DYNAMICS OF PRECIPITATION AND TRANSFORMATION OF CARBIDES IN A Ni-BASE SUPERALLOY

The quantitative analytical method combining the electrolytic extraction with X-ray diffraction analysis to determine the carbides and TCP in a Ni-base superalloy was developed.The variation of decomposition of MC and precipitation of M_(23)C_6 and M_6C with hot exposure time at 850—1000℃ is shown to conform to hyperbolic law.The elemental con- stitution of M_(23)C_6 changes continutously during the hot exposure process.At the primary stage the constitution of the precipitates is(Cr_(0.67)Mo_(0.13)Ni_(0.13)Co_(0.07))_(23)C_6.Then with in- creasing Cr and decreasing Mo,Ni and Co it finally becomes(Cr_(0.88)Mo_(0.07)Ni_(0.03)Co_(0.02))_(23)C_6. The higher the hot exposure temperature,the faster the final constitution of M_(23)C_6 may be achieved.