Effect Of Heat Treatment On Microstructure And Properties Of A Kind Of Superalloy Designed For Additive Manufacturing

Ni-based superalloy is the preferred material for hot end parts in aerospace and other fields due to its excellent high temperature strength and oxidation resistance.With the development of superalloy structural parts towards lightweight and complex,the microstructure of superalloy prepared by traditional technology is difficult to control and the yield is low,which limits the further application and development of superalloy.Laser additive manufacturing technology is a new type of preparation technology in recent years.It breaks through the limitation of preparing porous,hollow and other complex structures by traditional process.The structural parts prepared by laser additive manufacturing technology show better performances,with respect to that of the traditional preparation process.In this work,a new type of additive manufacturing Ni-based superalloy ZGH451 is taken as the main research object.The alloy has good printability and the as-deposited samples show none crack.As an important material processing technology,heat treatment is an effective means to improve the properties of Ni-base superalloy.The microstructure and properties of ZGH451 alloy formed by LMD were improved by three steps of stress relief annealing,solution and aging.A reasonable heat treatment process was established and the evolution of microstructure and properties during the heat treatment process was studied.The heat treatment process is beneficial to regulate the grain boundary state of the alloy and the morphology and distribution of the alloy phase,further improving the comprehensive properties of the alloy.In this paper,the microstructure of ZGH451 alloy formed by LMD was studied.Different solution temperature(1180～1350°C),first aging temperature(1050～1150°C)and second aging time(16/20/24 h)were designed to systematically studied the effects of different heat treatment processes on the microstructure and tensile properties of new additive Ni-based superalloy ZGH451.The results show that:(1)The microstructure of as-deposited alloy is mainly composed of fine columnar grains growing parallel to the deposition direction.The dendrite structure and interdendritic region withγ/γ’eutectic indicate that there is a certain degree of element segregation in the alloy,resulting in the difference in the size ofγ’phase between the dendritic region and interdendritic region,which are 100 nm and 250 nm,respectively.(2)The microstructure and properties of alloy with varying heat treatment processes are different:as the solution temperature increases from 1180℃ to 1350℃,the segregation degree of the alloy decreases gradually until the dendrite structure basically disappeared at 1280℃ and the initial melting microstructure is found at1350℃.With the first aging temperature increasing from 1050℃ to 1150℃,the size ofγ’phase increases gradually,and its shape changes from spherical and other irregular shape to regular cube shape.(3)After a series of process optimization,the heat treatment process suitable for the alloy is explored:(ASA2:950℃/2 h/AC+1280℃/2 h/AC+1120℃/4h/AC+850℃/20 h/AC).Compared with the as-deposited alloy,the grain size of ASA2alloy increases obviously,and the dendritic structure andγ/γ’eutectic structure of the alloy are eliminated.ASA2 heat treatment process not only significantly improves the high temperature strength of the alloy,but also has a higher elongation(11%)on the basis of ensuring the room temperature strength.