Study On Homogenization Treatments Of High Niobium Fe-Ni Based GH4061 Superalloy

With the development of aerospace engines,GH4061 alloy,as a new type of high-alloyed Fe-Ni based deformation superalloy,was developed by scientists.The alloy has good comprehensive properties in a wide temperature range of-253?750?,and has good low temperature performance and anti-burning characteristics.However,the higher Nb content in the alloy makes the solidification process of the alloy complicated,the segregation in the as-cast microstructure is severe,and a large number of low-melting phases are precipitated between the dendrites,which brings great difficulty to the subsequent hot working and heat treatment processes.The homogenization treatment is to eliminate dendrite segregation and low melting point phase,and obtain uniform composition and structure,thereby improving the hot workability of the alloy.The basic theoretical research on the homogenization treatment process of domestic GH4061 alloy is relatively blank,and the optimization of the homogenization treatment process in industrial production lacks theoretical and data support.Therefore,this study used GH4061 alloy as the research object,and used thermodynamic calculation combined with microstructure observation and high temperature tensile test thermoplastic evaluation method to analyze the as-cast microstructure characteristics of the alloy.The effects of homogenization process parameters on the low melting point phase and dendrite segregation in the alloy were investigated,and the effect of the homogenization process on the thermoplasticity of the alloy was verified,provide theoretical and data support for the formulation and optimization of the homogenization process in the industrial production of GH4061 alloy ?508 mm ingot.The low melting point phase in the as-cast microstructure of GH4061 alloy is Laves eutectic phase,and the segregation degree of Nb element is the most serious among the main segregation elements of as-cast alloy.The main purpose of the homogenization treatment is to eliminate segregation dominated by Nb elements.With the increase of homogenization temperature or prolongation of holding time,the enriched elements of Laves eutectic phase will be dissolved back into the matrix,and the efficiency of resolving is higher in the range of 1160??1190?.With the increase of temperature and the prolonged holding time,the diffusion of segregation elements is more sufficient.The main segregation element Nb reaches the industrial homogenization standard when it is kept at 1160? for 20 h.When it is kept at 1200?for 20 h,the segregation of Nb element reaches the standard of high quality homogenization.According to the research results of this paper,two different two-stage homogenization systems were designed,which were 1160?×20 h+1190?×50 h and 1190?×20 h+1200? x20 h.After the homogenization treatment,the Laves phase was completely dissolved,and there was no obvious segregation phenomenon.It was judged by the thermoplasticity that the sample after the homogenization treatment was greatly improved in thermoplasticity compared with the as-cast sample.The second homogenization system takes a short time and is highly efficient,which can save a lot of cost.