Effects Of Element W On Microstructure Stability And Creep Properties Of Nickel-Base Superalloys

By means of Md and Nv methods, nickel-base superalloys with different content of tungsten have been designed to predict the tendency of TCP phase precipitated. The influence of tungsten content on the tendency of TCP phase precipitated, the lattice parameters and the misfits have been investigated through preparing alloys, the applied of heat treatment of alloys and X-ray diffraction analysis method. And the influence of element tungsten on microstructure stability and creep properties of the single crystal nickel-base superalloys have been investigated by means of preparing of single crystal superalloys, creep properties testing and microstructure observation.Results show that the TCP phase is precipitated while the ratio of additions of elements Mo, W, Ta and Al to the total additions is over 60%, and determining that the TCP phase is precipitated while Md > 0.98 and Nv > 2.10 by means of Md and Nv methods to optimize compositions of the nickel-base superalloys with different tungsten content. After the alloy aged for 50h at 1040℃, the TCP phase is precipitated along the {111} crystal planes in the form of the slice-like, and arranged in the form of the upright each other or 60°angle each other when the alloys are observed on the {100} or {111} crystal planes, respectively. In the further, the TCP phase is determined asμphase by means of the electric diffraction analysis. The lattice parameters ofγ' andγphases in alloys are increased with the element W content, and the absolute value of the lattice misfits are transformed into the positive value from negative one. The lower lattice misfits of theγ'/γphases appears in the alloy with the full heat treatment state, and the lattice parameters and misfits of theγ'/γphases are increased after the alloy is crept for longer time at high temperature. The elements Al, Ta and W are richer distributed in the dendrite regions, while the elements Mo, Cr and Co are richer distributed in the interdendrite regions. Compared to the solution treated at 1310℃, the segregation extent of the elements distributed the dendrite/interdendrite regions decreases after the alloy solution treated for 4 h at 1325℃. The casting defects existed in the alloy may obviously decrease the creep life of the one. The homogenization extent of the elements and the effect of the solution strengthening in alloys may be improved by means of enhancing the solution treatment temperature and the element tungsten content, in the further, this may effectively enhance the creep properties of the alloys. During high temperature creep, the single crystal nickel base superalloy exhibits an obvious sensibility of the applied stresses and temperatures. In the range of the applied temperatures and stresses, the activation energy and the stress exponents of alloys during steady state creep are measured as Q = 426.96kJ/mol and n = 4.38, respectively.