High Temperature Creep Damage Mechanisms in a Directionally Solidified Alloy: Impact of Crystallography and Environment

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

“…[23] At 900°C, cracks initiate from sub-surface carbides. Indeed, elevated temperature is sufficient to crack carbides in 5 minutes [44] which then become preferential sites for initiating oxidation-assisted damage. In this study, ultrasonic tests require a 40 minutes stabilization at 1000°C before initiating the mechanical solicitation.…”

Damage nucleation during transverse creep of a directionally solidified Ni-based superalloy

“…A decrease in creep lifetime is reported for the DS200 specimens extracted along the longitudinal direction in comparison to the single crystal Mar-M200 specimen. It is classically associated with the average orientation of the DS200 specimens extracted along the longitudinal direction being misoriented to the optimum <001> orientation [13,25,14]. In contrast, a tertiary creep regime at 900 • C and 350 MPa and secondary creep regime at 750 • C and 800 MPa is not observed for DS200 specimens extracted along the transverse direction.…”

“…The last heat treatment step consisted of a hold at 870 • C for 16 hours, followed by an air quench to optimize the γ′ precipitate size and morphology. The experimental details of this procedure are provided elsewhere [13,25]. The resulting microstructure of the DS200 specimen is presented in Figure 1.…”

Very high cycle fatigue durability of an additively manufactured single-crystal Ni-based superalloy

“…We may only mention that a directionally solidified alloy (DS200+Hf), presenting several ≈ <001> columnar grains within the gauge part of VHCF specimens (i.e. low angle grain boundaries with respect to the loading direction [36]), performs slightly worse in VHCF at 1,000 °C/Rε = -1/f = 20 kHz compared to SX specimens solidified with the same casting parameters [15]. Hence, highly misoriented grains from the perfect [001] crystallographic orientation is critical to the VHCF life.…”