The effect of energy density and porosity structure on tensile properties of 316L stainless steel produced by laser powder bed fusion

Abstract

Understanding the influence of process parameters and defect structure on the properties of parts produced via laser powder bed fusion (L-PBF) is a fundamental step towards the broader use of additive manufacturing technologies in critical applications. Furthermore, the ability to predict mechanical properties by simply considering information on the process parameters and defects observed via X-ray computer tomography (XCT) allows one to avoid expensive destructive testing, provide an in-depth understanding of the process quality and represents a viable solution towards process optimisation. Most of the previous works showed that energy density could be used as an excellent synthetic indicator to predict the mechanical properties of parts produced by L-PBF. This paper explores the effect of different energy density levels on the tensile properties of 316L stainless steel parts produced by L-PBF. Different from previous works in the literature, the same level of energy density is obtained considering various combinations of process parameters (speed, power and hatch distance). While energy density is shown to be a good synthetic indicator for predicting ultimate tensile strength (UTS) and yield strength (YS), a different behaviour is observed for elongation. Elongation shows a significant variability even when samples are produced at the same level of energy density, which contrasts with results obtained for UTS and YS. Synthetic indices representing the porosity structure are shown to be quite significant for predicting elongation even when the optimal energy density is considered. By combining process parameters with porosity structure, we show that almost a full prediction of the tensile properties can be achieved, paving the way for a significant reduction in expensive destructive tests.

Performance Improvement for the CuCrZr Alloy Produced by Laser Powder Bed Fusion Using the Remelting Process

“…Previous studies have shown that laser power, hatching space, and scanning speed affect the density, and thus, the study of a single variable is not accurate [29,30]. Most studies have attributed the factors to the volume-based energy density E [31][32][33][34][35]. Similar to other studies, LOF defects occurred when E was insufficient, and keyhole defects appeared when E was too high.…”

Mechanical properties of additively manufactured AlSi10Mg under quasi‐static and cyclic loading

“…On the other hand, if the energy is too high, keyhole porosity defects can occur. 33,34 Lack of fusion defects are identified by the unmelted powders and can be aligned perpendicular to (lack of fusion between layers) or parallel to the building direction (lack of fusion between scan tracks). According to Yang et al, 11 irregularly shaped defects with unmelted regions are sometimes aligned either perpendicular or parallel to the building direction due to a lack of fusion.…”

“…If the energy density is insufficient, lack of fusion defects may form. On the other hand, if the energy is too high, keyhole porosity defects can occur 33,34 …”

Investigating+Energy+for+Porosity+Control+in+Regolith+Sintering

“…This equation takes the assumption that the melt pool is in the liquid phase until the next hatch. can be related to part quality since low energy levels result in a lack of fusion porosity, meaning that the energy is not sufficiently melting the powder, causing large, irregular porosities throughout the part [27], [28]. Conversely, at higher energy levels, a phenomenon called balling can occur.…”

“…Conversely, at higher energy levels, a phenomenon called balling can occur. Moreover, when surface tension forces overcome a mixture of dynamic fluid, gravitational, and adhesion forces, a ball of molten metal will form [11], [27], [29], [30]. Therefore, it can be understood how part quality can be determined via energy density.…”