PSI - Issue 82

Tomáš Babinský et al. / Procedia Structural Integrity 82 (2026) 162–168 Tomáš Babinský et al. / Structural Integrity Procedia 00 (2026) 000–000

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Fig. 3. STEM micrographs show the microstructure of direct aged PBF-LBM IN939 superalloy, focusing on (a) intragranular honeycomb structure of dislocation cells and (b) spherical γ' nanoprecipitates. 4. Results and discussion Table 1 presents tensile properties of direct aged PBF-LB/M IN939, and other material states, namely cast, PBF LB/M with and without full heat treatment, investigated by Babinský et al. (2025) are added as reference. Results show that direct ageing facilitates further strengthening of the cellular microstructure by γ’ precipitation resulting in ca. 300–350 MPa higher yield and ultimate tensile strength. The trend in yield and tensile strength is as follows: PBF-LB/M direct aged > fully heat-treated > not heat-treated (as-built and machined). Extraordinary yield strength and ultimate tensile strength comes at the cost of reduced ductility, which still competes with the ductility of cast, fully heat-treated IN939 without HIP treatment. Considering ductility, the trend is opposite. For all considered PBF LB/M thermodynamical states, horizontally-oriented specimens withstand notably higher tensile stresses while ductility is slightly (not always!) reduced. This is in line with the majority of PBF-LB/M materials (Tang et al. (2021)) while some conflicting reports might occur (Kanagarajah et al. (2013)) due to different scanning strategies. Table 1. Tensile properties of direct aged PBF-LB/M IN939 superalloy. For reference, also cast and other PBF-LB/M states as reported by Babinský et al. (2025) are included.

Batch

Cast

PBF-LB/M V no HT

PBF-LB/M V aged

PBF-LB/M V direct aged

PBF-LB/M H no HT

PBF-LB/M H aged

PBF-LB/M H direct aged

Young’s modulus (GPa) Yield strength (MPa)

210±28 153±6 674±22 703±3

171±3 965±24

189±3

190±4 739±14 1093±9

228±2 1095±5 1515±5

238±22 1423±24 1673±17 6.5±0.9

1317±21

Ultimate tensile strength (MPa) 995±42 1070±20

1337±12 1610±0

Elongation (%)

7.9±1.3 30.30±5.3 14.4±2.7 7.7±0.4

28.2±0.3 19.7±0.6

Fig. 4a–b show fatigue life curves in stress-life and plastic-strain life representations. Experimental points were derived at half of the fatigue life and fitted using the power law as follows: $ = % & % ' (2) $( = % & % ! (3) where σ f ’ stands for fatigue strength coefficient, b for fatigue strength exponent, ε ap for plastic strain amplitude, ε f ‘ for fatigue ductility coefficient and c for fatigue ductility exponent. Low-cycle fatigue behaviour corresponds to