Tishta Das

The present work investigates the multilayer deposition of 15-5 Precipitation Hardening (PH) stainless steels via Laser based Direct Energy Deposition (L-DED). The laser power and scanning speed are kept constant at 450 W and 5 mm/s with energy density of 75 J/mm 2. At present, very limited literatures are available on the thermal behavior of 15-5 PH multi-layer deposition in relation with its micro structural characteristics. The complex thermal phenomena include repetitive heating and cooling cycles were simulated using 3-D multi-physics model. Through this numerical investigation temperature data of the specific region was captured and correlated with the micro structural morphology. The 15-5 PH multilayer deposition showed clear columnar grains and ferrite transformation. The XRD result revealed that austenite (ɣ) phase fraction increased with the increase in layer deposition. The IPF phase fraction map shows 1.5 % increase in retained austenite phase fraction with each layer addition. In 15-5 PH multilayer deposition the grains are primarily oriented along the 〈101〉/〈001〉 direction and with addition of layer High angle grain boundary (HAGB) fraction increases. The detailed texture analysis shows that as the layer increases, there is formation of brass, copper, shear and rotated goss structure. Similarly, it exhibited proportional rise in hardness due to its δ-ferrite dominating phases and higher HAGB percentage.

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The present work investigates the multilayer deposition of 15-5 Precipitation Hardening (PH) stainless steels via Laser based Direct Energy Deposition (L-DED). The laser power and scanning speed are kept constant at 450 W and 5 mm/s with energy density of 75 J/mm 2. At present, very limited literatures are available on the thermal behavior of 15-5 PH multi-layer deposition in relation with its micro structural characteristics. The complex thermal phenomena include repetitive heating and cooling cycles were simulated using 3-D multi-physics model. Through this numerical investigation temperature data of the specific region was captured and correlated with the micro structural morphology. The 15-5 PH multilayer deposition showed clear columnar grains and ferrite transformation. The XRD result revealed that austenite (ɣ) phase fraction increased with the increase in layer deposition. The IPF phase fraction map shows 1.5 % increase in retained austenite phase fraction with each layer addition. In 15-5 PH multilayer deposition the grains are primarily oriented along the 〈101〉/〈001〉 direction and with addition of layer High angle grain boundary (HAGB) fraction increases. The detailed texture analysis shows that as the layer increases, there is formation of brass, copper, shear and rotated goss structure. Similarly, it exhibited proportional rise in hardness due to its δ-ferrite dominating phases and higher HAGB percentage.

In metal additive manufacturing (MAM), laser direct energy deposition (L-DED) and wire arc direct energy deposition (W-DED) are commonly used methods that also possess challenges in the part quality due to the effect of different process parameters. Very little knowledge is currently available on the single-layer thermal behavior, cooling rate, melt pool dimension and their correlation with the microstructure for the DED processes (L-DED and W-DED). In this study, a comparative analysis of the microstructural characteristics along with hardness of austenitic stainless steel (SS 316L) samples is conducted to understand the variations between the L-DED and W-DED processes. It is observed that the microstructure of the W-DED samples possesses more columnar dendritic structure than the L-DED due to slower cooling rate in W-DED. It is also found that the ferrite (δ) phase fraction is 23% higher in W-DED than L-DED. There is also the formation of carbide precipitation at the fusion boundary in the L-DED samples. In L-DED, the grains are mostly oriented along the < 001 > / < 111 > direction, whereas in W-DED, the dominant orientation is < 111 > / < 101 >. The W-DED samples have significantly higher HAGB fraction (49%) than the L-DED samples. The detailed texture analysis of the samples showed that the L-DED has lower average grain misorientation than the W-DED along with ND rotated cube, twin copper, and cube structures. The hardness data reveals that the W-DED samples possess much higher hardness compared to the L-DED samples.