Paula D. Freyer

ULTRASONIC EVALUATION OF TRANSIENT LIQUID PHASE BONDING IN SINGLE CRYSTAL SUPERALLOY CASTINGS

Transient liquid phase bonding (TLPB) is an effective means for joining high performance metal components. It differs from welding and conventional brazing in that it produces very little chemical segregation or microstructural demarcation at the bond-line. The method of transient liquid phase bonding was originally developed in the 1970’s [1] and has been used in the joining of titanium and nickel based superalloy components. In this method, a bonding alloy containing a melting point suppressing element is sandwiched between the parent metals to be joined. The temperature is raised to a point where the bonding alloy melts but the parent metals remain solid. The melting point suppressing element then diffuses away from the bondline, thus raising the melting point and solidifying the bond. Since the temperature never exceeds the melting point of the parent metal, single crystals may be joined without destroying their crystalline structure.

Modeling of Irradiation Embrittlement and Annealing/Recovery in Pressure Vessel Steels

The results of reactor pressure vessel (RPV) annealing studies are interpreted in light of the current understanding of radiation embrittlement phenomena in RPV steels. An extensive RPV irradiation embrittlement and annealing database has been compiled and the data reveal that the majority of annealing studies completed to date have employed test reactor irradiated weldments. Although test reactor and power reactor irradiations result in similar embrittlement trends, subtle differences between these two damage states can become important in the interpretation of annealing results. Microstructural studies of irradiated steels suggest that there are several different irradiation-induced microstructural features that contribute to embrittlement. The amount of annealing recovery and the post-anneal re-embrittlement behavior of a steel are determined by the annealing response of these microstructural defects. The active embrittlement mechanisms are determined largely by the irradiation temperature and the material composition. Interpretation and thorough understanding of annealing results require a model that considers the underlying physical mechanisms of embrittlement. This paper presents a framework for the construction of a physically based mechanistic model of irradiation embrittlement and annealing behavior.