A comparison of the microstructure and creep behavior of cold rolled HAYNES® 230 alloy™ and HAYNES® 282 alloy™

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Abstract

HAYNES 282 and HAYNES 230 nickel-based superalloys were subjected to cold rolling deformation and heat treatments in order to investigate processing–microstructure–property relationships to understand the effects of thermomechanical processing on their microstructure and tensile-creep behavior. The sheet materials underwent four cycles of 20% reduction in thickness followed by a solution treatment. The resultant microstructures were characterized using electron backscattered diffraction and electron microscopy, and the high-temperature (973–1088 K (700–815 °C)) creep and fatigue behavior was evaluated and compared to the commercially available sheet alloys. The thermomechanical processing treatments did not significantly affect the grain boundary character distribution and almost half of all the boundaries in the microstructures were twin boundaries. The creep resistance was shown to degrade with the additional thermomechanical treatments, which resulted in finer equiaxed grain sizes. The HAYNES 282 alloy was shown to be significantly more creep resistant than the HAYNES 230 alloy. The fatigue behavior indicated that creep ratcheting occurred more prominently in the HAYNES 230 alloy than in the HAYNES 282 alloy and this was explained to be a result of the superior creep resistance exhibited by the HAYNES 282 alloy. Overall, this study suggests that additional energy-intensive processing treatments, beyond those involved in the commercially available sheet products, may not be beneficial for additional creep resistance.

Highlights

► The creep behavior of two recently developed superalloys is provided. ► We attempted to increase the creep resistance through GBE type processing. ► Comparison of the creep behavior and microstructure–property relations are provided. ► HAYNES 282 was found to be significantly more creep resistant and this is discussed.

Introduction

HAYNES 282 alloy is an advanced wrought γ′-strengthened nickel-based superalloy which is solid solution strengthened by cobalt (Co), chromium (Cr), and molybdenum (Mo). It was designed for improved high-temperature creep resistance, and its creep resistance surpasses that for Waspaloy and approaches that for R-41 alloy [1]. HAYNES 282 alloy possesses a unique combination of creep strength, thermal stability, weldability, and fabricability, and it is being considered for the transition sections and other hot-gas-path components in land-based gas turbines and for critical aircraft gas turbine applications, such as sheet fabrications, seamless and flash butt-welded rings, exhaust and nozzle components, and cases found in compressor, combustor, and turbine sections. It is easily deformed at room-temperature (RT) in its solution-treated condition, and it requires an aging treatment to obtain its exceptional high-temperature strength and creep resistance.

HAYNES 230 alloy, which contains Cr and tungsten (W) as its primary alloying elements, is another recently developed high-temperature, high-oxidation resistant, high-strength alloy. It can be worked, usually forged, in the temperature range between 1198 and 1448 K (925 and 1175 °C) [2], and it is projected for applications including gas turbine hot section components, such as combustion cans, thermocouple protection tubes, heat exchangers and industrial furnace fixtures and muffles. Unlike that for HAYNES 282 alloy, the solid solution strengthened HAYNES 230 alloy does not require an age-hardening heat treatment. HAYNES 230 alloy was designed for applications at higher temperatures where the γ′-strengthened alloys, such as HAYNES 282 alloy, lose strength due to γ′ solutionizing.

Each of these two alloys exhibits good fabricability, RT ductility, and an attractive balance of high-temperature tensile properties and oxidation resistance. However, HAYNES 282 alloy was designed for improved creep resistance in the temperature range of 922–1200 K (649–927 °C), which encompasses the target temperature range for this study (973–1088 K (700–815 °C)). HAYNES 230 alloy was designed for higher temperatures as mentioned above.

The current work was an attempt to identify and compare the processing–microstructure–property relationships in each alloy. As the mechanical deformation, creep behavior, and corrosion resistance of other superalloy systems have been improved through grain boundary character alteration using strain–recrystallization thermomechanical processing (TMP) treatments [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], the thought at the beginning of this work was there is the potential to improve the creep performance of HAYNES 230 and 282 alloys using a similar grain boundary engineering strategies. However, the TMP treatments used in this work resulted in decreased creep resistance, and a significant difference in the grain boundary character distribution (GBCP) between the baseline and TMP materials was not observed. The reasons for this behavior will be discussed and the results will be compared to that for a cobalt-based Udimet 188 alloy [20].

Section snippets

Experimental

Commercially available HAYNES 282 alloy sheet was originally provided by HAYNES, International (Kokomo, IN) in the solution-annealed condition, where it can be easily deformed. The typical commercially used solution annealing temperature is in the range of 1394–1422 K (1121–1149 °C). In this study, the commercial sheet was cold rolled to 20% reduction then solution-treated at 1367 K (1094 °C), 1394 K (1121 °C), 1422 K (1149 °C), and 1450 K (1177 °C) for 20 min followed by water quenching (WQ) to evaluate

Microstructure

Fig. 2 illustrates a BSE SEM image of HAYNES 282 alloy in the baseline condition. The dark precipitates, which were typically finer than 1 μm, were Ti-rich (see Fig. 3b) and made up 0.34% ± 0.2% of the microstructure. These precipitates were evident after solutionizing followed by quenching as well as after aging. Fig. 4 illustrates the TMP HAYNES 282 alloy microstructure before the final aging treatment. A very small volume of Mo-rich (see Fig. 5) precipitates, bright phase in Fig. 4, was present

Summary and conclusions

This work evaluated the effect of TMP on the microstructure, creep, and fatigue behavior of HAYNES 282 and HAYNES 230 nickel-based superalloys. The TMP treatment did not significantly affect the GBCD. HAYNES 282 alloy was shown to be significantly more creep resistant than HAYNES 230 alloy within the temperature range examined (973–1088 K (700–815 °C)) independent of TMP. The TMP treatment resulted in reduced creep resistance of the alloys. The reduced grain size of the TMP materials, induced by

Acknowledgements

The authors are grateful to Drs. Lee Pike and Michael Fahrmann of HAYNES International (Kokomo, IN, 46904-9013) for overseeing the alloy processing and for useful comments on the manuscript. The authors acknowledge the assistance of Dr. Yukinori Yamamoto of Oak Ridge National Laboratory (ORNL) for overseeing the heat treatments. A portion of this research was conducted at the SHaRE User Facility, which is sponsored by the Division of Scientific User Facilities, Office of Basic Energy Sciences,

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