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

Cobalt-based superalloys have become ideal materials for various turbine blades and engines,attributing to high initial melting temperature,high temperature strength,thermal corrosion resistance and oxidation resistance.With the rapid development of science and technology,complex working environments have put forward higher requirements for the comprehensive performance of cobalt-based superalloys.The additions of Cr,Ni,W,Al,Zr,Mo,Ru and other alloying elements are the important method to improve the comprehensive performance of cobalt-based superalloys.For example,the addition of Zr element can reduce grain boundary defects,effectively improve the high-temperature strength and the service life of cobalt-based superalloy.The addition of Ru element will change the element distribution behavior between ? and ?' phase in the cobalt-based superalloy,and enhance their creep resistance and microstructure stability.However,some brittle phases should precipitate when adding excessive Zr and Ru,which should deteriorate the high temperature performance and the service life of the alloy.Therefore,the experimental phase equilibria information of some Co-based superalloys containing Zr and Ru is very necessary.The obtained results have important guiding significance for improving the overall performances of cobalt-based superalloys,and it has important guiding significance for the composition design and microstructure control of cobalt-based superalloys.In this study,the phase equilibria of ternary systems including Co-W-Zr,Co-Al-Zr,and Co-Mo-Ru which containing Zr and Ru elements were determined.The main results are concluded as follows:(1)The phase equilibria of Co-W-Zr ternary system at 1200? and 1300? were experimentally determined.The Co2Zr phase and W2Zr phase have the same crystal structure(C15),but the two phases cannot formed continuous solid solution compound phase,instead of the two-phase equilibria of Co2Zr+W2Zr is formed.No ternary compound phase was found in this ternary system.(2)The phase equilibria of Co-Al-Zr ternary system at 1000? and 1200? near the Co-Zr side were experimentally determined.There are three ternary compounds CoAl2Zr6,CoAlZr and Co2AlZr in the Co-Al-Zr ternary system near Co-Zr side at both isothermal sections.The solid solubility of Zr in the(?Co)matrix phase is 1.3 at.%(1000?)and 2.6 at.%(1200?).The solid solubility of Al in the(?Co)matrix phase is 12.5 at.%(1000?)and 14.9 at.%(1200?).(3)The phase equilibria of Co-Mo-Ru ternary system at 1100? and 1300? were experimentally determined.At 1100?,the Ru element has limited solid solution in Co2Mo3,and its solubility is 8.0 at.%.At 1300?,the high-temperature phases Mo3Ru2 and Co2Mo3 has the same structure D8b which will form a continuous(Co,Ru)2Mo3 solid solution from the Co-Mo side to the Ru-Mo side.