The fatigue life of components manufactured by the laser powder bed fusion (L-PBF) process is dominated by the presence of defects, such as surface roughness and internal porosity. The present study focuses on the relative effect of surface roughness and porosity in determining the fatigue properties of AlSi10Mg alloy produced by L-PBF built in the Z direction for as-built (ASB), machined (M) and machined & polished (M&P) conditions. As-built L-PBF samples possess higher surface roughness (1.5-2 µm) compared to the machined (0.8-1.0 µm) or polished ones (0.3-0.75 µm). For ASB samples, surface roughness was found to be the dominant factor affecting fatigue life. However, for M or M&P samples with relatively low surface roughness, the subsurface porosity becomes the dominant factor affecting fatigue failure rather than variations in the surface roughness. The pore size and location effects are analysed using linear elastic fracture mechanics theory, and the critical stress intensity factors (SIF) for L-PBF AlSi10Mg alloy samples are estimated.
EXTENDED ABSTRACT

Additive manufacturing as a mean to produce near net shape components of metal alloys has evolved in many commercial applications during the last decade. Still, development of additive processes and alloy grades requires new research knowledge. In the present study focus is on advanced high strength martensitic steels and fatigue properties. They are used in demanding tooling and high performance applications where high strength and toughness, both static and dynamic, are required. Fatigue strength and failure defect distributions of one AISI H13 AM grade and one corresponding ingot cast and forged grade have been characterized and modelled.
EXTENDED ABSTRACT

Literature results indicate that the hydrogen environment-assisted cracking susceptibility of additively manufactured (AM) 17-4PH steel fabricated using laser powder bed fusion is increased relative to comparable wrought 17-4PH. This study seeks to understand the mechanistic origins of this increased susceptibility through a detailed examination of near-crack deformation, alloy microstructure, and hydrogen-metal interactions. Based on these data, it is determined that sub-micrometer porosity present in the AM material provides a primary contribution to the degradation in HEAC resistance. The mechanistic basis for the influence of porosity is considered in the context of an existing model for HEAC. The implications of these findings on the broader AM community are then discussed.
EXTENDED ABSTRACT

The widespread use of 316L stainless steel for applications requiring increased corrosion resistance has motivated interest in leveraging additive manufacturing (AM) for in-service production of replacement components. However, while a large number of studies have examined the effect of AM processing parameters on yield strength and fracture toughness, detailed assessments of the environment-assisted cracking (EAC) susceptibility of AM alloys are limited. The objective of this study is to compare the corrosion fatigue and stress corrosion cracking behavior of AM and wrought 316L with similar yield strengths in aqueous chloride environments at temperatures ranging from 293 to 358 K. As built material will be compared with cold drawn bar, and hot isostatic pressed (HIP) material will be compared with plate in the annealed state to minimize the effect of different yield strength between material form. Differences in microstructure and build-introduced stresses are correlated with EAC performance, thereby providing mechanistic insights into the factors governing EAC behavior of AM 316L. In particular, the influence of build direction, residual stresses, texture, and compositional heterogeneities are all assessed.
EXTENDED ABSTRACT

Defects in additively manufactured metals are detrimental to the manufactured components. Due to the rapid melting and solidification during printing, a non-homogeneous microstructure is typical in the metal specimens additively manufactured using laser powder bed fusion. The present study aims to understand the fracture initiation mechanism in as-built and heat-treated additively manufactured 17-4 stainless steel. To this end, 17-4 stainless steel unnotched and notched specimens additively manufactured using direct metal laser sintering were used. Solution annealing and subsequent aging were performed as the post-heat treatment of the stainless steel test specimens. Postmortem fractography using scanning electron microscopy (SEM) of the fracture surface and micro-computed tomography (micro-CT) of the test specimens before and after fracture revealed that the large coalesced microvoids with sizes greater than 120 µm significantly influence the ductile fracture initiation in the additively manufactured steel specimens.
EXTENDED ABSTRACT