scholarly journals Non-Destructive X-ray Characterization of a Novel Joining Method Based on Laser-Melting Deposition for AISI 304 Stainless Steel

Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7796
Author(s):  
Muhammad Arif Mahmood ◽  
Diana Chioibasu ◽  
Sabin Mihai ◽  
Mihai Iovea ◽  
Ion N. Mihailescu ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Operating Conditions ◽  
304 Stainless Steel ◽  
Filler Material ◽  
Laser Melting ◽  
Aisi 304 Stainless Steel ◽  
Optimal Operating ◽  
Aisi 304 ◽  
X Ray ◽  
Laser Melting Deposition

In this study, an application of the laser-melting deposition additive manufacturing technique as a welding method has been studied for the laser welding (LW) of AISI 304 stainless steel, specifically 0.4 mm and 0.5 mm thick sheets. The welding was carried out without and with filler material. Inconel 718 powder particles were used as filler material in the second case. A series of experiments were designed by changing the process parameters to identify the effect of operating conditions on the weld width, depth, and height. The welds were examined through metallographic experiments performed at various cross-sections to identify the defects and pores. All the deposited welds were passed through a customized mini-focus X-ray system to analyze the weld uniformities. The optimal operating conditions were determined for 0.4 mm and 0.5 mm sheets for the LW with and without filler material. It was found that laser power, laser scanning speed, powder flow rate, and helium to argon gases mixture-control the weld bead dimensions and quality. X-ray analyses showed that the optimal operating conditions gave the least peak value of non-uniformity in the laser welds. This study opens a new window for laser welding via additive manufacturing with X-ray monitoring.

scholarly journals Mesoscopic Computational Fluid Dynamics Modelling for the Laser-Melting Deposition of AISI 304 Stainless Steel Single Tracks with Experimental Correlation: A Novel Study

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1569
Author(s):  
Asif Ur Rehman ◽  
Muhammad Arif Mahmood ◽  
Fatih Pitir ◽  
Metin Uymaz Salamci ◽  
Andrei C. Popescu ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Laser Beam ◽  
Marangoni Convection ◽  
304 Stainless Steel ◽  
Laser Melting ◽  
Aisi 304 Stainless Steel ◽  
Aisi 304 ◽  
Melt Pool ◽  
Powder Particles ◽  
Laser Melting Deposition

For laser-melting deposition (LMD), a computational fluid dynamics (CFD) model was developed using the volume of fluid and discrete element modeling techniques. A method was developed to track the flow behavior, flow pattern, and driving forces of liquid flow. The developed model was compared with experimental results in the case of AISI 304 stainless steel single-track depositions on AISI 304 stainless steel substrate. A close correlation was found between experiments and modeling, with a deviation of 1–3%. It was found that the LMD involves the simultaneous addition of powder particles that absorb a significant amount of laser energy to transform their phase from solid to liquid, resulting in conduction-mode melt flow. The bubbles within the melt pool float at a specific velocity and escape from the melt pool throughout the deposition process. The pores are generated if the solid front hits the bubble before escaping the melt pool. Based on the simulations, it was discovered that the deposited layer’s counters took the longest time to solidify compared to the overall deposition. The bubbles strived to leave through the contours in an excess quantity, but became stuck during solidification, resulting in a large degree of porosity near the contours. The stream traces showed that the melt flow adopted a clockwise vortex in front of the laser beam and an anti-clockwise vortex behind the laser beam. The difference in the surface tension between the two ends of the melt pool induces “thermocapillary or Benard–Marangoni convection” force, which is insignificant compared to the selective laser melting process. After layer deposition, the melt region, mushy zone, and solidified region were identified. When the laser beam irradiates the substrate and powder particles are added simultaneously, the melt adopts a backwards flow due to the recoil pressure and thermocapillary or Benard–Marangoni convection effect, resulting in a negative mass flow rate. This study provides an in-depth understanding of melt pool dynamics and flow pattern in the case of LMD additive manufacturing technique.

scholarly journals Analysis of Melt-Pool Behaviors during Selective Laser Melting of AISI 304 Stainless-Steel Composites

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 876 ◽  
Author(s):  
Abolhasani ◽  
Seyedkashi ◽  
Kang ◽  
Kim ◽  
Woo ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Temperature Gradient ◽  
Eutectic Mixture ◽  
304 Stainless Steel ◽  
Reinforcement Particle ◽  
Laser Melting ◽  
Aisi 304 Stainless Steel ◽  
Aisi 304 ◽  
Reinforcing Particles ◽  
Melt Pool

The melt-pool behaviors during selective laser melting (SLM) of Al2O3-reinforced and a eutectic mixture of Al2O3-ZrO2-reinforced AISI 304 stainless-steel composites were numerically analyzed and experimentally validated. The thermal analysis results show that the geometry of the melt pool is significantly dependent on reinforcing particles, owing to the variations in the melting point and the thermal conductivity of the powder mixture. With the use of a eutectic mixture of Al2O3-ZrO2 instead of an Al2O3 reinforcing particle, the maximum temperature of the melt pool was increased. Meanwhile, a negligible corresponding relationship was observed between the cooling rate of both reinforcements. Therefore, it was identified that the liquid lifetime of the melt pool has the effect on the melting behavior, rather than the cooling rate, and the liquid lifetime increases with the eutectic ratio of Al2O3-ZrO2 reinforcement. The temperature gradient at the top surface reduces with the use of an Al2O3-ZrO2 reinforcement particle due to the wider melt pool. Inversely, the temperature gradient in the thickness direction increases with the use of an Al2O3-ZrO2 reinforcement particle. The results of melt-pool behaviors will provide a deep understanding of the effect of reinforcing particles on the dimensional accuracies and properties of fabricated AISI 304 stainless-steel composites.

Corrosion Behaviour of AISI 304 Stainless Steel with Solar Salt Heat Transfer Fluid

2014 ◽  
Vol 922 ◽  
pp. 13-17 ◽  
Author(s):  
Omar Ahmed ◽  
Le Zhou ◽  
Nahid Mohajeri ◽  
Yong Ho Sohn
Keyword(s):  
Heat Transfer ◽  
Stainless Steel ◽  
Iron Oxide ◽  
Corrosion Behavior ◽  
304 Stainless Steel ◽  
Salt Mixture ◽  
Aisi 304 Stainless Steel ◽  
Aisi 304 ◽  
Solar Salt ◽  
X Ray

In an effort to understand the compatibility between the heat transfer medium and the structural materials used in concentrated solar power plants, the corrosion behavior of AISI 304 stainless steel (18 wt.% Cr, 8 wt.% Ni) in a molten solar salt mixture (53 wt. % KNO3, 40 wt. % NaNO2,7 wt. % NaNO3) has been investigated. The 304 stainless steel coupon samples were fully immersed and isothermally exposed to solar salt at 530°C for 250, 500, and 750 hours in air. X-ray diffraction and scanning electron microscopy with X-ray energy-dispersive spectroscopy were employed to examine the extent of corrosion and identify the corrosion products. Oxides of iron were found to be the primary corrosion products in the presence of the molten alkali nitrates-nitrite salt mixture because of the dissolution of the protective chromium oxide (Cr2O3) scale formed on 304 stainless steel coupons. The corrosion scale was uniform in thickness and chromium-iron oxide was found near the AISI 304. This indicates that the scale formed, particularly on the upper layer with presence of sodium-iron-oxide is protective, and forms an effective barrier against penetration of fused solar salt. By extrapolation, annual corrosion rate is estimated to reach 0.784 mils per year. Corrosion behavior of AISI 304 stainless steel is discussed in terms of thermodynamics and reaction paths.

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