Ni-based superalloys play an important role in aircraft engine propulsion. However, many experiments demonstrated that these alloys as well as Ni always show ductility loss at intermediate temperature, which constrains further development. A comparison of published papers by various authors reveals considerable differences in understanding the mechanism of intermediate temperature embrittlement. To clarify this situation, the present article first confirms the generality of intermediate temperature embrittlement of Ni and Ni-based alloys by the experimental results reported in the literature. The existing interpretations of the mechanism are then outlined. Based on the generality, these interpretations are discussed through the representative investigations on intermediate temperature embrittlement. It is shown that the mechanism of intermediate temperature embrittlement has not been satisfactorily explained yet and “nonequilibrium interface segregation” of impurities taking into account the effect of str...

Mechanism of Intermediate Temperature Embrittlement of Ni and Ni-based Superalloys

First-principles prediction of partitioning of alloying elements between cementite and ferrite

A unique feature of the environment of nuclear power reactors is the presence of high energy neutron radiation, which can lead to degradation processes in the materials of critical components. An understanding of the operative elevated temperature radiation damage mechanisms enables these effects to be minimised by appropriate alloy selection together with compositional optimisation. An overview of these aspects relevant to advanced fission and fusion reactor systems is presented. Several key examples are highlighted and include radiation embrittlement of low alloy pressure vessel steels for pressurised water reactors, coating designs for fuel in high temperature pebble bed reactors, and selection and design of low activation materials for proposed tokomak fusion reactor devices. In addition, void swelling, non-equilibrium solute segregation and radiation induced precipitation processes in alloys at high displacement doses and relevant to several reactor systems are covered. Likely trends in futur...

Development of radiation resistant materials for advanced nuclear power plant

An Auger electron spectroscopy study of phosphorus and molybdenum grain boundary segregation in a 2.25Cr1Mo steel

Equilibrium grain boundary segregation of phosphorus in a 2.25Cr1Mo steel was studied by means of Auger electron spectroscopy (AES). After quenching from 980 °C and tempering at 650 °C, the steel samples were aged for different periods of time at 560, 520 and 480 °C, respectively, followed by AES measurements. Based on the experimental values of the equilibrium segregation levels at different temperatures along with equilibrium segregation theories, the thermodynamic parameters of segregation were evaluated. With the use of Charpy impact testing along with the AES results on phosphorus grain boundary concentration, a relationship between ductile-to-brittle transition temperature (DBTT) and phosphorus boundary concentration was established. On the basis of this relationship, predictions of the DBTT were made through predicting the grain boundary segregation of phosphorus.

Dependence of ductile-to-brittle transition temperature on phosphorus grain boundary segregation for a 2.25Cr1Mo steel

Phosphorus segregation to grain boundaries in a commercial grade 2.25Cr–1Mo steel subjected to a variety of heat treatments has been examined using X-ray spectroscopy in a field emission gun scanning transmission electron microscope. A number of points have been established. Segregation of phosphorus to grain boundaries is present after austenitising and quenching. Tempering for 2 h at 650°C enhances phosphorus segregation during the following aging processes at 520°C. A higher austenitisation temperature (larger grain size) makes subsequent segregation more intense. For specimens austenitised at 1100°C, the concentration of phosphorus segregated to grain boundaries steadily increases with aging time after tempering (from 0 to 210 h). For specimens austenitised at 900°C, the phosphorus concentration at grain boundaries first increases, reaches a maximum at an aging time of ∼ 210 h and then decreases with aging time (480 h).

T. S. Rong

Papers

Phosphorus segregation in 2.25Cr-1Mo steel