Effect of Cooling Rate on Precipitation Behavior of Gamma Prime in a Newly Developed Co-based Superalloy
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https://doi.org/10.1007/s11837-020-04241-1 2020 The Minerals, Metals & Materials Society
PROCESS DESIGN AND MATERIALS DEVELOPMENT FOR HIGH-TEMPERATURE APPLICATIONS
Effect of Cooling Rate on Precipitation Behavior of Gamma Prime in a Newly Developed Co-based Superalloy H.R. ABEDI
,1,3 O.A. OJO,1,4 and XINJIN CAO2,5
1.—Department of Mechanical Engineering, University of Manitoba, Winnipeg R3T 5V6, Canada. 2.—Institute of Laser Advanced Manufacturing, College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310014, Zhejiang, China. 3.—e-mail: [email protected]. 4.—e-mail: [email protected]. 5.—e-mail: [email protected]
The influence of the cooling rate on the precipitation behavior of gamma prime (c¢) in a newly developed Co-based superalloy has been investigated by using differential scanning calorimetry. In addition, changes to the c¢ precipitate morphology and size were analyzed by scanning electron microscopy. It was observed that increasing the rate at which the alloy was cooled from high temperatures increased the c¢ precipitation rate at different temperatures but also reduced the temperature at which the maximum precipitation rate occurred and retarded the complete precipitation of the c¢ precipitates. The activation energy required for c¢ precipitation was calculated by using the Kissinger model, revealing that the present alloy exhibits higher activation energy than some Ni-based superalloys, which can be attributed to lower rates of atomic diffusion in cobalt-based superalloys.
INTRODUCTION Due to the ever-increasing demand for improved jet engine efficiency and reduction of greenhousegas emissions, advanced heat-resistant materials such as novel Co-based superalloys are being developing to replace conventional Ni-based superalloys. Recently, Co-Al-W ternary alloys have received profound attention due to their superior high-temperature mechanical properties compared with conventional Ni- and Co-based superalloys. Over the years, several alloying elements such as Ni,1 Ti,2 Ta,3 Hf,4 Cr,5 B,6 Si,7 Mo,8 and Zr and C 9 have been added to enhance the high-temperature performance of Co-Al-W ternary alloys. The newly-developed polycrystalline CoWAlloy1 is considered to be a potential candidate for use in high-temperature applications above 750C. The alloy consists of L12 ordered gamma prime (c¢)-Co3(Al,W) strengthening phase in a gamma matrix. Neumeier et al.9 reported a monomodal precipitate size distribution (PSD) of c¢ with size ranging from 0.2 lm to 0.5 lm in CoWAlloy1.9 CoWAlloy1 is a potential replacement for several Ni-based superalloys, making it critical to study its c¢ precipitation behavior during service and material processing such as additive manufacturing,
welding, and work hardening. It has been reported that continuous and rapid cooling during these processes can change the c¢ characteristics, which will directly influence the strength of the material; For example, Bennett et al.10 investigated the effect of the cooling rate on the mechanical prop
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