Experimental Investigation On Phase Equilibria Of Ternary Systems Containing Re/Ru In Co-based Superalloys

The Co-based superalloys are often used to manufacture high temperature components in aviation industry because of their excellent properties of oxidation resistance,corrosion resistance and high temperature resistance such as turbines and engines.Thus,the Co-based superalloys are one of highly competitive high-temperature materials.However,the Co-based superalloys are just developed recently and the research on the superalloys is not mature enough to meet the development needs of the aviation industry.Alloying is a common method to improve the structure and high temperature properties of alloys,such as adding Re,Ru,Ta,Mo,Nb,Ti and other elements in alloys.The addition of Re can significantly improves the creep and fatigue properties of the alloys at high temperature.However,excessive Re will result in the formation of brittle and harmful TCP phase in the alloys under high temperature and pressure,damaging the high temperature properties and reducing the service life of the alloys.The addition of Ru can inhibit the formation and growth of TCP phase,thus improving the stability and creep resistance of the materials.Therefore,the phase equilibria of ternary system containing Re/Ru have theoretical guiding role in the development of the Co-based superalloys.In this work,the phase equilibria of ternary systems containing Re/Ru elements(Co-Re-Ta,Co-Nb-Re and Mo-Ru-Ti)in the Co-based superalloys were carried out by means of microstructure observation,electron probe analysis and X-ray diffraction.The main results are concluded as follows:(1)The phase equilibria of Co-Re-Ta ternary system at 1100?,1200? and 1300 ? were experimentally determined.The results showed that the.3 phase surrounded the phase of,2 from left to right and dissolved a lot of Re.The composition range of(?Co,Re)phase was very wide,extending from the Re-rich side to the Co-rich side,and the solubility of Ta in(?Co,Re)was large.(2)The phase equilibria of Co-Nb-Re ternary system at 1200 0? and 1300 ? were experimentally determined.The results showed that the X3 phase was stable at 1300 ?isothermal section and surrounded the ?2.phase from left to right because of the addition of Re to the Co-Ta alloys.The solubility of Re in the X3 phase was large.The solubility of Re in the ?.-Co7Nb6 phase was large,more than 30 at.%.(3)The phase equilibria of Mo-Ru-Ti ternary system at 1100 ? and 1300 ? were experimentally determined.The results showed that the addition of Ti stabilized the binary a-Mo5Ru3 phase at 1100 ? isothermal section and the solubility of Ti in the ?-Mo5Ru3 phase was small.The solubility of Mo in TiRu phase was large.