Key Takeaways & Executive Findings
- •• At 650 °C, yield strength decreases almost linearly with increasing recrystallization (RX) fraction, while elongation drops significantly up to 4.9% RX fraction, then stabilizes. • At 950 °C, both yield strength and elongation decrease as RX fraction increases from 0% to 4.9%, indicating detrimental effect at high temperatures. • Fracture modes change with temperature: mixed transgranular/intergranular cleavage at 650 °C, and ductile/intergranular dimple fracture at 950 °C. • Failure is driven by transverse grain boundaries introduced during RX, which act as crack initiation sites and propagation paths, leading to premature failure.
Abstract
Surface recrystallization (RX) is a typical grain defect observed in directionally solidified (DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single-crystal (SC) superalloys, with limited research on its influence on the high-temperature mechanical properties of DS superalloys. This study systematically investigated the effect of RX on the high-temperature tensile properties of a DS DZ409 superalloy. The results show that at 650 °C, the yield strength decreases almost linearly with an increase in RX fraction. A significant reduction in elongation is observed as the RX fraction increases from 0% to 4.9%. However, beyond this point, further increase in RX fraction leads to minimal changes in elongation. At 950 °C, both yield strength and elongation decrease as the RX fraction increases from 0% to 4.9%. At 650 °C, fractures in the RX DS superalloys exhibit a mixed mode of transgranular and intergranular cleavage fracture, while at 950 °C, it features a combination of ductile and intergranular dimple fractures. The failure mechanism of the RX DS superalloy is associated with the introduction of transverse grain boundaries (GBs) during RX. In the early stages of tensile testing at intermediate and high temperatures, cracks can easily initiate at these GBs. Subsequently, the cracks propagate along the GBs into the DS matrix, ultimately leading to failure of the DS superalloy.
1. Introduction
Due to the elimination of transverse grain boundaries (GBs) and the alignment of GBs parallel to the main stress axis, directionally solidified (DS) blades and vanes made from Ni-based superalloys exhibit excellent mechanical properties at elevated temperatures. These components are widely used in advanced aircraft engines and heavy industrial gas turbines (IGTs) [1, 2].
Surface recrystallization (RX) is a critical defect in these components, causing by the residual strain. During the heat treatment processes, the residual strain serving as the impetus for the initiation and progression of RX under the promotion of high temperature [3]. As the advanced directional alloys have been developed and blade and vane designs have become increasingly complex, surface RX has emerged as a major defect contributing to high scrap rates of DS components. Researchers generally believe that surface RX can diminish the high-temperature performance of these parts. Nonetheless, research works on the effects of surface RX on the high-temperature mechanical properties of DS blades and vanes are surprisingly limited in the open references. Most studies have focused on the behavior of surface RX in directionally solidified single-crystal (SC) superalloys [4-16], as well as its impact on the room temperature mechanical properties of SC superalloys [17-23], with little research addressing its influence on the high-temperature mechanical properties of DS blades and vanes [24, 25].
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Qiang Yang, Ya-zhou Li, Fu Wang, Jing Wang, Di-chen Li, Jian-tao Wu (2025). Effect of surface recrystallization on high-temperature tensile properties of a directionally solidified DZ409 Ni-based superalloy. China Foundry. https://doi.org/10.1007/s41230-025-4265-0
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Frequently Asked Questions
What is the effect of surface recrystallization on the yield strength of DS DZ409 superalloy at 650°C?
At 650°C, the yield strength decreases almost linearly with an increase in recrystallization (RX) fraction.
How does recrystallization affect elongation at intermediate and high temperatures?
At 650°C, elongation significantly reduces as RX fraction increases from 0% to 4.9%, but further increase causes minimal changes. At 950°C, elongation decreases as RX fraction increases from 0% to 4.9%.
What are the fracture modes of RX DS superalloys at different temperatures?
At 650°C, fractures exhibit a mixed mode of transgranular and intergranular cleavage fracture. At 950°C, they feature a combination of ductile and intergranular dimple fractures.
What is the failure mechanism of RX DS superalloys?
The failure is associated with transverse grain boundaries introduced during recrystallization. Cracks initiate at these boundaries early in tensile testing and propagate along them into the DS matrix, leading to failure.
Why is this study important for the aerospace industry?
DS Ni-based superalloys are used in turbine blades and vanes. Understanding the impact of surface recrystallization on high-temperature mechanical properties is crucial for quality control and life prediction of these critical components.
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