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; M 6C carbide is most stable above 1000 °C; M 23C 6 carbide appears in the 950–1000 °C temperature range. The rate of MC decomposition increases with the rise of thermal exposure temperature. Some M 6C carbide particles, which are transformed from MC carbide, have irregular morphology and adhere to the original MC carbide; the other M 6C carbide particles are precipitated in the forms of needle and tiny block. Furthermore, needle-shaped M 6C carbide is the most prevalent and has the coherent relationship with the matrix. M 6C and script-like MC carbide particles are detrimental to room temperature tensile and stress rupture properties of the alloy. M 23C 6 particles are precipitated in grain boundaries, but have little effect on the properties of the alloy because of their small amount.