PSI - Issue 68
Amy Milne et al. / Procedia Structural Integrity 68 (2025) 666–673 Milne et. al. / Structural Integrity Procedia 00 (2025) 000–000
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4. Results and Discussion 4.1. Post-Test Metallography
The fatigue and CCG path on a Y (horizontal) sample is shown in Figure 2. The fatigue pre-crack is relatively straight and continuous, as expected. The creep crack shows some deviation from the initial crack path and discontinuity. It is also evidently influenced by the surrounding defects – noticeable porosity and discontinuous cracking can be seen along the image.
Figure 2: Post-test Y-built (horizontal) sample crack path, with arrows indicating build and loading directions
Figure 3 depicts the crack path at the mid plane of a Z (horizontal) specimen post-test. Again, the fatigue pre crack is relatively straight and continuous, whereas the CCG region is discontinuous. Numerous creep microcracks can be seen above the main creep crack in the vicinity of the crack tip, and porosity is also visible in the sample.
Figure 3: Post-test Z-built (horizontal) sample at with arrows indicating build and loading directions.
The crack path post CCG testing at both surfaces of a non-side grooved X orientated (vertical) sample is shown in Figure 4. For the surface labelled (a) the fatigue crack is relatively straight, but for surface (b) the fatigue pre-crack has deviated between build layers, possibly influenced by porosity which are evident on the images. Multiple creep micro-cracks are visible on both surfaces, however surface (b) has many discontinuous creep cracks along different build layers, and initiated at different stress concentration regions of the fatigue pre-crack. The interface between the build layers (melt pool boundaries) can contain a number of stress concentration features since it is region of potential microstructural and compositional change. Solutes may segregate at these boundaries and furthermore melt pool boundaries may contain lack of fusion defects that, for vertical samples, are subjected to the worst case loading as detailed in Ronneberg et al. (2020).
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