Effect Of Heat Treatment On The Microstructure And Mechanical Properties Of W-Containing Nickel Based Superalloys

Cast nickel-based superalloys are widely used in aerospace and other fields due to their excellent high-temperature structural stability,good oxidation resistance and high-temperature thermal erosion resistance.Usually,nickel-based alloys are based onγphase and a variety of precipitated phases A highly alloyed material composed together.After different processes,whether the precipitation ofγ’phase with L1₂ structure can significantly improve the strength of the alloy.In addition,a certain amount of refractory metal element W can increase the bonding force between atoms,which is also considered as a method to improve the high temperature performance of the alloy,but with the increase of W element content,the alloy is easy to precipitate Laves phase during solidification or heat treatment,Thus affecting the mechanical properties of the alloy at room temperature and the stability of the microstructure at high temperature.In this paper,the microstructure is regulated by heat treatment,and the influence of alloy composition and heat treatment process changes on the mechanical properties of nickel-based superalloys is studied,which provides a reference for the subsequent research and application of the alloy.In this paper,the influence of alloy composition adjustment on the microstructure and mechanical properties of as-cast alloys was studied,and nickel-based superalloys with different W element concentration gradients were prepared,and the changes in microstructure and mechanical properties during heat treatment were studied.Characterization and Analysis.There are a large number of dendrite structures inside the as-cast alloy,and there are a large number of eutectic structures with low melting points between the dendrites.These eutectic structures are prone to stress concentration and microcracks during the stretching process,resulting in poor room temperature plasticity of the as-cast alloy are about 2%.The precipitation temperature and solidification sequence of each phase in the alloy were determined by differential thermal analysis.The liquidus temperature of the 0W alloy was 1312℃,and the liquidus temperature of the 5W alloy was 1332℃.The addition of W element increased the phase transition temperature of the alloy,and based on this,the solution heat treatment process was designed.First,the as-cast alloy was kept at 1050°C,1100°C,1150°C,and 1200°C for 0.5 h,1 h,and 2 h,respectively.After different solid solution treatments,the internal microstructure of the material is mainly eutectic structure with irregular distribution in the grain,and with the increase of temperature or the extension of holding time,its volume fraction gradually decreases,and finally all return to the internal composition of the alloy is uniform,and the plasticity of the material is improved.Among them,the 0W and 1W alloys are kept at 1100℃for 2 hours,the3W alloy is kept at 1150℃for 2 hours,and the 5W alloy is kept at 1200℃for 2 hours.The comprehensive mechanical properties of the alloy the performance is the best.Secondly,the effects of aging temperature and aging time on the microstructure and mechanical properties of the alloy were studied by aging the samples after solution treatment at 600℃and 700℃for 6 h to 24 h.The research shows that only the 5W alloy undergoes aging treatment at 700°C.With the increase of the holding time,the precipitate phase will gradually precipitate inside the grain and segregate at the grain boundary.decline.Due to the precipitation of the Laves phase of the hexagonal close-packed structure（HCP）at the grain boundary,the brittleness of the grain boundary is caused,and the plasticity of the alloy is reduced.The tensile strength reached 1270 MPa,and the plasticity remained at 25%.Finally,by comparing the high-temperature mechanical properties of the alloy at 600℃and 700℃,it is found that with the increase of W element in the alloy,its high-temperature mechanical properties show a trend of first increasing and then decreasing.Studies have shown that the addition of W element promotes the generation of{001}<110 texture,but at the same time increases the size of theγ’phase and increases the mismatch between it and the matrix.This precipitation The decrease of the binding force between the phase and the matrix is the main reason for the change of the high temperature mechanical properties of the alloy.