High Temperature Creep Properties of Cast Cobalt-Based Superalloys: A Comparison
Cast cobalt-based superalloys have already found applications in the glass industry to construct glass shaping tools. The present study deals with the high temperature characterization of the two cast cobalt-based CoNb and CoTa superalloys which have been developed for precision casting of a rotary fibreglass spinner disc for glass industry. The superalloys have been characterized through constant load creep tests at 1000, 1050 and 1100 °C in a tensile stress range from 20 to 100 MPa, with the aim to simulate the variation of mechanical properties occurring in a rotary fibreglass spinner disc at operational conditions. The results have been compared and discussed, with the aim to link the difference in creep properties to the evolution of creep damage and fracture in superalloys. It was found that the CoNb superalloy possesses longer creep life compared to the CoTa superalloy under the same loading conditions. Fractographic investigations of the creep fractured specimens of the examined superalloys revealed that the dominating creep fracture of the CoTa is of the ductile transgranular dimple fracture mode due to a loss of an external section of specimen (necking). By contrast, the final brittle fracture in the CoNb superalloys occurs via relatively fast propagation of the longest cracks after the ultimate state of creep damage is reach.
KeywordsCobalt-based superalloys Creep damage and fracture Breakage of primary carbides
The authors acknowledge financial support for this study provided by the Ministry of Industry and Trade of the Czech Republic within the framework program MPO ČR Trio under the Project No. FV10699. The research infrastructure IPMinfra supported by the Ministry of Education, Youth and Sports through the Project No. LM2015069 was used.
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