PSI - Issue 68

Yasith H. Rajashilpage et al. / Procedia Structural Integrity 68 (2025) 981–987 Y.H. Rajashilpage, R.A. Yildiz, M. Malekan / Structural Integrity Procedia 00 (2025) 000–000

984 4

Table 2 presents overall outcome of all the tensile testing experiments for both SS 316L and IN625 alloys. In general, higher annealing temperatures enhance the ductility, though a slight reduction in UTS was observed. Overall, larger layer thicknesses reduced both ductility and UTS, while higher scanning speeds led to a more pronounced decrease in elongation and UTS. These findings highlight the critical role of both heat treatment and printing parameters in determining the mechanical behavior of these materials, emphasizing the need for precise optimization to achieve the desired performance. Table 2. Mechanical properties of SS 316L and IN625 from the tensile tests.

UTS (MPa) ! (%)

UTS (MPa) ! (%)

SS 316L

IN625

Layer thickness – Scanning speed

Temperature (°C)

E (GPa) 207.3 221.1 210.3 232.2 196.6 112.4 191.7 244.0 200.1 138.2 153.7 157.8 159.0 148.6 166.5 124.9 97.2 105.9 145.5 178.3 148.4 129.3 141.2 116.8

Temperature (°C)

E (GPa) 176.9 157.6 209.3 166.2 165.5 131.5 192.1 176.9 217.1 158.4 134.3 148.8 160.2 173.4 124.7 129.8 135.3 104.7 145.9 137.5 123.2 139.5 127.8 118.1

700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100 700 900 1100

556.2 522.3 501.8 616.9 560.6 539.3 696.3 620.6 524.6 549.1 538.8 501.4 540.6 518.3 506.1 451.7 422.9 415.9 518.0 470.3 449.8 390.1 378.9 321.1 256.3 249.1 226.4

35.2 44.6 43.6 28.2 29.9 36.4 35.2 35.4 37.5 42.1 43.2 44.3 32.1 32.6 31.2 10.1 15.5 11.5 21.8 33.3 27.0 4.7 10.2 7.7

756.0 781.0 744.1 766.2 761.9 724.8 783.6 769.0 721.7 713.7 687.1 668.2 676.4 661.8 642.9 643.5 615.5 572.9 666.8 640.3 621.4 561.2 550.9 533.4 374.0 364.6 359.4

19.6 24.2 29.3 19.1 21.7 29.9 16.7 20.2 25.5 17.1 21.1 27.2 15.7 18.7 23.9

900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100 900 1000 1100

30 µ m - 1400mm/s

30 µ m - 1700mm/s

30 µ m - 2000mm/s

55 µ m - 1400mm/s

55 µ m - 1700mm/s

9.8 8.2 9.8

55 µ m - 2000mm/s

13.7 17.8 19.6

80 µ m - 1400mm/s

7.1 8.4 8.5 4.1 3.0 6.0

80 µ m - 1700mm/s

55.3 59.2 51.3

3.6 4.1 2.4

41.8 37.5 30.3

80 µ m - 2000mm/s

The initial reduction in ductility observed in post-heat-treated samples, as compared to as-built specimens, was attributed to the precipitation of the brittle sigma phase at grain boundaries, which restricts plastic deformation (Wu et al., 2019, Zhou et al, 2020). The observed increase in UTS can be explained by precipitation strengthening due to nano-sized particles, which hinder dislocation motion, thereby increasing the material's resistance to deformation (Ura Bińczyk et al, 2022). The subsequent increase in ductility after annealing is linked to key microstructural changes, including grain recrystallization, reduction of cellular structures, and phase transformations. Recrystallization leads to a more refined and uniform grain structure. During LPBF process, dislocation density typically increases but annealing reduces this density facilitating the formation of new strain-free grains, thus improving plastic deformation and increasing ductility. Cellular structures formed during the LPBF process can negatively affect ductility in as-built samples, but annealing at temperatures above 700°C can eliminate these structures, improving ductility (Krakhmalev et al, 2018). Additionally, prolonged annealing can induce phase transformations, such as the formation of gamma phase austenite, which impedes crack propagation and further enhances ductility (Chen et al, 2019). The results show that higher annealing temperatures promote greater elongation, linked to composition homogenization and the formation of a stable microstructure, which not only enhances ductility but also improves corrosion resistance (Ura-Bińczyk et al, 2022). However, the reduction in UTS observed after annealing can be attributed to factors similar to those that enhance ductility, particularly grain growth due to recrystallization. As grain sizes increase, there are fewer grain boundaries to impede dislocation movement, reducing UTS, consistent with the