混晶组织对镍基变形高温合金持久性能的影响与机制研究

Study on Influence and Mechanisms of Mixed-Grain Structures on the Rupture Creep Properties of Nickel-Based Wrought Superalloys

摘要:

通过控制镍基变形高温合金锻造和热处理工艺，制备了粗晶体积分数为0%~100%的混晶组织，测试了不同混晶组织730 ℃/530 MPa的持久性能变化，获得了混晶组织对合金持久性能的影响规律与机制。结果表明：经730 ℃/ 530 MPa持久性能测试后，粗晶体积分数为0%~100%的混晶组织表现出差别较大的持久性能，粗晶体积分数15%的混晶组织持久寿命最短，粗晶体积分数100%的粗晶组织持久寿命最长；较低粗晶体积分数0%~15%的混晶组织试样高温持久断口呈现出典型的韧性断裂特征，而较高粗晶体积分数50%~100%的混晶组织试样持久断口呈现出沿晶断裂特征。所有混晶组织试样高温持久变形均以位错运动主导的晶内变形和晶界滑移为变形机制，但随着粗晶体积分数改变，{111}晶面上强织构及粗、细晶粒内部位错分布均产生变化，位错塞积与晶界滑移诱导的应力集中和孔洞形核倾向存在差异，影响了合金的高温持久性能。

Abstract:

Through controlling forging and heat treatment processes of nickel-based wrought superalloy, the microstructures with coarse grain volume fractions ranging continuously from 0% to 100% were prepared, and the stress rupture properties of different mixed-grain structures were tested under the condition of 730 ℃/530 MPa to explore the influence regularity and mechanism of mixed-grain structures on the stress rupture properties. The research results show that the mixed-grain structures with coarse grain volume fractions from 0% to 100% exhibit significantly different stress rupture properties. The mixed-grains structure with coarse grain volume fraction of 15% presents the shortest stress rupture life, while the coarse-grained structure with coarse grain volume fraction of 100% possesses the longest stress rupture life. The high-temperature stress rupture fracture surfaces of the mixed-grain structure specimens with low coarse grain volume fraction from 0% to 15% show typical ductile fracture characteristics, whereas those of the specimens with high coarse grain volume fraction from 50% to 100% present intergranular fracture characteristics. The high-temperature stress rupture deformation mechanisms of all mixed-grain structure specimens take the form of intragranular deformation governed by dislocation motion and grain boundary sliding. However, with the increase in coarse grain volume fraction, the high-temperature stress rupture properties of the superalloy are improved as the strong textures on the {111} crystal planes is changed, the internal dislocation distribution in coarse and fine grains is inhomogeneous, and the tendencies of stress concentration and cavity nucleation induced by dislocation pile-up and grain boundary sliding are significantly changed.