Key Takeaways & Executive Findings
- •• High-temperature stress rupture failure in CLM Ni-based superalloys is primarily due to intergranular fracture in <110> grain regions, with sub-grain boundary fracture occurring only under high temperature and low stress (980 °C/260 MPa). • Stray grains, formed due to unstable heat flow in the melt pool during LPBF, severely reduce stress rupture life under both tested conditions. • Despite shorter stress rupture lifetimes, deformation twins are activated within <110> grains, contributing to excellent plasticity under both test conditions. • Future optimization of CLM via LPBF should focus on eliminating high-angle grain boundaries in <110> grains to enhance high-temperature performance.
Abstract
Abstract: The unique crystallographic lamellar microstructure (CLM) Ni-based superalloys fabricated by laser powder bed fusion (LPBF) exhibits excellent tensile properties. This study aims to investigate CLM’s high-temperature stress rupture behavior and use these findings to improve the additive manufacturing process. The result shows that the high temperature-induced intergranular fracture in <110> grain region is responsible for stress rupture failure under both conditions of 760 °C/780 MPa and 980 °C/260 MPa. Among them, the sub-grain boundary fracture occurs only under high temperature and low stress, 980 °C/260 MPa. Due to the severe intergranular fracture induced by stray grains, the stress rupture life is very low under both conditions. According to the finite element simulation, the formation of stray grains stems from the unstable heat flow within the melt pool during the process. In addition, the shorter stress rupture lifetime does not excite a more pronounced dislocation network around the γ′ phase. However, the deformation twins can still be activated inside the <110> grains, so it has excellent plasticity under both test conditions. Finally, this work indicates that the future optimization of CLM by LPBF should focus on eliminating of high-angle grain boundaries in <110> grains.
1. Introduction
In the past decade, among various additive manufacturing technologies in the superalloy field, laser powder bed fusion (LPBF) has significant potential for developing complex shape components such as turbine blades due to its high design accuracy enabled by minimal spot size [1, 2]. Unlike conventional wrought or cast routes, the extremely rapid solidification rate (R) in LPBF significantly suppresses elemental segregation and promotes dislocation accumulation in as-built alloys [3, 4].
In addition, the LPBF-build parts experience a top-down temperature gradient (G) and cyclic thermal history, which assemble prominent grain texture and strength anisotropy. It is widely acknowledged that the solidification conditions (G/R) at the liquid/solid interface in LPBF are fundamentally governed by melt pool morphology, which is intricately regulated by laser printing parameters [5, 6]. Consequently, divergent processing conditions give rise to diverse solidification microstructures and corresponding mechanical properties.
In recent years, the crystallographic lamellar microstructure (CLM) in Ni-based superalloys fabricated by LPBF has received widespread attention owing to its unique alternate <001>//BD and <110>//BD-oriented grains. Previous reports have demonstrated that CLM possesses excellent tensile properties in Ni-based superalloys [5-7]. The most substantial contributors to tensile performance of CLM are texture-related strengthening mechanisms, including the Schmid factor, Taylor factor, and stress-transfer coefficient [5]. Besides short-term tensile properties, the superalloy is widely applied in the aviation industry, where it operates in a severe environment characterized by elevated temperatures and long-term stresses [2, 7, 8]. To enhance its high-temperature service capability (a critical requirement for this application), a robust texture coexisting with a directional grain morphology is often essential, which is similar to what is typically observed in the CLM. Hence, it is valuable to further explore the underlying high-temperature stress rupture/creep mechanism of CLM. Previous studies focus on CLM’s room temperature tensile or corrosion properties in Inconel 718 alloy, which has a service temperature below 750 °C [5]. In the context of 1,000 °C tensile deformation, the activation of deformation twins within the <110>//BD-oriented lamellar microstructure has been identified as the primary mechanism underlying CLM’s exceptional plasticity in our recent research [9]. Furthermore, both literature reports and our own results indicate that the failure mechanism of CLM is attributed to intergranular fracture, which arises from the high-temperature failure caused by transverse high-angle grain boundaries [8, 9]. However, based on the results of the present studies, it is not sufficient to explain the deformation mechanism under high-temperature stress rupture conditions.
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Peng Wang, Jing-jing Liang, Yu-ping Zhu, Wei Song, Qiao-lei Li, Yi Qiu, Ying-ju Li, Yi-zhou Zhou, Han-lin Liao, Lei Shi, Li-ming Lei, Xiao-feng Sun, Jin-guo Li (2026). Stray grains evolution and high-temperature stress rupture behavior of crystallographic lamellar microstructure in Ni-based superalloys prepared by laser powder bed fusion. China Foundry. https://doi.org/10.1007/s41230-025-5024-y
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Frequently Asked Questions
What is the crystallographic lamellar microstructure (CLM) in Ni-based superalloys?
CLM is a unique microstructure formed in Ni-based superalloys during laser powder bed fusion (LPBF), characterized by alternating <001>//BD and <110>//BD-oriented grains. It exhibits excellent tensile properties due to texture-related strengthening mechanisms.
What causes stress rupture failure in CLM Ni-based superalloys at high temperatures?
Stress rupture failure is primarily caused by high-temperature-induced intergranular fracture in the <110> grain regions. Under high temperature and low stress (980 °C/260 MPa), sub-grain boundary fracture also occurs. Stray grains, formed due to unstable heat flow in the melt pool, exacerbate intergranular fracture and reduce rupture life.
How do stray grains affect the stress rupture life of CLM superalloys?
Stray grains severely reduce stress rupture life under both tested conditions (760 °C/780 MPa and 980 °C/260 MPa) because they induce severe intergranular fracture. Their formation is attributed to unstable heat flow within the melt pool during the LPBF process.
What is the role of deformation twins in the plasticity of CLM superalloys?
Deformation twins are activated inside <110> grains during stress rupture testing, contributing to excellent plasticity even though the stress rupture lifetime is short. This twinning mechanism helps maintain ductility under high-temperature conditions.
What future optimization is suggested for CLM by LPBF?
The study suggests that future optimization of CLM via LPBF should focus on eliminating high-angle grain boundaries in <110> grains to improve high-temperature stress rupture resistance and overall mechanical performance.
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