It is well known that carbides at grain boundaries play an important role in affecting mechanical properties of nickel based superalloys. In order to deeply understand the relationship between grain boundary structures and properties, in this work, we have investigated the microstructure of grain boundaries with different misorientation angles in bicrystals of nickel based superalloys. It is found that the bicrystals with smaller misorientation angles contain denser M 23 C 6 but sparse MC particles at grain boundaries, and this kind of bicrystals presents longer stress rupture lives. It was observed that MC carbides were decorated by M 23 C 6 and M 6 C particles at grain boundaries. The formation of these carbide particles, therefore, is likely due to the local fluctuation of chemical composition around MC carbides. In addition, the orientation relationships between MC carbides and γ/γ matrix were also determined.
Xiaoming DongXiaoli ZhangKui DuYizhou ZhouTao JinHengqiang Ye
One of the most unique structural characteristics of carbon nanotubes(CNTs) differentiating from other carbon materials is their hollow nanochannles,which can be utilized for encapsulating and loading foreign matters.The anodic aluminum oxide(AAO) template technique enables the diameter,length,and cap structure control of the replicated CNTs,and thus shows advantages in pore structure control over the traditional CNT growth approaches.This review details the synthesis of CNTs with tunable diameter,length,wall thickness,and crystalline by using the AAO template method.The doping of heteroatoms and filling of foreign matters into AAO-CNTs are also addressed.Moreover,the main challenges and developing trends of the AAO template method are discussed.
We report a facile approach to synthesize narrow and long graphene nanoribbons (GNRs) by sonochemically cutting chemically derived graphene sheets (GSs). The yield of GNRs can reach ~5 wt% of the starting GSs. The resulting GNRs are several micrometers in length, with ~75% being single-layer, and ~40% being narrower than 20 nm in width. A chemical tailoring mechanism involving oxygen-unzipping of GSs under sonochemical conditions is proposed on the basis of experimental observations and previously reported theoretical calculations;it is suggested that the formation and distribution of line faults on graphite oxide and GSs play crucial roles in the formation of GNRs. These results open up the possibilities of the large-scale synthesis and various technological applications of GNRs.
