N在γ-Ni/γ′-Ni_3Al相界区域的占位趋势与脆化作用

Site preference of N and N-induced embrittlement at γ-Ni/γ′-Ni_3 Al interface

采用第一原理赝势平面波方法研究迹量元素N在γ-Ni/γ′-Ni3Al相界区域的占位趋势及其对相界断裂强度的影响。结果显示:以气态形式存在的N不易掺杂到Ni/Ni3Al相界,而以固态形式存在的N则很容易被掺进Ni/Ni3Al相界;N在Ni/Ni3Al相界中不仅能稳定存在,而且掺杂到八面体间隙比置换其中的基体原子具有更高的形成能力与结构稳定性;N掺杂将削弱Ni/Ni3Al相界的断裂强度,其中尤以间隙位掺杂最为明显。电子结构分析表明:置换型掺杂时,相界断裂强度的降低可归结为Frenkel缺陷导致的掺杂相界层间电子相互作用的减弱;而间隙位掺杂,除了基体原子间电子相互作用因掺杂原子与基体原子间的强相互作用而减弱外,晶格畸变导致的局域弹性应变能增加也是一个重要的原因。

Using a first-principles plane-wave pseudopotential method,the site preference of N and its influence on the fracture behavior of the γ-Ni/γ′-Ni 3 Al interface were investigated.The results show that the gaseous N 2 is difficult to be joined into the Ni/Ni 3 Al interfacial region,but solid N impurity can be easily doped into the Ni/Ni 3 Al interface.The N-doped interfacial system can stably exist either for substitution for host atoms or for occupation at octahedral interstices,and N prefers to occupy the octahedral interstitial sites.N-doping,especially at octahedral interstitial sites,makes the fracture strength of the Ni/Ni 3 Al interface be weakened.For the substitutional interface,the N-induced embrittlement can be attributed to the decrease of electronic interactions between adjacent atomic layers caused by the Frenkel defect.While in the case of interstitial doping,a multiple influence of a decreasing electronic interaction between host atoms induced by a strong bonding between N and its nearest host atoms and a increased elastic strain energy originated from lattice distortion should be responsible for the harmful effect of N on strengthening of the Ni/Ni 3 Al interface.