标题： 高Ti诱导的CoNi基高温合金中的局部Eta相转变与蠕变孪生现象 显示英文标题

标题： High-Ti inducing local Eta-phase transformation and creep-twinning in CoNi-based superalloys

摘要： 本工作研究了不同Ti/Al比的含L12相CoNi基合金在压缩蠕变过程中析出相剪切的机制。在空气气氛下以恒定载荷应力241 MPa进行了中断蠕变试验，温度为950°C。结果表明，随着CoNi基合金中Ti/Al比的增加，蠕变抗力增大。此外，我们首次发现，在析出相剪切过程中(111)面上平面缺陷的类型从反相边界(APB)转变为超点阵外延堆垛层错(SESF)，随着Ti含量的增加——γ'相的剪切主要由无Ti和低Ti合金中的APB主导，但在高Ti合金中则主要由SESF主导。通过采用密度泛函理论(DFT)，发现在无Ti和低Ti合金中APB能低于复杂堆垛层错(CSF)能，但这种情况在高Ti合金中相反。另外，在L12-(Co,Ni)3Ti结构中，SESF能低于简单堆垛层错(SISF)能，这有力地支持了高Ti合金中SESF的形成。通过扫描透射电子显微镜模式下的能量色散X射线光谱分析，观察到的化学偏聚使无Ti和低Ti合金中的APB成为无序γ相结构，并使高Ti合金中的SESF成为局部有序Eta相结构。然而，在高Ti合金中也发现了微孪晶，通常它引起的蠕变应变高于其他平面缺陷，如SESF和APB。这一发现为合理利用合金设计中的Ti含量提供了新的见解。 显示英文摘要

摘要： Precipitate shearing mechanisms during compressive creep of L12-containing CoNi-base alloys with different Ti/Al ratio have been investigated in this work. Interrupted creep tests were conducted at 950 degree under air with constant load stress of 241 MPa. It was found that the creep resistance increases with Ti/Al ratio rising in CoNi-based alloys. In addition, we firstly found that the type of planar defects on (111) planes during precipitate shearing change from antiphase boundary (APB) towards superlattice extrinsic stacking fault (SESF) with Ti content increasing - shearing of the gamma' phase is mainly dominated by APB in Ti-free and low-Ti alloys but dominated by SESF in high-Ti alloys. By employing density functional theory (DFT), the APB energy was found be lower than complex stacking fault (CSF) energy in Ti-free and low-Ti alloys but this situation becomes opposite in high-Ti containing alloys. Additionally, the SESF energy is lower than SISF energy in L12-(Co,Ni)3Ti structure strongly supporting SESFs formation in high-Ti alloys. By energy dispersive X-ray spectroscopy analysis under the scanning transmission electron microscope mode, the observed chemical segregation enables APB becoming disordered gamma phase structure in Ti-free and low-Ti alloys and enables SESF becoming local ordered Eta phase structure in high-Ti alloys. However, the microtwins were found as well in high-Ti alloys which usually contributes higher creep strain than other planar defects, e.g. SESF and APB. This finding provides a new insight how to use Ti content reasonably in superalloy design.