Pore Formation in Laser-Assisted Powder Deposition Process

Abstract

Pore formation remains a concern in the area of rapid manufacturing by the laser engineered net shaping process. Results usually conflict on the origin of these pores; whether it should stem from an effect due to the physical/mechanical properties of the material or from an effect purely related to the processing parameters. We investigated this problem spanning a range of process parameters for deposition and using three different material powders, namely, an AISI 410 grade stainless steel, AISI 316L grade stainless steel, and AISI 4140 grade medium-carbon low alloy steel. The volume fraction, number density, and size distribution of pores were quantified using X-ray computed tomography and optical microscopy. Pores formed both at the interface between the adjacent layers and within the bulk of the layer. They were systematically sensitive to both the powder material composition and the process parameters.

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“…An alternative cause for attenuation could be clusters of fine voids, perhaps as gas entrained porosity as imaged by Wang [8] and described quantitatively by Susan [9] , who proposes an in-cycle remelting step to allow the gas to escape; such a smoothing operation would support inspection by generating a smoother reference surface. For microporous materials, absorption depends on size, shape and clustering characteristics.…”

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“…According to the literature, the reasons for porosity could be inconsistent powder flow, powder with too low of a particle-to-void ratio, high oxidation kinetics, or unmelted powder. 51,52 In the case of the thin-wall structures, the likely cause was partial melting of the powder.…”

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“…Enclosed gas may come from contamination, entrainment during turbulent impact of particles into the molten pool, contamination by powder-feed gases, gases contained within the powder particles, or vaporization of high vapor pressure alloy constituents. Due to the rapid solidification rates, the dissolved gases may not The effect of process parameters and type of materials on porosity formation was studied in Wang et al 44 AISI 410 martensitic stainless steel was used for the study. The powders were produced with gas atomization with a nominal size of 53 to 173 µm in diameter.…”

“…Optical photography of AISI 410 thin plate for sample S2 showing gas porosity: (A) transverse direction, and (B) longitude direction 44. …”

“…Optical photography of AISI 410 thin plate for sample S1 showing gas porosity in the transverse direction: (A) gas pores about 50 µm in diameter, and (B) gas pores about 100 µm in diameter 44. …”