Study On Electron Beam Refining Of Ti-Ni Master Alloy For High Purity Nickel Base Superalloy

Nickel base superalloys are widely used in the fields of aerospace and petrochemical industry due to their excellent corrosion resistance,creep fatigue resistance,red hardness and thermal fatigue resistance.Ni element is the matrix element in Ni base superalloy.As an important strengthening element,Ti plays an important role in improving the properties of Ni base superalloy The proportion of titanium in?solid solution is about 10%.This 10%titanium plays a role of solution strengthening in superalloy,and about 90%titanium enters into?'phase.Under the condition of a certain amount of aluminum element,with the increase of the amount of?'phase,the increase of the amount of?'phase can increase the room temperature and high temperature strength of high temperature alloy.In the melting process of nickel base superalloy,there are two ways to add alloy elements:one is to add pure elements directly;the other is to add intermediate alloy of this element.Due to the high melting point of pure elements,in the temperature range of high temperature alloy melting,the pure elements added directly can not melt rapidly,but dissolve into the melt through alloying.In this process,Ti element is easy to combine oxygen and nitrogen.If there are a certain amount of oxygen,nitrogen and other gas impurities in the alloy melt,it will quickly form oxides and nitrides that are difficult to decompose,which will seriously affect the properties of the alloy.However,the melting point of the intermediate alloy is relatively low.If the intermediate alloy is added in the melting temperature range,it will melt rapidly and mix with the alloy melt fully to avoid the formation of inclusions.Based on the above problems,the primary master alloy was prepared by electron beam melting.The distribution of oxygen and nitrogen elements in the alloy matrix was analyzed.The removal method of solid solution oxygen,nitrogen elements and their inclusions in the purification process was defined.The best process of refining and purifying the master alloy was obtained.The results show that the melting point of Ti₃Ni alloy is the lowest,and it is suitable to be the target alloy.There is a layer of solidified shell on the surface of the ingot.The main phase composition of the solidified shell is?-Ti.In addition,a small amount of Ti₂Ni phase,TiN and TiO₂ precipitated phase are produced.The matrix consists of Ni rich Ti₂Ni phase,Ti rich?-Ti and Ti₂Ni eutectic phase and a small amount of dispersed?-Ti phase.The content of O and N elements in the solidified shell is much higher than that in the matrix.The O and N elements in the matrix are mainly concentrated in the eutectic structure of?-Ti and Ti₂Ni,and the least in the structure of Ti₂Ni.TiO₂ inclusions on the melt surface and near the surface are mainly removed by dissolution.In addition,the lowest temperature of TiN dissolution is2671.5k,and the highest temperature of molten pool under the action of electron beam is2681.2k,which is slightly higher than the dissolution temperature of inclusions.Therefore,inclusions near the surface of melt can be removed by dissolution.The lowest temperature for inclusion decomposition is 1847.6k,which is far lower than the local maximum temperature?2681.2k?.Therefore,TiN inclusions floating up to the melt surface are bombarded by electron beam,resulting in bond breaking,and the decomposed products are pumped out of the furnace in high vacuum environment.Therefore,the removal mechanism of TiN is mainly decomposition removal.