Effects of intermediate temperature on the grain boundary and ?' precipitates of nickel-based powder superalloy under interrupted cooling

The serrated grain boundaries obtained by solution treatment followed by slow-cooling can improve the creep properties of nickel-based superalloy, but such heat treatment simultaneously gives rise to coarse gamma' precipitates and deteriorates the high-temperature strength. Herein, the interrupted cooling during solu-tion treatment was used to obtain the serrated grain boundaries and the fine gamma' precipitates in a nickel -based powder superalloy by regulating the intermediate temperature. The effects of intermediate tem-perature on the grain morphology and secondary gamma' precipitate size distribution in the alloy were sys-tematically investigated. Flat grain boundaries were formed in the sample at the intermediate temperature of 1140 degrees C. The serrated grain boundaries appeared in the samples with an intermediate temperature below 1120 degrees C. The amplitude of the serrated grain boundaries increased from 0.62 to 1.03 mu m as the intermediate temperature reduced from 1120 degrees to 100 0 degrees C. With the decrease of the intermediate temperature, the sec-ondary gamma' precipitates in the alloys changed from spherical to butterfly shapes, and then split. The size of secondary gamma' increased from 312 to 456 nm for the alloys with the intermediate temperature between 1120 and 1000 degrees C. Meanwhile, the tertiary gamma' precipitates were produced under the intermediate temperature of 1120-1050 degrees C, forming a multimodal size distribution of gamma' precipitates in the superalloys. The micro -hardness values of the samples were improved with the increasing intermediate temperature during the interrupted cooling, which was closely related to the size of gamma'. As the intermediate temperature rose from 1050 degrees C to 1120 degrees C, the tensile strength of the samples increased from 1297 MPa to 1425 MPa at room temperature and from 985 MPa to 1100 MPa at 650 degrees C. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

By regulating the intermediate temperature and employing interrupted cooling during solution treatment, serrated grain boundaries and fine gamma' precipitates can be achieved in a nickel-based powder superalloy, leading to improved properties.