Abstract

Laser powder bed fusion has become one of the major techniques within metal additive manufacturing, especially when delicate structures and high geometric accuracy are concerned. Lately, the awareness of the material-specific macroscopic anisotropy has risen and led to widespread investigations on the static mechanical strength. However, little is known about the fracture behavior of the layer-wise fabricated metal components and their affinity of crack propagation between consecutive layers, which is particularly important for aluminium–silicon alloys containing embrittled zones in double-irradiated areas. A recent study indicated that there is a significant drop in fracture toughness in case the crack growth direction is parallel to the layering. To investigate this matter further and to shed light on the fracture toughness behavior in the range of a 0°–45° angle offset between the crack growth direction relative to the layering, notched samples with varying polar angles were subjected to mode I fracture toughness testing. Our results indicate that the fracture toughness is an almost-stable characteristic up to a mismatch of about 20° between the crack propagation path and the layering, at which point the fracture toughness decreases by up to 10%.

Highlights

  • Additive manufacturing (AM) methods, such as laser powder bed fusion (L-PBF), are outstanding freeform fabrication techniques, capable of fabricating directly deployable components without the necessity of special tooling, and are extremely efficient when only small quantities are required [1,2,3]

  • This indicates a marked influence of the cross-head speed on the fracture toughness, which is the case for the average maximum force reached in the fracture toughness tests (Table 2)

  • It should be noted that both studies, the past as well as the current study, neglected the crack initiation phase, and due to the simplifications made, the obtained results for the fracture toughness results may be higher than under ideal testing conditions

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Summary

Introduction

Additive manufacturing (AM) methods, such as laser powder bed fusion (L-PBF), are outstanding freeform fabrication techniques, capable of fabricating directly deployable components without the necessity of special tooling, and are extremely efficient when only small quantities are required [1,2,3]. The complete melting of the raw material enables the generation of fully dense parts within a single production step and—due to the rapid cooling rates—exhibit an almost. The material characteristics are known to be potentially anisotropic, whereby the magnitude of anisotropy depends on the fabrication settings, such as the irradiation parameters and the scan strategy, as well as the chosen raw material [4, 5]. For aluminium–silicon (AlSi) alloys, inhomogeneities are twofold. On the macroscale, varying age-hardening states may occur for AlSiMg alloys in all cases where the preheating temperature employed during fabrication is within the artificial ageing regime. Samples or components in their as-fabricated state exhibit a height- and built-timedependent fluctuation in strength and hardness [6, 7]. The rapid cooling results in an increased (nonequilibrium) solubility of silicon in the α-Al crystal structure and favours the formation of distinct Si-segregations along grain boundaries and predominantly along scan track

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