CARBIDE EVOLUTION BEHAVIOR OF K416B AS-CAST Ni-BASED SUPERALLOY WITH HIGH W CONTENT DURING HIGH TEMPERATURE CREEP

As-cast Ni-based superalloys with high W content are used extensively in the turbine vane of aeroengine due to their good heat resistance and temperature capability. During high temperature service, the creep deformations and microstructure evolution are occurred in the using materials, and the creep behavior mainly depends on their chemical composition and microstructure, such as size, distribution and morphology of gamma' phase and carbides. Thereinto, the mophologies of carbide phases are closely related to creep resistance of the alloy. Generally, the carbide particles displaying dispersive distribution may enhance the creep resistance of the alloy, while the carbide with continuous morphologies distributed in the boundaries, they may provide easy paths for crack propagation and degrade the mechanical properties of the alloy. Besides the creep life of the alloy also depends on the microstructure evolution under high temperature. But the evolution mechanism of carbides in K416B superalloy during creep is still unclear up to now. For this reason, by means of creep property measurement and microstructure observation, the evolution behavior of precipitates in K416B Ni-based superalloy with high W content during high temperature creep has been investigated. The results show that the size of gamma' phase is inhomogeneous in the as-cast alloy, and the stripe MC-carbide distribute in the inter-dendrite regions displaying Chinese structures. During high temperature creep applied stress, fine M6C carbide discontinuously precipitate in the deformed gamma matrix. The thermodynamics analysis indicates that the carbon element segregates in the regions of stress concentration and combines with carbide-forming elements W etc, which promoted the fine M6C carbide to precipitate from the gamma matrix. At the same time, the grooves are formed on the surface of stripe MC carbide, and then gradually decomposed and transformed into M6C particles. Thereinto, the additional press formed in the surface of stripe MC carbide is the main factor to promote the MC phase continuous dissolution and spheroidizing.