中温形变热处理对新型镍基高温合金组织和力学行为的影响

Effect of medium temperature deformation heat treatment on microstructure and mechanical behaviour of a novel Ni-based superalloy

摘要:

本文采用EBSD、SEM和准静态室温单轴拉伸试验研究了不同中温形变热处理工艺与新型镍基高温合金微观组织和室温力学性能之间的关系。研究表明,新型镍基高温合金经中温形变热处理后可明显提高退火孪晶的长度分数,最高可达40.6%。退火孪晶的形成主要以晶粒的“生长意外”机制为主。同时,相比于固溶+双级时效处理试样的力学性能(σ_y=1018 MPa,ε_f=17.44%),合金在750 ℃轧制变形30%后在1120 ℃退火30 min并经双级时效处理,其σ_y可提高499 MPa,为1517 MPa,而其ε_f仅降低了4.69%。在750 ℃轧制变形50%后在1120 ℃退火30 min并经双级时效处理,其σ_y可提高352 MPa,为1370 MPa,而其ε_f基本保持不变。这种强度的升高主要归因于晶粒细化和退火孪晶的共同作用,这为高性能镍基高温合金提供一种新的强化策略。

Abstract:

In this study, the relationship between different medium-temperature deformation heat treatment processes and the microstructure and room-temperature mechanical properties of a novel Ni-based superalloy was investigated using EBSD, SEM and quasi-static room-temperature uniaxial tensile tests. It is shown that the length fraction of annealed twins of the novel Ni-based superalloy can be significantly increased up to 40.6% after the medium temperature deformation heat treatment. The formation of annealed twins is mainly based on the "growth accident" mechanism of the grains. At the same time, compared with the mechanical properties of the solid solution + double-stage aging specimens (σ_y = 1018 MPa, ε_f = 17.44 %), the alloy annealed at 1120 °C for 30 min after 30 % roll deformation at 750 °C and double-aged, the σ_y increased by 499 MPa to 1517 MPa, while the ε_f decreased by only 4.69 %. After rolling at 750 °C for 50 % of the deformation and annealing at 1120 °C for 30 min with double-stage aging, the σ_y increases by 352 MPa to 1370 MPa, while the ε_f remains essentially unchanged. This increase in strength is mainly attributed to the combined effect of grain refinement and annealing twinning, which provides a new strengthening strategy for high performance Ni-based superalloys.