Supriya Koul, Akihiro Kushima, and their colleagues at University of Central Florida published work using their Hummingbird Scientific in-situ biasing nano-manipulator TEM sample holder to perform in-situ tensile deformation on additively manufactured Inconel 718 exposed to different heat treatments. The samples were printed using selective laser melting and push-to-pull devices were created using focused-ion beam.

Nanoscale lamellae were extracted from as-printed and solution heat-treated (1065°C for 1 hr, 720°C for 8 hr, and 650°C for 7 hr) samples.  In-situ tensile deformation was performed on an as-printed lamella, a lamella heat-treated in situ at 800°C in the TEM, as well as the solution heat-treated lamella, and the fracture process was captured. A crack developed slowly in the as-printed sample, with a linear relationship between notch opening and crack length indicative of ductile fracture, while the sample heated in situ showed a rapid increase in crack length indicative of brittle fracture. The solution heat-treated sample showed slower crack growth and retained its strength and hardness, indicating slower ductile fracture impeded by the needle-like δ-phase precipitates that formed during heat treatment. The in-situ exploration of heat treatment and effect on alloy strength and fracture mechanisms can also be applied to other material systems and manufacturing processes.

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Reference:

Supriya Koul, Le Zhou, Omar Ahmed, Yongho Sohn, Tengfei Jiang and Akihiro Kushima, Microscopy and Microanalysis27 (2) 250-256 (2021) DOI: 10.1017/S1431927621000052