cell spacing on calculated cooling rate follows the well-established relationship for aluminum alloys. The implication is that cell spacing can be manipulated by changing the heat input. Microscopy of polished sections through particles of the metal powder used to build the parts showed that the particles have a dendritic-eutectic structure; the dendrite arm spacings in metal powder particles of different diameters were measured and also agree with literature correlations, showing the expected increase in secondary dendrite arm spacing with increasing particle diameter.
Heat treatment of Type 304 stainless steel in the range of 1273 K (1000 °C) to 1473 K (1200 °C) can transform manganese silicate inclusions to manganese chromite (spinel) inclusions. During heat ...treatment, Cr reacts with manganese silicate to form spinel. The transformation rate of inclusions depends strongly on both temperature in the range of 1273 K to 1473 K (1000 °C to 1200 °C) and inclusion size. A kinetic model, developed using FactSage macros, showed that these effects agree quantitatively with diffusion-controlled transformation. A simplified analytical model, which can be used for rapid calculations, predicts similar transformation kinetics, in agreement with the experimental observations.
The finite-element （FE） model and the Rosenthal equation are used to study the thermal and microstructural phenomena in the laser powder-bed fusion of lnconel 718. A primary aim is to comprehend the ...advantages and disadvantages of the Rosenthal equation （which provides an analytical alternative to FE analysis）, and to investigate the influence of underlying assumptions on estimated results. Various physical characteristics are compared among the FE model, Rosenthal equation, and experiments. The predicted melt pool shapes compared with reported experimental results from the literature show that both the FE model and the analytical （Rosenthal） equation provide a reasonably accurate estimation. At high heat input, under conditions leading to keyholing, the reported melt width is narrower than predicted by the analytical equation. Moreover, a sensitivity analysis based on choices of the absorptivity is performed, which shows that the Rosenthal approach is more sensitive to absorptivity, compared with the FE approach. The primary reason could be the effect of radiative and convective losses, which are assumed to be negligible in the Rosenthal equation. In addition, both methods predict a columnar solidification microstructure, which agrees well with experimental reports, and the primary dendrite arm spacing （PDAS） predicted with the two approaches is comparable with measurements.
This work investigated the use of FactSage macros to simulate steel–slag and steel–inclusion reaction kinetics in silicon-manganese killed steels, and predict oxide inclusion composition changes ...during ladle treatment. These changes were assessed experimentally using an induction furnace to simulate deoxidation and slag addition. The average steel mass transfer coefficient for the experimental setup was calculated from the analyzed aluminum pick-up by steel. Average oxide inclusion composition was measured using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Confocal laser scanning microscopy was used to assess the physical state (solid or liquid) of oxide inclusions in selected samples. The changes in the chemical compositions of the oxide inclusions and the steel agreed with the FactSage macro simulations.
Iron ore pellets, reduced with hydrogen, were isothermally carburized in CH
4
-H
2
-N
2
at 823 K, 923 K, and 1023 K (550 °C, 650 °C, and 750 °C). Temperature strongly affected the total carbon ...concentration after carburization; significant unbound carbon deposited at the highest temperature. For the range of sizes tested (10 to 12 mm), pellet size did not affect carburization. The variability between pellets was much smaller than for industrial pellets; inhomogeneous gas distribution likely affects carburization under large-scale industrial conditions.
Structure of Solidified Films of Mold Flux for Peritectic Steel Long, Xiao; He, Shengping; Wang, Qian ...
Metallurgical and materials transactions. B, Process metallurgy and materials processing science,
06/2017, Letnik:
48, Številka:
3
Journal Article
Recenzirano
In this study, an improved water-cooled copper probe was used to obtain solidified films of a mold flux used to cast peritectic steel. Different bulk temperatures of molten mold flux and different ...probe immersion times were used. The results reveal that the surface roughness of the slag film (in contact with the copper probe) has no direct relationship with solidification crystallization or devitrification in the slag film. Higher bulk temperatures (of molten flux) gave rougher surface slag-probe interfaces. Pores contribute to the surface roughness.
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•A geometry-based model for predicting lack-of-fusion porosity is presented.•The model relies on melt pool dimension, hatch spacing and layer thickness.•Porosity (or density) ...predicted with the model agrees well with reported literature data.
A geometry-based simulation is used to predict porosity caused by insufficient overlap of melt pools (lack of fusion) in powder bed fusion. The inputs into the simulation are hatch spacing, layer thickness, and melt-pool cross-sectional area. Melt-pool areas used in the simulations can be obtained from experiments, or estimated with the analytical Rosenthal equation. The necessary material constants, including absorptivity for laser-based melting, have been collated for alloy steels, aluminum alloys and titanium alloys. Comparison with several data sets from the literature shows that the simulations correctly predict process conditions at which lack-of-fusion porosity becomes apparent, as well as the rate at which porosity increases with changes in process conditions such as beam speed, layer thickness and hatch spacing.
Based on equilibrium considerations, copper sulfide is not expected to form in manganese-containing steel, yet previous workers reported finding copper sulfide in transmission electron microscope ...samples which had been prepared by electropolishing. It is proposed that copper sulfide can form during electrolytic dissolution because of the much greater stability of copper sulfide relative to manganese sulfide in contact with an electrolyte containing copper and manganese cations. This mechanism has been demonstrated with aluminum-killed steel samples.
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