Relative stability of carbides and their effects on the properties of K465 superalloy

Thermal exposure specimens of K465 superalloy are carried out at 850, 950, 1000, 1050 and 1100 °C in order to investigate the stability of carbides. MC carbide is stable from 850 to 950 °C; M6C carbide is most stable above 1000 °C; M23C6 carbide appears in the 950–1000 °C temperature range. The rate of MC decomposition increases with the rise of thermal exposure temperature. Some M6C carbide particles, which are transformed from MC carbide, have irregular morphology and adhere to the original MC carbide; the other M6C carbide particles are precipitated in the forms of needle and tiny block. Furthermore, needle-shaped M6C carbide is the most prevalent and has the coherent relationship with the matrix. M6C and script-like MC carbide particles are detrimental to room temperature tensile and stress rupture properties of the alloy. M23C6 particles are precipitated in grain boundaries, but have little effect on the properties of the alloy because of their small amount.