A micro specimen testing method to study the anisotropy of creep-fatigue interaction for SLM GH4169 alloy

Abstract

Nickel-based alloys fabricated by selective laser melting (SLM) offer significant advantages without constrained by geometric shapes in high-temperature equipment applications, but the anisotropic mechanical properties restrict its safety application. In this paper, small punch creep test (SPCT), small punch fatigue test (SPFT) and small punch creep-fatigue test (SPCFT) are applied to study the anisotropy of creep-fatigue interaction for SLM GH4169 at 650℃ using two disc specimens (i.e., X and Z) with flat surfaces parallel and perpendicular to the build direction, respectively. The failure life of X-specimen exceeds that of Z-specimen at all loading conditions, indicating homogeneity in anisotropy. However, the significance of anisotropy is inhomogeneity, and it is substantial in SPCT, weak in SPFT, and moderate in SPCFT. Moreover, the creep-fatigue interaction is negative at the short hold time as 2 s due to the relieving of fatigue damage, but it is positive at the long hold time as 22 s, since the creep and fatigue damages coexist. And the Z-specimen exhibits stronger interaction than the X-specimen. At last, the anisotropic fracture mechanism diagrams of SPFT, SPCT and SPCFT are constructed. The surface crack propagation of X-specimen is parallel to the build direction, while that of Z-specimen shows a star shape along the radial direction. The crack propagation mode is primarily transgranular fracture for SPFT, and is intergranular fracture for SPCT, while is the coexistence of transgranular fatigue crack and intergranular creep void for SPCFT. This paper innovatively develops the SPCFT to study the anisotropy of creep-fatigue interaction for SLM GH4169 alloy, which provides a reference for the structural design and life prediction of SLM fabricated nickel-based alloys under high-temperature creep-fatigue conditions.