高钨镍基高温合金K416B富W相的析出行为

Precipitation Behavior of W-Rich Phases in a High W-Containing Ni-Based Superalloys K416B

研究了K416B合金中富W相的析出行为与合金浇注温度和凝固速率的关系。结果表明,在相同冷却速率下,合金的浇注温度由1500℃降低到1450℃时,晶粒尺寸明显减小。在不同浇注温度下,合金中均有块状α-W相在残余共晶中析出,α-W相形貌差别不大。合金的残余共晶中存在大尺寸的M6C相,而残余共晶的边缘处有小尺寸的M6C相。高凝固速率时,合金中富W相数量减少、尺寸减小,表明富W相析出受到明显抑制。对于铸造高钨镍基高温合金,选择合适的浇注温度以及保温体系加快凝固初期的冷却速率,可以控制富W相的析出和转变,从而优化合金性能。

The high temperature strength of Ni-based cast superalloys can be significantly improved by adding tungsten(W),a solid solution strengthening element.Hence,superalloys with high W content have been developed as key materials for the preparation of aircraft engine blades.However,the high segregation coefficient of W results in inconsistent composition and microstructure during the solidification process,which can be difficult to eliminate via heat treatment leading to deteriorated mechanicalproperties.The Ni-based superalloy K416 B contains approximately 16.5%W(mass fraction)and exhibits a high tendency to precipitate W-rich phases,such as theα-W and M6 C phases,which not only consume a large amount of W in the matrix but also reduce the solid solution strengthening ability of the alloy.Wrich precipitates also become the origin and propagation paths of cracks during stress-rupture testing.Much research on high W-containing,Ni-based superalloys has focused on the effects of W content on W-rich phase formation and mechanical properties.However,the roles of casting temperature and cooling rate on the formation of the W-rich phase are still unclear.In this work,five groups of K416 B alloy test bars with the same composition were prepared with different processes.Three casting temperatures were chosen,and the cooling rate was controlled by burying sand in the thick shell and single shell,respectively.The relationship between the precipitation behavior of the W-rich phase in the K416 B alloy and casting temperature,and solidification rate under different casting processes were analyzed using SEM and EDS.When the casting temperature is lowered from 1500°C to 1450°C,the grain size is significantly reduced.Results show massiveα-W phases in the residual eutectic of the alloy at different casting temperatures,and the morphology of theα-W phase show few differences.The larger M6 C phase in the alloy exists with residual eutectic,and the small M6 C phase is embedded at the edge of the residual eutectic.At a high solidification rate,the precipitation of the W-rich phase is inhibited,which is primarily manifested by the decreased number and size of the W-rich phase in the alloy.When casting high Wcontaining Ni-based superalloys,choosing an appropriate casting temperature and adopting an appropriate heat preservation system to accelerate the cooling rate during solidification will affect the precipitation and transformation of W-rich phases,and optimize the properties of the alloy.