Powder characterization and part density for powder bed fusion of 17-4 PH stainless steel

Abstract

Purpose

Characteristics of the metal powder are a key factor in the success of powder bed fusion (PBF) additive manufacturing. Powders for PBF from different manufacturers may have a different particle size and/or bulk packing and flow behavior. Powder properties change as the powder is reused for multiple builds. This study seeks to measure the variability of commercial 17-4 PH stainless steel powders to determine the effect of powder variability on part density and demonstrate characterization methods that ensure part quality.

Design/methodology/approach

Commercial atomized metal powders from four different vendors were produced with two different atomizing gases (N2 and argon). Powder was characterized in both new and extensively reused conditions. All powders were characterized for flow and packing behavior, particle size and internal porosity. Coupons were manufactured using the laser PBF process with optimized scan strategy and exposure parameters. The quality of fabricated parts was measured using bulk density measurement.

Findings

Despite differences in powder flowability and particle size, fully dense parts (>99 per cent) were produced using all powders, except one. Residual porosity in these parts appeared to result from gas trapped in the powder particles. The powder with extensive reuse (400+ h in machine fabrication environment) exhibited reduced flowability and increased fraction of fine particles, but still produced full density parts.

Originality/value

This study demonstrates that full density parts can be fabricated using powders with a range of flowability and packing behavior. This suggests that a single flowability measurement may be sufficient for quality assurance in a production environment.

Citation

Dobson, S.D. and Starr, T.L. (2021), "Powder characterization and part density for powder bed fusion of 17-4 PH stainless steel", Rapid Prototyping Journal, Vol. 27 No. 1, pp. 53-58. https://doi.org/10.1108/RPJ-01-2020-0023