热力耦合对一种第四代镍基单晶高温合金1100℃蠕变组织演变的影响

以一种第四代镍基单晶高温合金为研究对象,采用变截面蠕变试样,在1100℃、43~96 MPa条件下进行200 h蠕变中断实验,利用SEM和TEM观察了微观组织演变规律,利用同步辐射高能XRD和EPMA分析了高温低应力条件下镍基单晶高温合金的蠕变组织演变。结果表明:随着应力的增大,镍基单晶高温合金的γ′相体积分数降低,筏化程度增大且筏排厚度下降,同时,γ相通道宽度逐渐增大,而γ/γ’两相界面位错网间距逐渐减小。固溶强化元素Re、Mo和Cr等在γ相中的富集导致γ/γ’两相错配度绝对值增大。蠕变过程中γ’相体积分数降低和γ’相筏排厚度减小显著降低了合金的强度。另外,位错在γ′相溶解所导致的弯曲相界处的塞积,使位错易于切入γ′相,也是镍基单晶高温合金室温硬度下降的重要原因。

Thermal-Stress Coupling Effect on Microstructure Evolution of a Fourth-Generation Nickel-Based Single-Crystal Superalloy at 1100℃

The mechanism of microstructure evolution and its effect on the mechanical properties of nickel-based single-crystal superalloys during creep at high temperatures and low stresses are critical to the development of advanced single-crystal superalloys for aeroengines with high thrust:weight ratios.In this work,the microstructural evolution of a fourth-generation nickel-based single-crystal superalloy during creep at 1100 oC for 200 h at various stress levels was investigated using a specially designed sample with variable cross-sections,with the aim of obtaining different applied stresses synchronously on a single sample.The effects of applied stress onγ/γ’microstructure,interfacial dislocation configuration,alloy element partitioning behavior,and lattice misfit ofγ/γ’phases of the used single-crystal superalloy were al-so studied,as were the effects on room temperature Vickers hardness.The results indicated that the typical rafting microstructure was formed during creep over the 200 h period at 1100 oC under various stress levels.With increasing applied stress,the volume fraction and rafted thickness of theγ’phase gradually decreased,while the rafting degree of theγ’phase and the channel width of theγphase gradually increased.A dense interfacial dislocation network was formed at theγ/γ’interface,and interfacial dislocation spacing decreased with increasing applied stress.Simultaneously,increased partitioning of solutionstrengthening elements Re,Mo,and Cr to theγphase and increased partitioning ofγ’-strengthening element Ta to theγ’phase resulted in a larger absolute value ofγ/γ’lattice misfit at higher stress.In addition to the decreases in volume fraction and rafted thickness of theγ’phase and the increase in channel width of theγphase,another important factor in the strength decline of the single-crystal superalloy was the pile-up of dislocations at bentγ/γ’interface boundaries,mainly caused by the dissolution of theγ’phase and promotion of dislocation shear into theγ’phase.This work provides a basis for quickly establishing the relationship between creep conditions and microstructure evolution of nickel-based single-crystal superalloys.