The Study Of Interfacial Reactions Between K423A Alloy And ZrSiO₄ Ceramic Mold And Ni-Al-Co-Ti Systems Phase Equilibrium

The aerospace industry has become more and more demanding in terms of high temperature and corrosion resistance of the turbine cassettes,the main load-bearing component of the engine with the increasing temperature of the turbine inlet of the aero-engine in recent years.During the casting process of the turbine cassettes,the alloy melt and ceramic mold contact closely for a long time at high temperature,which is prone to a variety of complex effects,causing sticky sand,increasing roughness and decreasing the surface quality of product.In this work,the interfacial reaction behaviors between K423A alloy and Zr Si O₄ceramic mold and the influence of temperature and time on the interfacial reaction have been investigated.The phase relationship between the main elements Ni-Al-Co-Ti in K423A alloy at 1150? has been studied,which offered a seris of thermaldynamics date in alloy design.The main research results are as follows.1.The specimens of K423A alloy were prepared by the method of directional solidification,and it was found that the sticky sand on the surface of the castings consisted of Zr Si O₄and Zr O₂particles,alloy oxides and Al₂O₃interfacial reaction layer.X-ray diffraction results detected a large amount of Al₂O₃,trace Ti O2 and Si on the surface of the castings,indicating that the alloy melt reacted with the shell material.2.The interfacial reaction between K423A alloy and Zr Si O₄ceramic mold at temperature of 1450?,1480? and 1510? included the decomposition reaction of Zr Si O_4,which was Zr Si O₄?Zr O₂+Si O₂and the replacement reaction between Al element and Si O₂by Al+3/4Si O₂?3/4Si+1/2Al₂O₃.There was a reaction at the interface at1510?,Ti+Si O₂?Si+Ti O₂,leading to the formation of a small amount of punctate Ti O₂.The Gibbs free energy calculations for each reaction at all temperatures were less than zero,which justified the obtained reactions.3.With the increase of casting temperature,the type of interfacial reactions between K423A alloy and Zr Si O₄ceramic mold did not change significantly when the holding time was certain.But the degree of interfacial reaction from weak to strong,which manifasted as a change in interfacial reaction product Al₂O₃from dispersed dot and strip to continuous layer.There was also a increasing of the number and the area of reaction zones with the thickness of reaction layer changing from 3?m to more than 10?m.The degree of chemical reaction increased by which the average thickness of the interfacial reaction layer changed from 5.6?m to 27.2?m with the increase of holding time in a certain temperature.And the reaction layer thickness increased the fastest when the holding time from 13min to 17min.4.The phase relations of the Ni-Al-Ti and Ni-Co-Ti ternary system(60at.%Ni)at1150? were determined by experiments,which offered the phase composition of the60Ni-Al-Co-Ti(at.%)isothermal cross-section boundary at this temperature.The isothermal section of the Al-Co-Ti ternary system at 1150? was determined experimentally,and 13 three-phase regions at this temperature were identified.The ternary compounds which named Al₂Co Ti phase has a large range at this temperature,betweening 28at.%Al-27at.%Co-45at.%Ti and 58at.%Al-22at.%Co-20at.%Ti.The ternary compound Al₆₇Co₄Ti₂₉in a stable present.5.By the equilibrium alloy method,5 three-phase equilibrium regions were studied in the 60Ni-Al-Co-Ti system at 1150? included??+?₄+?₁???+?+?₄??₂+?+?₄?(Co,Ni)+??+???+?₄+?₂and one four-phase region presented as?₂+L₃+?+?₄.No new quaternary compounds were found.