Influence Of The Element Re On Microstructure And Creep Properties Of Nickel-Based Superalloys

In this dissertation, by means of Md and Nv method, two kinds compositions of the single crystal nickel-based superalloys containing Re have been designed to predict the precipitated tendency of TCP phase, and investigating the effects of the heat treatment regimes and TCP phase on the microstructure and creep behaviour of the single crystal nickel-based superalloys by means of the heat treatment, creep curve measurement and microstructure observation.The results show that the compositions of the superalloys may be designed to forecast the precipitated tendency of TCP phase by means of Md and Nv method, and the critical value of TCP phase precipitated are determined to be Md> 0.987 and Nv> 2.25, respectively. In the further, the slice-like TCP phase in 4.5%Re single crystal nickel-based superalloy during high temperature aging is precipitated along{111}<110> orientation, and the TCP phase is transformed into the sphere-like morphology as the aging time prolongs. The solution treatment of 4.2%Re single crystal superalloy is made for 4 h at 1320℃, which may reduce the composition segregation in the dendrite/interdendrite regions to enhance the creep resistance of alloy. But the initial melting of 4.5%Re alloy occurs in the period of the solution treatment at 1325℃. After the high temperature solution treated alloy is aged at 1080℃, the cubicalγ' phase about 0.3μm in size is coherently precipitated in the y matrix phase, and the cubicalγ' phase about 0.45μm in size is precipitated when the aging temperature is increased to 1100℃. But, theγ' phase in the alloy has been grown up into the sphere-like morphology when the aging temperature is increased to 1120℃and 1150℃. No TCP phase is precipitaed in 4.5%Re alloy during aging at lower temperature, therefore, the alloy displays a better creep resistance, and the deformation mechanism of the alloy is that theγ' phase is sheared by<110> dislocations which may be decomposed to form the configuration of the partial dislocation and the stacking fault. But the TCP phase is precipitated in the 4.5%Re alloy during high temperature creep, which may decrease to a small extent the creep lifetime due to the spheroidization of TCP phase. Compared to 4.5%Re alloy,4.2%Re alloy displays a better creep resistance and longer lifetime during high temperature creep. Thereinto, the rafted structure ofγ' phase in the alloy during creep is formed along the direction vertical to the applied stress axis, which may effectively hinder the dislocation movement, this is the main reason of the alloy possessing a better creep resistance and longer lifetime.