Experimental Investigation On Phase Equilibria Of Important Ternary Systems In Nb-Si Based Superalloys

Superalloys are widely used in the aerospace industry,especially in various high-temperature components,such as turbine blades,guide vanes and combustion chambers in aircraft engines.In recent years,several researchers have found that Nb-Si based superalloys have the advantages of high melting point(>1750?),low density(6.67.2 g/cm3)and good high-temperature strength,and have been considered as potential one of the candidates for replacing Ni-based single crystal superalloys.However,Nb-Si-based superalloys exhibit poor room-temperature toughness and high-temperature oxidation resistance,which restrict their actual applications.At present,alloying is an important method to improve structures and properties of Nb-Si based alloys,and multi-component of Nb-Si-Ti-Cr-Al-Hf-V system has been developed.With the diversification of alloying elements,the alloy exhibits complex phase equilibrium relationships and microstructure,which are extremely difficult for the composition design and microstructural control of alloys.Therefore,establishing an integrated thermodynamic database of Nb-Si-Ti-Cr-Al-Hf-V system is important and meaningful,which can provide powerful support for the design of new alloys.In the present work,the phase equilibria of partial Nb-Si based ternary systems are experimentally determined,providing experimental information for the establishment of Nb-Si based thermodynamic database.The main results of this work are as follows:(1)The phase equilibria of Nb-V-Al ternary system at 1100 and 1200 ? were experimentally determined.There are five three-phase regions and one large single-phase region of(Nb,V)solid solution in the isothermal sections at 1100 and 1200 ?.(2)The phase equilibria of Nb-V-Hf ternary system at 1100 and 1300 ? were experimentally measured.There is a large(pHf,Nb,V)solid solution and ternary compound single phase region in the isothermal sections of 1100 and 1300 ?.(3)The phase equilibria of Hf-Ti-V ternary system at 1100 and 1300 ? were experimentally determined.As the temperature increases from 1100 to 1300 ?,the single-phase region of ?(Hf,Ti)solid solution expands significantly,while the three-phase region of a(Hf,Ti)+ ?(Hf,Ti)+ HfV2 disappears.(4)The phase equilibria of Hf-Ti-Al ternary system at 1300 ? was experimentally measured.The results show that there is also a large ?(Hf,Ti)single-phase region in the Hf-Ti-Al ternary system.