Research On Semi-solid Microstructure Evolution And Short-Time Oxidation Behavior At High Temperature Of GH3536 Alloy

Due to its high temperature strength,good resistance to oxidation and corrosion and good plasticity and ductility,superalloy is widely used in many industrial fields.Nickel-based superalloys are widely used in the aerospace industry because of their excellent comprehensive properties.However,the thermal processing performance of nickel-base superalloys is poor,which restricts its development and application to some extent.If the semi-solid thixoforming technology is applied to nickel-based superalloys,the technical characteristics of near-net forming can improve the processing disadvantages of nickel-base superalloys.Therefore,this paper takes GH3536 nickel-based superalloy as the research object.Based on the research on the semi-solid billet preparation process of superalloys before thixoforming,semi-solid isothermal treatment is used to prepare GH3536 alloy semi-solid billet,and the evolution law and influencing factors of the process were studied.Considering the existence of oxidation behavior,the high temperature oxidation experiment was designed to investigate the high temperature oxidation of GH3536 alloy,and necessity of the oxidation protection of GH3536 alloy during the preparation of semi-solid billet by isothermal treatment was discussed,in order to provide some theoretical support for the GH3536 nickel-based alloy using semi-solid thixoforming technology.In this paper,semi-solid isothermal processing technology is used to prepare GH3536 alloy semi-solid billet.Studies have shown that due to the combined effects of various mechanisms in the evolution of the microstructure,the holding temperature and holding time have no obvious influence on the grain size and roundness of the semi-solid billet of GH3536 alloy,but the grain size and roundness have an upward trendency genernally.The holding temperature suitable for the preparation of GH3536 alloy semi-solid billet is 1364¹367°C,and the optimum parameters is 1364°C for 60 min.In addition,after isothermal treatment,the microstructure of the alloy has refractory and complex carbides precipitated in the intragranular droplets and the intercrystalline liquid phase.The short-time high-temperature oxidation experiment was carried out to study the composition of the oxide film on the surface of the alloy and the influence of experimental parameters on the thickness of the oxide film.The mechanism of the formation of the oxide film on the surface of the alloy was discussed and the necessity of the oxidation protection during the semi-solid billet process is explained.The results show that the oxide film on the surface of the alloy consists of the outer layer of?Fe,Cr?₂O₃?Fe₃O₄,complex spinel oxide and a small amount of transitional NiO,and the inner layer of continuous,cohesive Cr₂O₃ layer.The formation of the oxide film is mainly caused by the diffusion of the active element,the solid phase reaction and the"oxygen absorption"reaction.The thickness of the oxide film increases with the increase of the oxidation temperature and the oxidation time,and the influence of the temperature is more obvious.At the semi-solid temperature,due to the increase of the liquid phase,the oxidation reaction is severe,and the oxide film is detached seriously without good oxidation resistance,so it is necessary to carry out antioxidant protection in the process of semi-solid billet preparing.