Journal of Advanced Materials in Engineering

Journal of Advanced Materials in Engineering

Effect of Increasing Solution Annealing Temperature on Microstructural Uniformity, Hardness, and Stress-Rupture Behavior of IN738LC Superalloy

Document Type : Original Article

Authors
Reza Sahihi
Rouholah Ashiri
School of Metallurgy and Materials Engineering, Iran University of Science and Technology (IUST), Tehran, Iran
10.47176/jame.46.1.1202
Abstract
Introduction and Objectives: Inconel 738 low-carbon (IN738LC) nickel-based superalloy is widely used in high-temperature turbine components due to its high strength and thermal stability. However, microstructural heterogeneity resulting from the solidification process can lead to a non-uniform distribution of strengthening precipitates and deterioration of mechanical performance. The objective of this study was to investigate the effect of increasing the solution heat treatment temperature beyond the standard cycle on the microstructural evolution and mechanical properties of the superalloy.
Materials and Methods: Two heat treatment cycles, including a standard cycle and a proposed cycle, were applied to cast specimens. Microstructural changes were evaluated using optical microscopy, scanning electron microscopy, and quantitative image analysis. In addition, hardness and stress rupture tests were conducted to evaluate the mechanical behavior of the alloy.
Results: The results showed that increasing the solution temperature significantly reduced microstructural heterogeneity between dendritic core and interdendritic regions. The size of coarse precipitates in interdendritic areas decreased, leading to a more uniform precipitate distribution. Furthermore, the volume fraction of strengthening precipitates increased from 39% to 45%. Carbide investigations indicated that the blocky morphology of MC carbides was preserved, and no evidence of significant decomposition was observed. Hardness increased from 363 HV to 447 HV, while stress rupture life improved from 35 h to 45.8 h.
Conclusion: The findings demonstrated that a controlled increase in solution heat treatment temperature can simultaneously improve mechanical properties and high-temperature performance through enhanced microstructural homogenization, increased strengthening precipitate fraction, and preservation of MC carbide stability. These results provide useful insight for designing optimized heat treatment schedules for high-temperature turbine components.
Keywords
IN738LC superalloy, Gamma-prime (&gamma
') precipitates, MC carbides, Microstructural evolution, Stress rupture
Subjects
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Journal of Advanced Materials in Engineering
Volume 46, Issue 1
Winter 2027
Pages 127-148

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